1
1
Introduction
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CIRIA C683
1
1 Introduction
CHAPTER 1 CONTENTS
1.1 Use of rock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Background to the manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3 Structure of the manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3.1
Chapters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3.2
Use of the manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.4 Target readership and experience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.5 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.5.1
Changes from earlier manuals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.5.2
Structure types considered . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.5.2.1 Marine structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.5.2.2 Closure works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.5.2.3 River and canal structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2
CIRIA C683
1.1 Use of rock
1
Introduction
1
This flow chart shows the links between the technical chapters that follow this introductory
chapter. It is repeated at the start of each chapter and expanded to show more detail of the
contents of the relevant chapter. Use it in conjunction with the contents page and the index
to navigate the manual.
2
2 Planning and designing
rock works
3 Materials
5 Physical processes and
design tools
3
4 Physical site conditions and
data collection
4
6 Design of marine structures
7 Design of closure works
8 Design of river and canal structures
5
9 Construction
6
10 Monitoring, inspection,
maintenance and repair
1.1
USE OF ROCK
7
Rock is a commonly used construction material in the hydraulic environment. It is used in
the marine and fluvial environments to provide protection against scour and erosion and to
limit wave overtopping and flooding.
Rock is quarried to produce armourstone, defined as coarse aggregate used in hydraulic
structures and other civil engineering works. This may be produced in masses ranging from
approximately 1 kg up to 20–30 tonnes. Rock may be employed as an armouring material, as
a filter or underlayer, or as a fill material.
Where armourstone of sufficient size or quality is not available then artificial units (generally
of concrete) may be used. Gabion boxes or mattresses filled with smaller armourstone are
another alternative. Other materials, such as industrial by-products, may also be used instead
of quarried rock.
Standard solutions do not generally exist in this field of engineering. To develop a robust,
site-specific rock-based solution for a project it is necessary to consider a wide range of issues
including materials, environmental conditions, construction methodology, maintenance
regime and health and safety for construction personnel and the general public.
CIRIA C683
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8
9
10
1 Introduction
1.2
BACKGROUND TO THE MANUAL
In 1991 CIRIA/CUR published the original Manual on the use of rock in coastal and shoreline
engineering, commonly referred to as “The Rock Manual”. This was followed in 1995 by the
Manual on the use of rock in hydraulic engineering by CUR. Two French reference books were
produced during the late 1980s: Le dimensionnement des digues à talus (EDF-LNH, 1987) and
Les Enrochements (LCPC, 1989). Since these books were published there have been many
advances in the understanding of rock as a material and of the design and behaviour of rock
structures in the hydraulic environment. This new edition of The Rock Manual presents
current good practice for the design and construction of rock structures. Where appropriate,
it presents new or emerging technologies that have not, at the time of writing, become
standard practice, to allow the reader to be fully aware of, and make best use of, the latest
research findings. Section 1.5 defines the scope of this updated manual and includes a list of
changes from the earlier versions.
The manual has been updated by a principally British, Dutch and French team and has
benefited from extensive international review to ensure that it provides guidance on current
good practice worldwide. The manual collates available research data and technical
information together with practical experience gained by practitioners. In doing this, care
has been taken to indicate current limitations in the design processes and the extent to which
empirical methods and engineering judgement are involved.
A full list of acknowledgements to the organisations and individuals who have contributed to
the updating of The Rock Manual is provided at the beginning of this manual.
1.3
STRUCTURE OF THE MANUAL
1.3.1
Chapters
4
1
Introduction explains the philosophy behind the manual, the key features of the update
and the structure of the contents.
2
Planning and designing rock works discusses key considerations for a rock project in
the hydraulic environment. This chapter is an important first point of reference in the
manual, as it provides an aide memoire of issues that should be addressed. Readers are
encouraged to read this chapter before proceeding with other chapters. The contents
have been kept concise and focused to aid usability.
3
Materials discusses the range of issues with regard to armourstone and other material
selection, including concrete armour units. The chapter considers source evaluation,
properties, performance prediction, quarry yields and quarry operations. It describes
the various testing methods to determine rock and armourstone properties. It crossreferences to the European armourstone specification EN 13383.
4
Physical site conditions and data collection describes how to derive hydraulic,
geotechnical and ice conditions and summarises data collection. Designers can use this
chapter as the starting point for design, but it is also relevant to contractors and
suppliers who need information on environmental conditions for construction
operations.
5
Physical processes and design tools presents design methods for rock structures in both
marine and fluvial environments. It covers hydraulic performance, structural stability
and geotechnical behaviour. The hydraulic and geotechnical parameters derived in
Chapter 4 and the material characteristics derived from Chapter 3 are the key inputs to
this chapter.
CIRIA C683
1.3 Structure of the manual
6
Design of marine structures. See below.
7
Design of closure works. See below.
8
Design of river and canal structures. See below.
1
Chapters 6, 7 and 8 provide practical guidance for the design of different types of
structure. These chapters take the outputs from the design methods in Chapter 5 and
provide guidance for the geometry (plan layout, cross-section) and structure details
taking into account the constraints that exist, such as buildability and access (discussed in
Chapter 9), availability of resources (discussed in Chapter 3) and maintenance (discussed
in Chapter 10). In particular, Chapters 6–8 cover plan layout, geometry of cross-sections,
structural details (toe, crest etc), transitions and joints, design-related construction, cost
and maintenance considerations, and repair and upgrading of existing structures.
Selection of appropriate design conditions is also covered in these chapters.
9
Construction covers commonly used equipment and transport, site and location
considerations (including site preparation), quality control in rock structures (including
placing and packing, survey and measurement techniques), health and safety, and risks.
Some methods of construction are described for the most common hydraulic structures
using rock.
3
4
10 Monitoring, inspection, maintenance and repair discusses monitoring techniques,
appraisal of structure performance, and repair and construction methods.
1.3.2
2
5
Use of the manual
The following features are designed to assist readers in navigating the manual:
!
CIRIA C683
Diagram of general structure. Figure 1.1 provides a flow chart of the structure and contents of the complete manual. It also suggests a relationship between the advice given
and key phases of a typical project.
!
Diagram of content relevance to different users. Table 1.1 presents an evaluation of the
content from different users’ perspectives to assist the reader in finding information
relevant to his or her needs.
!
High-level contents list. This is given for the complete manual at the start of the book.
!
Detailed contents list. At the start of each chapter there is a contents list for that
chapter only.
!
Structure of each chapter. The front end of each chapter includes:
–
a detailed contents list for that chapter
–
an introductory box that describes what is included in the chapter
–
a flow chart to demonstrate how the chapter links with other chapters.
6
7
!
Where am I? Each page tells the reader their current location in the manual. The chapter
number is shown on the navigation bar running down the outer edge of right-hand
pages, the chapter number and title are given on the left hand page header, while the
section number and title are given on the right hand page header.
!
Index of key topics. The index lists key topics by section number. A complete index of
words is not included as most subjects should be easily locatable through the high-level
contents list at the front of the book and the detailed chapter contents pages. The index
is particularly useful for locating discussion of topics that span several chapters.
!
Electronic version. The complete manual is available on the CD-Rom attached to the
inside back cover of the book and on the web at the CIRIA and CETMEF websites
<www.ciria.org/> <www.cetmef.equipement.gouv.fr/>. It incorporates a navigation
facility permitting users to make rapid searches for words or phrases.
8
9
10
5
1 Introduction
PROJECT PHASE
RELEVANT MANUAL CONTENT
Understanding the problem
!
!
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Defining project requirements
Technical considerations
Economic considerations
Environmental considerations
Social considerations
Information requirements
Chapter 3: Materials
Obtain all necessary site information:
!
!
!
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Available materials
Hydraulic conditions such as waves, currents,
water levels
Bathymetry and topography
Ice conditions
Ground conditions
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Chapter 4: Physical site conditions and data
collection
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Developing solutions
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Chapter 7: Design of closure works
Chapter 8: Design of river and canal structures
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Armourstone production and control
Specifications
Construction
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Operation
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Plan layout
Geometry of cross-sections
Structure details – toe, crest design
Transitions, joints
Design-related construction aspects
Cost aspects
Repair and upgrading
Design-related maintenance aspects
Chapter 9: Construction
!
!
Hydraulic interactions
Structure response to hydraulic loading
Geotechnical interactions
Geotechnical response
Chapter 6: Design of marine structures
!
!
Bathymetry
Water levels
Waves, currents
Ground conditions
Geotechnical properties of materials
Chapter 5: Physical processes and design tools
Develop conceptual designs
– develop structure layouts and types
– identify information requirements
– review project feasibility
Prepare preliminary designs
– perform required analytical studies and
modelling
– determine typical armourstone size and
structure profile
– assess alternatives against performance
criteria and constraints
– cost estimates
– compare alternatives (technical,
environmental and economic)
– select preferred solution
Produce detailed designs
– review possible failure mechanisms
– calculate suitable armourstone gradings,
design underlayers and filters
– calculate structure dimensions
– design toe and crest details
– design transitions, end protection, drainage,
services etc
Implementation
Quarried rock
Concrete
Recycled materials
Social considerations (2.6)
!
!
Environmental considerations (2.5)
!
Functional requirements
Performance criteria
Constraints: budget, access, materials,
environment, maintenance
Economic considerations (2.4)
!
Technical considerations (2.3)
!
Chapter 2: Planning and designing rock works
Monitoring
Maintenance
Decommissioning or removal
Equipment and working conditions
Transport
Aspects of site and location
Placement, packing and tolerances
Survey, measurement and quality control
Construction risk, health and safety
Appendix A1)
Construction specification (A
Chapter 10: Monitoring, inspection, maintenance
and repair
!
!
!
Monitoring
Appraisal of structure performance
Repair and rehabilitation
Note
Relevant section numbers are given in brackets.
Figure 1.1
6
Structure of the manual and relationship to project phases
CIRIA C683
1.4 Target readership and experience
1.4
1
TARGET READERSHIP AND EXPERIENCE
The target audience for the manual is wide and includes planners, developers, engineering
consultants and designers, architects, building managers, facility managers, contractors,
producers and suppliers, owners, staff from regulators, funders and educational institutions.
The guidance is suitable for worldwide application.
The manual assumes that the reader has a level of technical knowledge typically
corresponding to a minimum of:
2
a degree in civil engineering and two years’ experience
or
3
equivalent qualification or experience.
The manual is appropriate for the non-specialist in that it provides the reader with an
understanding of the principles and procedures involved. It is, however, emphasised that
the manual itself cannot convert a non-trained person into a specialist and the guidance
should not be used as a substitute for experience and judgement.
4
The manual addresses the needs of a range of users who may refer to it in different ways
depending on the stage they become involved in the project. Table 1.1 presents an evaluation
of the content from the perspectives of different users to assist the reader in finding
information relevant to their needs.
Table 1.1
Relevance of chapters for different stakeholders and users
5
1. Introduction
2. Planning and
designing rock works
3. Materials
4. Physical site
conditions and data
collection
5. Physical processes
and design tools
6. Design of marine
structures
7. Design of closure
works
8. Design of river and
canal structures
9. Construction
10. Monitoring, inspec tion, maintenance and
repair
Chapter
Armourstone producer
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Supplier
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Transport agent
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Contractor
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Consulting engineer
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Structure owner
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Funding bodies
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Regulatory bodies
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Environmental organisation
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Rock-testing laboratory
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Geotechnical consultant
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Hydraulics consultant
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Educational institution
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Stakeholder/user
6
7
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9
Note
10
The relevance of material to each stakeholder or user group is indicated by the following symbols: ●
high, " medium-high, ☼ medium-low, " low.
CIRIA C683
7
1 Introduction
1.5
SCOPE
The manual provides guidance that starts from the stage in a project when it has been
decided to construct a structure in a hydraulic environment using rock as the only
material, or as the primary material where it is one of a combination of materials.
Guidance is not provided on early feasibility studies.
Guidance on concrete armour units is given where these may be used as an alternative to
armourstone. Only large concrete armour units are covered. This manual does not cover
concrete revetment blocks.
Guidance on other alternative materials is provided only where these materials are used with,
or in place of, quarried rock.
References to “the project” throughout the manual refer only to activities associated with the
rock works.
1.5.1
Changes from earlier manuals
The updated manual includes the following new features:
!
previous manuals completely reviewed, with updating and rewriting where appropriate
!
scope extended (from the 1991 edition) to cover coastal, inland waterway and closure
structures
!
guidance on design and construction using concrete armour units
!
an updated construction specification for rock structures
!
cross-referencing to the new European armourstone specification EN 13383, which
supersedes sections of the previous manuals
!
cross-referencing to the new Eurocodes for geotechnical considerations
!
updated guidance on wave climate description and representative wave parameters,
including wave height distribution in shallow waters
!
new research on block integrity and on packing and placement
!
new research on predicting quarry yield and block size distributions
!
new research on the performance of falling aprons
!
updated guidance on wave overtopping, wave run-up and wave transmission
!
new guidance on rear-side stability of rock structures
!
new guidance on the stability of near-bed rockfill structures
!
updated guidance on the stability of low-crested structures and the stability of rockarmoured slopes with shallow foreshores
!
new guidance on design and construction of statically stable berm breakwaters
!
new guidance on the structural response to ice loads
!
a new section on design of rock protection works in ports
!
a completely revised chapter on monitoring, maintenance, inspection and repair.
The following changes or omissions from the earlier versions have been made in this update:
8
!
gravel beaches have been omitted, as these are covered in other texts on beach design
!
detailed guidance on scour is omitted, as this subject is covered in other reference texts
and manuals
!
appendices on rock measurement, hydraulic and geotechnical data collection have been
omitted
CIRIA C683
1.5 Scope
!
1.5.2
the appendix on structure monitoring techniques has been omitted, as this subject is now
covered in Chapter 10.
Structure types considered
This manual provides guidance on the use of rock in a range of hydraulic structures. The
various structures in scope, and their key functions, are summarised in Table 1.2. A range of
structures is shown in Figures 1.2 to 1.18.
Table 1.2
Chapter 7
Chapter 6
Structure type
2
Rock structure types covered by the manual
Description
Functions
Breakwater (Figures 1.2,
1.3 and 1.4)
Usually rubble (rock) mound structure
projecting into the sea, comprising
gradations of stone, armoured with large
armourstone or concrete armour units
Rock protection to port
structures (Figure 1.5)
Usually rock protection at the toe of a vertical Provides protection against propeller wash and
wall or beneath a piled deck
ship-induced waves
Revetment (Figure 1.6)
Protective structure normally placed on
Protects coast against erosion
embankment or profiled fill material, often to Protects low-lying areas against flooding
form a seawall
Seawall (toe) (Figure 1.7)
Rock berm at toe of structure, often applied
to existing structures experiencing scour
problems
Prevents undermining of seawall
Groynes and artificial
headlands (Figure 1.8)
Rock mound structure generally constructed
on a beach perpendicular to the shore
Intercepts and traps beach material
Detached or reef breakwater
(Figure 1.9)
Rock mound structure generally constructed
parallel to, but not connected to, shore
Intercepts and stabilises beach material
Sill or berm
Rock mound structure generally constructed
parallel to shore at toe of beach
Traps or holds beach material in elevated
position
Rock protection to pipelines
and cables (Figure 1.10)
Rock bund on sea bed or rockfill in trench
Maintains stability of pipeline
Provides protection against impact, eg from
anchors, fishing gear
Shelters vessels and structures from waves
and currents
Prevents siltation of navigation channel
Prevents thermal mixing (eg cooling water intakes)
3
4
5
6
Scour protection of slender
Rock protection around base of structure
structures such as monopiles
Prevents undermining of structure
Scour protection for large (eg
concrete gravity) structures
Rock protection at toe of structure
Prevents undermining of structure
Rockfill closure dams
(Figure 1.11)
Closure dam composed of loose rock, usually Stops water flow and in some cases acts as a
dumped in place, characterised by high flows temporary dam (cofferdam) protecting a site
during the final stages of the closure
where a dam or other major structure is to be
built in a construction dock
Estuary closure (Figure 1.12)
Dam at a location where water levels and
currents are determined mainly by the tide;
in most cases the closure dam is
incorporated in the final estuary dam
River closure
River structure involving a closure dam or
Diversion of rivers (temporary or permanent),
cover dam either to divert the discharge or to eg for river control, temporary works, irrigation,
store it temporarily
or water level control for navigation
Rock protection of reservoir
dams (Figure 1.13)
Dam to create a reservoir, often involving a
rock protection to dam face, on downstream
slope or in filter drains and possibly a rockfill
dam
The rock protection prevents erosion of dam
core material that may also be partly
constructed from rock (rockfill dam)
Rock protection to barriers,
sills, weirs, barrages,
diversion dams, spillways
(Figure 1.14)
Generally low structures relative to water
level designed for through-flow or overflow
for a large proportion of the time
Rock is used to provide protection to areas
downstream of these structures, for armouring
and bed protection and for filter layers
CIRIA C683
1
7
Possible functions are flood control, land
reclamation, creation of a freshwater reservoir,
creation of a tidal energy basin, or providing a
road or rail connection
8
9
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9
1 Introduction
Table 1.2
Rock structure types covered by the manual (contd)
Chapter 8
Structure type
Description
Functions
Bank protection (Figures
1.15 and 1.16)
Rock or gabion revetment to protect riverbank
Prevents bank erosion
Controls river development, preventing
outflanking of adjacent structures
Spur-dikes (Figure 1.17)
Bund protected by rock, generally perpendicular
to riverbank
Controls river channel position
Constricts low-water channel to control water
depth
Diverts flow from riverbank
Longitudinal dikes (also
called guide banks or guide
bunds) (Figure 1.18)
Bund protected with rock, generally orientated
along same axis as river
Prevents bank erosion
Controls river flow and development,
preventing outflanking of adjacent
structures
Bed protection
Rock or gabion armouring to river bed
Prevents bed scour, including vessel-induced
scour
Fish passes
Rock-armoured channel
Provides open passage to enable fish to
pass a river control structure. Rock provides
scour/erosion protection
Bridge scour protection
Rock berm or bed protection around base of
bridge piers
Prevents scour of river bed around bridge
piers
1.5.2.1
Marine structures
Marine structures using rock are shown in the following figures. Design guidance for these
structure types is given in Chapter 6.
Figure 1.2
Rubble mound breakwater (courtesy Brien
Wegner, USACE)
Figure 1.3
Construction of breakwater using concrete
armour units (courtesy CUR)
10
CIRIA C683
1.5 Scope
1
2
Figure 1.4
Breakwater – eventually to contain
reclamation (courtesy Edmund Nuttall)
Figure 1.5
3
Rock protection to port structures
(courtesy Edmund Nuttall)
4
5
Figure 1.6
Rock revetment (courtesy HR Wallingford)
Figure 1.7
Scour protection to seawall (courtesy Clive
Orbell-Durrant)
6
7
8
Figure 1.9
Figure 1.8
Detached or reef breakwater (courtesy Clive
Orbell-Durrant)
9
Groynes and artificial headlands (courtesy
Halcrow)
10
CIRIA C683
11
1 Introduction
Figure 1.10
Rock protection to pipelines – using a fall-pipe dumping
vessel (after CUR 1995, courtesy Van Oord nv)
1.5.2.2
Closure works
Various types of closure works using rock are shown in the following figures. Design
guidance for these structure types is given in Chapter 7.
Figure 1.11
Rockfill closure dam under construction
(courtesy KARICO)
Figure 1.12
Sea dike (courtesy KOWACO)
12
CIRIA C683
1.5 Scope
1
2
3
Figure 1.13
1.5.2.3
Reservoir dam (courtesy KOWACO)
Figure 1.14
Weir with rock glacis (courtesy Andrew
Pepper)
River and canal structures
River and canal structures using rock are shown in the following figures. Design guidance for
these structure types is given in Chapter 8.
4
5
6
Figure 1.15
Rock revetment being constructed on
geotextile (courtesy Mott MacDonald)
Figure 1.16
Rock protection to outfall structure on bank
(courtesy Charlie Rickard)
7
8
9
Figure 1.18
Figure 1.17
Gabion guide bank (courtesy Mott
MacDonald)
Spur-dikes (after CUR 1995)
10
CIRIA C683
13
1.6
REFERENCES
CIRIA/CUR (1991). Manual on the use of rock in coastal and shoreline engineering. CIRIA Special
Publication 83/CUR Report 154, London
CUR (1995). Manual on the use of rock in hydraulic engineering. CUR Report 169,
Civieltechnisch Centrum Uitvoering Research en Regelgeving (CUR), Gouda
EDF-LNH (1987). Le dimensionnement des digues à talus. Collection des études et recherches no
64. Eyrolles Ed, Paris, 172 pp
LCPC (1989). Les Enrochements. Ministère de l’Equipement. LCPC, Paris, 106 pp
14
CIRIA C683
2
1
Planning and designing rock works
2
3
4
5
6
7
8
9
10
CIRIA C683
15
2 Planning and designing rock works
CHAPTER 2 CONTENTS
2.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.2 Defining project requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.2.1
The design process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.2.1.1 Stages in the life of the works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.2.1.2 Working at different scales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.2.1.3 Degrees of specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.2.1.4 Factors to be considered for an integrated design . . . . . . . . . . . . . . . . 22
2.2.2
Knowledge required for the design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.2.2.1 Information needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.2.2.2 Functional requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.2.2.3 Physical conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.2.2.4 Technical considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.2.2.5 Economic information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.2.2.6 Environmental information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.3 Technical considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.3.1
Rock systems and responses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.3.2
Structural design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.3.2.1 Structural components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.3.2.2 Structure loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
2.3.2.3 Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
2.3.3
Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
2.3.3.1 The design process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
2.3.3.2 Technical design criteria. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
2.3.3.3 Design approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
2.4 Cost considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
2.4.1
2.4.2
Whole-life costing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Cost elements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
2.4.2.1 Cost categories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
2.4.2.2 Fixed and variable costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
2.4.3
Cost estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
2.4.4
Rock sourcing, production and transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
2.4.5
Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
2.4.6
Maintenance and repair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
2.4.7
Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
2.5 Environmental considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
2.5.1
Sustainable use of rock as a construction material. . . . . . . . . . . . . . . . . . . . . . . . 49
2.5.2
Assessing environmental impacts through the project cycle . . . . . . . . . . . . . . . . 49
2.5.2.1 Project concept and design stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
2.5.2.2 Project approvals stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
2.5.2.3 Project construction stage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
2.5.2.4 Project operational stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
16
CIRIA C683
Contents
2.5.2.5 Project decommissioning stage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
2.5.3
2.5.4
1
Opportunities for environmental enhancement . . . . . . . . . . . . . . . . . . . . . . . . . 55
Environmental impact assessment process – an overview . . . . . . . . . . . . . . . . . . 57
2.5.4.1 EIA legislation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
2.5.4.2 Environmental statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
2.5.4.3 EIA process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
2
2.6 Social considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
2.6.1
Health and safety. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
2.6.2
Construction and operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
2.6.3
Engaging stakeholders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
3
2.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
4
5
6
7
8
9
10
CIRIA C683
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2 Planning and designing rock works
2
Planning and designing rock works
Chapter 2 provides an overview of the design process and project considerations. General
principles for rock works, applicable throughout the manual, are included here.
Key inputs from other chapters
starting point " for a rock project.
!
Key outputs to other chapters
project requirements – environment, cost, technical issues and functional
requirements " all chapters.
!
NOTE:
The project process is iterative. The reader should revisit Chapter 2 throughout the
project life cycle for a reminder of important issues.
This flow chart shows where to find information in the chapter and how it links to other
chapters. Use it in combination with the contents page and the index to navigate the manual.
Chapter 2 Planning and designing rock works
2.1 Introduction
2.2
Defining project
requirements
2.3
Technical
considerations
2.4
Cost
considerations
design stages
failure mechanisms
whole-life costing
integrated design
structural design
information needs
design criteria
fixed and variable
costs
design approaches
cost estimation
2.5
Environmental
considerations
environmental
impacts
opportunities for
environmental
enhancement
2.6
Social
considerations
health and safety
engaging
stakeholders
EIA
3 Materials
5 Physical processes and
design tools
4 Physical site conditions
and data collection
6 Design of marine structures
7 Design of closure works
8 Design of river and canal structures
9 Construction
10 Monitoring, inspection,
maintenance and repair
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CIRIA C683
2.1 Introduction
2.1
1
INTRODUCTION
All users of the manual are recommended to read this chapter before continuing to
subsequent chapters, as it provides an overview of key issues to be considered throughout
project development.
Chapter 2 emphasises the need to consider the whole life cycle of works from conception to
decommissioning (if appropriate) when planning and designing rock structures. Technical
aspects should be integrated together with social, environmental, economic and other factors.
The chapter introduces general issues that should be considered for the rock structures
discussed in this manual. The information in this chapter is at a high level and cross-refers to
other sections of the manual that provide more detailed information.
The chapter aims to raise general questions that the designer should be asking, for example:
!
what does the structure need to achieve?
!
what does the designer need to know?
!
what are the potential problems and/or constraints?
!
how should the designer approach the problem and develop solutions?
2
3
4
A project generally begins long before the conceptual design of any works is undertaken. The
need for particular works is usually established by feasibility studies that should have
considered factors such as economic justification and the project’s physical, social and
environmental impacts. These studies – which may be extensive – are often essential to
determine the viability and acceptability of the project. The subsequent input invested in the
design of the works can sometimes be small by comparison. Feasibility studies or wider
strategic planning prior to a scheme are beyond the scope of this manual.
5
This chapter, and the rest of the manual, assumes that the need for works that involve the
use of quarried rock has already been demonstrated and that alternative options have been
shown to be less suitable or less preferred. The guidance may be helpful when reaching that
decision during any pre-design/planning assessments. Consequently, references to the project
throughout the manual apply only to the activities associated with the rock works.
6
NOTE: The principles described in this chapter apply to the whole planning and design
process and indeed to any stage in the asset life cycle. Planning and design are not always
restricted to project stages before work starts on new structures. There is increasingly a need
to maintain, repair, modify or upgrade existing structures, and these activities also require
planning and design. The asset management life cycle is illustrated in Figure 2.1.
7
8
9
Figure 2.1
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10
The asset management cycle
19
2 Planning and designing rock works
2.2
DEFINING PROJECT REQUIREMENTS
2.2.1
The design process
2.2.1.1
Stages in the life of the works
During the life of any works there are several typical stages where the design of works needs
to be considered:
!
project definition
!
concept design
!
preliminary (or outline) design
!
detailed design
!
construction including working drawings and works preparation
!
operation, including monitoring, maintenance, repair and upgrading, if required
!
decommissioning, including removal where applicable.
All projects start with a need: something that is desired, required or lacking – the lack of
shelter in a harbour, for example. The project definition stage defines this need by setting
project objectives, typically based on the project promoter’s aspirations. These objectives will
present requirements (ie what is stipulated) and restrictions (ie what is not wanted or not
allowed). Clear objectives will assist in establishing the appropriate engineering solution to
meet the identified need. This is the starting point for the designer.
At the concept design stage broad solutions are generally developed, such as typical structure
types and locations, often to assess the feasibility of the scheme. One of the main activities at
this point tends to be the identification of the functions, constraints and information
requirements that will enable the design to go forward. Factors for consideration might
include permissions needed and the physical conditions data that are required in order that
the next stage of scheme development can proceed.
Preliminary design is when many of the investigation and study activities should be carried
out, including determination of wave climate or current regime, environmental assessments
and economic analysis. At this stage there should be greater focus upon technical feasibility.
Designs are likely to be developed to a level where the main structural dimensions such as
profiles, elevations and widths are quantified and the principal materials are identified.
During preliminary design a number of alternative outline designs may be developed for
assessment. The assessment should consider factors such as:
!
practicality of the option (including construction)
!
achievement of political, social and legislative conditions
!
environmental impacts and optimum use of resources
!
whole-life costs
!
identification of risks (technical, economic and environmental)
!
complexity of operation and maintenance.
This should be an interactive process, involving many parties, to gain agreement and select a
preferred solution.
Once the various criteria have been satisfied, detailed design should involve the
development of all structural elements, using further in situ investigation and physical and
technical data, to produce drawings, specifications and bills of quantities. It may be necessary
to work with other parties such as environmental and planning authorities in the design,
before approvals to proceed with construction are granted.
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CIRIA C683
2.2 Defining project requirements
During the construction stage further detailed working drawings are prepared and further
design modifications may be necessary as a result of on-site difficulties such as unforeseen
ground conditions or changes in working approaches. Where this happens, the designer
should ensure that the original design concepts are fully understood and the design changes
do not compromise any other aspect of structure performance.
In the operational stage the continued performance of the structure is ensured by
implementing a monitoring and maintenance programme. This may identify the need for
repair works. A change in use of a facility may mean that modification or upgrading works
are required to ensure that the structure delivers the required performance. These changes
need to be made with an understanding of the original structure design and the
consequences need to be fully determined.
If a structure has to be removed, it is important to understand the original design as well as
any subsequent modifications to allow decommissioning with minimum health and safety
risk, and also to allow the environmental impact(s) of the decommissioning to be understood.
2.2.1.2
Working at different scales
Satisfying needs and wishes, solving problems and developing solutions usually take place at
three levels:
!
macro-scale: the system (in this case, typically the structure or structures, where a
number of structures are required to work together, such as in a groyne system)
!
meso-scale: the components of the system (including the components within the
structure, such as the armour layer or toe, and the zone of influence such as the ground
affected by the structure)
!
micro-scale: individual elements (armour stones, concrete blocks, sheet piles, capping
beams).
2
3
4
5
6
In general, the designer is involved in all three levels.
2.2.1.3
1
Degrees of specification
The design process exists as a number of design cycles, increasing in level of detail:
1
A first cycle maps out clearly the objectives of the project – the need or wish that must
be fulfilled – for example, provision of a sheltered harbour or protection of riverbanks
against erosion.
2
A second cycle yields quantitative and measurable functions or performance requirements,
which describe unambiguously what has to be achieved in order to reach a certain goal –
eg protection against waves of 3 m height or a water velocity of 4 m/s in a river.
3
A third cycle results in the main form and features or shape of the structures – such as a
curved, trapezoidal breakwater or groynes or dikes in a river.
4
A fourth cycle results in specifications, how the structure shall be built – eg materials,
dimensions and tolerances.
7
8
9
10
CIRIA C683
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2 Planning and designing rock works
2.2.1.4
Factors to be considered for an integrated design
All structures are designed to fulfil a specified purpose or purposes – the functional
requirements, sometimes called performance requirements. In addition to these there will
be other criteria that the structure will have to meet, which may impose additional design
constraints. These can be categorised as:
!
technical considerations – physical conditions, engineering, construction, maintenance
(Section 2.3)
!
economic considerations – capital and maintenance costs, benefits, whole-life costs
(Section 2.4)
!
environmental considerations – impacts on the natural environment (Section 2.5)
!
social considerations – impacts on the human environment comprising the workforce,
stakeholders, general public etc (Section 2.6).
These considerations and typical factors under each heading are given in Table 2.1 and are
discussed further in the sections of this chapter indicated above. It should be noted that this
list is not exhaustive and each project may generate specific issues that need to be
considered. Table 2.1 provides cross-references to the sections of this manual where detailed
guidance is provided.
All of the factors listed in Table 2.1 may influence the design, although not all of these will be
known at the outset of a project. Consequently, the design process is an iterative one.
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CIRIA C683
2.2 Defining project requirements
Table 2.1
Aspect
!
Functional requirements
(performance)
!
!
!
!
!
!
Physical conditions
!
!
Technical considerations
!
!
!
!
Technical data
!
!
!
!
!
!
Construction
!
!
!
!
!
!
Maintenance
!
!
!
!
!
Economics
!
!
!
!
!
!
Environment
!
!
!
!
!
Social considerations
1
Planning and design considerations
!
!
Considerations
Section
Achievement of functional requirements (eg limiting overtopping, reducing wave
activity in a harbour, preventing riverbank erosion)
Acceptable structural stability and residual risk of failure (factors of safety and
choice of design conditions)
Changes in acceptable probability of failure over time
Adaptability (for example, change of use of the structure over time)
In-service health and safety requirements
Section 2.3
2
Geotechnical ground conditions
Topographic and bathymetric conditions
Hydraulic forces – waves, currents, water levels, flows, ice
Morphological changes
Sediment load and movement
Uncertainties in physical conditions (confidence limits)
Chapter 4
3
Material properties (eg armourstone grading), quality, durability and availability
Accuracy of design information, parameters and analytical methods
Structure-specific design methods
Nature of failure (progressive or instantaneous, complete or partial)
Chapter 3
Chapter 5
Chapters
6,7,8
Buildability
Contractor experience and resources
Health and safety issues
Conditions during construction (eg storm or flood frequency and magnitude)
Access of construction plant
Construction materials – properties and quality
Alternative material availability (sources)
Site area for storage of materials and operations
Chapter 9
5
Characteristics of structure response
Frequency and type of intervention
Availability of suitable resources for repair (materials, plant, expertise)
Funding
Accessibility for construction plant
Chapter 10
Derivation of alternatives
Benefit vs cost (the balance between full or limited achievement of functional
requirements for higher or lower cost)
Acceptable operational risk
Capital cost constraints
Potential maintenance costs
Section 2.4
Accommodating environmental requirements
Preserving resources (water, rock etc)
Potential environmental impacts of construction
Risk of vandalism
Potential environmental benefits of scheme
Morphological and sedimentological impacts
Acceptability of physical appearance
Section 2.5
Health and safety
Construction and operation
Stakeholder participation
Section 2.6
6
7
8
9
The outcome of a successful integrated design should be a structure (eg a revetment, bank
protection, closure or breakwater) that delivers the required performance and which is
robust, easy to build and maintain, socially and aesthetically acceptable, cost-effective and
produces the fewest negative impacts on its environment.
In practice, any project will have to achieve an appropriate balance between all of these
requirements. Project economics generally aim to balance the value of the project, mainly
CIRIA C683
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10
23
2 Planning and designing rock works
dictated by functional performance and the impact on the environment, and cost, dictated by
technical or engineering aspects and by construction. The level of attention paid to these
aspects changes over the course of the design. For example, attention to functional
performance (and hence value) decreases at later stages, whereas attention to construction
(and hence costs) increases.
The planning and design of a structure should take into account all future life stages of the
works, including construction, operation and, if appropriate, decommissioning. Changes to
conditions or functional requirements within the projected life of the structure should also be
considered. Where appropriate, the structure and its planned maintenance should be
designed to allow some adaptability to cope with changes in the environment or in functional
requirements during the lifetime of the structure. This might include a change of use for the
structure, altered wave conditions, rising water levels, variations in scour or sedimentation
rates, increased traffic, and changes in the availability of local materials and labour for
maintenance etc.
2.2.2
Knowledge required for the design
2.2.2.1
Information needs
Information relating to understanding the problem and/or constraints upon the project would
usually be provided by the client/operator and planning or regulatory authorities.
Information is often very specific to project type and location. When it relates to function and
expected use of the structure, information may be broadly defined. The details of
performance expectations and constraints might not have been determined at the outset,
however, and may need to be defined further by the designer and accepted by the client.
Table 2.1 identified the main design aspects that should be considered. Information will be
required on all these aspects to develop an appropriate design, in particular:
!
functional requirements
!
physical conditions
!
technical data (including construction and maintenance requirements)
!
economic considerations (including acceptable operational risks)
!
environmental conditions and requirements.
Project constraints also dictate aspects of the design. Typical examples might be:
!
level of exposure to hydraulic loads at the site that may preclude or dictate the use of
certain materials or construction techniques
!
ground conditions, such as soft silts that may need to be removed as part of the
construction process
!
lack of availability of certain materials or plant, which could influence the form and
structure of the works
!
nature conservation or other environmental interests that may influence the type of
construction or maintenance operations possible, or the footprint of the structure itself
!
visual intrusiveness, precluding the building of a certain type of structure or restricting it
to a certain maximum elevation
!
financial balance between the budget available for construction and that for maintenance.
Ultimately it is the designer’s responsibility to obtain as much detail as possible on these
issues. This information can be used to develop solutions that address the needs, constraints
and preferences that exist throughout the life of the project. The available information and
knowledge will vary throughout the development of the works and the design should be
re-evaluated accordingly as this occurs.
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CIRIA C683
2.2 Defining project requirements
2.2.2.2
1
Functional requirements
With any project it is important to have a full understanding of the functions that the
structure should fulfil, particular problem(s) that need to be resolved and the requirements
for the solution. Performance expectations should be clearly defined at the outset with the
client/operator, as problems may arise if each party has different expectations when a design
proceeds. Before embarking upon the design, maintenance or rehabilitation of a structure
the following questions should be asked:
!
what is this structure being designed or maintained to do?
!
what are the design performance requirements?
Although these questions seem obvious, they are not always addressed. It is good practice to
produce a set of functional requirements for the structure that can be agreed upon and used
as design criteria.
As an example, for a port breakwater the following key considerations all have an influence
upon the structural design:
2.2.2.3
!
the purpose of the structure
!
the use of the facility and the extent of protection required – for example, different
levels of protection are advocated for ports, fishing harbours and small boat marinas
!
layout of the facility – for example, whether the area directly behind the breakwater is to
be used for berthing or storage, or whether access along the breakwater is required
!
acceptable downtime – for example, tolerable frequency of exceedance of the above
conditions, downtime for operations, offloading of vessels etc
!
design life of the facility – not necessarily the same as the return period of the design
parameters
!
acceptable risks during the structure lifetime, which should influence the choice of
design parameters
!
level of maintenance and ease of operations or availability of material or plant – inherent
damage allowances within designs should be identified and minimised if this is an issue.
3
4
5
6
Physical conditions
Physical conditions are generally the primary determinant in the design and construction of
a rock structure. They include hydraulic loading parameters that influence the form of the
structure in terms of plan shape, height, profile, width and material composition, and how it
is built. Project cost uncertainty can be controlled by increasing understanding of the physical
conditions. This may be by investing in data collection on, for example, wave or foundation
conditions. The extra effort needed to gather this knowledge is often a small fraction of the
cost saving that can be achieved.
Physical site conditions of principal interest include bathymetry, topography and morphology,
geotechnical conditions (foundation soil characteristics and pore water pressures), hydraulic
conditions (water levels, winds, waves, currents) and other potential loads such as ice or ship
collision. Chapter 4 provides details on these information requirements and methods of
derivation for environmental loading parameters, for example numerical modelling of waves
and water levels. It also discusses how to derive combinations of physical site conditions to be
used in design, both for normal service conditions and for extreme conditions. Access to the
site for construction and maintenance purposes should also be taken into account.
In terms of whole-life asset management and the possible need to modify the structure in the
future, attention should also be paid to monitoring (see Section 10.3). The measurement may
be of changes to the structure itself, achievement of performance criteria, and/or impacts
upon the surrounding area.
CIRIA C683
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25
7
8
9
10
2 Planning and designing rock works
2.2.2.4
Technical considerations
Technical considerations relate to both design and construction. For design, these include
selection of an appropriate design approach and tools. It is important to understand how a
structure behaves and the function of the various component parts of the structure. These
are discussed in Section 2.3, which contains an overview of the technical aspects of design
development, primarily focusing on technical principles. More details about the design tools
are given in Chapter 5. Design guidance for different structure types is covered in Chapters
6, 7 and 8.
Construction and maintenance considerations usually act as boundary conditions to the
solution rather than to the problem and so become part of the iterative design process. Where
information is available on the quality of available materials or local constraints on particular
working methods, this can be key to defining the solution (see Box 2.1).
Box 2.1
Key construction considerations for rock solutions
Essential construction considerations to plan and develop a rock solution include the following:
!
Availability of materials. In particular, this may influence the choice of armouring (eg armourstone,
concrete armour units or other alternatives) and the shape of the structure (such as the adoption of
shallower slopes or berm breakwater profile).
!
Local construction resources. If the quality of construction is questionable, make due allowances in
design sizing and tolerances.
!
Best use of materials. The exact dimensions of a breakwater should ideally be proportioned to
optimise the use of the quarry yield, for example gradings designed to use the quarry’s whole
production. Consider tailoring the design to suit local availability of material.
!
Type of plant. Consider the maximum reach of plant, particularly in placing large armour units. For
example, construction of a breakwater from a barge can take twice as long as construction from the
crest, but the latter requires ample working space on the crest.
!
Movement of plant. For example, consider whether there is sufficient crest width at a construction
level above water level to enable plant movement, material supply, crane manoeuvrability, inclusion
of passing places as features in final construction.
!
Uncomplicated details. Strive for simplicity in terms of stone layers etc; keep the number of different
construction activities to a minimum.
Construction issues should not compromise or dictate the solution, but they should play a
major part in determining the design. Account should be taken of the likely construction
method, as invariably the simpler the method, the faster and cheaper the structure can be
built, even though it may require more material. This is even more important where the
structure forms only one component of a larger development, for example a port breakwater
that is required for protection to allow other construction activities to start safely. However, it
can be difficult to convince a client or operator that the smallest material volume may not
equal the lowest cost. In some circumstances it may be appropriate to design and tender two
alternatives, one reflecting lowest volume and the other the simplest construction solution.
Future maintenance requirements form an important element in the planning and design of
any rock structure. The designer needs to consider similar issues to those of construction, but
should recognise that maintenance matters may be more challenging. For example, access
along a structure and the suitability of plant are likely to be of greater significance for
maintenance than construction. Activities may be limited by constraints that did not exist
during construction, such as the need to avoid disrupting operations or endangering life
through a temporary reduction in the standard of protection usually afforded by the structure.
More details on construction, monitoring and maintenance of structures are provided in
Chapters 9 and 10.
26
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2.2 Defining project requirements
2.2.2.5
1
Economic information
The cost of a project is always a major consideration during design and is affected by many of
the factors listed in Table 2.1. Generally only a few of these – usually relating to either
material volume or constructability – have a major influence. Other costs may be relatively
minor, but should still be considered.
The availability and sources of funds are important. Publicly funded projects may need to
satisfy economic criteria, perhaps progressing in stages as criteria are met at each stage.
The client/operator may not at the outset recognise all the economic consequences of
performance and level of risk over time (see Section 2.3.3.2). An option may be a structure
with a lower initial cost but a higher risk of damage during its operational life. This choice
may be acceptable where capital outlay is constrained, but the client should be aware that
higher maintenance costs are possible. If so, there should be a degree of certainty that an
adequate maintenance budget will be available in the future. Other criteria, such as
requirements for public safety or safe working conditions, also need to be established.
3
4
Section 2.4 provides detail on the cost considerations of a rock project.
2.2.2.6
Environmental information
The designer, supplier, contractor and operator need to be aware of the environmental
implications of using rock in hydraulic engineering. Consideration of environmental issues
should normally begin at the definition stage of a project and should continue to be looked at
regularly throughout the course of the project. These issues will relate to the works
themselves, such as the materials and the methods of construction, and to the impacts of the
works. The environment includes the physical surroundings, natural habitats and species,
and human/ social activities. The use of resources, pollution of air, water or land, and adverse
effects on habitats, flora and fauna by construction-related activities are all examples of
environmental impacts. The use of rock may also provide opportunities for environmental
enhancement, such as its beneficial use where rock is a by-product of other activities or
recycled from previous works, or even the creation of new habitats.
Many environmental considerations are site-specific, relating to local regulations and local
features. An environmental assessment might have to be conducted for the project. The
assessment procedure is outside the scope of this manual, but it needs to be understood by
those involved in the planning and design of a project.
5
6
7
Complying with environmental requirements, which often are driven by legislation or
planning policy, can be time-consuming, requiring comprehensive studies and provision of
mitigation measures. Planning permissions and licences may have to be obtained from a
range of organisations and consultations may be needed. It is important, therefore, that
developers, designers and contractors engage with the appropriate authorities as early as
possible during the project to ensure the process runs smoothly.
8
Environmental requirements vary significantly between countries and types of works, so they
cannot all be discussed within this manual. However, throughout much of the world some
form of environmental impact assessment (EIA) is normally a prerequisite to a scheme being
accepted. Section 2.5 presents the general principles of EIAs and discusses specific issues for
rock structures.
Methods of construction and working practices may be dictated by environmental and social
impacts, greatly affecting the cost of a structure. For example, the stockpiling of rock may be
restricted, the ability to transport material by road may be prohibited or it may be critical to
prevent losses of fines into the air or water during placement of quarried rock.
CIRIA C683
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2 Planning and designing rock works
Environmental considerations also include the sustainability of material selection, which requires:
!
efficient use of materials
!
waste minimisation
!
recycling of waste.
These factors may be critical to the design, either through using the full quarry production
to minimise waste and by-products, using recycled materials, or ensuring the materials can be
recovered and reused in the future. Social aspects, such as health and safety of construction
workers and stakeholder consultation, are also relevant. A brief discussion on these issues is
given in Section 2.6.
Environmental and social aspects should be considered for the whole life cycle of a structure –
including operation, maintenance and decommissioning – not just its design.
Sections 2.5 and 2.6 provide more detail on environmental and social considerations.
2.3
TECHNICAL CONSIDERATIONS
The section will help the user to understand how rock structures perform as well as how to
design and build them effectively. The information presented here is generic to any type of
rock structure. The reader should refer to Chapters 6, 7 and 8 for details of the different
structure types and discussion on their design. Supporting those chapters, the tools that are
used to develop designs are presented in detail in Chapter 5.
2.3.1
Rock systems and responses
This section describes the general principles of rock systems and their responses.
A rock system is schematised with its hydraulic and structural responses in Figure 2.2. Design
methods based on these responses are presented in Chapter 5.
Figure 2.2
28
A rock system and its responses to hydraulic loading (waves)
CIRIA C683
2.3 Technical considerations
1
A range of scenarios should be considered in the design of hydraulic structures, including
those related to normal functioning of the structure in service and also to ultimate or
accidental situations. Some degradation or even failure of the structure or elements of the
structure may occur as a result of the loadings generated in these situations.
Failure occurs when the response exceeds a value of performance that relates to the structure’s
functional requirements. Failure is a response that corresponds to a defined loading (the
failure loading) for a given design scenario. In general, failure mechanisms are named after
their consequent displacements or movements. Failure is thus characterised by a relatively
large increase in response that is generated by a minor increase in loading. An overview of
the principal failure mechanisms for rock structures and corresponding loadings is given in
Figure 2.3.
Each of the failure modes shown in Figure 2.3 should be considered in the design of rock
structures, although the degree to which these are relevant will vary for different structures,
locations and design scenarios. Some failure modes can be allowed to occur repeatedly up to
a certain limit during normal service life, for example overtopping up to an acceptable
threshold or displacement of stones on a dynamically stable slope. Other failure modes, such
as ship collision or ice loading in normally mild regions, are rarer events that may be
considered as ultimate design scenarios. For some failure modes not even a single occurrence
can be accepted, such as liquefaction of the subsoil under a breakwater.
In general, very limited damage to the structure is accepted for normal service design
scenarios, as the structure is expected to fulfil its functional requirements. For rarer types of
event, such as ultimate or accidental situations, some level of damage of the structure or
some under-performance may be accepted, as it is usually not cost-effective to design for no
damage under extreme conditions. The designer should identify a range of normal service
and ultimate design scenarios and evaluate the potential degradation or failure that each one
may induce, so they can be compared with defined acceptable levels of performance, ie
limited degradation or some degradation. The client may need to confirm selected acceptable
levels of performance. Further discussion on acceptable risk levels and selection of design
conditions is given in Section 2.3.3. The use of the above approach is fully developed for
geotechnical verification of the structure in Section 5.4.
It should be noted that often these failure modes are interrelated: for example, settlement of
the structure may lead to increased overtopping, which may cause instability of the inner
(rear-side) slope of the structure. Table 2.2 presents a summary of the key failure
mechanisms and their characteristic parameters and notes some of the interactions between
failure modes, with cross-reference to Figure 2.3. Further discussion on failure mechanisms is
given below.
2
3
4
5
6
7
8
9
10
CIRIA C683
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2 Planning and designing rock works
Figure 2.3
30
Typical failure modes of rock structures
CIRIA C683
2.3 Technical considerations
Table 2.2
Main failure mechanisms and characteristic parameters
Mechanism
Principal loading parameters
Overtopping Waves – height, period
Water levels
1
Ref in
Fig 2.3
System characteristics
Response characteristics
Crest level; slope angle
roughness and energy
dissipation
characteristics of outer
face and crest
Damage to crest and rear- 1, 2
side slope; undesired
water discharge to the
rear side
Settlement,
tilting
Weight – specific density of
materials; saturation degree;
pore water pressure; time
Soil compressibility;
soil permeability; layer
thicknesses
Crest lowering; horizontal
deformations; increased
overtopping; increased
loading in structure
(eg caisson)
3, 4
Slope
instability
Water levels – differential water
levels
Internal friction angle
of material
Rotational failure of slope
5, 6
7
2
3
Waves – weight of construction
materials; pore pressures; slope
angle
Sliding of
structure
Weight of structure or elements –
weight of construction materials;
pore water pressures (influenced
by wave height and period);
slope angle
Friction angle (between
layers); cohesion and
permeability of soil,
core and cover layer(s)
Sliding of (a significant
part of) the structure;
collapse (may also take
place at the base of a
caisson)
Movement
of rock
cover
Waves – height, period, angle of
incidence
Stone size and density;
permeability of the
cover layer
Rocking; sliding; lifting;
8, 9
rolling; loss of armour
units leading to erosion of
front face and local
instability (may induce
stone breakage)
Migration of Water level changes – waves,
sub-layers
ship-induced water movements,
other dropping water levels;
hydraulic gradients; internal flow
velocities
Layer permeabilities
and thicknesses; grain
sizes
Internal material transport 8, 9
rate; local instability or
deformation
Piping
Hydraulic gradients – internal
channel flow velocities
Flow path length;
hydraulic resistance;
grain size
Internal material transport 10
rate
Erosion of
foreshore
Waves – height, period
Sediment grain size;
Scour of sea bed in front
structure slope;
of structure
permeability of structure
11
Permeability;
compaction; thickness
of layers; friction
angles
12
Currents – turbulence, velocities
Ice – layer thickness and drift
intensity
Currents – velocities,
turbulence
Liquefaction Waves – height and period
Earthquakes – acceleration,
frequency; number of loading
cycles; pore water pressures;
(relative) shear stress amplitude
Serious deformation of
structure; collapse
4
5
6
7
8
Overtopping
Combinations of waves and water levels or extreme water levels alone can lead to water
overtopping the crest of a structure. Small volumes of overtopping water may be acceptable,
but larger volumes may damage the structure crest and rear-side face or cause flooding of
the hinterland, which may be classed as a failure of the structure in terms of its service
requirements. The amount of acceptable overtopping will depend on the robustness of the
crest of the structure and its ability to withstand high-velocity flows over the crest.
9
Settlement
The weight of a structure causes an extra load on the subsoil. As a result it may be compacted
or squeezed, either instantaneously or, for low-permeability compressible layers, over time. A
CIRIA C683
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2 Planning and designing rock works
further consequence may be the collapse of underground cavities. In addition, the structure
itself may become more densely packed during construction or in the first stages of its
operation; this can equate to 5–10 per cent of the height for a rubble mound structure.
The above processes cause the crest level to settle, reducing the structure’s effectiveness in
limiting overtopping during high water levels and/or wave attack. Differential settlements
produce uneven surfaces, which can make some stones more susceptible to being displaced.
Differential settlements can also lead to undermining of support for crest structures.
However, for submerged structures, settlement can improve armour layer stability as the
structure moves farther from the zone of highest hydraulic loads.
Slope instability
Low or loss of internal friction within a rock structure can generate slip failures. Where the
structure slope angle is close to the angle of repose, small changes in loading may also induce
slope instability. Erosion of the foreshore may lead to slope instability if scour damages or
undermines the toe of the slope.
Instability can also be caused by wave action or rapid changes in water level, for example when
tide levels fall and the internal water level in the structure lowers more slowly, as the structure
is subjected to additional forces. Overtopping may contribute to slope instability on the inner
(rear-side) face of the structure because of the additional hydraulic loading on the crest.
Sliding of (parts of) structure
The stability of a rock slope is determined by slope angle, specific weight, pore pressures
caused by water level differences and wave motion, internal friction and interlocking. Also of
importance are horizontal accelerations, which may arise during earthquakes or wave shock
loading, for example. Sliding is also more likely along interfaces between different materials,
for example armour and underlayer, because the local friction here is reduced, or indeed
where other materials are incorporated, such as geotextiles or membranes.
The subsoil plays a part in supporting the structure and can lead to excess pore pressures in
the structure and in the foundation. Liquefaction in any fine layers beneath rock structures
may be important for toe stability and slope support. Excess pore water pressures also have
to be considered when the stability of the slope is calculated, for example where the water
level drops more rapidly than the groundwater, which is common in tidal conditions.
Crest structures – usually concrete walls – may move, typically by sliding, under wave loading,
so adequate friction between the structure and the underlying rock is critical for stability.
Movement of rock cover
Waves and currents determine the lift and drag forces acting on the stones in the cover layer.
The inertial forces are also determined by the stone characteristics. The stone weight and
forces due to friction and interlocking are stabilising factors.
The dynamic loss of balance of all these forces may cause stone movements. Displacements
are generally associated with the outer (seaward or riverside) face of structures but may also
occur on the rear-side face of breakwater roundheads, the lee side of groynes and the
landward side of structures as a result of excessive overtopping. These responses may be
allowed for in the design, but care is needed to avoid responses large enough to initiate other
degradation or failure modes such as damage to the filter layer.
Over time the materials in the structure may become susceptible to deterioration. This can
take the form of degradation of the rock, including rounding of stones and reduced
32
CIRIA C683
2.3 Technical considerations
interlock. Breakage may occur, as wave action redistributes stones over time. This may loosen
the cover layer or reduce the unit weight of the armourstone, making it more prone to failure.
In some circumstances, especially where wider gradings of smaller stone are used such as riprap, longshore transport of the cover stones may take place if the angle of the structure is
acutely orientated to the direction of wave attack.
Migration of sub-layers
An internal flow may be established because of a difference in water level or local excess pore
water pressures. When a certain critical hydraulic gradient and the corresponding flow
velocities occur, the finer grains are transported out from the inner layers through the
coarser material of the upper layers. Often these finer grains pass easily through the cover
layer, resulting in a loss of material from the sub-layers (filter, underlayer) and/or from the
core, which may ultimately lead to local settlements.
1
2
3
Piping
Piping refers to the formation of stable open channels in a granular skeleton created by
migration of particles out of the system. These short pipes may connect up and thus allow
progressive internal erosion, eventually causing the structure to collapse. This phenomenon
is more likely to occur at structural interfaces, such as boundaries between permeable and
less permeable materials, or where loosely packed and densely packed granular materials
adjoin one another.
Erosion of foreshore
Waves and currents may generate sediment mobility. Interactions with the structure (wave
reflection, wave draw-down, generation of turbulence) may result in scour of bed or beach
materials directly in front of the toe of the structure, with the potential to cause undermining.
Liquefaction
Cyclic loadings can generate excess pore pressures when the deformations resulting from the
loading cause compaction at the same time that the drainage capacity for dissipation of the
resulting increases in pore pressure is low. Liquefaction refers to a situation in fine granular
materials where excess pore pressures are generated to such a degree that intergranular
contact is lost. The whole medium loses its shear strength and behaves like a thick fluid.
Under these circumstances any shear loading may cause sliding or stability failure.
2.3.2
Structural design
2.3.2.1
Structural components
4
5
6
7
8
This section provides an overview of how a structure is designed and built to accommodate
and counter the failure modes discussed in Section 2.3.1.
A structure comprises various components, each having a specific function critical to the
structure’s overall performance and adequacy. The most critical elements for rock structures
are generally stability of the cover layer, a secure foundation to minimise settlement, toe
protection to prevent undermining, and a suitable crest for protection. The components of
any rock structure and their relative importance differ according to the structure type. These
are described in more detail in Chapters 6, 7 and 8, which cover marine works, closure works
and river and canal structures, respectively. For all structures, the main requirement is to
understand each component’s functions and its importance to the overall design. It should be
noted that not all structures require all of the components in order to function properly.
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2 Planning and designing rock works
The functions of component parts fall into two categories:
!
functions related to the primary function of the structure
!
functions related to maintaining the structural integrity of the structure.
These functions are best appreciated by an example. Figure 2.4 illustrates the key component
parts of a breakwater, which are also listed in Table 2.3 along with the primary functions they
perform. It can be seen that the core of a breakwater fulfils a primary function by preventing
or significantly attenuating wave transmission, but it also provides support to the armour
layer and overall geotechnical stability.
Figure 2.4
Component parts of a typical rock structure
Table 2.3
Functions of typical component parts of a rock structure
Component
Function
Scour protection
!
Prevents erosion and undermining of the toe
Core
!
Attenuates wave transmission
Supports armour layer and underlayers
Provides geotechnical stability
!
!
Berm
!
Attenuates wave action, run-up and overtopping
Provides additional geotechnical stability
Toe
!
Provides stable footing to armour layer
Underlayer
!
Acts as a filter
Protects subsoil/core from erosion
Provides in-plane drainage
Regulating or levelling layer that provides appropriate surface for armour layer
placement
Separates armour from smaller sized materials and reduces hydraulic gradient into
subsoil/core
!
!
!
!
!
Armour layer
!
!
Crest
!
!
34
Prevents erosion of underlayer and core by wave action
Dissipates wave energy
Attenuates wave overtopping
Allows access for maintenance
Crown wall
(not shown in
Figure 2.4)
!
!
Attenuates wave overtopping
Allows access for maintenance
Provides support for facilities such as cabling and pipework
Roundhead
(not shown in
Figure 2.4)
!
Terminates the structure in a stable manner
!
Diffracts waves
!
CIRIA C683
2.3 Technical considerations
2.3.2.2
1
Structure loading
When designing a structure it is important to understand which loading cases (intensity and
duration) apply to each element of the structure. For example, the design of toe or scour
protection of a structure should take into account a range of water levels, in combination
with waves if appropriate, to establish the critical conditions for stability. By contrast, in the
design of a structure crest for satisfactory overtopping performance, the highest water levels
are generally the most important. A typical example of loads and the zones of the structure
where they apply is presented in Figure 2.5, illustrating a coastal structure in a tidal region.
The four loading zones are defined as follows:
!
Zone I – permanently submerged zone below mean low water (MLW)
!
Zone II – zone between mean low water (MLW) and mean high water (MHW) with
continuous low-intensity wave action
!
Zone III – the zone between MHW and the design (extreme) water level, which can be
heavily attacked by waves; the frequency of wave attack decreases moving further up the
slope
!
Zone IV – the zone above design level, which will experience wave run-up and
overtopping.
2
3
4
5
6
Figure 2.5
7
Exposure zones for a structure exposed to waves
Similar zones may be identified for river structures, depending on the range of expected
water levels under normal and extreme conditions. These zones will be categorised in terms
of flow conditions, although, where appropriate, consideration may also have to be given to
ship-induced waves under various navigable conditions.
Considering a structure in terms of loading zones should ensure that it is designed against
the relevant failure modes for each zone. The appropriateness of the design for each zone
should also be checked, including the identification of appropriate materials, the construction
and maintenance methods to be employed, the potential environmental consequences of the
construction and the cost implications.
8
9
More details on hydraulic loading conditions can be found in Chapter 4.
10
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2 Planning and designing rock works
2.3.2.3
Analysis
As a minimum, the design of a rock structure typically needs to include analysis and design
of the following:
!
armour layer (seaward/riverward face, crest, rear-side face protection)
!
toe (anti-scour protection)
!
underlayers and filters
!
core and foundation (drainage/settlement).
The design should consider the overall plan geometry, main cross-sections, arrangements at
the limits and transitions in the structure and avoidance of outflanking.
Section 3.1.2 discusses material functions and properties that are important for design,
relating to the different structure components. More detail on the requirements for design of
each component for specific structure types is included in Chapters 6, 7 and 8. Chapter 5
provides information on the design tools for the structural design relating to each of the
above components. Typical structural analyses for different structure types are listed in Box
2.2, although it should be noted that this list is not exhaustive and other site-specific analyses
may also be required.
Box 2.2
Typical analyses required for rock structures
Typical analysis for a structure in the marine environment, exposed to waves, currents and tidal water
levels, should include the following:
!
run-up, and overtopping of waves to define structure profile and elevation
!
armour stability, to establish required material sizes and placement method for slope, toe and crest
!
filter criteria calculations to design underlayers etc
!
wave reflections and currents to help determine scour potential (and, occasionally, the effect on
navigation or reflection performance)
!
wave transmission to confirm crest elevation
!
scour potential for toe design
!
geotechnical stability related to pore pressures including settlement, piping etc
!
slope stability and foundation stability
!
flooding and rear slope integrity where breaches occur
!
ship-wash, propeller cavitation and squat (where in close proximity to vessels, eg in a port or harbour).
Typical analysis for a structure in a fluvial environment, exposed to waves, currents and water levels,
should include the following:
36
!
range of water levels to define structure profile and elevation
!
armour stability, to establish required material sizes and placement method for slope, toe and, if
required, crest protection
!
filter criteria calculations to design underlayers etc
!
scour potential for toe design
!
pore pressures for geotechnical stability, allowance for settlement
!
local and global slope stability
!
impact of waves if relevant (eg wind-generated waves in a flood storage reservoir, or boat wash on
navigable rivers).
CIRIA C683
2.3 Technical considerations
2.3.3
Design
2.3.3.1
The design process
1
After selecting one or more solutions that meets the functional requirements of the project
(see Section 2.2.2.2), the next stage is design and detailing. Figure 1.1 (Chapter 1)
summarises the project and design process and includes cross-references to relevant chapters
of this manual. The design stage consists of a series of calculations, and possibly model tests,
to check and adjust as necessary all details of the structure and its construction. This is often
an iterative process that starts with the development and assessment of various preliminary
design options, from which a preferred one is selected. This preferred option will be
developed at the detailed design stage, but further alternatives may be identified as part of
the process of balancing the greatest functional efficiency with the least total cost. At this
stage, the alternatives are usually minor variations on the basic design option.
Early in the design process, alternative solutions should be considered. Simple methods can
be used to develop these preliminary designs, but a more thorough approach is required for
the detailed design stage. The hydraulic and geotechnical tools used to check and adjust the
hydraulic and structural performance in the detailed design should be a combination of
established theoretical and empirical approaches, along with numerical and/or physical
modelling where appropriate, notably for complex or very large projects. These approaches
are presented in detail within Chapters 4 and 5.
NOTE: Empirical methods do not always cover the range of situations that may be
encountered – the range of applicability for any empirical method used should always be
checked. Physical modelling can be useful as a way to gain more accurate measurements of
stability or performance for a particular design. Such modelling may also be useful to
optimise designs and can produce cost savings.
Technical design criteria
As stated in Section 2.2.2.2, it is good practice to produce a set of functional requirements for
the structure that can be agreed upon and used as design criteria. Acceptable damage levels
should be properly defined before the design process proceeds. The criteria should relate to
the design methods being used. For example, maximum permissible overtopping discharges
should relate to a particular frequency of event occurrence and must be clearly stated.
The balance of economics and operational safety relating to performance and level of risk
over time should also be calculated. It should be expressed in terms of risk of nonperformance or exceedance of specified conditions. This is illustrated by Table 2.4, which
presents the risk of event occurrence during the lifetime of a structure. For example, a
structure built to last for 30 years (ie it has a 30-year design life) has a 45 per cent chance of
being exposed to a 1 in 50-year wave condition, and a 14 per cent chance of being exposed
to a 1 in 200-year wave condition. Designing to resist damage for the latter condition might
be more expensive, but it will mean there is a much lower likelihood that the structure will
have to be repaired during its operational lifetime.
CIRIA C683
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4
5
The objective of the calculations and model tests is to ensure that the final structural design
meets the functional requirements, given the physical site conditions and other boundary
conditions. All available information on boundary conditions should be included, particularly
details of physical site conditions. Depending on the schedule, results from surveys
commissioned earlier in the design process may only become available during the detailed
design stage. Where possible, the preferred construction techniques for the project should
also be considered, preferably in consultation with potential contractors.
2.3.3.2
2
37
6
7
8
9
10
2 Planning and designing rock works
Table 2.4
Percentage chance of a particular return period event occurring during the design life of
a structure
Design
life
(years)
5
10
20
30
50
100
200
500
1000
1
20
10
5
3
2
1
<1
<1
<1
2
36
19
10
7
4
2
1
<1
<1
3
49
27
14
10
6
3
1
<1
<1
5
67
41
23
16
10
5
2
1
<1
7
79
52
30
21
13
7
3
1
1
10
89
65
40
29
18
10
5
2
1
15
96
79
54
40
26
14
7
3
1
20
99
88
64
49
33
18
10
4
2
30
> 99
96
78
64
45
26
14
6
3
50
> 99
99
92
82
64
39
22
9
4
75
> 99
> 99
98
92
78
53
31
14
7
100
> 99
> 99
99
97
87
63
39
18
10
150
> 99
> 99
> 99
99
95
78
53
26
14
200
> 99
> 99
> 99
> 99
98
87
63
33
18
300
> 99
> 99
> 99
> 99
> 99
95
78
45
26
500
> 99
> 99
> 99
> 99
> 99
99
87
63
39
1000
> 99
> 99
> 99
> 99
> 99
> 99
99
86
63
Event probability (per cent) for various return periods (years)
Designers should identify and calculate responses for a range of events, including conditions
above and below the nominal design level, and not just for a single design event. This provides
the necessary inputs into sensitivity analysis and/or risk analysis and into whole-life costing.
For consistency in evaluation it is suggested that, as a starting point, responses are calculated
for the events of the return periods given in Table 2.5.
Table 2.5
Key events for use in project appraisal and performance evaluation
Subject of evaluation
Permanent structure design
(lifetime 30–100 years)
Design for temporary state
during construction
(duration: a few months or
years)
2.3.3.3
Event frequency and return period (years)
Frequent
Probable
Occasional
Remote
Improbable
0.1
1
10
100
1000
In addition, if the structure is designed to be optimal, or if its performance is to
be changed significantly, at other annual frequencies of event occurrence,
information should be given and evaluation prepared for those events as well
0.01
0.1
1
10
100
Design approaches
A technically sound design is essential to ensure the level of stability and protection of any
particular area of the structure is delivered as intended. The primary risks are either underdesign, leading to potential failure, or over-design, producing a safe but possibly more
expensive and inefficient structure than necessary. The likelihood of either of these situations
arising depends to some extent upon the design approach used.
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2.3 Technical considerations
1
Three generic approaches to design are:
!
deterministic – single characteristic values are used for all variables and input values,
giving a single value as the output, therefore not acknowledging uncertainty in the result
!
deterministic with sensitivity analysis – the above method is repeated with a range of
input values to assess the sensitivity of the results
!
probabilistic – input values are described by probability distributions, giving a result as a
probability distribution.
Traditionally design practice has been deterministic, usually with sensitivity analysis to give
confidence in the selected design. In the past there has been little comprehensive application
of probabilistic approaches. This is a consequence of three factors.
1
Existing data on progressive failure mechanisms has been sparse because of the past lack
of problems.
2
Structural response models (eg design equations) are largely deterministic, because they
have been developed from failure criteria.
3
There is a mistrust of results and a desire on the part of those involved to ensure that
any design is robust, providing a comfort factor.
2
3
4
While the first two points can limit the application of particular analytical methods, the last
arises from not knowing enough about the actual risks inherent within a design.
There may also be an assumption in design approaches that the structure remains safely
intact, providing the same level of protection until the end of its theoretical design life. In
most cases this is not realistic: as structures age, the likelihood of failure usually increases.
Furthermore, the uncertainties in the performance of an ageing, deteriorating structure are
inevitably higher than for a new structure. A risk-based design approach allows for the
changing probability of failure, which accounts for uncertainty instead of assuming that data
values and prediction/design methods are known precisely. This approach can be constrained
by points 1 and 2 made above, but does not necessarily require complex analysis. It can
simply involve a rational assessment of potential failures employing engineering judgement.
The alternative approach, which goes some way to addressing all three points, is to assess the
sensitivity of failure to variation in different parameters and incorporate this into the design
development. A useful tool for undertaking this type of assessment is the fragility curve
approach to describing structure performance – see Box 2.3.
The design assessment should identify a range of scenarios for evaluation, taking into
account loading conditions, potential for degradation, and relevant failure modes and
mechanisms. In designing flood defence structures, for example, this is likely to include at
least a breaching mode, and overtopping or overflow without breaching. It can prove useful
to develop possible failure mechanisms in the form of fault trees or event chains. Where more
than one mechanism may lead to failure, these should be analysed separately to establish
their relative likelihood and importance. If necessary, they should be combined to determine
the overall probability of failure; the strength of the structure is equal to the weakest failure
mechanism.
Particular attention should be paid to unusual structures and features for which typical
failure mechanisms may not be applicable. The question to ask is “what mechanism or
sequence of events could result in degradation or failure?”.
6
7
8
9
Further details on probabilistic design methods can be found in Vrijling (2001), Schiereck
(2001), Mockett and Simm (2002), Oumeraci et al (2001), Van Gelder (2000). Also see the
website of the Joint Committee on Structural Safety, <www.jcss.ethz.ch/>.
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10
39
2 Planning and designing rock works
Box 2.3
Fragility curves
Calculations of structural response for loading events of the return periods in Table 2.5 allow derivation of
the probability of failure for that event. Failure can be described as the situation where the reliability, Z,
becomes negative, when the relevant design equations or model is expressed in the general form:
Z (reliability) = R (strength) – S (loading)
(2.1)
where R represents the characteristic strength of the structure and S represents the characteristic
magnitude of the loading.
Monte Carlo simulation based on the reliability function given in Equation 2.1 can be used to derive the
probability of failure. The values for probability of failure (or probability that Z is negative) can be
expressed in the form of a fragility curve. A fragility curve (see example in Figure 2.6) expresses the
probability of a failure response, Di, with respect to failure mode, i, P(Di|x), conditional upon the given
loading condition, x.
Figure 2.6
Example fragility curve
To identify which responses should be calculated, reference should be made to the design objectives and
the models described in Chapter 5. Typically it will be necessary to calculate the probability of a relevant
hydraulic response (eg maximum desirable overtopping rate) and a relevant structural response. The
hydraulic response may need to be calculated taking account of the probability of a particular structural
response occurring (eg crest lowering.) The fragility curve can be converted into a performance curve in
which the horizontal axis is the probability of the loading event and the vertical axis represents the
probability of a failure response, P(Di|x) (see Figure 2.7). The area under this curve is the annual
probability of failure, a very useful number, which can be incorporated directly into whole-life cost analysis.
Further discussion on the use of fragility curves is given in Dawson and Hall (2001) and Buijs et al (2005).
Figure 2.7
40
Example performance curve for a rock structure
CIRIA C683
2.4 Cost considerations
2.4
1
COST CONSIDERATIONS
It is essential to have a good understanding of the project costs throughout the life cycle.
There are various methods and requirements for determining costs, many being specific to
particular countries or the structure’s function.
2.4.1
Whole-life costing
2
As for all projects, a fundamental principle in the design of rock structures in hydraulic
engineering is minimisation of total cost over the life cycle within the limits of the functional
requirements and boundary conditions, including its construction and its eventual removal
or replacement. It includes the costs of maintaining and operating the structure. It may also
include the potential reuse of the materials in the future.
3
Whole-life costing can be used to support the decision-making process for investment. For
example, it can be used to identify whether a higher initial capital cost for a structure is
justified instead of a lower initial cost with higher maintenance costs during the operational
phase of the project. In this approach, costs are often expressed in terms of their present value
(present value is the capitalised value of a stream of future costs, damages and benefits) using
an economic technique called discounting, see Equation 2.2:
Present value or capitalised costs =
N

Ct
t =1 
where:

∑  (1 + r ) 
N
=
design life (years)
t
=
time (years)
Ct
=
cost expenditure in year t (¤) or (£)
r
=
market interest minus inflation rate (–).
t
(2.2)

5
This permits the calculation of a total whole-life cost based on the capital and discounted
mean annual maintenance (monitoring, appraisal, repair) costs, together with the discounted
costs of any major repair, rehabilitation or removal works expected during the lifetime of the
structure.
The economic optimum may be a reduced capital cost requiring more frequent maintenance
expenditure. However, high-maintenance solutions may be unrealistic for practical or
environmental reasons and will need to be considered together with the economic case.
Obtaining funding for maintenance may also be difficult. Owners or public authorities may
make a policy choice to fund projects with high initial investments, to ensure better safety
and less maintenance over the structure’s lifetime. There can be a high degree of uncertainty
in the calculation of repair costs because of the high number of variables involved. This
uncertainty may also influence the final decision. For commercial developments, cash flow
can be important. In some cases a rapidly built structure with low capital cost but high
maintenance costs may be attractive because it generates an earlier revenue stream, which
can then fund future maintenance.
In addition to the above costs, allowance might need to be made for the interest charges
involved in financing a project. The relative balance of the cost components is not only
project- and site-specific but is also affected by the economic conditions in the countries in
which (or from which) engineering, material production, construction, maintenance and
financing resources originate.
6
7
8
9
For further discussion on whole-life costing, see Mockett and Simm (2002) and PIANC (1998).
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2 Planning and designing rock works
2.4.2
Cost elements
2.4.2.1
Cost categories
The costs involved in a rock structure generally fall into the following categories:
!
sourcing of materials
!
construction
!
maintenance and repair
!
removal.
These categories are discussed in more detail in Sections 2.4.4–2.4.7 below. In addition there
are costs of investigations and studies leading to detailed design and preparation of contract
documents. These costs usually constitute no more than 5–10 per cent of the overall project
costs. Additional investment at the earlier planning and design stages is often relatively
inexpensive and can reduce uncertainty and bring about significant savings for the project as
a whole. For example, the cost of detailed numerical wave modelling studies or physical
model tests are often equivalent to only 2–3 m of constructed breakwater. This illustrates the
advantage of undertaking appropriate levels of initial study to fine-tune the design. Similar
arguments may be applied to other aspects of the design process.
2.4.2.2
Fixed and variable costs
The costs of a project may be split into fixed and variable costs. Variable costs relate to the
time expended or to the quantity of material handled. Examples of all of these are presented
in Box 2.4, while further details are presented with reference to construction in Section 2.4.5.
Box 2.4
Examples of fixed and variable costs related to rock construction
Fixed costs
!
Opening/closing of dedicated quarry (if necessary or beneficial)
!
Mobilisation/demobilisation of floating or land-based plant
!
Establishment/removal of accesses
!
Trials and testing to identify general material properties and site characteristics.
Variable (time-related) charges
!
Maintenance of quarrying activities
!
Maintenance of floating/land-based plant
!
Standing time for plant (eg when weather or hydraulic conditions prevent work progressing)
!
Maintenance of accesses
!
Designer’s quarry inspections
!
Supervision and administration
!
Maintenance of survey and monitoring equipment (eg wave buoys).
Variable (quantity-related) charges
!
Site investigations including geotechnics, wave measurement etc
!
Excavation (and re-excavation)
!
Excavation ancillaries (eg trimming of slopes)
!
Filling (eg placing armourstone in bulk or individually)
!
Filling ancillaries (eg trimming slopes, placing geotextiles)
!
Testing (to confirm continuing acceptability of materials).
Generally, cost assessment should concentrate on the following:
42
!
items that give the largest contribution to the total cost
!
elements that are subject to significant uncertainties or have a major impact on the project.
CIRIA C683
2.4 Cost considerations
For example, time-related charges may be important when there is risk that the programme
will not be met. The economic consequences of higher or lower production rates may have to
be considered where planning and cash flow consequences for the owner are critical. In this
situation, a reduced construction time at the expense of higher production costs may prove
most economical to the owner.
2.4.3
1
2
Cost estimation
In the design process, cost optimisation takes place at different levels and different phases of
the design (see Table 2.6).
The project definition and conceptual design phases lead to alternative solutions that should
be cost-analysed. Since this will generate choices, one of which is likely to form the basis for
the final design of the project, every effort should be made to make the solution as realistic
as possible.
Because of the inherent inaccuracies in the initial estimates, it is often advisable to bring
forward more than one solution, eliminating options as the estimating process is refined.
Design and construction (production, transport, phasing) costs are estimated with greater
accuracy than maintenance and repair costs because the latter involve greater uncertainties
(see Section 2.4.1). In assessing the options, the minimum cost for each should be considered,
plus the potential risks attributable to errors in the estimates at this stage together with the
reliability of the various estimates. At this stage it is often advisable to err on the side of a
slightly higher capital cost and lower maintenance cost.
In the early stages of the process, estimates based on historic rates are adequate for arriving
at an approximation of the cost. A rudimentary approach is to take the major quantities, cost
them and add an allowance to cover the cost of the remaining minor items. The problems
with this technique are that the rates may be broad-brush, or site-specific and difficult to
update (even the update information is likely to be historic). Better accuracy can be obtained
by using analytical estimating techniques once the major features of the design(s) are known.
An analytical estimate can be considered as a mathematical model of the project that gives
cost as the final output. It involves looking at each operation required to execute the works,
deciding what resources in terms of labour, plant and materials are needed to do it in what
time, then applying up-to-date cost rates and summing the costs for all operations. There are
computer programs available to help with this. This technique will also generate a realistic
construction programme. It will be necessary to add allowances for mobilisation, demobilisation
and any essential temporary works, operating costs, profit margin and risk or contingency.
During the tender phase, the various contractors will carry out the same estimating process,
taking into account their unique experience and optimising the use of any specialist
equipment they may own or be able to source and adding allowances for supervision,
overheads, profit margin and risk to arrive at their final submission. Various procurement
approaches may be adopted, such as a priced bill of quantities or a target cost based on an
activity schedule. Incentives on early completion and cost may also be agreed between client
and contractor. This process will also differ where a dedicated quarry is used and the design
is supply-based – see Section 3.9.5.
Table 2.6 gives more detail on costs at each of the phases described above. It provides an
indication of the typical accuracy that might be expected at each stage, although this can vary
dramatically depending upon uncertainties associated with structure type, location and
available information.
3
4
5
6
7
8
9
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2 Planning and designing rock works
Table 2.6
Stage
Cost estimation associated with different stages in a project
Key word in cost
determination
Typical basis for cost determination
Notes/example
Design stage
Project definition
Rough estimate
Historical data and reference projects
including whole-life maintenance
(Accuracy: ±40%)
1 breakwater × price of similar
breakwater + inspection and
maintenance record
Conceptual design
Estimate
Standard rates or approximate unit rates +
whole-life costs
(Accuracy: ±20–40%)
800 m of rock structure × rate per
linear m of similar size rock structure
plus maintenance costs
Preliminary design
Approximate
calculation
Typical unit rates and approximate
quantities of each material + administration
(contractor’s and designer’s) and whole-life
costs
(Accuracy: ±10–20%)
80 000 m3 of armourstone × typical
price per m3 of armourstone for similar
projects in the region plus maintenance
costs
Detailed design,
including bills and
specifications
Engineer’s estimate
Unit rates and quantities + additions as
above
(Accuracy: ±5–10%)
80 000 m3 of armourstone × price per
m3 of armourstone, ancillaries,
enabling works, constraints and wholelife costs
Market stage
Tendering
Target budget
As above less whole-life costs
Inclusive of project management,
insurances, taxes etc
Project acquisition
Tenderer’s calculation Analytical estimate based on the total
resources required to construct the project
Company’s data
Submission of
tender
Tenderer’s bid
As above + profit and risk
Contractor’s experience of similar
projects and conditions
Award of contract
Contract value
Agreed price
Target budget versus price
Construction stage
Preparation of
works
Project budget
Last modifications, including contractor’s
suggestions
Changed opinions, cost variations
Execution
Project cost
Planning and production control
Project management
Execution
Contract price
Monitoring
Resident engineer
Maintenance stage
Routine
inspections
Planned monitoring
As identified in arriving at whole-life costs
Annual inspections for damage, wear
and degradation
Routine
maintenance
Planned maintenance As identified in whole-life costs modified by
or modifications
actual requirements
May feed back to modify monitoring
programme and future maintenance
costs
Critical inspections Required after any
major event that may
have caused damage
Critical repairs – these should have been
anticipated in the whole-life costs modified
by a relevant formula based on probability
and time
Serious departure from original
scenarios may call for modifications to
control future maintenance costs
Unplanned
modifications
This is likely to require a full-scale
re-evaluation, starting from the design
stage; a key factor will be how much of the
existing facilities can be incorporated in the
new design
Loss of fish stocks may lead to a
fishing port being adapted as a marina;
an offshore oil strike may lead to
modification to allow support vessel
facilities; collapse of undersea minedout coal seams; changing bathymetry
or sea levels may alter the wave climate
44
Unexpected change
of use or physical
conditions
CIRIA C683
2.4 Cost considerations
2.4.4
1
Armourstone sourcing, production and transport
A significant part of the cost of a rock project is the expense of sourcing, producing and
transporting the armourstone and core material.
Sourcing and production
One of the first considerations for a project should be whether armourstone of sufficient size,
quantity, quality and durability is available. There are constraints upon the maximum size of
armourstone that can be produced from any particular quarry. Where a local quarry is to be
used, the design will need to reflect the size, quality and quantity of armourstone available,
where this is practical (known as “supply-based design”). Local quarries are often preferred,
as it may be impractical to obtain larger stones or material of superior quality from another
source because of transport, cost and environmental factors. For example, several berm
breakwaters in Iceland were designed and constructed making maximum use of the quarry
yield obtained from areas adjacent to the site. Selection of a local rock source may require the
use of lower-quality (less durable) rock (see Section 3.6). The design and maintenance
planning for the structure should take this into account (see Section 10.2) and this aspect
should be evaluated in terms of the whole-life costs of the project (see Section 2.4.1). Section
3.1 provides further details on the selection of appropriate materials.
2
3
4
Transportation
Transportation to the site – for example by water or by land – can dictate the source of rock.
Factors influencing the choice include the preferred method of construction, accessibility,
environmental constraints and costs, recognising that the costs are directly influenced by each
of these factors. Market forces may also be involved, for example the regional availability of
appropriate barges to service all ongoing projects.
2.4.5
Construction
The largest item within the whole-life cost of a project is usually the construction. This will
break down into three types of cost, which will vary in importance with the nature of the
project, the type of contract and the equipment used. The latter is particularly important
when there is a significant element of the works needing floating plant as much of the
available plant is unique and there are likely to be issues of availability and precise suitability
to the task. Costs can be divided into three categories.
1
CIRIA C683
Fixed costs. These include mobilisation, demobilisation and remobilisation of offices and
plant; establishment and removal of the site compound and any temporary works or
accesses; insurances, trials, opening and closing dedicated quarries or casting yards,
manufacture of moulds; temporary fencing or barriers to separate the public from the
works or for health and safety reasons; personal protection for operatives, public viewing
areas and information boards, road and footpath closures/diversions; liaison with fishing
authorities, moorings, anchorages and temporary jetties etc; and final site clearance.
Most contractors will include allowances for risks they are required to assume under the
contract in this category (weather downtime, subsidence etc), together with any inflation
allowances.
2
Time-related costs. Included in this category are site supervision, plant (particularly
equipment that is not fully employed but is needed full time on site, such as reexcavation machines, cranes) and office hire; control of public at work/public interfaces,
update of information boards and maintenance of any of the items listed above.
3
Remeasureable costs. These are costs directly related to the quantity of work done, such
as the quantities of materials incorporated (with allowances for conversion and waste) and
the actual labour and plant required to manufacture, handle, prepare for and place them.
45
5
6
7
8
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2 Planning and designing rock works
Some items may not always fall in the same category, such as divers (who may be employed
on a minimum charge per shift), drilling and blasting operations, quality control operations,
mould filling and re-preparation, part-load costs, tidal and phased working. The method of
costing these items will depend on the sensitivity of the unit cost rates to changes in quantity.
To optimise the costs of the works, the designer and/or employer need to address a number
of issues. These can be resolved into a series of questions that should be answered clearly
before the design and tender documents are finalised. The following list includes many of the
questions associated with a major coastal project, including the placing of armourstone or
concrete armour units.
!
Can the contractor get the plant and materials to site efficiently? If not, how can this be
achieved?
!
Does the contractor have adequate space for offices, storage and a safe area in the event of
bad weather affecting the works? If not, where and how can these facilities be provided?
!
Is a production facility (casting yard, quarry etc) needed? If so, where can it be sited?
!
Does the programme allow sufficient lead-time to set up the facility, manufacture
moulds, open the quarry, build up or cure initial stocks, and begin production at a slow
rate as the site team moves up its learning curve?
!
Are working hours or phasing required, for example tidal working? If so, can the
contractor complete the works in the allotted time? What are the implications for costs,
especially if expensive equipment, such as floating plant, cannot work efficiently?
!
Can local materials be used? This concerns quality, durability, size and delivery rate.
!
Is there an advantage in ensuring that the full range of quarry products is used? This is
usually an issue for dedicated quarries (or quarry faces) or for local quarries that do not
usually produce the grades required and need to maintain their core business.
!
What is the maximum load to be placed and at what reach? Can the reach requirement
be reduced by modifying the design?
!
Is geotextile to be placed under water? If so, what ballasting methods are acceptable?
!
Are the contract tolerances and profiles consistent with what can be achieved under the
placing conditions?
!
Does the design dictate that floating plant will be needed? Can the design be modified to
allow use of much cheaper land-based plant?
!
Are adequate labour skills available locally? If not, is accommodation for travelling
labour available? Could redesign allow better use of local skills?
!
Is the design over-complicated? Can it be simplified to use fewer armourstone gradings
or types and hence allow the more efficient working of a reduced amount of equipment?
!
Is there a key plant item needed to do the work? Can the design be modified to increase
its productivity?
Following this checklist should provide best value for money given the prevailing conditions
and constraints at any one site. The reader should refer to Chapter 9 for a detailed
discussion on the construction issues that should be considered during the development of
the design.
Typical cost breakdowns for different rock structures are given in Box 2.5.
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2.4 Cost considerations
Box 2.5
1
Examples of relative costs for rock structures
The case studies given here illustrate how costs can vary, depending on whether the armourstone is
supply- or demand-based, and on the method of transport. They are indicative only and site-specific
factors will affect costs for any particular project.
Case study 1: Modifying production from an existing aggregate quarry, delivery by road (courtesy
Jo n e s B r o s )
2
For this project a protective rock bund was constructed to contain dredged fill material as part of a port
expansion, using 120 000 t of core material and 30 000 t of 1–3 t armourstone. The contractor took over
operation of four faces in two aggregate producing quarries and accessed the construction site from land.
Surplus production from the quarry was stockpiled and used in surfacing fill areas after the fill was placed.
Relative percentages of the cost for the core and armourstone production and supply are given in Figure 2.8.
3
4
5
Figure 2.8
Breakdown of costs – Case Study 1
Case study 2: Modification of design to use existing quarry production, delivery by sea (courtesy Foster
Yeoman and RJ McLeod)
This project consisted of a harbour development on the west coast of the UK. Quarried rock quantities
were: 700 000 m3 of fill/core material, of which 550 000 m3 was imported and 150 000 m3 was
obtained by reusing material on site, 29 500 m3 of primary armourstone and 14 250 m3 of armourstone
for the underlayer. Armourstone was sourced from an existing quarry located about 50 km from the
project site. The contractor produced an alternative, more economical design that made use of available
gradings. Armourstone was delivered to site in approximately 40 000 t cargoes on a specialised self
discharging vessel. A percentage breakdown of the key cost items for the imported armourstone is given
in Figure 2.9. This includes tax that had to be paid on the newly produced aggregate.
6
7
8
9
Figure 2.9
Breakdown of costs – Case Study 2
10
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2 Planning and designing rock works
2.4.6
Maintenance and repair
There are ongoing costs associated with a structure, including the following:
!
monitoring and inspection of the structure and surrounding environment (eg beach levels)
!
evaluation of condition and performance
!
repair
!
rehabilitation or replacement.
The level of activity, and thus cost, of any of the above tasks depends on aspects such as
frequency and severity of storm events and accidental damage. It is also influenced by
decisions on design life, design damage levels and monitoring frequency that were made at
the time of planning and design of the works (see Section 2.3.3.2). Cost items whose
probability of occurrence in a particular year can be estimated (eg from fragility curves – see
Box 2.3), can be included as a multiple of the cost item and its probability of occurrence. For
example, an item costing !10 000 with an equal probability of occurrence of 10 per cent in
any one year in a 10-year period (eg between years 10 and 20) could be included in each of
these years as 0.1 × !10 000 = !1000.
For rehabilitation or replacement of a structure, the factors described for construction in
Section 2.4.5 apply, for example the cost of sourcing and delivering materials, plant and
accessibility.
Chapter 10 discusses monitoring, maintenance and repair strategies and methods in detail.
2.4.7
Removal
Under some circumstances a structure may be expected to be decommissioned in the future
and require removal. The costs of this may include:
!
equipment
!
removal of materials from site
!
dumping or reuse
!
dealing with polluted materials.
In such situations, these costs should be recognised at the design stage and are likely to
influence the choice of design.
2.5
ENVIRONMENTAL CONSIDERATIONS
Rock works have the potential to cause serious impacts on the environment and there are
different pressures at each stage of the project. This section outlines the environmental issues
that arise when planning, designing or constructing rock structures. Environmental issues
are of consequence not only in the construction area but also at the sites where materials are
quarried and stored and along transport routes. They apply, too, where modification of the
physical conditions could induce damage to habitats or cause changes in activities.
There is a considerable amount of literature and legislation attached to environmental
assessment of projects. This section focuses on specific environmental considerations for the
use of rock in hydraulic engineering and identifies the type of information that can be used
in environmental assessment of rock structures. An overview of the Environmental Impact
Assessment (EIA) process is provided in Section 2.5.4. In addition, Section 3.13.4 deals with
the environmental risk analysis of alternative and secondary materials.
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2.5 Environmental considerations
2.5.1
1
Sustainable use of rock as a construction material
Alternative materials should be evaluated on their environmental performance rather than
simply because a particular material is preferred. The Brundtland Report (WCED, 1987)
encourages increased use of materials from alternative sources to meet quarried rock needs
for construction. These include secondary materials, industrial by-products and wastes. This
principle of sustainability in the construction industry requires:
!
efficient use of materials
!
minimisation of the production of waste
!
recycling of wastes.
Sustainable rock works should aim to reduce energy and rock resource consumption,
transport and waste production. For each project option, whether using rock or alternative
materials, the source, transport, placing, use and dismantling should be studied over the
whole life cycle – from “cradle to grave”. Criteria such as energy, waste, raw materials and
human perception may be assessed to rank the preferred options. A tool for scoring the
whole-life environmental impact of project options is given by Masters (2001) in a guidance
document on sustainable use of new and recycled materials in coastal and river engineering.
Calculations are based on the quantities of each type of material, the distances required to
transport them to the construction site and the anticipated service life. These parameters are
then related to the anticipated environmental impacts, such as greenhouse gas emissions,
associated with the production and transport of each material.
Alternative materials to quarried rock and associated issues are specifically addressed in Section
3.13. Reviews of alternative materials are given in Brampton et al (2004) and Masters (2001).
2.5.2
3
4
5
Assessing environmental impacts through the project cycle
Many environmental matters need to be addressed when planning, designing, constructing
and operating rock structures. Many of these are common to any project constructed in a
marine or fluvial environment, and include effects on the physical environment
(geomorphology, landscape) and those on physical processes (waves, currents). Often these
impacts are actually the primary function of the works! Projects can affect ecology, social
function, recreation, amenity, human senses, air and water quality etc. These factors all
require consideration as part of any project, but are not considered in further detail here.
The remainder of Section 2.5.2 relates only to aspects specific to rock structures for those
conducting such assessments. The discussion looks at the following environmental issues:
!
physical features
!
ecological and biological features
!
air, water and soil quality
!
heritage and landscape
!
social and socio-economic features
!
natural and industrial risks.
6
7
8
Typical considerations under each of these headings are given in Table 2.7. This list includes
many factors that are relevant to a range of projects, not only those involving quarried rock.
This list is not exhaustive and different projects may encounter other site-specific issues. Later
sections discuss environmental aspects for rock works at each project stage. Many of the points
listed in Table 2.7 require data that may also be necessary for design, so it is advantageous to
address environmental issues as early as possible in the design process. This will allow data
collection programmes to be designed to provide data to meet the needs of the design studies
and the environmental studies, as well as any data required for construction planning.
CIRIA C683
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49
9
10
2 Planning and designing rock works
Further general discussion on environmental assessment can be found in a range of
literature, eg Morris (1995), Simm et al (1996), Budd et al (2003), VNF (1998), Michel (1998,
2001), SETRA (1996), CETMEF (1978).
Table 2.7
Key environmental considerations for rock structures
!
!
Physical aspects
!
!
!
!
!
!
!
!
!
Ecological and biological
aspects
!
!
!
!
!
!
Human sensory, heritage
and landscape aspects
Air, water and
soil quality
!
!
!
!
!
!
!
!
!
!
!
!
!
!
Social and socio-economic aspects
!
!
!
!
!
!
!
!
!
!
!
Natural and
industrial
risks
!
50
!
!
!
!
Climate change: sea level rise, changes in physical processes, eg sediment transport
Weather and ice conditions
Changes to waves, tides, currents, flows due to project using rock structure
Physical data for design, construction and monitoring (bathymetry, waves, flows, water levels)
Potential for changes in design conditions during project life
Interruption of drainage from land
Potential geomorphological changes to existing physical systems: coastal estuaries, shorelines, saltmarshes, dune systems, river bathymetry and morphology
Coastal squeeze
Stabilisation of active sediment feeds, reducing sediment supply, affecting coastal evolution
Scour, outflanking and need for future extension of defences
Loss of designated geological landforms or rock exposures beneath structure footprint
Direct impact on or reduction of protected habitats (mudflats, saltmarsh, dunes, river
banks) and species because of structure footprint
Indirect loss of habitats or landforms – transfer of erosion to another location, scour, beach
lowering
Stabilisation of naturally dynamic habitats or landforms in lee of structure
Risk of disturbance to feeding and roosting birds etc during construction
Change in habitat due to rock structures
Impact of construction or maintenance access on habitats
Destruction of potential habitat on rock structures during decommissioning
Emissions from rock transport, construction and maintenance
Accidental releases of pollutants during rock transport, construction and maintenance
Potential exposure of existing contamination
Change in water and air quality due to suspension of fine particles during construction
Leaching from construction materials
Visual intrusion, eg colour, shape of armourstone and type of placement
Noise and vibrations caused by armourstone production, transport and placing
Odour attributable to collection of debris or organic matter
Impact on amenity beaches from stone fragments following construction
Modification of landscape
Effect on views from local housing
Covering over archaeological features
Other issues: light, historical, cultural aspects, palaeontology
Changes in local employment during construction and operation
Immigration into small community during construction
Effects on local commerce
Effects on recreation, eg loss of amenity beach due to structure footprint, loss of safe areas
for children’s play
Effect on pedestrian and vehicle access to beach, shoreline or river, including disabled access
Effects on fishing
Effect on flood risk of adjacent properties
Vulnerability to vandalism
Public health and safety risks
Safety of rock structures
Effects on navigation
Sustainability of development
Health and safety of construction workers
Safety of rock structures
Presence of cables or pipelines
Need for consents where works are in hazardous industrial sites
CIRIA C683
2.5 Environmental considerations
2.5.2.1
1
Project concept and design stage
There are many opportunities for reducing environmental impacts during scheme concept
and design stages. These include material selection and specification and integrating
environmental considerations into the comparison of project options.
Rock structures are generally considered to be less reflective to waves than vertical structures.
This may be of significance where foreshore or riverbed scouring is a concern. Where a
physical habitat adjacent to the structure is protected by legislation (eg in Europe by the
Habitats Directive) adverse impacts on this physical habitat must be avoided.
Transport of materials can be the most significant environmental issue. A suggested hierarchy
of material sourcing options for consideration during design is given below (see Masters, 2001).
1
Suitable materials available on site from a previous project or structure.
2
Locally sourced reclaimed or recycled materials appropriate to fulfil the needs identified
in the functional analysis.
3
Reclaimed or recycled materials from further afield that can be delivered by sea or rail
or locally sourced primary materials.
4
Reclaimed or recycled materials transported from further afield by road or primary
materials transported from further afield predominantly by sea or rail.
5
Primary materials transported from further afield by road.
Avoiding over-specification of materials in the design process can help reduce waste and
encourage recycling of materials. Some organisations have already implemented site waste
management plans that analyse the waste likely to be produced on site and minimise what is
sent to landfill. Where possible, environmental factors should be included in benefit-cost
analysis. This might be by using contingent valuation, which involves asking people in a
survey how much they would be willing to pay for specific environmental services or,
alternatively, the amount of compensation they would be willing to accept to give up specific
environmental services.
The public perception of the advantages or disadvantages of a project needs to be addressed.
Public consultation exercises will be of greatest value when there is an intention to allow
those views to influence the design of the project. There may be statutory requirements for
public notification and consultation. Early consultation and communication with site users
and associations (recreational, fisheries and environmental bodies) is advised to improve
public perception of the scheme both when planning to use quarried rock and perhaps
especially when alternative materials are proposed.
The issues listed in Table 2.7 should be reviewed to assess which should be considered at this
stage. In particular, key issues to be considered during design are:
!
localised changes to waves, tides and currents and consequent patterns of scour and
deposition
!
provision of alternative habitats on soft shorelines, estuaries or rivers
!
identification of potential mitigation measures with environmental monitoring
!
landscape issues, especially with regard to colour and shape of armourstone and type of
placement
!
coverage of archaeological features
!
safety of the rock structure.
2
3
4
5
6
7
8
9
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2 Planning and designing rock works
2.5.2.2
Project approvals stage
As described in Section 2.5.4.2, the Environmental Statement (ES) will form a principal part
of the planning (or other) application. The Environmental Impact Assessment (EIA) tackles
issues such as impacts on protected habitats and reduction of the marine habitats area. The
EIA forms an integral part of the public consultation process.
2.5.2.3
Project construction stage
When considering the use of quarried rock, the following environmental matters need to be
taken into account at the construction stage:
!
sourcing armourstone
!
transportation of armourstone
!
placing armourstone.
Sourcing armourstone
Armourstone in hydraulic engineering is usually a primary aggregate and is a non-renewable
resource. In some cases, however, armourstone is a secondary aggregate obtained as a byproduct from quarrying other material, eg dimension stone, road or concrete aggregate, so it
is used as waste from other operations.
Armourstone is generally quarried using drilling and blasting or diamond cutting. Rock
material suitable for particular uses is selected and processed by various sorting methods
(detailed in Section 3.9.7) and by rock cutting. Potential environmental impacts of quarrying
and associated rock processing operations, include:
!
noise and vibration from blasting, crushing and sorting
!
habitat disturbance and removal
!
disturbance and removal of topsoil
!
particulate emissions to air and water
!
interruption of surface water and groundwater flows
!
traffic disruption to local communities
!
carbon dioxide emissions from fossil fuel burning
!
energy consumption during screening, sorting, crushing, drilling and transportation
!
production of solid waste
!
visual impacts.
The use of quarried rock should be compared with alternative materials commonly used in
hydraulic engineering structures, for example timber and concrete. Timber for use in the
marine environment generally has to be tropical hardwood because of its durability and
resistance to marine borers. This is theoretically a renewable resource, but, despite
considerable efforts (eg by the Forestry Stewardship Council in the UK and other
certification organisations), doubts remain over the sustainability of harvesting practices for
preferred timber such as greenheart. Timber can be recycled from coastal structures but has
a limited life, after which it has to be replaced. Concrete is a manufactured material but
requires raw materials such as aggregates and cement; many of the same arguments apply as
for sourcing rock.
A full appraisal of the relative environmental impacts of rock and other construction
materials requires a life cycle analysis. This looks not only at the sustainability of raw materials
but also at the environmental impacts associated with material sourcing or production,
transportation, use and eventual disposal, including the relative energy consumption to
52
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2.5 Environmental considerations
1
source or produce different materials. A wide range of concepts and analytical tools have
been developed to assist in this process (eg Howard et al, 1999). The outcome of such an
appraisal will inevitably depend on the weighting assigned to each factor through multicriteria analysis. However, in view of its durability and flexibility for reuse, it is at least
arguable that rock, particularly if obtained as a quarry by-product, is often more
environmentally acceptable and sustainable than timber, and no more environmentally
damaging than sourcing materials for concrete.
2
Transportation of armourstone
For many projects, in particular maritime structures, rock is delivered directly to site by barge
from its source. This avoids an impact on the road network, which may be counted as an
advantage of quarried rock over other bulk materials that are usually delivered by lorry. Barge
transport also uses significantly less energy and produces lower carbon dioxide emissions
than road transport. However, it should be noted that double handling usually takes place.
Short distance road transport may first be required to reach barge loading facilities; cargoes
from large barges often have to be offloaded into smaller barges that can reach the shore.
(Accidental release must be avoided when discharging the armourstone from one barge into
the other.)
Barge transport has implications for other marine uses and users such as recreation, shipping
and especially fishermen. Fixed fishing gear such as nets and pots are vulnerable to damage
from barges that need to approach close inshore to discharge their loads. This is usually
addressed by agreeing a single point of delivery on each frontage, with an associated barge
route, notified and, where possible, agreed with fishermen in advance. Standard marine
safety rules should cater for possible conflicts with other vessels, though recreational activities
may have to be restricted while quarried rock deliveries are in progress. Local requirements
may make it necessary to give advance notice to mariners of works that are to take place.
Water-borne transportation of construction materials may be possible in navigable rivers and
canals, but for many rivers and streams the only practicable means of transportation will be
by road. Appropriate methods of transport and routes of access should be chosen, taking due
account of environmental sensitivities.
Rail transport has a high capacity and a limited impact on the environment, allowing
transport of large quantities of armourstone. Depending on the vicinity of the rock source
and the construction site to the rail network, there may be a need for additional handling
and also road transport in some cases.
4
5
6
7
Armourstone deliveries may have implications for nearby residents, particularly if they have
to be made at night as a result of 24-hour or tidal working. Unloading usually requires the
use of heavy plant, which inevitably generates noise. Reversing alarms on plant are typically
found to be the most disturbing noise source owing to their pitch, tone and volume. Unless a
method can be found to enable these to be safely turned off, night-time disturbance is likely
to occur while working close to residential areas. Approaches to mitigation can include:
!
confining deliveries that are closest to residences to daylight hours, with deliveries to
other parts of the scheme at night
!
erecting temporary noise barriers between residences and the working area
!
on frontages where tourism is important, scheduling armourstone deliveries outside the
peak months.
An alternative in coastal locations is for stone to be tipped from a specially designed ship
directly on to the beach, which not only avoids the use of excavators, dump trucks and
shovels for unloading but also reduces both energy consumption and noise generation.
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2 Planning and designing rock works
Placing armourstone
Environmental impacts of armourstone placement include:
!
noise nuisance
!
effects on the physical environment (eg beach or river bed), habitat and sediment
disturbance as a result of excavation (though this is generally less than for concrete
structures, as armourstone does not require such substantial foundations)
!
visual impact and habitat disturbance from stone stockpiles
!
energy consumption by vehicles
!
disturbance of local fauna such as birds, limiting the area for feeding and roosting.
Environmental benefits of using rock include relatively low wastage and reduced risk of air
and water pollution, compared with construction using ready-mixed or locally batched
concrete. Surplus armourstone can be added to the structure or stockpiled to provide a
resource for future maintenance operations.
The construction work itself may provide much-needed employment or it may interfere with
the livelihood of existing residents. Other social impacts may result from the influx of an
outside workforce during construction of a major project in a sparsely populated area.
Once in place, rock structures are unlikely to cause any particular noise problems and have a
low vulnerability to vandalism. Measures to mitigate environmental issues on site may be
found in Environmental good practice – working on site (Coventry et al, 1998) and in the Coastal
and marine environmental site guide (Budd et al, 2003).
2.5.2.4
Project operational stage
Rock structures can provide habitats and new ecological niches for organisms such as
crustaceans, molluscs, fish, algae and birds. Since rock is usually foreign to the location at
which it is used, such habitats may be considered alien, particularly within soft coast
environments. For this reason, biodiversity gain may not be accepted as contributing to
nature conservation objectives. The impact on fisheries resources may, however, be beneficial.
Monitoring on the north-east Norfolk coast in the UK, for example, has shown that the
construction of a series of large offshore breakwaters is associated with a large increase in
shrimp populations. On the other hand, the breakwaters have limited the access of trawlers
to the inshore zone where shrimps are concentrated.
Rock structures generally require maintenance, as they are located in a dynamic hydraulic
environment. Stones can be displaced, abraded or fractured. Heavy plant may be needed to
undertake such maintenance, though associated environmental impacts are generally small.
Unless buried beneath natural material or under water, rock structures can have significant
effects on the landscape and visual amenity. This is often raised as a concern when such
structures are proposed. Nonetheless, it can be argued that timber structures such as groynes
have a similar impact, but through long periods of use they have become accepted as part of
many beach scenes. Over time, rock structures may become similarly accepted.
Effects on recreational amenity are another area of concern. Rock structures may trap weed
and litter, which can be unattractive and cause an odour problem as it decays. This is less
likely to be a problem where voids are largely filled (with beach sand, for example) or in
high-energy locations where voids are regularly scoured and kept clear by wave or current
action. It may be more troublesome in areas already prone to accumulation of vegetation or
litter, in which case a commitment may have to be made by the owner or operating authority
to clean the rock structures periodically.
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2.5 Environmental considerations
Rock structures do present potential safety hazards to the public, because of the risk of
people slipping or falling. Pedestrian access along rock structures can be difficult to provide.
In certain cases it may be necessary to maintain public access along a particular stretch of
shoreline or riverbank. However, while members of the public would see access along a
breakwater as advantageous, it may be cheaper and safer to prevent it. Concerns have also
been expressed that people could become trapped in voids between armour stones and
drown. These risks are generally addressed through signs warning the public not to climb on
the structures. Localised packing of stones to provide ramps and footways to selected areas
can also mitigate this. The safety risks of rock structures are potentially no greater than those
associated with other types of coastal structures such as concrete walls; both types present a
risk of injury from falling.
!
direct loss or coverage of coastal habitats under the structure footprint
!
visual intrusion and impact on the landscape (eg sea view from houses)
!
effects on recreation (including change in access to shoreline and loss of safe or shallow
areas for children’s play)
!
safety of rock structures
!
need for ecological monitoring.
!
destruction of potential habitats on rock structures
!
re-activation of a former sediment feed and re-creation of natural coastal habitat and
transition
!
accidental release during demolition, or unintended failure to remove the entire rock
structure
!
modification of the landscape once again
!
presence of services within the structures.
5
6
Environmental aspects that should be considered at the decommissioning stage include:
7
Opportunities for environmental enhancement
Rock structures can offer opportunities for environmental enhancement, for example by
providing habitats for marine and river life. Some guidance is given by Jensen et al (1998),
who discuss habitat creation, present suggestions to encourage colonisation of aquatic life that
is naturally attracted to hard surfaces, and identify the types of species that may be attracted.
Structure design should aim to reproduce rock environments such as foreshores and river
beds as found in nature. Typical features should be a range of stone and crevice sizes,
irregular outlines and surface orientations to provide a variety of micro-habitats for small
mobile and immobile species as well as larger species. For structures in the littoral zone,
features of a rocky shore may be reproduced by providing hollows and crevices to form rock
pools, projections to create overhangs and placing stones in isolation from the main works to
create scour pools. As with all design aspects, costs and practicality will need to be considered.
CIRIA C683
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Project decommissioning stage
Environmental matters to be considered at the decommissioning stage of rock structures are
mostly the same as for the other stages in the structure’s lifetime. An often-quoted advantage
is that rock structures are relatively straightforward to dismantle and constituent rock can be
reused or recycled into other projects. Even if rock has been severely abraded and degraded
in the marine environment, it can still be recycled into primary aggregate.
2.5.3
2
3
Other potential environmental impacts associated with the operational stage of rock
structures include:
2.5.2.5
1
55
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2 Planning and designing rock works
The colonisation and distribution of plants is subject to their ability to survive at various
levels of dryness (normally linked to height above low water) or light penetration when
under water. For marine structures, elements at or below low water level may be colonised by
kelp, which, like most seaweeds, attracts a wide range of animal communities for shelter or
feeding. At mid-beach levels, seaweeds like bladder wrack may colonise.
Fish and crustaceans can use the crevices between stones and concrete blocks to hide from
predators, lay eggs, or feed on organisms growing on the structure. If the structure is
submerged, shelters for edible crab (crevices on the outside of the structure) and lobsters
(galleries within the structure), and shelter for fish species such as wrasse, lumpsuckers and
conger eels can all be incorporated.
Under normal conditions, surfaces of concrete or quarried rock structures in the marine or
fluvial environment are rapidly colonised by naturally occurring micro-organisms that
consume many of the dissolved and suspended substances in water. Settlement of larger
organisms, such as barnacles and mussels, which can directly filter suspended matter for their
food, can also occur. Grazing and browsing organisms living on rock structures devour many
of the plants and animals living sedentary lives on the hard surfaces, creating scope for
continued colonisation.
When a structure is constructed there is inevitably a loss of habitat and, with it, associated
species. Sandy or muddy sea beds and foreshores and river beds and riverbanks contain a
multitude of organisms (worms, crabs, molluscs etc) many of which are important to the food
chains of commercially fished species and birds (particularly in the intertidal zone).
As a starting point for ecological enhancement, the points in Box 2.6 should be considered
when planning rock structures in the hydraulic environment. See also Irving and Northen
(1999) for details of ecological survey of rock structures.
Box 2.6
Considerations for ecological enhancement of rock structures
The following points should be considered to provide opportunities for environmental enhancement
(adapted from Jensen et al, 1998):
56
1
Location. Consider the appearance of rocky habitat and reproduce it where you plan to build the rock
structure. For marine structures below the low tide level, opportunities for fishery habitat
enhancement increase with water depth.
2
Maximise the diversity of crevices created. The greater the heterogeneity of the habitat the more
diverse the final biological community is likely to be.
3
Consider using a mix of materials – does everything have to be made from the same rock type?
4
Be creative. Provide a structure that has rough surfaces rather than one that is smooth, neat and
symmetrical.
5
Build in animal-friendly features, intertidal rock pools, isolated boulders for scour pools, projections to
create overhangs.
6
Consult local residents and users. Conservation groups or environmental organisations at local and
national level, local authority ecologists, academics and fishery organisations are professionals too
and will be delighted that nature conservation and/or fishery provision is being considered.
7
Use the fact that you are taking extra care to promote your approach to rock structure construction.
A project that blends into the existing landscape will be more popular than one that visually conflicts.
8
Be realistic. No single project will do everything. Take a long-term view and over time the benefits will
mount up.
9
To assess these benefits be prepared to monitor. Quantification of benefits may require professional
surveys, especially sub-tidally, but descriptive evaluation allows local enthusiasts to become involved.
Encourage local schools and colleges and/or conservation groups to adopt the structure as a study
site (shore or river ecology is a favourite theme for field trips). You will be able to use their data and
images to follow the biological community development over time.
CIRIA C683
2.5 Environmental considerations
2.5.4
Environmental Impact Assessment process – an overview
2.5.4.1
EIA legislation
1
Projects have to comply with a large number of statutory requirements. For many projects
there is a need to prepare an Environmental Impact Assessment (EIA) before the project can
proceed. This is a tool for assessing construction and operational impacts. Where European
sites of nature conservation importance Special Protection Areas (SPAs) and Special Areas of
Conservation (SACs) or Ramsar sites may be affected by construction, there is a need to
comply with the requirements of the EU Habitats Directive. Some authorities require projects
to seek biodiversity gains, particularly relating to protected habitats and species. In the UK
these are covered by Biodiversity Action Plans (BAPs). Increasingly, EIAs are also expected to
consider environmental issues associated with material sourcing.
This document does not fully describe the legal requirements for environmental assessment,
as these vary internationally and are also subject to changes with time, but some of the main
European and international legislation to be complied with is summarised in Table 2.8.
Reference is made in this section to this legislation although it is recognised that outside
Europe some of the requirements may not apply.
Table 2.8
European community law
4
International law
!
!
Environmental Impact Assessment Directive
85/337/EEC amended by 97/11/EC
Surface Waters Directive 75/440/EEC
Bathing Waters Directive 76/160/EEC
Dangerous Substances in Water Directive
76/464/EEC
Fisheries Directive 78/659/EEC
Agricultural Sewage Sludge Directive
86/278/EEC
Urban Wastewater Directive 91/271/EEC
Nitrates Directive 91/676/EEC
Environmental Strategy Assessment
Directive 2001/42/EEC
Shellfish Directive 79/923/EEC
Birds Directive – 79/409/EEC
Habitats Directive – 92/43/EEC
!
Water Framework Directive – 2000/60/EEC
!
!
!
!
!
Wildlife and nature
conservation
3
Main international and European environmental laws related to Environmental Impact
Assessment
Issue
!
!
!
!
!
!
!
Water and marine
pollution
2
!
!
!
!
!
!
Ramsar Convention on wetlands of international importance – 1971
Convention on protection of world cultural
and natural heritage Stockholm declaration – 1972
World Charter for Nature – 1982
Bonn Convention on the conservation of
migratory species of wild animals – 1979
Bern Convention on the conservation of
European wildlife and habitats – 1982
Rio Convention on biological diversity declaration – 1992
Espoo Convention – 1991
5
6
7
!
!
!
!
Marpol Convention 1973-78
London Convention – 1972
Ospar Convention – 1992
Barcelona Convention – 1976, amended in
1985
Bremen Declaration – 2003
8
Note
Table compiled from Fowler et al (2001), André (2003), Sunkin et al (1998) and Morris and Therivel
(1995).
The project promoter may perceive environmental assessment as an additional financial
burden. However, the cost of Environmental Impact Assessment, which depends on project
size, existing environmental data and sensitivity of the environment, will in most cases be a
small proportion of overall project costs.
9
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2 Planning and designing rock works
The environmental assessment procedure has the following advantages for the promoter:
!
identifying environmental impacts during the planning and design stage will lead to the
most cost-effective inclusion of measures to mitigate adverse impacts
!
liaison and consultation, which is normally an integral part of the assessment, will reduce
the risk of an unexpected refusal of development consent at a late stage
!
probable areas of objection to a project will be identified at an early stage and enable
sensitive matters to be addressed and project delays minimised
!
the opportunity for public consultation can result in greater acceptance of a project in
the affected community
!
minimisation of unforeseen adverse environmental impacts that may incur considerable
future financial liabilities
!
establishing licences or consents that are required can facilitate some aspects of the
development.
Failure to conduct appropriate environmental assessment at the correct time can be costly, as
the start of the project may be delayed.
2.5.4.2
Environmental Statement
The results of an EIA are normally presented in an Environmental Statement (ES). For
mandatory assessments this report will form a principal part of the planning (or other)
consent application.
The Environmental Statement contains:
2.5.4.3
!
a full description of the proposed project
!
a description of the existing environment in which the project is to be situated and that
may be affected by the proposed project
!
a brief description of other options considered (including the option of doing nothing)
and reasons for their rejection
!
a statement of the predicted environmental impacts of the proposed project
!
where the predicted impacts are adverse, a description of the measures that will be
adopted to mitigate those impacts
!
a description of analysis methods used.
EIA process
The European EIA Directive sets out the main phases of EIA:
58
!
compilation of information on the likely environmental effects of the project into an
Environmental Statement (essentially the four steps referred to below)
!
publicising of the ES and the project to which it relates to seek public response on the
project and ES
!
determination of the acceptability of the project by the relevant authority, referred to as
the competent authority (normally the local authorities where the project is to be located),
taking into account the ES, possible mitigation measures proposed and any feedback or
comments received from the consultation.
CIRIA C683
2.5 Environmental considerations
1
There are four main steps for compiling information on the likely environmental effects.
1
Scoping, to identify priority issues for detailed assessment.
2
Baseline survey, to define the existing environment.
3
Projection of the proposed project on to the existing environment and the assessment of
probable impacts (beneficial or adverse).
4
Investigation of measures to mitigate impacts that are found to be adverse, and the
possible incorporation of those measures into the design.
2
Scoping
Scoping identifies the priority issues to be assessed. The environmental aspects that rock
engineering works may affect or may be affected by include those listed in Table 2.7 together
with the interactions between them.
Initial consultations should take place with the planning, coast protection, river drainage and
navigation authorities and other statutory bodies whose consent will be required to allow the
project to proceed. Statutory bodies advise on designations relating to nature conservation
(eg wildlife) and other environmental aspects (eg water, air, landscape, geology). It is usually
beneficial to consult all organisations whose interests are likely to be directly affected by the
proposed works. As a general rule, consultation should be as widespread as practicable.
Baseline studies
Environmental data can be collected by existing literature and in situ surveys. The latter can
be time- and money-consuming but may be the only way of securing local information. The
objectives should be focused on the description of the existing environment with background
data in order to assess future modifications due to the proposed engineering project.
3
4
5
6
Impact identification and prediction
This step identifies the range of potential environmental effects and ascertains the significance
of each. It can be complex and time-consuming. Environmental effects can be categorised as
follows: beneficial or adverse, direct or indirect, widespread or localised, permanent or
temporary, reversible or irreversible, short- or long-term, cumulative or immediate.
7
Mitigation and enhancement
To obtain consent, it may be necessary to identify mitigation measures that will avoid, reduce
or compensate for predicted major negative environmental impacts of shoreline, coastal or
estuarine and riverine engineering projects. They may also aim to enhance positive effects.
One such measure is to put in place an environmental monitoring programme (see below).
8
Environmental monitoring
The aims of environmental monitoring are to provide:
!
before construction of the works: input data for calibration of numerical models and
baseline study
!
during and after the construction of the works: indicators or environmental parameters
for quantification of predicted impacts and mitigation, as well as of remedial measures or
warning of unexpected impacts.
The site and the probable impacts of the project will dictate the frequency and extent of the
monitoring.
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2 Planning and designing rock works
2.6
SOCIAL CONSIDERATIONS
Construction works are generally undertaken to benefit society in some way. These social
factors need to be considered in planning and design. These include:
2.6.1
!
health and safety
!
social impacts of construction and operation
!
engaging stakeholders.
Health and safety
Working in water is often hazardous because of the nature of the environment. The coastal
marine environment can be highly volatile, and at times unpredictable, with sudden, strong
changes in winds, waves, currents and water levels. Rivers can be equally challenging, subject
to flash floods and strong seasonal flows. The risks to the works, equipment and human life
cannot be overstated and must be addressed during planning, design and construction.
The potential risks to safety in this dynamic physical environment include changing ground
conditions (on the river or sea bed), access and working space. Planning and design should
aim to avoid such hazards. Protecting operatives is a fundamental requirement. The designer
should consider how the structure will be built, to ensure that the design allows appropriate
safe working practices to be adopted.
Protecting the public and/or future users of the facility is important. Rock structures in areas
where the public have access are often hazardous. For example, small children could become
trapped within the voids of the cover layer or injured and crushed by the movement of
unstable armour stones. Such issues should be addressed at an early stage, perhaps by
stipulating that armourstone be correctly shaped (eg sharp and angular, not smooth and
rounded) to ensure it interlocks securely.
Signs can be used to inform the public of the safety hazards of structures and raise awareness
of their purpose.
It is essential to remove or reduce risks at source early in the project planning stage. Section
9.5.3 discusses these health and safety matters and measures for addressing them. Further
details can be found in Simm and Cruickshank (1998).
2.6.2
Construction and operation
Construction works can be disruptive and intrusive for local communities. Constraints and
opportunities should be determined through public engagement (see Section 2.6.3) and
identified during the planning stage. Where possible, constraints should be overcome at the
design phase. Points to address include:
60
!
local employment opportunities
!
plant access to the site
!
restricted working time
!
specified construction methods
!
public access over and around the structures
!
potential aesthetic or amenity value (eg angling or waterfront access).
CIRIA C683
2.7 References
2.6.3
1
Engaging stakeholders
More acceptable designs can be produced and problems avoided if stakeholders are
approached at an early stage. There can be a significant gap between what the designer
perceives to be an issue and the stakeholders’ views. In many cases, accommodating local
needs has little impact upon the cost or constructability of a scheme, but may enhance the
quality of service provided by the structure.
2
Engaging stakeholders early helps to educate those affected by the technical processes –
about how and why certain decisions need to be taken, for example. This understanding can
result in acceptance of preferred construction methods despite short-term disruptions.
3
In some parts of the world the use of local materials and labour provides major benefits to
the local population in terms of money and employment. Different designs might be
expected in these circumstances.
2.7
REFERENCES
4
André, P, Delisle, E, Reveret, J P and Sene, A (2003). L’évaluation des impacts sur
l’environnement: processus, acteurs et pratique (Environmental impact assessment: process,
implementers and practice), 2nd edition. Ecole Polytechnique de Montréal
Budd, M, John, S, Simm, J and Wilkinson, M (2003). Coastal and marine environmental site
guide. C584, CIRIA, London
Brampton, A, Wallis, M and Holliday, E (2004). Potential use of alternatives to primary aggregates
in coastal and river engineering. C590, CIRIA, London
5
Buijs, F, Segura Domìnguez, S, Sayers, P B, Simm, J D, Hall J W (2005). “Tiered reliabilitybased methods for assessing the performance of coastal defences”. Proc ICE conf breakwaters,
coastal structures and coastlines, Apr 2005. Thomas Telford, London
CETMEF (1978). Les études préalables aux aménagements portuaires (Preliminary study on
harbour development). CETMEF, Compiègne
6
Coventry, S, Kingsley, M and Woolveridge, C (1998). Environmental good practice – working on
site. C503, CIRIA, London
Dawson, R J and Hall, J W (2001). “Improved condition characterisation of coastal defences”.
Proc ICE conf breakwaters, coastal structures and coastlines, Sep 2001. Thomas Telford, London
Fowler, R E, Harvey, R N, Harding, C and Atkins, R W (2001). “Implementation of
European Union Habitats Directive in developing and designing coastal defence schemes”.
Proc ICE conf breakwaters, coastal structures and coastlines, Sep 2001. Thomas Telford, London
7
Howard, N, Edwards, S and Anderson, J (1999). Methodology for environmental profiles of
construction materials, components and buildings. Building Research Establishment, Garston
Jensen, A C, Hamer, B A, Wickins, J F (1998). “Ecological implications for developing coastal
protection structures”. Proc ICE conf coastlines, structures and breakwaters, 1998. Thomas
Telford, London
8
Irving, R and Northen, K (1999). An ecological survey of selected rock islands and rock groynes on
the West Sussex coast. Environment Agency, Southern Region, Worthing
Masters, N (2001). Sustainable use of new and recycled materials in coastal and fluvial construction: a
guidance manual. Thomas Telford, London
9
Michel, P (1998). L’étude d’impact des ports de plaisance (EIA of marinas). Secrétariat d’état
chargé de l’environnement/Délégation à la qualité de la Vie, Atelier Central de
l’environnement, Imprimerie Nationale, Paris
Michel, P (2001). L’étude d’impact sur l’environnement (Study of environmental impacts).
Ministère de l’Aménagement du Territoire et de l’Environnement, Paris
CIRIA C683
10
61
Mockett, I D and Simm, J D (2002). Risk levels in coastal and river engineering: a guidance
framework for design. Thomas Telford, London
Morris, P and Therivel, R (1995). Methods of environmental impact assessment. Oxford Brookes
University, Oxford
Oumeraci, H, Kortenhaus, A, Allsop, N W H, De Groot, M B, Crouch, R S, Vrijling, J K
and Voortman, H G (2001). Probabilistic design tools for vertical breakwaters. AA Balkema,
Rotterdam, 373 pp (ISBN 90-5809-248-8)
PIANC (1998). Life cycle management of port structures – general principles. PTC II-WG 31,
PIANC, Brussels
Schiereck G J (2001). Introduction to bed, bank and shore protection – engineering the interface of soil
and water. Delft University Press (ISBN 90-407-1683-8)
SETRA (1996). Projets routiers: Le dossier d’étude d’impact: guide méthodologique (Road project:
EIA guide). SETRA, Bagneux
Simm, J D, Brampton, A H, Beech, N W et al (1996). Beach management manual. Report 153,
CIRIA, London
Simm, J D and Cruickshank, I C (1998). Construction risk in coastal engineering. Thomas
Telford, London
Sunkin, M, Ong, D and Wright, R (1998). Sourcebook on environmental law. Cavendish, London
van Gelder, P H A J M (2000). Statistical methods for the risk-based design of civil structures.
Communications on Hydraulic and Geotechnical Engineering, Report no 00-1, Faculty of
Civil Engineering and Geosciences, Technische Universiteit Delft (ISSN 0169-6548 00-1)
VNF (1998). Les barrages mobiles de navigation – guide du chef de projet (Movable navigational
dams: project manager’s guide). Groupe Moniteur, Paris
Vrijling, J K (2001). “Probabilistic design of water defence systems”. The Netherlands Reliability
Engineering and System Safety, vol 74, no 3, Dec 2001, pp 337–344
WCED (1987). Our common future. Report of the 1987 World Commission on Environment and
Development (the Brundtland Report). Oxford University Press
62
CIRIA C683
3
1
Materials
2
3
4
5
6
7
8
9
10
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63
3 Materials
CHAPTER 3 CONTENTS
3.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
3.1.1
Materials considerations for concept stage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
3.1.1.1 Scale of project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
3.1.1.2 Planning and timescales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
3.1.1.3 Top sizes of armour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
3.1.1.4 Rock source and procurement options . . . . . . . . . . . . . . . . . . . . . . . . . 73
3.1.1.5 Holistic considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
3.1.1.6 Cost of project. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
3.1.1.7 Towards preliminary design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
3.1.2
Important design functions and properties of materials . . . . . . . . . . . . . . . . . . . 79
3.1.2.1 Functions of materials in the structure . . . . . . . . . . . . . . . . . . . . . . . . . 79
3.1.2.2 Material properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
3.1.3
Durability considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
3.1.3.1 Mitigation strategies for low-durability scenarios of rock armour . . . . 83
3.1.3.2 Durability considerations for material other than armourstone. . . . . . 83
3.1.4
Standards for armourstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
3.2 Quarried rock – overview of properties and functions. . . . . . . . . . . . . . . . . . 86
3.2.1
Introduction to quarried rock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
3.2.2
Introduction to engineering geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
3.2.3
Quarry evaluation principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
3.2.4
Properties and functions – general. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
3.3 Quarried rock – intrinsic properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
3.3.1
Aesthetic properties of armourstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
3.3.2
Petrographic properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
3.3.3
Mass density, porosity and water absorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
3.3.3.1 Phase relations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
3.3.3.2 Density definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
3.3.3.3 Degree of saturation in stability calculations . . . . . . . . . . . . . . . . . . . . . 97
3.3.3.4 Density variation in a quarry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
3.3.3.5 Mass density as a durability indicator . . . . . . . . . . . . . . . . . . . . . . . . . . 98
3.3.3.6 Mass density as a design parameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
3.3.4
Resistance to breakage and armourstone integrity . . . . . . . . . . . . . . . . . . . . . . . 98
3.3.5
Armourstone resistance to wear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
3.4 Quarried rock – production-induced properties . . . . . . . . . . . . . . . . . . . . . 101
3.4.1
Shape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
3.4.1.1 Length-to-thickness ratio (LT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
3.4.1.2 Blockiness (BLc) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
3.4.1.3 Cubicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
3.4.1.4 Roundness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
3.4.1.5 Proportion of crushed or broken surfaces. . . . . . . . . . . . . . . . . . . . . . 104
3.4.1.6 Shape for specification purposes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
64
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Contents
3.4.1.7 Shape for design and dimensioning purposes . . . . . . . . . . . . . . . . . . 104
3.4.1.8 Factors controlling armourstone shape during quarry production . . 106
3.4.2
Dimensions of pieces of armourstone. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
3.4.3
Size and mass distribution of armourstone gradings. . . . . . . . . . . . . . . . . . . . . 107
3.4.3.1 Grading width and common terminology . . . . . . . . . . . . . . . . . . . . . . 108
3.4.3.2 EN 13383 system for standardisation of gradings. . . . . . . . . . . . . . . . 109
1
2
3.4.3.3 Rosin-Rammler curves for mass and size distributions and idealised
gradings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
3.4.3.4 Graphical illustration of EN 13383 standard grading curves . . . . . . . 114
3.4.3.5 Fragments and effective mean mass, Mem . . . . . . . . . . . . . . . . . . . . . . 114
3.4.3.6 Requirements and compliance of EN 13383 standard gradings . . . . 114
3.4.3.7 Additional information on EN 13383 standard gradings . . . . . . . . . . 115
3
3.4.3.8 Relationship between Mem and M50 , and grading widths including
practical experience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
3.4.3.9 Non-standard gradings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
3.4.4
Core materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
3.4.4.1 Core materials terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
4
3.4.4.2 Core materials in a design context. . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
3.4.4.3 Calculating the porosity of bulk-placed materials . . . . . . . . . . . . . . . . 121
3.5 Quarried rock – construction-induced properties . . . . . . . . . . . . . . . . . . . . 123
3.5.1
Layer thickness and porosity of individually placed armourstone . . . . . . . . . . 123
5
3.5.1.1 Importance of layer thickness coefficient kt and porosity nv . . . . . . . . 125
3.5.2
Effect of rock density on design parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
3.6 Rock quality, durability and service-life prediction . . . . . . . . . . . . . . . . . . . 131
3.6.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
3.6.2
Durability and degradation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
3.6.3
Procedure for source evaluation of rock quality . . . . . . . . . . . . . . . . . . . . . . . . 133
3.6.4
Principles of degradation modelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
3.6.5
In-service degradation models for general wear of armourstone . . . . . . . . . . . 140
3.6.5.1 Micro-Deval (MDE) method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
6
7
3.6.5.2 Armourstone quality designation (AQD) method . . . . . . . . . . . . . . . . 142
3.6.5.3 Comparison between MDE and AQD methods. . . . . . . . . . . . . . . . . . 145
3.6.6
Modelling degradation due to breakages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
3.6.6.1 Effects of minor breakages and major breakage . . . . . . . . . . . . . . . . . 147
3.6.6.2 Quantitative effect of breakages on armourstone grading using
statistical model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
8
3.6.6.3 Prediction of the effect of major breakages using a dedicated
degradation model specific for breakage. . . . . . . . . . . . . . . . . . . . . . . 151
3.6.7
Summary of recommendations for degradation modelling . . . . . . . . . . . . . . . 154
3.7 Preparing the armourstone specification . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
3.7.1
EU context. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
3.7.2
Non-EU context . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
3.8 Testing and measuring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
3.8.1
CIRIA C683
Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
65
9
10
3 Materials
3.8.2
Testing of physical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
3.8.2.1 Petrography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
3.8.2.2 Aesthetic properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
3.8.2.3 Rock density, water absorption and porosity. . . . . . . . . . . . . . . . . . . . 164
3.8.3
Testing properties of individual pieces of armourstone . . . . . . . . . . . . . . . . . . 165
3.8.3.1 Shape. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
3.8.3.2 Mass and size. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
3.8.4
Testing geometrical properties of armourstone as a granular material . . . . . . 167
3.8.4.1 Shape. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
3.8.4.2 Mass distribution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168
3.8.5
Mechanical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
3.8.5.1 Resistance to breakage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
3.8.5.2 Armourstone integrity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
3.8.6
Durability and accelerated weathering tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
3.8.6.1 Freeze and thaw test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
3.8.6.2 Salt crystallisation test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
3.8.6.3 Test for breakdown by sonnenbrand . . . . . . . . . . . . . . . . . . . . . . . . . . 179
3.8.6.4 Non-European tests and other source evaluation tests . . . . . . . . . . . . 180
3.8.6.5 Chemical analysis, organic matter and leaching tests . . . . . . . . . . . . . 180
3.9 Quarry operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
3.9.1
Exploration and evaluation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
3.9.1.1 Quarry evaluation of armourstone in general. . . . . . . . . . . . . . . . . . . 182
3.9.1.2 New armourstone quarry in a greenfield site . . . . . . . . . . . . . . . . . . . 182
3.9.1.3 Principles of armourstone yield assessment. . . . . . . . . . . . . . . . . . . . . 183
3.9.2
Assessment of in situ block size distribution, IBSD. . . . . . . . . . . . . . . . . . . . . . . 184
3.9.2.1 Scanline mapping of discontinuities . . . . . . . . . . . . . . . . . . . . . . . . . . 186
3.9.2.2 IBSD by Wang’s equation method . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
3.9.2.3 IBSD by the dissection method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
3.9.2.4 IBSD by 3D stochastic network modelling . . . . . . . . . . . . . . . . . . . . . 190
3.9.2.5 IBSD from drill core data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
3.9.3
Blasting and blast design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
3.9.3.1 Factors affecting blasting for armourstone . . . . . . . . . . . . . . . . . . . . . 191
3.9.3.2 Fragmentation processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
3.9.3.3 Comparison of armourstone and aggregates blast design . . . . . . . . . 192
3.9.3.4 Suggestions for improving the yields of armourstone . . . . . . . . . . . . 193
3.9.4
Prediction and assessment of yield curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
3.9.4.1 Kuz-Ram Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
3.9.4.2 Bond-Ram Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
3.9.4.3 KCO model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200
3.9.4.4 Simplified guidance for BBSD prediction . . . . . . . . . . . . . . . . . . . . . . 201
3.9.4.5 Mass distribution assessment by image analysis . . . . . . . . . . . . . . . . . 202
3.9.4.6 Photo-scanline methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203
3.9.4.7 Direct screening and block measurement methods . . . . . . . . . . . . . . 204
3.9.5
Matching yield curves and demand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208
3.9.6
Quarry layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
3.9.6.1 Extraction face . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
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Contents
3.9.6.2 Sorting and selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
3.9.6.3 Secondary breakage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
1
3.9.6.4 Stockpiling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
3.9.6.5 Loading areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
3.9.7
Selection, sorting and processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
3.9.7.1 Production technique for heavy armourstone. . . . . . . . . . . . . . . . . . . 215
3.9.7.2 Production technique for coarse armourstone and lighter gradings of
light armourstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
2
3.9.7.3 Production technique for core material directly from muckpile . . . . 217
3.9.7.4 Technologies for the different selection or processing methods. . . . . 218
3.9.7.5 Secondary breakage of oversized stones . . . . . . . . . . . . . . . . . . . . . . . 224
3.9.8
Handling and transport at the quarry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
3
3.9.8.1 Choosing loaders and trucks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
3.9.8.2 Placing wire loops in stones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
3.9.9
Loading trucks or trains at the quarry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
3.10 Quality control of armourstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232
4
3.10.1 Production quality control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
3.10.2 Quarry inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236
3.10.3 Quality control during deliveries and construction . . . . . . . . . . . . . . . . . . . . . . 240
3.10.4 Third-party quality control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244
5
3.11 Armourstone costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
3.12 Concrete armour units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248
3.12.1 Properties. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249
3.12.1.1 Historical development of concrete armour units. . . . . . . . . . . . . . . . 249
3.12.1.2 Classification and structural strength of concrete armour units. . . . . 250
6
3.12.1.3 Description of concrete armour units . . . . . . . . . . . . . . . . . . . . . . . . . 252
3.12.1.4 Intrinsic properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
3.12.2 Widely used units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
3.12.2.1 Cubic-type blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
3.12.2.2 Hollow units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256
7
3.12.2.3 Interlocking units used in a double layer . . . . . . . . . . . . . . . . . . . . . . 257
3.12.2.4 Interlocking units used in a single layer . . . . . . . . . . . . . . . . . . . . . . . 258
3.12.2.5 Layer placement dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260
3.12.3 Production and placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260
3.12.3.1 Formworks and moulds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260
8
3.12.3.2 Casting of concrete armour units. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261
3.12.3.3 Control of the production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263
3.12.3.4 Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263
3.12.3.5 Placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264
3.13 Recycled and secondary materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264
9
3.13.1 Types of alternative material. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266
3.13.2 Mechanical and chemical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267
3.13.3 Experience from existing uses in hydraulic structures . . . . . . . . . . . . . . . . . . . 269
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3.13.4 Environmental risk analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270
3.13.4.1 Status of knowledge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
3.14 Gabions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
3.14.1 Classification of gabions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273
3.14.2 Gabion components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274
3.14.2.1 Properties of gabion mesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274
3.14.2.2 Specification for durable gabion stone. . . . . . . . . . . . . . . . . . . . . . . . . 276
3.14.3 Properties of gabion stone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
3.14.3.1 Physical properties of gabions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
3.14.3.2 Hydraulic properties of gabions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277
3.14.4 Applications of gabions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278
3.15 Grouted stone materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279
3.15.1 Concrete grouts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279
3.15.2 Bituminous bound materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280
3.15.2.1 Asphaltic concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280
3.15.2.2 Asphalt mastic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
3.15.2.3 Asphalt grout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
3.15.2.4 Open stone asphalt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
3.15.2.5 Lean sand asphalt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282
3.16 Geotextiles and geosystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282
3.16.1 Functions of geotextiles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283
3.16.2 Types of geotextile. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283
3.16.2.1 Non-woven geotextiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283
3.16.2.2 Woven geotextiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284
3.16.3 Geotextile properties and testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
3.16.4 Construction issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287
3.16.5 Geotextile specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288
3.17 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290
3.17.1 Publications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290
3.17.2 Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298
3.17.2.1 ASTM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298
3.17.2.2 British standards. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298
3.17.2.3 Euronorms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298
3.17.2.4 French standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299
3.17.2.5 ISO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299
3.17.2.6 EC Directive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299
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Flow chart
3
1
Materials
2
Chapter 3 presents guidance on material properties for use in design.
Key inputs from other chapters
!
Chapter 2 " project requirements
3
Key outputs to other chapters
!
material properties " Chapters 5 to 10
NOTE:
The project process is iterative. The reader should revisit Chapter 2 throughout the
project life cycle for a reminder of important issues.
This flow chart shows where to find information in the chapter and how it links to other
chapters. Use it in combination with the contents page and the index to navigate the manual.
2 Planning and designing
rock works
4
5
Chapter 3 Materials
3.2–3.11
Quarried
rock
properties
gradings
durability
testing
quality control
quarry operations
3.12
Concrete
armour units
armour unit
types and
characteristics
production
quality control
placement
3.13
Recycled and
secondary
materials
construction
waste
recycled
materials
steel slags
experience and
risks
3.14
Gabions
3.15
Grouted
stone
materials
3.16
Geotextiles
and
geosystems
box gabions
concrete grouts
gabion
mattresses
bituminous
bound materials
woven and nonwoven geotextile
mesh and infill
5 Physical processes
and design tools
6
7
types of
geosystems
8
4 Physical site conditions
and data collection
6 Design of marine structures
7 Design of closure works
9
8 Design of river and canal structures
9 Construction
10
10 Monitoring, inspection,
maintenance and repair
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3 Materials
3.1
INTRODUCTION
The main considerations for a rock project are its scale and the availability, quality and
handling of materials. Large projects that require a new quarry to be opened will be very
different to smaller projects in regions where there are many established sources of rock
products. The availability and quality of materials should be established at an early stage, as
material production and transportation costs can be an important consideration when
selecting a design solution. Also, the prescribed execution methods and available equipment
associated with a choice of materials may influence this selection process. In some cases,
labour availability may promote the use of local rock that is both selected and placed in a
structure by hand.
This manual focuses on materials for structures where armourstone and concrete unit cover
layer solutions are typically the most viable. Information is also provided on a range of other
materials usually incorporated into such structures.
This introductory section presents the materials issues that should be addressed during the
concept stage of the design. It also gives a summary of the functions that the materials have
in the design and discusses durability considerations. Subsequent sections then cover the
different material types – rock, concrete units, alternative granular materials, gabions,
grouted stone composites and geotextiles.
The wide range of stakeholders in rock projects has been highlighted in Chapter 1 (see Table
1.1). The logic diagram in Figure 3.1 is designed to help the reader identify relevant sections
of this chapter, identifying links between data to be gathered, materials evaluation and the
main design process.
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1
2
3
4
5
6
7
Figure 3.1
Flow chart relating sections to the materials evaluation and design process
8
9
10
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3.1.1
Materials considerations for concept stage
Materials considerations should be addressed in a logical, iterative and inclusive process (see
Figure 3.2) at the concept design stage (see Section 2.2.1) before preliminary design is
started. This may mean that one or more potential contractors will go through a preliminary
evaluation process in parallel. This should consider available materials sources, specification
requirements, site conditions and available transport. After a detailed design is tendered, the
contractor works out the best choice of rock source, transport method, construction method,
and the total cost. The successful contractor should go through further cycles of iteration and
refinement to finalise the plan for handling of materials. Bringing design and construction
expertise together, for example in design and build and partnering alliance contracts, has the
advantage of simplifying design optimisation with respect to materials considerations.
The principles informing the early thinking about materials in the design process are
summarised in the following sections and then illustrated in Boxes 3.1 to 3.3 using case
histories that emphasise different materials aspects.
Figure 3.2
3.1.1.1
Flow diagram of materials consideration process to be applied at concept stage
Scale of project
The scale of project is usually related to the total investment cost and/or to the level of
technical difficulties but for the purpose of this manual, the scale of the project is defined in
terms of rock quantities, ie including armourstone, core and granular materials. For example:
!
small local
eg < 50 000 tonnes
!
medium regional
eg 50 000 – 500 000 tonnes
!
large national/international
eg > 500 000 tonnes.
The scale of a rock project, whether small, medium or large, is normally expressed in terms
of total quarried rock tonnages, a function of the spatial scale and water depths, or cost. It
may be possible to compare cost directly with data from recently completed similar projects.
For greater accuracy, tonnages can often be estimated from initial approximate site data, eg
using rules of thumb for packing densities (see Section 3.5) and volumes based on simple
cross-sections and metre-run linear distances, for example using other similar designs.
Small and medium-size projects are more dependent on established sources of armourstone
such as aggregate quarries. Many repair and upgrade projects will be small. As project scale
increases, it becomes increasingly important to locate an acceptable source of material, while
minimising its distance from the project site and hence transport cost. For very large projects,
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1
demanding large volumes of core material, dedicated quarries opened in greenfield sites
within a few kilometres from the site are the most attractive option, but they may take a
considerable time to set up.
3.1.1.2
Planning and timescales
Suppliers and contractors can assist designers to estimate the likely time for delivery of the
first consignment of suitable armourstone to site. For small and medium-scale projects, it will
be necessary to evaluate stockpile volumes from within existing quarries, and their future
supply rates, together with other quarry information. Aggregate-producing quarries differ in
their ability to adjust normal practices to achieve greater rates of armourstone production.
Production rates from dedicated quarries can more easily be maximised to match ideal
construction rates, eg by utilising extra machine power, resources or time. Project planning
usually includes an estimation of the time required to obtain planning permissions, complete
detailed design, conduct a risk analysis, obtain funding, submit tender, mobilise site and
complete construction. The project plan must be compatible with the lead time to achieve a
certain rate of materials supply (eg of armour stones or concrete units) and the specific client
restrictions for the construction site and transportation time windows.
3.1.1.3
Top sizes of armourstone
The mass of individual armour stones required for stability in the armour layer of a structure
can be obtained from boundary conditions at the site, as discussed in more detail in Chapter
5. The maximum stone size may be critical at the concept stage. For example, a demand for
10–15 t armourstone may rule out many or all the locally available and established sources
within economic transport distances because the quarries only have smaller top sizes
available. The top size for a design may be constrained by the construction plant available for
placing such large sizes, or the cost of supply. Where large stone sizes are required, it is
always advisable to consider alternatives to armourstone; in particular, concrete armour unit
solutions may be appropriate. Concrete units offer possibilities for steeper slopes, which in
turn require smaller material volumes and land-take, permit the use of shorter-reach
construction plant and may provide environmental benefits (see Section 3.12).
The maximum armourstone size that can be produced in a quarry is determined by the
geology. Geological and geotechnical expertise are required to locate sources with a desired
range of stone mass or to predict the best location of large stone sources within a certain
kilometre radius. Tools for such evaluations are outlined in Section 3.9.2.
If a local quarry is an obvious potential source, the heaviest grading that can be produced (ie
without unprofitable over-production of finer material) should be considered in relation to
the top sizes demanded by conventional (statically stable) structures. Many less conventional
rock structure designs – eg with berms, dynamically stable structures, thicker layers and
gentler slopes – may enable use of local sources with restricted top sizes for the supply of all
materials required for a viable design.
3.1.1.4
3
4
5
6
7
8
Rock source and procurement options
All projects have a responsibility to assess the potential use of secondary or recycled granular
materials as alternatives to primary sources of armourstone, especially for use as core
material. Possible local sources of these materials should be assessed (particularly within a
mining, power generating, minerals processing or urbanised region), to minimise transport
costs compared with more distant sources.
Quarries are typically aggregates quarries, dedicated armourstone quarries or dimension
stone quarries (see Section 3.9). For rock supply, the range of procurement options generally
fits one of the following scenarios:
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!
demand-based competitive market
!
existing local quarry
!
new quarry dedicated to the project.
Demand-based competitive market scenario
Within Europe, demand has stimulated an increasingly recognised market in armourstone
such that designs are often demand-based, predicated on producers competing to supply
satisfactory materials. Confidence that the required materials will be available has grown in
Europe, because material property requirement categories for hydraulics works have been
defined by agreement between European designers and producers in the form of a standard
specification for armourstone (EN 13383:2002). Details of the available materials should have
only a minor impact on the design process provided the armour stone sizes demanded are
not exceptionally large for the region. Despite factory production control of armourstone in the
European market, quarry inspections by the structure owner’s representative, prior to source
approval, are highly recommended (see Section 3.10.2). For example, in rare cases visual
appearance can be the overriding requirement for client approval of projects in amenity areas.
Local existing quarry scenario
The considerable environmental and economic advantages of reduced materials transport
suggest that every effort should be made to design a satisfactory supply-based solution where
a local quarry exists. This should include careful consideration of design solutions that may
require higher maintenance, including the public nuisance impact that maintenance works
may have. A major part of the materials should be obtained from the local source and where
possible any timely availability of local secondary and recycled sources should also be
accommodated. Careful analysis of available sizes, quality, durability, transport implications
and environmental acceptability should be undertaken. The need for transport of large
consignments of core materials over great distances should be avoided. Known local quarries,
together with local concrete unit manufacture or imported stones for heavier armour, may
provide an optimal mix to meet demands for different sizes of materials.
Dedicated quarry scenario
For large projects where the geology near to the site is favourable for good armourstone and
a legal/planning framework for granting quarrying permissions exists, new dedicated quarry
sources are generally most economical.
3.1.1.5
Holistic considerations
In general, a project design team should consider the technical engineering, ecological and
construction site consequences of using different materials from the different sources, paying
particular attention to responsibilities of the various parties.
Technical innovation
Possibilities exist for utilising extremes of rock density and rock durability. Section 3.5
presents the advantages of volume filling below water using rock of low density and
armouring against wave or current attack with rock of high density. Section 3.6 describes
degradation models to inform mitigating strategies for designing with low-durability stones
(often associated with low-density rock), eg over-dimensioning, gentler slopes, higher
maintenance.
The shape characteristics of certain potential sources of armour stones (blocky armourstone
pieces) combined with possible individual placement construction methods may introduce
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1
opportunities to design and build stable structures with tighter packing of smaller sizes or
fewer layers at lower cost (see Section 5.2.2.2).
In general, smaller sizes of armourstone used for riverbank and dam-face designs impose less
severe constraints on material sources. Use of local superficial deposits, such as glacial
deposits and river boulders, should be considered in addition to crushed rock quarry
sources, especially for river training works. Design innovations can often arise from creative
use of materials such as gabions, grouting or hand-pitching to improve the stability of
otherwise undersized stones. Even unconventional, high-maintenance options become viable
where there is access to readily available labour and cheap supplies of easily transported and
handled materials. In beach control and coastal structures, the characteristics of local materials
may promote the adoption of less conventional, but viable, low-cost designs (see several
examples in Crossman et al, 2003, and also discussion in Section 6.3.5).
Large-scale breakwater projects using dedicated quarries will benefit considerably from
designs that are tailored to minimise waste and ensure the total utilisation of rock that is
blasted. An early understanding of yield curves in dedicated quarries can have a major
impact on total project costs. This requires reasoned predictions of the armour stone size
distribution (or block size distribution) to be generated upon fragmentation by blasting.
Preliminary design should not progress without such quarry yield predictions. Both
preliminary and detailed design should be kept informed of progressive results from
geotechnical investigations. These will usually involve a rock drilling programme. The
predictions enable the total materials costs of conventional, berm (dynamically stable) and
Icelandic-style (statically stable) breakwater designs to be compared (see Section 6.1.6). See Box
3.1, Section 3.9.4 and Section 3.9.5 for yield prediction and examples of cost comparison analysis.
2
3
4
5
Ecology
Many projects will disrupt ecology and the design should aim to encourage the most rapid
return to a healthy ecology, in part, through appropriate material choices. Disruption to
ecologically sensitive foreshores that are required to act as foundations to revetments and
seawall rehabilitation projects may be minimised by designs that have a smaller footprint ie
steeper structures with larger armour. The additional conservation value of artificial marine
habitats such as those provided by rock armoured structures, most notably rock reefs, is
influenced by material choice and is receiving increased attention. Recolonisation of fluvial
environments may be more rapid with biosystems comprising gabions that incorporate
planting during construction. These issues are discussed further in Section 2.5.
6
7
Site constraints
Limited materials transport options are likely to restrict the range of potential sources. River,
closure dam and coastal works may have site constraints that forbid either road or
waterborne transport. If the design involves concrete units, extensive areas will be needed for
casting yards. A common constraint to minimise nuisance in built-up amenity areas requiring
coastal works is a requirement that materials should be delivered by sea and within a certain
seasonal window. This can rule out apparently viable land-won local sources. Sea delivery
options, eg for imported materials, will often incur additional costs for construction of
temporary landing or other transport-related infrastructure to enable transhipment of sea
deliveries. Transport issues are discussed further in Section 9.4. Among other issues
influencing the choice of materials is the ease of creating staircases for public access to
beaches at the foot of old seawalls upgraded by armourstone revetments. Public safety
concerns may encourage material options where a smooth rubble pavement finish to a
revetment surface is easier for a contractor to achieve. For repairs to degraded structures,
armourstone reuse is the first choice, as it is an extremely flexible construction material.
Where the new is to blend with the old, visual impact and functional performance are of crucial
importance. A mix of concrete units and armour stones in cover layers is a last resort.
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Responsibilities
If materials are considered too late in the design process, and if contractors are insufficiently
involved, the designer should expect alternative designs to be submitted at tender stage,
which can delay the project considerably. The contractor will not usually risk proceeding with
an alternative design, such as one based on a rock source with properties that vary from the
materials specification of the detailed design. An exception would be if the contractor agrees
with the terms that the designer and/or owner have made for liability, in the event of
unsatisfactory structural performance. To deliver best value to the owner, the designer may
need to rewrite the design specification, and even consider redesigning the structure, around
the material properties and armourstone gradations that are available from the contractor’s
designated rock source. Although based on a highly developed understanding of rock
sources, construction methods and grading optimisation, economically better designs
proposed by contractors are often not adopted because of responsibility issues.
3.1.1.6
Cost of project
Initial estimates of approximate project costs should be developed from available data such as
the cost of comparable projects, construction cost information supplied by contractors,
projected production costs for the preliminary stone or concrete tonnages, and the
potentially overriding cost of transporting material to site. Social acceptability and
sustainability of materials use, as well as cost, should influence decision-making.
3.1.1.7
Towards preliminary design
The objective of the next phase, preliminary design, is to:
!
generate potentially viable design options
!
provide enough detailed data to select and dimension the final design
!
specify the materials requirements.
Precise design data are needed, including final design dimensions, materials volumes,
construction methods, aggressiveness of the site environment, design life and maintenance
requirements. Before the preliminary design can be prepared, guidance on properties of
armourstone and how these are related to functional requirements (see Sections 3.3–3.5)
should be considered, especially for local and dedicated supply-based design scenarios where
the best use should be made of all the available material. Identifying and working with the
vast range of possible armourstone quality requires practical methodologies for assessing
service life, as presented in Section 3.6. To appreciate the new legislative context of the
Eurostandards and EU Directives, guidance on the preparation of the materials specification
for rock materials and setting requirement levels is given in Section 3.7. How to sample and
test to evaluate material properties is also explained (see Section 3.8). The efficiency of
quarrying operations for armourstone production (see Section 3.9) can seriously affect
project costs especially for dedicated quarries. Great effort is often needed to understand the
rock resource before production. As rock is not an off-the-shelf material, an understanding of
quality control and peculiarities associated with different rock sources and quarry procedures
is essential. Setting up quality control in the quarry (see Section 3.10) and on site (see Section
9.6) is therefore also explained. Sections 3.12–3.16 provide information on materials other
than quarried rock and refer the reader to key references and specifications.
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Box 3.1
1
Dedicated quarry (Melkoya, Hammerfest, Norway)
A liquified natural gas plant development and breakwater construction project on the island of Melkoya
required levelling part of the island consisting of foliated gneiss. Where possible, the excavated stone was
to be utilised for breakwater materials. The project site and dedicated quarry were therefore part of the
same complex. Crest elevation, water depth and dimensioning for a dynamically stable berm breakwater
design indicated that for significant wave height, Hs = 7 m, this would be a large project requiring about
700 000 m³ of armourstone exceeding 1.5 t with a top size of 17 t.
Initial investigations in 1998 concluded that the Melkoya rock would need to be supplemented with
150 000 m³ of imported armour stones in the size range of 4–17 t from a good gabbro quarry. The
potential cost implications necessitated a further geotechnical investigation. Estimates of armourstone
yields on Melkoya were drastically revised after an investigation of the geology below the weathered
surface rock, based on detailed diamond-drilled cores, which was completed in October 2001. The typical
joint spacing and three-dimensional configuration of in situ blocks at significant depths in the planned
quarry and the expected size distribution after blasting were calculated using methodologies now
beginning to be applied to armourstone quarry investigations but rarely used in conventional stone
excavation, aggregate quarries and mining site investigations. The analysis was undertaken with sufficient
levels of confidence for the design team to be reassured of predicted yields of 3–5 per cent of stones in
the 20–35 t heavy grading class that would be suitable for the most exposed breakwater sections. A
statically stable berm breakwater design that closely matched this yield curve prediction for Melkoya was
later submitted for tender, with the option of obtaining a small fraction of 10 000 m³ of 20–35 t armour
stones from outside the island. The application of technically innovative approaches to quarry site
investigation and increased confidence in favourable quarry yields eventually enabled the design phase to
move from preliminary to final.
2
3
4
The contractor did not have access to the quarry yield predictions used by the breakwater design team.
The contractor had sufficient experience, through work on similar projects, to use the size distribution in
breakwater design to make his own requirements for quarry yield and thus was able to contribute to
maximising the usage of quarried rock.
The rock excavation, breakwater construction and levelling of the island was carried out in a nine-month
period from July 2002 to April 2003 and the maximum weekly production exceeded 100 000 m³. The
completed breakwater required 670 000 m³ of armour stones exceeding 1.5 t with a top size of 35 t. All
breakwater material was obtained from Melkoya and not a single stone needed to be imported.
5
6
7
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Box 3.2
Use of local materials as alternative, Le Havre, France
Since 1994 the Port Authority of Le Havre has been undertaking studies and construction to double its
container throughput capacity by 2007. The solution adopted was the creation of a 200 ha reclamation in
the estuary of the River Seine to be closely linked to the hinterland through a road, railway and canal
network. The first breakwater was constructed to form a containment bund for dredged material for the
landfill reclamation during the construction phase. A second 5.5 km-long breakwater was then constructed
to form the port and provide protection for navigation and terminal operations. The initial concept for the
breakwater design was based on three elements.
1
2
3
A core of highly variable low-quality stone consisting of flinty chalk (nodular siliceous chalky limestone).
Sublayers and filters composed of siliceous chalky limestone armourstone.
Cover layer of Antifer cubes.
Alternative designs were proposed and the construction of the final design began in 2001. The materials
modifications included the use of the following materials.
1
2
3
4
34 000 units of 1.5 m³ and 3 m³ Accropode to reduce the armour to a single-layer system, gradings
of armourstone being modified accordingly.
Close to 5 million tonnes of the breakwater core was constructed using material dredged from the
channel instead of quarried rock, to maximise the reuse of dredged material and limit transport of
core material from distant quarries.
110 000 m³ of high-quality armourstone was replaced by the flinty chalk armourstone in specially
selected locations of the structure where loads are not aggressive, high quality being retained for the
crest where traffic of dumpers during construction is significant.
A quarry in the flinty chalk was re-opened locally in a protected environment zone to produce both
tout-venant core materials and some armourstone gradings.
Transport times by barge decreased from 7 h for coastal deliveries down to 2.5 h for delivery by canal and
river. The cost of this material, delivered to site, was reduced by an estimated one-third.
Figure 3.3
General view of the Le Havre port extension
project with reference to the rock sources
and main access to the local flinty chalk
quarry
The dedicated quarry was an old quarry, closed in the 1930s and re-opened for this contract. Different
geological horizons were identified early for use as core material or for armourstone. The old quayside was
refurbished and used for barge loading, solving the potential problem of nuisance from local truck traffic.
The regional environmental body, Parc de Brotonne, required high-quality rehabilitation of the quarry area
as a remediation to the quarry work. Much of the project’s success resulted from creative use of materials
that were locally available but of variable quality.
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Box 3.3
1
Selection from alternative solutions, River Lochy, Scotland
The River Lochy, Scotland, is subject to substantial flood flows and scour had been developing around the
piers of the Lochy Bridge. The scour was likely to have resulted from a combination of the following
factors: extreme river flow velocities associated with relatively small-sized bed material; misalignment of
the bridge piers; and exposure of the pier foundations, which increased the potential for scour. Several
potential solutions were considered for the protection of the piers.
1
2
3
4
5
Armourstone around the bridge piers.
Rock bund downstream of the bridge.
Concrete-filled mattress.
Gabion mattress.
Interlocked concrete blocks.
The advantages and disadvantages of each option were weighed against their cost and applicability. For
example, gabion mattresses were ruled out because of potential difficulties in shaping the gabions around
the complicated pier structures. The recommended solution, armourstone, was not the lowest cost
solution but presented the most advantages:
!
!
!
rock was available locally (several quarries supplying igneous roadstone and armourstone were
present within a radius of about 10 km)
transport of the material through towns was negligible, which limited disturbance to local residents
it is a proven technology that withstands high-velocity flows and has the necessary flexibility to adjust
to the realignment of the bed.
This solution required a maximum size of 1–3 t armourstone to ensure stability. The volume used was
1550 m³. This illustrates the case of river projects where the quantities of stone required are relatively
small and tend to be specified in terms of size and volume rather than tonnage, and where there are
numerous alternatives to armourstone that may present advantages.
3.1.2
Important design functions and properties of materials
3.1.2.1
Functions of materials in the structure
2
3
4
5
This section provides an overview of the principles governing the functions of loose stones
and other appropriate materials systems. Section 3.1.2.2 explains the link between properties
and functions for armourstone in general terms. The details of the properties are given in
Sections 3.2–3.6 for quarried rock, Section 3.12 for concrete armour units, Section 3.13 for
alternative granular materials, Section 3.14 for gabions, Section 3.15 for grouted stone
composites and Section 3.16 for geotextiles.
6
The main functions of materials used in hydraulic structures are:
!
to provide volume filling
!
to provide a foundation and a filtering system
!
to protect the structure against wave or current action and scouring.
7
Detailed guidance for designing to provide the required functional performance for different
structure types is given in Chapters 6, 7 and 8.
The use of each different material has consequences, not necessarily hydraulic, that are
important to designers, as they may bring additional advantages or disadvantages in, for
example, visual appearance, durability, permeability to groundwater, ease of construction,
flexibility, availability, effectiveness, access, maintenance, public safety, hygiene and cost. Table
3.1 summarises the hydraulic functions that may be provided by the different types of
materials:
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Table 3.1
Hydraulic functions
Type of material
Function
Natural armourstone
Concrete armour units
Gabions
Alternative granular materials
Volume fill
***
–
–
**
Filtering
***
–
*
*
Armouring
***
**
**
*
Note
*** usually ideal, ** suitable for this function, * may be used to provide this function; a requirement
under specific conditions, – not suitable.
Volume filling
This is the principal function of materials used in the core of a hydraulic structure. The
materials’ structural characteristics should enable them to support internal loads such as selfweight and external loads such as difference in water level or traffic. Their compaction
characteristics should preclude significant, unacceptable post-construction settlement. Low
fluid velocities and mild exposure of the materials used for volume-filling mean that,
depending on the structure design and construction technique, it is usually acceptable to use
lower-quality materials and widely differing mean particle sizes when compared with
materials serving a filtering or armouring function. The hydraulic characteristics should be in
accordance with the overall degree of permeability required by the design of the structure.
Material for use in the core does not always require specification to an international
standard. It will nonetheless have certain property requirements depending on its intended
uses. Examples of different functional uses where property requirements for core materials
will differ include:
!
permanently submerged impermeable breakwater core
!
intermittently submerged permeable reef breakwater core
!
reef breakwater foundation for poorly consolidated clayey foreshores (low density for
reduced subsidence).
The core materials may consist of either primary rockfill such as quarry run, alternative
granular materials such as secondary or recycled aggregates, or dredged sand and gravel. In
the core of a structure, notably for underwater placement, the placed bulk density (see
Section 3.5.1) is the most important indicative material parameter, as it relates closely to
shear strength and possible settlement as well as to permeability. It is governed by grading
width and particle shape. For further discussion on geotechnical aspects, refer to Section 4.4
and Section 5.4.
Filtering
To prevent underlayer and core materials being piped or washed out by hydraulic forces
induced by waves, current or water level difference, they should be protected by a filtering
system. Filter systems are generally composed of granular materials, geotextile filters or a
combination of both (known as geosystems). In some structures, such as breakwaters, an
additional hydraulic requirement is sometimes expected and the filter system is also required
to contribute to the energy dissipation by turbulent flow through the void spaces.
The mechanical and durability characteristics of the filter material (including geotextiles, if
applied) should be compatible with the armour layer. For example, the use of filter layers
with limited durability may not be compatible with concrete armour units for which there is a
strong requirement for no settlement and unit deformation.
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The most important design considerations in this context are the grading curves, stone shape
characteristics and density of rock relative to site water. Layer packing is also important in
relation to the porosity and, together with particle shape and grading, will control interlock
between particles and hence the shear strength of particles within the pack and between layers.
Armouring
2
In most severe environmental conditions, the main structure is to be protected against:
!
hydraulic forces, such as wave action or current forces due to tide or stream
!
weathering agents such as cyclic stresses from freeze-thaw, salt crystal growth, thermal or
wet-dry cycles that will tend to exploit any of the stone’s inherent weaknesses
!
additional forces such as ice load or ship collision or the action of shingle abrasion.
In some structures wave attack may cause movement of armour stones. As the severity of the
wave action increases, this motion will vary from rocking through to rolling or sliding for the
worst wave conditions. For such structures, breakage and attrition leading to general wear
and rounding is potentially much more rapid. There will also be implications for the design
specification, as the stones’ mass will decrease with time. Consequently, high-durability
characteristics will be required as well as stringent geometric constraints on the production of
stone size, mass, shape and grading.
Some aesthetic functions may be required for the most visible part of the structure. For
architectural reasons, specific placement methods may be expected and their influence on
stability and hydraulic properties should, if relevant, be verified. Where structures are
accessible by the public, amenity value, safety and hygiene are functions that have to be
considered at both the design and construction stage. The armour layer may be a habitat for
some species that colonise the voids in the armour or its surface. If relevant, this habitat
function, which includes the organism’s capability to stay adhered to the armourstone, should
be considered when studying the grading and rock type to use, see Section 2.5.
3.1.2.2
1
Material properties
3
4
5
6
The European standard EN 13383 Parts 1 and 2:2002 defines armourstone as:
coarse aggregate used in hydraulic structures and other civil engineering works.
Armourstone therefore has a loose granular form and includes all alternative (manufactured
and recycled) armourstone as well as primary quarried rock. Along with other European
aggregates standards, the new armourstone standard treats primary, secondary and recycled
materials equally: provided a material meets the required standard for the application, its
origin is immaterial. This may lead to more countries redefining their descriptions of
armourstone in line with those of the EN standards:
!
natural armourstone: armourstone from mineral sources that has only been subjected to
mechanical processing
!
manufactured armourstone: armourstone resulting from an industrial process involving
thermal or other modification, excluding armour units
!
recycled armourstone: armourstone resulting from the processing of inorganic material
previously used in construction
!
concrete armour units: prefabricated concrete units for armouring.
In relating properties to functions, it is useful to distinguish the following three types of
property that relate to different phases in the life cycle of armourstone.
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Intrinsic properties (see Section 3.3) relate to the properties of the rock source, its geological
history or the industrial process involving thermal or other modification. They account for
engineering geology considerations such as mineral fabric characteristics, discontinuity sets,
weathering grade and the tectonic context of the quarry.
Production-induced properties (see Section 3.4) relate to the armourstone as an individual piece
or as a granular material composed of individual pieces. They are affected by the intrinsic
properties and controlled by the production technique such as blast design, selection,
handling and sorting techniques or devices.
Construction-induced properties (see Section 3.5), such as layer thickness or layer porosity, are
controlled by the construction of the armourstone as a granular material and are heavily
influenced by the placement technique, the shape and the conditions of execution, for
example above or below water.
Some of these properties are also susceptible to change with time as a function of loadings
from the physical, chemical and biological environment. These are considered further in
terms of durability in Sections 3.1.3 and 3.6.
A conceptual understanding of properties and functions of any material used in construction
(such as gabion stone, recycled materials, concrete units, grouted stone, and the many and
varied applications of aggregates and armourstone) is given by the scheme outlined in Figure
3.4, illustrated here for armourstone.
Intrinsic
property
Productioninduced property
Contructioninduced property
Functional
requirements
eg colour,
density,
discontinuities,
mineral fabric,
strength etc
eg block integrity,
grading, shape
eg layer
thickness,
porosity,
permeability,
shear strength
cover layers,
underlayers, core:
eg stability,
overtopping
reduction, filtering,
volume, filling
Figure 3.4
3.1.3
System response
Quality control
Quality appraisal
Durability characteristics
Performance on
functions with time
On-site loading
Conceptual scheme for material properties and functions, illustrated for armourstone
Durability considerations
The durability of a material component or system is defined as its ability to continue
performing adequately in a specific working environment. Durability may be quantified by
the rate of loss of performance in engineering time.
Durability is therefore a balance between the intrinsic resistance of the material and the
aggressiveness of the forces acting in service. Poor-quality materials may stand up well in
mild environments where degradation forces are virtually non-existent, for example in the
permanently submerged core of a relatively impermeable breakwater.
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The designer should assess the probability that material degradation will cause a rapid
change in, and loss of, structural and functional performance. This is one of the most difficult
judgements to be made. As guidance on this topic is often in demand, tools, though tentative,
are provided in Section 3.6 for quarried rock. Faced with an assessment that a source will
degrade rapidly, the designer has various options.
3.1.3.1
1
2
Mitigation strategies for low-durability scenarios of armourstone
The greater the movement of armour and material components that is expected in service in
a chosen design, the greater is the need for highly durable materials. Similarly, to reduce the
rate of degradation, low-durability material should be prevented from moving.
The decision to use lower-quality material for armouring and/or filtering may be justified in
the following circumstances:
!
satisfactory performance records for the same armourstone in similar uses are available
!
aggressiveness of the site conditions is extremely mild
!
a high frequency of maintenance and repairs are acceptable because they can be carried
out quite cheaply and with little disturbance
!
armouring has been over-dimensioned to reduce mobility in storms
!
slopes have been flattened and greater material volumes used to reduce mobility in storms
!
armour layer has been placed with higher interlock to reduce mobility in storms
!
there is no alternative, because more durable materials or concrete units are too costly
and a relatively short design life is therefore acceptable.
4
5
Some innovative low-cost options referred to in Crossman et al (2003) highlight the use of
materials of marginal quality in addition to less conventional design and construction practice
(see also Section 6.3.5). The innovation of grouting to achieve the necessary stability in the
cover layer is described in Section 3.15. It should be noted that reduction in binding
performance of the cementitious or bituminous grout is more rapid for sites affected by
severe climate.
NOTE: In choosing between armourstone or concrete armour units, armourstone may be
more appropriate if a very long life is required. Many sources of igneous and metamorphic
rock and some compact crystalline limestones have low water absorption and good integrity
and will be considerably stronger and more durable than unreinforced concrete.
3.1.3.2
3
6
7
Durability considerations for material other than armourstone
Armouring
For armouring, the main factors that cause breakdown of gabions and geotextiles are
abrasive agents, movements inducing localised rupture and ultraviolet breakdown of
polymers and plastic shielding wire. Corrosion prevention can be costly. Geosystems and
geobags are only rarely used for armouring but in such cases strength and durability of the
geotextile/geomembrane is critical as it is essential to prevent degradation from ultraviolet
exposure and puncture damage. For materials other than rock, such as concrete units and
gabions, suggestions and detailed references to durability assessment are included within
Sections 3.12–3.16.
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Volume-filling and filtering
For most projects where quarried rock is used for volume-filling, it should be emphasised
that degradation rates are insignificant in permanently submerged environments with low
water flows. There is one important exception: inland waters may become significantly more
acidic than sea waters, so dissolution of carbonate in softer limestone may result in settlement
of the core. The site water’s acidity should be considered and, especially in freshwater
applications, rock used for volume-filling should be free of soluble constituents such as
sodium chloride and gypsum, which may be removed in solution in quantities that could
affect the environment.
Use of alternative granular materials is particularly encouraged when employed as a coastal
reclamation fill material. For recycled or secondary materials, it is important to ensure that
their leaching characteristics, such as quantity and type of substance released, are compatible
with the environment of use. Risk of degradation, settlement and leaching can be most
effectively mitigated using a volume stability and water solubility testing regime together with
geotextile and/or clay liner systems to provide barriers to flow routes. Any secondary
minerals that may grow and thus alter the characteristics of the core should be identified and
appropriate treatments employed. The guiding principle is that volume filling and filtering
materials should be physically and chemically stable when in use and be prevented from
interacting harmfully with their environment. Risk assessment methodologies for secondary
and recycled materials are given in Section 3.13.
3.1.4
Standards for armourstone
A major development in Europe over the past decade has been to consider armourstone as a
standard construction material, which has led to the introduction of a dedicated European
standard for armourstone, EN 13383. This standard, along with a number of aggregates
standards, was introduced to comply with the requirements of the European Commission
mandate M125, Aggregates, given under the Construction Products Directive (89/106/EEC).
EN 13383 supersedes conflicting recommendations for armourstone in national standards.
Amendments to remove these conflicting recommendations have been introduced. EN 13383
is divided into two parts:
Part 1:
Specification – gives the requirements for armourstone to fulfil “essential
requirements” as expressed in Directive 89/106/EEC
Part 2:
Test methods – gives dedicated methods to test armourstone when standard
aggregate or rock mechanics methods are not suitable.
EN 13383-1 specifies a range of categories for properties to enable users to select the
appropriate limiting values for the wide range of armourstone produced in Europe (see
Section 3.7, which discusses armourstone specification). In most instances, provision is also
made for producers to identify a declared value for properties when the value of the
property is outside the indicated categories.
Owing to the special functions and large sizes of armourstone materials, some special test
methods and sampling methods, which differ from those associated with aggregates, have
been specified in EN 13383-2:2002. The remaining test methods required draw on new
European test method standards for aggregates that supersede the methods previously used
in European countries. A tabular summary of all sampling and testing requirements for a
particular property is given in EN 13383-2 Annex G as an aid for armourstone producers
and testing authorities. This summary is considered necessary because of the particularly
wide range of test types, test portions and sample reduction procedures needed to
accommodate armourstone tests both on individual test pieces of rock as well as on a sample
selection of stones.
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1
When considering the reasons for testing, it is useful to make the distinction between:
!
the mandatory tests performed by the producer for obtaining CE marking (see
Section 3.7.1)
!
other tests required by the designer or the contractor for a specific project or to control
the deliveries.
For CE marking, the type of compliance that the tests are intended for (see EN 133831:2002, Clause 8) are as follows:
!
!
Initial Type Testing (ITT) – tests are performed as one-off characterisations, either of
new sources or of existing sources where there is a major change in the rock mass being
quarried or the methods being used
3
Factory Production Control (FPC) – the producer periodically performs tests to ensure
the production process continues to generate materials of expected properties.
There is another context for ITT that has no direct part in the specification and compliance
process. This is where the test information for a test property outside the EN 13383 system is
not known through any previous testing, but obtaining and declaring the result is considered
of value to the producer and/or purchaser. In this context, for heavy gradings, block shape
characterisation and integrity testing by the Full-Scale Splitting Test (FSST) method are to be
encouraged because of their potential to assist the designer (see Section 3.8, which discusses
testing).
Examples of tests commonly applied for FPC would be particle density, while for the case of
coarse standard gradings, mass distribution checks are particularly important. Tests carried
out for ITT may include all tests carried out for FPC.
The system has produced clear benefits by defining geometric properties, such as standard
armourstone gradings that allow the producer to prepare materials in advance and inform
the designer of the availability of gradings. Caution is advised when using the standard, as
the requirements it sets out cannot ensure all aspects of durability or a given service life. For
certain scenarios, different requirements may be required to ensure satisfactory performance,
based on site-specific requirements. For example, full-scale armourstone integrity tests are
not included in EN 13383, which restricts its laboratory-testing programme to relatively small
homogeneous pieces and these cannot represent the long-term behaviour of full-scale
heterogeneous stones weighing several tonnes.
In many parts of Europe, there are abundant sources of armourstone of excellent quality.
Once the required gradings are determined, insufficient attention may be given to rock
quality and often high quality requirements from the standard specification are simply given.
This may exclude local armourstone of perfectly acceptable quality that is cheaper to supply.
Worldwide, projects typically use quarried rock that is locally available but gives only good,
marginal or even poor quality indications from test results. Outside Europe, therefore,
standards such as EN 13383 should be applied with care and may need to be adapted as
appropriate. In North America, where the range of climatic conditions is extreme and
excellent quarried rock is often scarce, ASTM D4992-94 (2001) Standard practice for the
evaluation of rock to be used for erosion control suggests rock be examined at source. It indicates
that the laboratory tests to be used will depend on the rock type. It does not attempt to say
which tests are required but mentions those available and lists the rock properties that are of
special concern. In many cases, evaluation by a qualified geologist, for example using a
systems approach (Lienhart, 2003), may be invaluable in preparing a specification. Extensive
evaluation of rock source suitability may be necessary, particularly if rock of less than
excellent quality is to be used (see Section 3.6). This will depend on project scale, complexity
and risk.
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3.2
QUARRIED ROCK – OVERVIEW OF PROPERTIES AND
FUNCTIONS
3.2.1
Introduction to quarried rock
Large quantities of quarried rock are often needed for marine projects, for example an
estimated 9.3 million tonnes per year were used over five years to build the new Hong Kong
Airport. A single large breakwater in Iceland required 1 847 000 t of quarried rock, of which
80 per cent was core material and 20 per cent armourstone. In contrast, a bridge pier scour
protection scheme in Scotland used 4 200 t of armourstone, and river training works may use
just a few hundred tonnes of armourstone or gabions. Whatever the scale of the project, a
good understanding of quarried rock, its production and processing will often prove as vital
to the economic success of a project as a good understanding of hydraulic design. This is
largely because armourstone is not an off-the-shelf building material, and each combination
of rock and site conditions is unique.
Unfortunately, an expert assessment of the expected service life rarely accompanies a
portfolio of standard test certificates or “fit-for-purpose” trade marks. Potential rock sources
therefore need to be evaluated and matched with their intended function at the site.
Sections 3.2 to 3.11 on quarried rock aim to explain the key properties of rock materials
and to:
!
introduce the main rock types and quarry evaluation process (see Sections 3.2.2, 3.2.3)
!
explain the main properties, functions and terminology needed for projects (see Section
3.2 to 3.5)
!
provide a systematic approach for service life prediction (see Section 3.6)
!
help the designer to prepare a suitable specification for rock materials (see Section 3.7)
!
summarise test methods for armourstone grading and armourstone quality (see Section 3.8)
!
provide guidance on quarry operations for production, selection and transport of
armour stones (see Section 3.9)
!
outline realistic quality control procedures (see Section 3.10)
!
highlight cost implications (see Section 3.11).
There are limits to the guidance that can be given here. Further reading of engineering
geology textbooks such as Blyth and De Freitas (1984), Waltham (2001) and Goodman (1993)
is recommended for those seeking a greater understanding of geological factors. In recent
years, useful special publications on use of stone and aggregate materials relating to
hydraulic structures include Smith (1999) and Smith et al (2001). For collections of papers
specifically on armourstone, including case history experience, see Magoon and Baird (1991),
McElroy and Lienhart (1993), Thorne et al (1995) and Latham (1998a). For seminal papers
on armourstone, see Lienhart and Stransky (1981) and Fookes and Poole (1981).
3.2.2
Introduction to engineering geology
Rock types
Geologists divide rocks into the following groups depending on their mode of formation:
86
!
igneous rock – formed by the crystallisation and solidification of a molten silicate magma
!
sedimentary rock – formed by sedimentation and subsequent lithification of mineral grains,
either under water or more rarely on an ancient land surface
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!
metamorphic rock – formed by the effect of heat and pressure on igneous, metamorphic or
sedimentary rocks for geological periods of time, resulting in new minerals and textures
developing within the pre-existing rock.
These groups may be split into 20 rock types. Each rock type has similar characteristics and
the engineering properties and use of these rock types can be presented in a general
summary form as shown in Table 3.2. Typically, rock materials are obtained by conventional
quarrying operations as discussed in Section 3.9. There are extensive areas where rock
outcrops are not present on the Earth’s surface and deposits of glacial till, river or marine
sediments may be used.
Table 3.2
Generalised evaluation of the use of unweathered rock in hydraulic structures
Rock
Metamorphic
Sedimentary
Igneous
Group
Use
Filter
Core
Density
(t/m!)
Maximum
size
Shape
Granite
*
*
*
2.5–2.8
HG
Equant
Diorite
*
*
*
2.6–3.1
HG
Equant
Gabbro
*
*
*
2.8–3.2
HG
Equant
Rhyolite
*
*
*
2.3–2.8
LG
Irregular to equant
Andesite
*
*
*
2.4–3.1
LG
Equant
Basalt
*
*
*
2.5–3.1
HG
Equant
Syenite
*
*
*
2.6–2.9
HG
Tabular to equant
Quartzite
*
*
*
2.6–2.8
HG
Tabular to equant
Sandstone
!
*
*
2.3–2.8
LG
Tabular
Siltstone
!
!
*
2.3–2.8
LG
Tabular
Shale
!
!
*
2.3–2.7
LG
Tabular
Limestone
*
*
*
2.3–2.7
HG
Tabular to equant
Chalk
!
!
*
1.5–2.3
LG
Equant
Slate
×
×
*
2.7–2.8
LG
Tabular
Phyllite
×
×
*
2.3–2.7
LG
Elongated
Schist
!
!
*
2.7–3.2
LG
Elongated to tabular
Gneiss
*
*
*
2.6–2.8
HG
Equant
Marble
*
*
*
2.7–2.8
HG
Equant
Serpentinite
*
*
*
2.5–2.6
LG
Irregular
Eclogite
*
*
×
3.3–3.6
HG
Irregular
4
5
6
7
8
9
Notes
10
* suitable for use; ! specific attention to ensure suitability; × not suitable
CG: coarse grading; LG: light grading; HG: heavy grading (see Section 3.4.3).
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3
Property
Armour
Type
1
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3 Materials
Discontinuities of the rock mass
Quarrying takes place in an in situ rock mass, consisting of intact rock and discontinuities
cutting through it. Both are important for production and use of armourstone. The
characteristics of a rock mass at outcrop scale are usually dominated by the naturally
occurring discontinuities (see Figure 3.5). In many respects, large armourstone pieces may
have similar characteristics to the rock mass; smaller aggregates, however, do not. Natural
discontinuities have geological or geomorphological origin, whereas artificial discontinuities
are generally induced by extraction techniques, such as blasting. Engineering geologists use a
special terminology (eg Blyth and De Freitas, 1984) to cover a variety of discontinuities, the
most common types being bedding planes that separate different successive beds of rock in
the ground, joints, schistosity planes and stylolites.
Discontinuities are generally characterised by their origin, orientation, persistence, frequency,
surface geometry and infill material. Significant decrease of mechanical characteristics can
occur at discontinuities. Evaluation of the discontinuity pattern of the rock mass will provide
the following essential information:
!
the block sizes in the rock mass prior to production, also called “In situ Block Size
Distribution” (IBSD). The IBSD is close to the largest size of the recoverable blocks to be
expected. In addition, it controls the excavated mass distribution and may be taken into
account in the blast design (see Section 3.9.3)
!
the likelihood and distribution of weathering in both the rock mass and the armourstone
produced (see Section 3.6)
!
the expected block shape of light and heavy armourstone pieces, Figure 3.5 (see Section
3.4.1)
!
the likelihood of armourstone integrity problems for light or heavy gradings (see
Section 3.3.4).
Figure 3.5
88
Idealised sketches of common discontinuity patterns in natural outcrop forms (showing
about 5–10 m)
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1
The discontinuity pattern may be analysed from:
!
!
rock faces, when accessible. Photogrammetric and laser-based hardware and software
systems for direct appraisal and discrimination of discontinuities are just becoming
available at the time of writing. The type of technology is illustrated in Slob et al (2002).
Direct analysis of scanlines at the face provides characteristic values or statistics of the
distribution of orientation, spacing and frequency. Details of scanline methods are given
in Priest (1993) and explained in Section 3.9.2
drill cores or borehole logs can provide typical spacing information in the borehole
direction and the Rock Quality Designation (RQD) index (see Zhang and Einstein, 2000,
for details). In addition, sonic velocity analysis using emitters and receivers down the
boreholes can provide information on estimates of the expected mass distribution and
shapes of blocks.
2
3
Application of these analysis methods to in situ block size distribution assessment is discussed
in Section 3.9.2. When service record information exists, sometimes it is possible to ascertain
whether discontinuities seen within blocks will be detrimental in projects. Discontinuity types
and patterns in the rock mass of the quarry and in the stockpiled armour stones can be
studied, together with a survey of the performance of the same discontinuity types both
during construction and in service. Marcus (1995) used such an approach to provide
qualitative guidance on the type of discontinuity likely to break, which he adapted to quality
control (see Section 3.10). This approach can also be used as guidance when selecting zones
for armourstone production that will best avoid problematic discontinuities.
4
Weathering grade of the rock
5
Rock weathering is brought about by the exposure of the rock over long periods of
geological time to the climatic conditions at the Earth’s surface and involves mechanical
disintegration and chemical decomposition acting together. The effects are most marked in
humid, hot climates, but it must be remembered that climatic conditions in the geological
past as well as present conditions may influence the weathered state of a given rock mass.
The influence of climate on the weathering profiles of rock is illustrated in Box 3.4 for typical
quarries in three different climates: north-western European, tropical hot-wet and hot dry
regions.
6
7
8
9
10
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Box 3.4
Influence of climate on weathering of rock in quarries
Proper recognition should be given to the weathering profiles existing within the rock face being excavated
(Fookes, 1980). In general, the igneous and metamorphic rocks, which were formed in conditions of high
temperature and pressure not found at the earth’s surface, show the greatest tendency for well-developed
weathering profiles, with the breakdown of their darker iron and magnesium bearing minerals in
particular, to form secondary minerals which can be clearly seen under the microscope. The sedimentary
rocks break down less easily because they were formed at conditions of temperature and pressure
existing at the Earth’s surface, which are probably similar to the climatic regime they experience at the
present ground surface.
Figure 3.6 shows three quarries in an extremely simplified form. The right-hand one (no 1) portrays an
igneous rock quarry in north-western Europe. Immediately prior to the current geological processes
operating on the Earth’s surface, the Pleistocene ice advances have planed off much of the existing
residual soil and weakened weathered rock to leave fairly fresh rock, generally containing only faintly to
slightly weathering grades of material. Often this rock is shattered near the surface by freeze-thaw cycles
and it may be covered with glacial or post-glacial debris (Fookes, 1980).
The centre quarry (no 2) shows the same rock in a tropical hot and wet climate. Here, physical planing by
ice during the Ice Ages did not occur, and therefore a thick development of residual soil still exists, which
is sometimes lateritic. The soil passes down into highly weathered rock, which in turn passes down into
less weathered and finally into the fresh rock. In such a quarry the various grades of weathering can easily
be seen and recognised.
The left-hand quarry (no 3) portrays a limestone quarry in a hot desert climate. The rock is usually fairly
porous and weakened some metres below the existing ground surface by leaching, but has a thick
hardened surface duricrust composed of calcrete (the specific type of duricrust formed by the upward
leaching of a limestone bedrock).
Figure 3.6
Three idealised quarries showing different types of weathering
Rock degradation processes may have taken place very slowly over geological timescales, due
to physical, chemical and biological weathering or hydrothermal alteration processes.
Depending on the degree to which this degradation has occurred, the general properties
expected for a fresh specimen as given in Table 3.2 may not apply. For example, weathering
over many thousands of years may have developed an abundance of microcracks in the
mineral fabric of an igneous rock, and originally strong interlocking minerals may have been
altered or completely replaced by weaker ones such as clays.
The severity of geological weathering disintegration is indicated by the weathering grade
which may be assessed subjectively and assigned to the rock mass or the intact rock at the
quarry, as follows:
90
!
Grade 1A – no sign of rock material weathering
!
Grade 1B – discoloration on major joint surfaces, sound mineral constituents
!
Grade 2 – discoloration on all joint surfaces, discoloration and some weakening of
mineral fabric
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!
Grade 3 – less than half the rock is decomposed and/or disintegrated to a soil
!
Grade 6 – the rock is reduced to an unstructured soil.
1
Numerous weathering grade assessment schemes exist. For rock engineering site
investigation work, BS 5930:1999 is widely recommended. Classifications and test procedures
designed for different rock types (Cassar and Vella, 2003; Lee and De Freitas, 1989) are
particularly useful.
Weathering of rock may occur in geological time (usually many tens of thousands of years)
and in service in engineering time (typically 50–100 years for coastal structures). For
example, a stone may not lack overall strength and quality at the time of excavation.
However, if the rock mass shows signs of weathering Grade 2 or above, the armourstone is
likely to break down more rapidly by splitting, spalling and abrasion when exposed to the
rigours of the site. This weakening should be suspected and laboratory tests, even if they
include tests for resistance to weathering, should be interpreted with caution, ideally with the
aid of thin-section petrographic analysis to identify secondary deleterious minerals and
microcracking in the rock fabric.
NOTE: If rock strength or density results for a rock type are unusually poor, the results may
still satisfy specification requirements. Such results may be indicative of geological weathering
of Grade 2 or higher, including the possibility of chemical weathering of the intact material.
Additional field evaluation and petrographic examination is recommended to improve
predictions of performance and to identify higher quality regions to concentrate
armourstone production within the quarry. In many European, temperate and hot wet
climates, weathering grade decreases with depth in the quarry so that quality and block size
increases. If improvement with depth fails, design concept changes and alternative sources
should be considered; see also quality control in Section 3.10. However, in hot and dry desert
climates, the best rock is found in the hardened duricrust layer near the surface; see Box 3.4.
3.2.3
Quarry evaluation principles
!
stone sizes and armourstone quantities; to establish that the required tonnages of the
necessary sizes can be produced and delivered at the desired time at the desired rate (see
Section 3.9 especially Section 3.9.5 on matching yield curves and demand, Section 3.10
on quality control, and Section 9.2 on site preparation)
4
5
7
armourstone quality; to provide data to make a prediction of the service life of the
armourstone (see Section 3.6).
The initial visit should establish first if the armour sizes and proportions are possible,
estimate quality visually and take test samples. It might then consider reserves, distances and
transport systems to the site, load-out facilities and stockpiling facilities, and finally issues of
confidence in the experience and quality control systems of the quarry. Methods for
prediction and evaluation of quarry yields are developed further in Section 3.9.2.
In adopting a systematic approach to the evaluation of armourstone quality, (Lienhart, 1998,
2003), and in addition to field evaluation at the project site of aggressiveness (frequency of
extreme loadings, mobility of armour, attrition agents) and site climate (in-service weathering
intensity, cyclic stressing), the field evaluation in the quarry should address the following:
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6
Field and laboratory examination of an existing quarry or new dedicated (greenfield) site
being considered as a materials source has essentially two distinct purposes:
!
2
!
geological setting – spatial variation of best rock units, intensity of faulting and jointing
!
rock type – intact rock strength and resistance to in-service weathering and attrition
8
9
10
91
3 Materials
!
regional in situ stress regime – faulting and folding suggests quarried blocks will tend to
split
!
weathering grade – geologically weathered rock decomposes faster in service
!
groundwater conditions – water flowing or seeping from the quarry walls suggests
weathered seams
!
discontinuities – in situ block sizes, stone shapes and integrity
!
production methods – non-blasting methods generate fewer internal cracks than
aggregates blasts
!
set-aside – stones cured by storing for several months before selection will rarely split
!
shape as seen in stockpiles – mean blockiness and aspect ratio
!
armourstone integrity as seen in stockpiles – proportion of stones with visible flaws
after known set-aside period
!
sampling – to obtain representative material for laboratory tests
!
block integrity testing – full-scale destructive testing.
Rock samples are tested in a laboratory and results interpreted for the site conditions. This
will allow an informed prediction of the service life of armourstone to be made (see Section
3.6), based on knowledge of rock mechanics and weathering properties of the various rock
types during engineering service conditions. The expected pattern and rate of degradation
of the stones should then be considered in design, in addition to damage caused by storms.
With an estimate of quarry yields, a more inclusive local scenario-based design can provide
better whole-life costing outcomes and the materials specification can be written accordingly.
The effort will be in proportion to the project scale and risk. In general, sources that yield
large blocks will have satisfactory physical and weathering resistance properties, but this is
not always the case. Furthermore, sources are inherently variable, so rock quality testing is
necessary.
The systems approach to quality evaluation can also work within the framework of EU or
other statutory or policy constraints, provided the potential stone sources are known prior to
design. A design based on selected armourstone category test requirements (eg for physical,
mechanical and resistance to weathering properties) without investment in evaluating the
quarry and making a service life prediction, is possible but may not be optimal. In the EU,
evaluation of armourstone from suppliers is simplified by the provision of certified test
results and production control documentation. This will help the quality of armourstone
sources to be assessed as nominally “excellent”, “good” or “marginal”, on the basis of handsized specimens and aggregate-sized test material. Producers with significant supplies of
armour-sized gradings for sale may also declare certain test results, so designers can consider
“marginal” and even “poor” property materials in appropriate circumstances. In many cases,
supplementary full-scale integrity testing of armour stones (Dupray et al (2003), see Section
3.8.5) will greatly increase confidence in assessing the relative suitability of several nearby
sources.
In practice, the evaluation of the two aspects, namely size and quality, is often carried out
simultaneously and can interact with the design process and decision-making in many ways,
as illustrated in Figure 3.7. Note that Step 3 is not applicable if there are no stocks of
armourstone available at the quarry. In this case, trial blasting may be required. Alternatively,
if blasts are performed for other applications such as aggregate production, sorting may
allow selection of suitable material to provide the information.
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1
Input: preliminary design
(top size and required quantities)
1 Initial site visit – design-related issues
Properties to assess:
See section
In case of poor results
Top size
By visual inspection
3.9.2
A,C
Quarry yield
First estimate, for greenfield quarries
3.9.2
B
Available quantity
First estimate, for existing quarries
3.9.1
A,B,C
Durability
First estimate
3.6
A,D
Shape
First estimate
3.4.1
B,E
2
2 Initial site visit – other issues
Issues to assess:
See section
In case of poor results
3.10
A,C
3.10
A,C
3.6, 3.10
A,C
3.9, 2.5
A,C
Stocking facilities
3.10
A,C
Site facilities
3.10
A,C
QA system in place
3.10
A,C,E
Reserves
Location
Expected performance of material
Environmental issues
Including existing stockpiles
In relation to construction site
and transport facilities
From experience/past projects
Especially for greenfield
quarries
3
4
3 In situ tests and measurements
Properties to test:
See section
Grading
3.4.3, 3.8
E
Integrity
3.3.4, 3.8
A,B,C,D,E
Weathering
Petrography
Discontinuities
In case of poor results
3.3.2
A,D
Quality
3.3.3, 3.6
A,C,D
Top size
3.9.2
B,C
Quarry yield
3.9.3
A,B,C
Shape
3.4.1
B,E
5
6
4a Sampling of the material (3.8.1)
4b Detailed investigations: laboratory tests (3.8)
Properties to test
Detailed petrography
See section
In case of poor results
3.3.2, 3.8.2
Accel. weath. test.
Physical properties
Water absorption, porosity
3.8.2
Accel. weath. test.
Accelerated weathering test
Only when required
3.8.6
A,B,D
Mechanical properties
(of the mineral fabric)
3.8.5
A,B,D
7
4c Detailed investigations: trial blasting (3.9)
Properties to test:
See section
In case of poor results
Top size
3.9.4
B,C
Quarry yield
3.9.4
A,B,C
Shape
3.4.1
B,E
Integrity
3.3.4, 3.8
E
8
Notes
Letters A to E identify proposed actions to be taken in case of poor results during the quarry evaluation
process:
A consider using another rock source
9
B consider revising the design
C consider using alternative material (eg concrete units etc)
D consider accepting higher maintenance
E consider adapting the quarry production/quality control system.
Trial blasts can be unreliable because different methods are often used in production blasts. The
armourstone may therefore be unrepresentative of the ultimately quarried rock mass due to near-surface
weathering in the trial blast rocks.
Figure 3.7
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General scheme for quarry evaluation
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3 Materials
3.2.4
Properties and functions – general
This section identifies where to find information on properties and functions of quarried
rock previously introduced in Section 3.1.2. Properties of armourstone can be geometrical,
physical (such as density), mechanical (such as strength), chemical and environmental (such
as leaching potential). Durability and service life are considered as a system outcome rather
than a property and are treated together with rock quality in Section 3.6.
Different properties may need consideration at different phases in the life cycle of the
armourstone, such as at the quarry prior to extraction, or after many years in service. To
reflect this, the following terms previously defined in Section 3.1.2 are used to structure the
main sections that follow, namely:
!
intrinsic properties
!
production-induced properties
!
construction-induced properties.
Table 3.3 lists and classifies the properties of natural armourstone, indicating the sections of
this chapter where the reader can find further information. Throughout the chapter
extensive reference is made to EN 13383:2002, the European standard for armourstone.
Production
-induced
Construction induced
Properties of quarried rock described in Chapter 3
Intrinsic
Table 3.3
Aesthetics
**
–
*
Petrography
**
–
–
Rock density
**
–
–
Physical
3.3.3
Rock porosity
**
–
–
Physical
3.3.3
Rock water absorption
**
–
–
Physical
3.3.3
Rock resistance to attrition and wear
**
–
–
Mechanical
3.3.5, 3.6.5
Rock resistance to weathering agents
**
–
–
Physical and
mechanical
3.6, 3.8.6
Rock fabric strength
**
*
–
Mechanical
3.3.4
Size of armourstone piece
**
**
–
Geometrical
3.4.2
Integrity of armourstone piece
**
*
–
Physical and
mechanical
3.3.4
Shape of armourstone piece
**
**
–
Geometrical
3.4.1
Armourstone mass or size distribution
*
**
–
Geometrical
3.4.3
Armourstone layer (or volumetric)
porosity
–
*
**
Geometrical and
environmental
3.5.1
Armourstone layer thickness
–
*
**
Geometrical
3.5.1
Armourstone integrity
*
**
*
Geometrical
3.3.4, 3.8.5
Property
Category of property
Physical and
environmental
Physical, chemical
and environmental
Discussion
3.3.1
3.3.2
Note
** very relevant; * relevant; – not relevant
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3.3 Quarried rock – intrinsic properties
3.3
QUARRIED ROCK – INTRINSIC PROPERTIES
3.3.1
Aesthetic properties of armourstone
1
The aesthetic requirements of armour in amenity areas can make the correct choice of rock
colour a vital consideration. Often, to help integrate the new structure with the landscape,
the public preference will be for a rock with an appearance similar to that in local cliff and
hill outcrops.
2
When specifying armourstone (see Section 3.7), selection of particular colours should be
avoided. Instead, the client should indicate which of the realistic possibilities offered from
suppliers’ sources are acceptable, with their associated ranges of shades or colour. Colour can
only be important for the visible part of armour layers. Biological colonisation (seaweed,
barnacles etc) may rapidly alter the shade as well as the overall appearance of the intertidal
zone.
3
Shape, grain size and roughness also have a significant influence on the aesthetic perception
of the armourstone material. Weathering phenomena, such as attrition, produce smooth,
rounded rocks and will thus modify the general appearance of the structure.
Finally, the placing method may have a significant visual impact and can affect the
acceptability of the structure on aesthetic grounds. In certain sensitive environments,
architectural placement may help the structure to fit to its environment. On riverbanks and
coastal revetments, a certain placement technique may give significant porosity and preferred
hydraulic properties, whereas public preference might well support a placement that looks
like a regular tight pavement.
3.3.2
4
5
Petrographic properties
The mineral composition and mineral texture of rock specimens can be the subject of
petrographic examination by hand specimen and thin section to classify the rock source and
to determine its suitability for construction materials. The extent to which microcracks have
formed and secondary minerals such as clays have replaced former harder minerals, for
example as a result of weathering, is an intrinsic property of the rock source that should be
evaluated by petrographic examination. Concerns can be addressed with specialised
durability and accelerated weathering tests (Section 3.8.6).
3.3.3
Mass density, porosity and water absorption
3.3.3.1
Phase relations
Figure 3.8 (left) shows an image of a real rock sample of sandstone in a dry situation. The
grey and white part of the image is mineral with a volume VM. The black part of the image
corresponds to voids (volume VP), which are empty here, but which may be filled totally or
partially by water depending on the value of degree of saturation, Sr. Figure 3.8 (centre and
right) presents schematically the different components of the rock ie minerals and pores
partially filled with water. Their respective masses and volumes are MM, VM and MP, VP. The
pores are filled by water (MW and VW) and/or air (MA = 0 and VA) to a certain extent, known
as the degree of saturation, Sr (-).
6
7
8
9
10
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Figure 3.8
3.3.3.2
Micro Computerised Tomography scan, schematic thin section and representation of
components of a porous rock specimen and their respective volumes and masses
(courtesy Ghent University)
Density definitions
Rock density definitions differ according to the approach considered, ie rock
characterisation, design of hydraulic works. The following list is an aide-mémoire of the
different densities that may be referenced. NOTE: the apparent mass density is to be used
for design of hydraulic works.
The real mass density, ρreal or ρmin (kg/m! or t/m!), of the rock is the mass density of the
mineral components of the rock as defined in EN 1936:1999. It is controlled by the
petrography of the rock and is not used for design.
The apparent mass density, ρapp (kg/m! or t/m!), is the mass density, being the ratio of mass
to its volume displayed by a sample of rock that may have water in its pores. It is mainly
controlled by the real density and the voids in the rock fabric but it also varies with the
degree of saturation of the rock. When the rock is in a totally dry state (oven dry), the degree
of saturation is zero. In this case, the apparent mass density is then known as ρrock. In test
results provided by a material laboratory, the mass density is ρrock. Test methods are described
in Section 3.8.2. NOTE: ρrock is not the density to be considered in the design but rather ρapp,
often called ρr.
The relative buoyant density, ∆ (–), is defined as:
∆ = ρapp /ρw - 1
(3.1)
where ρw is the density of water (kg/m!). ∆ is used in many hydraulic stability formulae and
related subjects (see Chapter 5).
The porosity of the rock, p (–), is the ratio of the pore volume to the total volume, p = VP/VT,
and should not be confused with the porosity of a bulk granular material.
The water absorption, WA (–), is the ratio of the maximum mass of water that can be
absorbed by the rock to the mass of the dry rock material. Equation 3.2 gives the relationship
between the water absorption and the porosity. Note the influence of water density, ρw ,
which can vary from 1000 kg/m! to above 1040 kg/m! for highly saline seas.
WA = ( ρw /ρrock ) ⋅ p/(1- p )
(3.2)
The degree of saturation, Sr (–), is the ratio of the water volume in the material to the volume
of the pores, Sr = VW/VP. Equation 3.3 gives the relationship between the apparent mass
density of the rock and its water content through this Sr value. Further discussion on the effect
of the rate of saturation on the apparent mass density is included in Box 3.5 and Figure 3.9.
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3.3 Quarried rock – intrinsic properties
ρapp = ρrock ⋅ (1- p ) + ρw ⋅ p ⋅ S r
(3.3)
1
NOTE: The apparent mass density is to be used for design of hydraulic works.
3.3.3.3
Degree of saturation in stability calculations
The value of mass density ρapp that is used when applying armourstone stability formulae, eg
Hudson and Van der Meer (see Section 5.2.2.2), has traditionally been assumed to be the
saturated surface dry mass density (ie ρrock) as it was considered the most applicable density
term for armourstone in the intertidal zone under wave action. When fully saturated, the
value of ρapp is therefore the value determined by testing in a saturated surface dry condition
(ie degree of saturation, Sr = 100 per cent). More recently, it has been recognised that
different degrees of saturation are appropriate for stones in different zones of the structure.
A correction to the density is now recommended for stability calculations to reflect the lower
stability of blocks in the intertidal zone when they are not fully saturated. An assumed
saturation of 25 per cent is recommended for armourstone that is not in permanent contact
with water and for armourstone permanently below water, a saturation of 50 per cent is
suggested (Laan, 1999); see also Table 3.17.
Box 3.5
Effect of water saturation on apparent mass density
For material with limited water absorption, the water content has a limited influence on the apparent
density. However, for rock displaying a larger water absorption or porosity, the additional mass density
attributable to the mass of water existing in the pores may be accounted for. Figure 3.9 gives the
additional mass density due to the amount of water absorbed in accordance with Equation 3.3.
2
3
4
5
6
7
8
Figure 3.9
Effect of degree of saturation Sr (-), on the apparent mass density of
porous rock ρapp. Contours indicate the correction value (in t/m³) to
be added to the dry mass density ρrock
For example, a rock with dry mass density of 2.4 t/m³ and a porosity of 10 per cent (p = 0.1) has a
correction value of 0.05 t/m³ for degree of saturation, Sr = 50 per cent and 0.10 t/m³ for a fully saturated
situation. In other words, the apparent mass density is 2.45 t/m³ or 2.50 t/m³ for 50 per cent or 100 per
cent saturation respectively.
9
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3.3.3.4
Density variation in a quarry
The rock mass density will generally correlate with the darkness of the rock’s minerals and
decrease with porosity and degree of weathering. Density variation is a good indicator of
quality variation and should be tested where variation is suspected. In general, the variability
of mass density of one type of rock in a quarry is limited and the 90 per cent exceedance
value is not more than 100 kg/m! less than the average density. Higher variability may be due
to genuine rock type variability in the source or the result of weathered zones.
3.3.3.5
Mass density as a durability indicator
Low-density material tends to have limited durability, generally because of the high porosity
(see Section 3.6). In 2006, the European armourstone standard EN 13383 specifies a mass
density greater than 2.30 t/m! to ensure minimum durability. Local material with a lower
density is therefore not supposed to be used within Europe. In areas deprived of goodquality rock, the use of low-quality rock should be studied, paying specific attention to
durability assessment using accelerated weathering tests.
3.3.3.6
Mass density as a design parameter
Design implications of variation in mass density due to varying rock sources can be very
significant (see point 1 below), whereas that resulting from different degrees of saturation is
important only in porous rock (see point 2 below).
3.3.4
1
Varying rock source. The designer or contractor may often select a default apparent
mass density value such as 2.7 t/m! or the known density of a given source to prepare a
design, specify the grading of armourstone and determine the dimensions of the various
layers. In the case of consideration of alternative rock sources with a different rock mass
density it is necessary to respecify and redesign the various components of the rock
structure. For the same hydraulic stability, the designer is interested in the consequent
reduction or increase of the median mass, M50, the total mass of the armour, the number
of armour stones and the layer thickness, as these are influenced by a change in density.
These density effects and the consequent effects on stability can be taken into account by
using the graphs of correction factors given in Section 3.5.2.
2
Effect of water saturation on porous rocks. The designer may also want to take into
account the degree of water saturation and then account for the increase of apparent
mass density and stability due to the amount of water in the rock pores. This variation in
density between dry and fully saturated density is usually negligible and only becomes
significant for porous rocks, see Box 3.5.
Resistance to breakage and armourstone integrity
Potential breakage of armourstone is of particular concern when many rough handling
events can be expected after purchase and when the rock is intended for dynamically stable
structures, eg berm breakwaters. Over-dimensioning the specified M50 and anticipating
breakages where broken and sub-size pieces can be removed during construction is
sometimes used to compensate for poor resistance to breakage, but this is a potentially highrisk approach. This risk can be mitigated by assessing likely changes in mass distribution
using an appropriate degradation model (see Section 3.6.6) and suitable assessment
techniques or test methods to measure resistance to breakage (see Section 3.8.5).
Armourstone resistance to breakage and armourstone integrity are generally distinguished
(Latham and Gauss, 1995; Dupray et al, 2003) since the former governs minor breakage
while the latter determines major breakage. During quarrying, construction and in service,
armourstone pieces may display these two types of breakage, as described below.
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3.3 Quarried rock – intrinsic properties
Major breakage refers to breakage of individual armour stones along pre-existing defects, as
shown in Figure 3.10 for armourstone with different geological origins. Any defects are
controlled by the geology of the rock source and the production technique. For example,
sedimentary rocks may contain bedding planes, stylolites, calcite veins or shaly partings, while
igneous rocks may contain mineral veins, contacts between distinct petrographic units or
cooling cracks. In addition, macro-flaws may be induced by blasting or fragmentation of the
rock mass during extraction. If these defects propagate, a proportion of stones will be
transformed into large fragments. If major breakage takes place on a significant number of
stones, this may significantly affect the mass distribution of the armourstone and
consequently the value of design parameters such as M50 or Dn50 (see Section 3.6.6).
Resistance to major breakage is known as integrity.
Minor breakage refers to breakages of asperities. This often occurs when stone edges or
corners are knocked off during routine handling, by the traffic of heavy plant during
construction, or during initial settlement of the structure (see Figure 3.11). This
phenomenon takes place along new fractures created through the mineral fabric of the stone.
It is often associated with bruising and crushing, and generally creates fragments of limited
size (up to a few tens of kilogrammes) depending on the armourstone grading. This
phenomenon has a limited impact on the mass distribution and the M50 value (see Section
3.6.6), but can contribute to edge rounding. Many strength tests exist for measuring the
resistance of mineral fabric to breakage and are discussed in Section 3.8.5 but they do not
correlate with armourstone integrity tests (Perrier et al, 2004).
In simple terms, armourstone integrity is the ability of armourstone pieces to withstand
excessive breakage during their life cycle. It should not be confused with resistance to
breakage through the mineral fabric, ie resistance to minor breakage that might be tested on
small laboratory specimens or aggregates. From a survey of feedback from 200 professionals,
including designers, contractors, quarry companies, port and waterways authorities,
armourstone integrity was identified as an essential property (Dupray, 2002). Two aspects of
integrity should be distinguished.
1
The integrity of armourstone as an individual piece is its ability not to display excessive
breakage. The threshold for excessive breakage is discussed in Section 3.8.5.
2
The integrity of armourstone as a granular material is the ability of a consignment not to
display excessive changes of mass distribution and especially of its characteristic masses.
Integrity is a property of heavy armourstone, among others such as shape characteristics,
that may be evaluated by initial type tests, ie one-off tests giving information about an
armourstone source to promote design optimisation. Such initial type testing is distinct from
routine testing of the quality of consignments in association with factory production control.
1
2
3
4
5
6
7
8
9
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3 Materials
Figure 3.10
Examples of major breakage taking place in sedimentary and igneous rock (courtesy
S Dupray and G Laan)
Figure 3.11
Examples of minor breakage taking place in sedimentary and igneous rock
(courtesy S Dupray)
Methods to assess and measure integrity are given in Section 3.8.5. A new approach to
predict degradation induced by breakages is given in Section 3.6.6. Common measures for
resistance to breakage are:
The breakage rate, Bn (-), defined as the number of stones that display major breakage
expressed as the fraction of the number of stones in the consignment. An objective method to
determine Bn is given in Section 3.8.5.
The relative decrease of characteristic percentage passing mass IMx, defined by Equation 3.4:
I Mx =
M x ,i − M x , f
M x ,i
(3.4)
where x is the percentage passing value, i is the value of Mx before degradation and f is the
value of Mx after degradation. For example the relative decrease of M50 induced by
degradation events is IM50, defined as (M50,i – M50,f )/M50,i.
Other indicators based on the bounded area between mass distribution curves before and
after degradation are introduced in Section 3.8.5.
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3.3.5
1
Armourstone resistance to wear
Materials handled in bulk (typically core and underlayer materials of less than 300 kg) and/or
loaded many times will undergo considerable mutual shearing, resulting in abrasive
degradation with greater proportional mass losses for finer materials. Resistance to abrasion
in service is most important for sites where shingle or sand in suspension can attack the
armour (Figure 3.12). Also, for structures using dynamic design concepts, the increased risk
of rocking, sliding and rolling of stone will require that materials used should be sufficiently
abrasion-resistant. Certain applications in river engineering need careful consideration of
resistance to wear, for example where high suspended loads act in torrents or at the base of
high-velocity fall channels or scour focus points. Suggested requirement levels and test
methods are given in Sections 3.7.1 and 3.8.5.
2
3
4
5
Figure 3.12
3.4
Rapid erosion and mass loss of oolitic limestone armour stones
by shingle wear (courtesy J-P Latham)
6
QUARRIED ROCK – PRODUCTION-INDUCED PROPERTIES
This section deals with the properties of shape, size and mass of individual armour stones
and the systems used for the assessment and representation of their statistical variability in
the bulk granular material. These properties are affected by the producer’s methods of
extraction and selection. They govern the bulk material properties that can be expected in
the structure. As the client usually bears the cost of production and selection of both
acceptable and reject materials, shape and grading specification should not be set tighter
than is functionally necessary.
The production of armourstone typically involves both loosening of joint and bedding-plane
bounded blocks and blast-induced fracturing. Shapes, sizes and the occurrence of flawed blocks
are controlled by the interplay between these processes. Although shape is mostly governed by
intrinsic properties for large stones, it is convenient to consider shape in this section.
3.4.1
8
Shape
9
Shape is particularly important for armouring material that is individually placed above
water, as it can significantly affect the armour layer stability.
For any size range of particles in a bulk granular material, the dominant factors governing
porosity are size and shape distribution. Shape therefore has an indirect effect on shear
strength, permeability and filtering properties of core and underlayer materials. Bulk
materials that are flaky may crush more easily, for example if subjected to traffic.
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101
10
3 Materials
For individually placed armourstone, shape will affect ease of construction, layer thickness,
packing density and hydraulic stability. For typical angular armourstone sources, two
uncorrelated armourstone shape descriptors are required to quantify these effects (Newberry,
2003; Stewart et al, 2003). One is for form and the other relates to compactness. Both are
practical and sufficiently reproducible.
3.4.1.1
Length-to-thickness ratio (LT)
Length-to-thickness ratio, LT (-), is defined as the maximum length, l (m), divided by the
minimum distance, d (m), between parallel lines through which the particle would just pass;
see Figure 3.13. This form description is the industry standard now embodied in EN 13383
for both armourstone and aggregates. LT is sometimes termed aspect ratio.
Figure 3.13
Note
Illustration of armour stone
shape measurement systems
For a cube X/Z = 1, LT = 1.73.
In EN 13383, the symbol E is used to denote thickness d.
3.4.1.2
Blockiness (BLc)
Blockiness, BLc (%), is defined as the volume of a stone divided by the volume of the
enclosing XYZ orthogonal box with a minimum volume (see Figure 3.14). Blockiness is
defined in Equation 3.5:

 M
1
BLc = 
⋅
(( ⋅ 100
ρ
X
⋅
Y
⋅
Z
app


(3.5)
Blockiness is a shape descriptor, sometimes termed the “volume reduction factor” or “shape
factor”. It relates to compactness, or “rectanguloidness” and correlates well with the packing
behaviour of individually placed stones. This is because higher blockiness promotes stone
positioning with more sub-parallel face alignments, giving higher density, greater numbers of
contact points and thus greater interlock.
Y
Y
Y
X
X
Figure 3.14
Z
Z
X
Z
Examples of different blockiness values (from left to right, BLc = 80%, 60% and 40%)
Note that to obtain this shape descriptor, the stone mass, M, and density, ρr, need to be
known. BLc is determined by measuring the maximum X, intermediate Y, and minimum
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3.4 Quarried rock – production-induced properties
rectangular dimensions Z of the smallest hypothetical box that would enclose the block, and
by weighing. To help find the X, Y, and Z dimensions, Z is set parallel to d and X and Y are
then defined by the axes of the perpendicular plane with projected minimum area.
1
Advantages of using blockiness, BLc, with LT include:
!
accurate prediction of porosity and packing
!
better stability and hydraulic performance prediction
!
ability to match armourstone behaviour in a hydraulic model with that in prototype.
2
To characterise the shape of an armourstone piece, the dimensions X, Y, Z, l and d are
required. It is often most convenient to obtain these data when a representative sample is
undergoing weighing during a mass distribution check. For blockier shapes, l differs
significantly from X and d tends to coincide with Z (see Figures 3.13 and 3.14).
3.4.1.3
3.4.1.4
3
Cubicity
The form index used in France, sometimes termed cubicity, is given by (L+G)/(2E), where L,
G and E are the longest, intermediate and shortest orthogonal dimensions starting by
defining L and then taking the orthogonals G and E. These dimensions differ from X, Y and
Z. For highly irregular shapes, cubicity can be more objectively measured than blockiness.
For blocky pieces, X, Y and Z are more relevant to characterise the shape since X is the
longest side of the enclosing box and L would be close to the longest dimension of the box, ie
its diagonal. For characterising the likely behaviour of armourstone, it is therefore not certain
whether cubicity discriminates unwanted pieces any better than length-to-thickness ratio, LT.
In some special cases, however, cubicity departs from unity more than LT, eg for certain disclike shapes, and has been suggested as an additional constraint parameter to help avoid platy
stones.
4
Roundness
6
Armourstone may be sourced from naturally abraded boulders and glacial deposits or from
core stones in weathered igneous rock. In such cases, the roundness may have a major
influence on bulk properties in the structure. Armourstone pieces may also become rounded
while in service. If the mineral fabric strength is poor, materials may become significantly
rounded during handling by the crushing of edges and corners. To quantify roundness,
visual comparison charts such as for Powers Roundness (Powers, 1953) are often the most
practical. The Fourier asperity roughness, PR (-), was introduced for quantifying wear and
rounding (Latham and Poole, 1988) and later used to compare the hydraulic stability of
different armourstone shapes (eg see Bradbury et al, 1991). The latter study is informative
for assessing reduction of stability with increased roundness as estimated using PR. Typical PR
values are very round: PR < 0.009; semi-round: PR = 0.009–0.011; angular: PR > 0.011 (see
Figure 3.15). For angular individually placed stones, however, these values are of minor
importance as the shape is primarily determined by the blockiness, BLc, together with lengthto-thickness ratio, LT. More detail is given in Sections 3.7.1 and 3.8.3.
5
7
8
9
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3 Materials
Figure 3.15
3.4.1.5
Visual comparison of stone shapes showing roundness quantified using the Fourier
asperity roughness. Left: Rounding of gneiss; very round. Right oolitic limestone by
shingle attack, 1 m scale bar; semi-round (courtesy J-P Latham)
Proportion of crushed or broken surfaces
In some European countries rounded glacial boulders, cobbles and core stones from basalt
and dolerite quarries have been used for hydraulic structures. In order to ensure adequate
mechanical interlock for these materials, the percentage of crushed or broken surfaces is also
specified where appropriate.
3.4.1.6
Shape for specification purposes
Shape is an example of a property that may be used in two distinct ways. It may be specified
in order to establish the stone consignment’s fitness for purpose. If quantified in more detail,
it can provide information useful for design. Integrity is a similar property in this respect.
For specification, it is desirable to limit the proportion of pieces with a length-to-thickness
ratio, LT, of greater than 3:1 to a level that is reasonable for the intended use. Because smaller
stones tend to have larger LT, in Europe (see Section 3.7.1) the following levels are suggested:
!
heavy armourstone in cover layers
typically < 5 per cent
!
light armourstone in cover layers (< 40 kg)
typically < 20 per cent.
Restricting the proportion of pieces with LT > 3, ie the flaky or elongated pieces, should
ensure reasonable interlock. It will also limit the damage from breaking eg induced by
construction plant trafficking over granular surfaces.
It has also been suggested that removal of all stones with cubicity values greater than 3 will
target the removal of flaky pieces more effectively than applying an LT limit at 3. In practice,
it remains unclear whether further criteria based on cubicity would have this desired effect.
3.4.1.7
Shape for design and dimensioning purposes
In Section 5.2.2.2 possible stability increases corresponding to lower armour layer porosities
achieved by tighter non-random placement methods are tentatively presented. These lower
porosities can only be achieved with certain armour shape characteristics. In Section 3.5.1
conversion charts for armour layer porosity of individually placed layers as a function of two
shape parameters (LT and BLc) and placement method are given to aid stability and
dimensioning calculations.
For CE marking LTA is required (ie a specified maximum percentage of stones with LT > 3)
to ensure shape control (see Section 3.7.1). However, average values for LT and BLc should
not be specified as a requirement for factory production control as, by doing so, there is a
risk of significantly decreasing the production rate, increasing the price of armourstone or
even excluding rock sources that have the potential to provide the most economic project
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3.4 Quarried rock – production-induced properties
outcome. A producer should nevertheless be encouraged to declare the average and standard
deviation values of LT and BLc as part of initial type testing, as it provides the client,
contractor and designer with valuable information. Average values of both LT and BLc for a
proposed armourstone source are required for an accurate prediction of constructioninduced properties of cover layers individually placed above water (see Section 3.5.1). Both
shape parameters are uncorrelated, so one cannot be deduced from the other. The variability
of shapes in a consignment of armourstone can be considerable – see Figure 3.16, where it is
clear that LT has no relationship with BLc. Note the parameter independence and wide
spread about the mean. Other rock types and gradings may show different forms of scatter
plot, eg dimension stone product. Examples of shapes of limestone and granite stones are
illustrated in Figure 3.17. When armourstone is placed in bulk rather than individually, BLc
appears to have no significant influence on bulk density, while LT has a considerable influence.
1
2
3
4
5
Figure 3.16
Distribution of shapes measured in a consignment of 1–3 t limestone blocks (BLc is
given as a percentage)
6
7
Figure 3.17
8
Comparison of shape parameters of heavy armourstone, where increase in blockiness
does not always correspond with increase or decrease in value of LT (mass shown in
tonnes) (courtesy S Newberry)
9
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3 Materials
3.4.1.8
Factors controlling armourstone shape during quarry production
An indication of the typical LT or BLc of a rock source is given by the pattern of dissecting
discontinuities in the outcrop (see Figure 3.5). Factors that influence the blockiness and other
shape characteristics of a proposed grading of armourstone also depend on the grading size
in question and its relationship to the discontinuity spacing, as illustrated in Figure 3.18.
The extent of blockiness reduction by fracturing depends on the thickness between bedding
planes. For example, a limestone sequence with mean bedding spacing of 2 m, (≈20 t in situ
blocks) is shown schematically on the left of Figure 3.18. After blasting, a typical grading
based on the largest stones, eg 10–15 t, will consist of many highly blocky stones still bounded
by their original orthogonal joint and bedding surfaces. The smaller blast-pile gradings (eg
0.3–1 t) are almost certainly derived from blocks bounded by new irregular blast-induced
fractures (ie low blockiness), as the natural in situ rock mass does not have these small
orthogonal blocks. In contrast, a smaller in situ mean spacing of 0.6 m (see example b in
Figure 3.18) means it is reasonable to expect relatively blocky pieces in the 0.3–1 t range
bounded by natural bedding and joint surfaces to be liberated by the blast.
(a)
Figure 3.18
(b)
Schematic illustration of the influence of discontinuity spacing and grading on the
blockiness of armourstone in orthogonally jointed rock masses. Any spacing is
possible; the 2 m spacing is an illustrative example (see text)
Armourstone shape is generally influenced by rock type and production as follows:
106
!
bedded sedimentary sequences can produce very blocky armour stones (see Figure 3.49)
!
discontinuity patterns and spacings vary in all rock types, igneous patterns are often less
orthogonal
!
columnar joints are common in basalts and dolerites: high blockiness often occurs when
columnar joint spacing is matched to grading dimensions, elongate columns are rarely
preserved after blasting
!
sub-horizontal sheeting joints in granite may provide a dominant discontinuity set
causing the rock mass to break up similar to bedded sedimentary rocks, promoting
blocky armourstone
!
metamorphic rocks exhibiting natural banding (ie foliation produced by mineral
alignment or mineral segregation), such as gneiss, often yield rocks with a higher aspect
ratio if the foliation is well developed and clearly visible.
CIRIA C683
3.4 Quarried rock – production-induced properties
Armourstone may also be obtained from dimension stone quarries. These quarries typically
produce blocks cut out (or pneumatically split using a row of closely spaced holes) and these
have a very orthogonal blocky shape. The materials that have not been selected for further
cutting and polishing are a good source for armourstone. Natural blocks that are bounded by
several angled joints are also of no use and, if very large, are further broken up, eg by a
breaker, to help manoeuvre them into the waste piles. In most cases, these by-products of the
dimension stone industry make excellent armourstone, and a large proportion of the stones
in any such consignment will retain the blocky characteristics resulting from the original
cutting and splitting processes.
3.4.2
Dn = (M/ρapp)1/3
or
M = ρapp Dn3
(3.6)
Ds = (6/π)1/3 (M/ρapp)1/3
or
M = (π/6) ρapp Ds³ ≅ 0.52 ρapp Ds3
(3.7)
Dn = (π/6)1/3 Ds ≅ 0.81 Ds
Dn50 = (M50/ρapp)1/3
or
M50 = ρapp Dn503
4
Dn = 0.84 D
(3.10)
The median sieve size D50, the median nominal diameter Dn50 and the median mass M50 are
related using the conversion factor Fs (-):
Fs = M50/(ρapp D50³) = (0.84)³ ≅ 0.60
5
(3.9)
D (without a subscript n or s) refers to the square opening sieve size (m). An adjustable square
gauge may be used to provide an objective measure of the sieve size of any armourstone
piece of acceptable size. The sieve size D and the nominal diameter Dn are proportional for a
given shape of armourstone. Laan (1981) experimentally determined a recommended
conversion constant based on a study of several different rock types and gradings of
armourstone.
6
7
(3.11)
The assumption of Fs ≅ 0.60 is considered best practice and compares well with values in the
field, which vary from 0.34 to 0.72. For model-scale armourstone materials used in hydraulics
laboratories the value of Fs ranges from 0.66 to 0.70. For different kinds of screening or
selection techniques the value of Fs varies from 0.35 to 0.70.
Size and mass distribution of armourstone gradings
A new European standard EN 13383 has been devised for armourstone. It includes a system
for gradings applicable to materials used for armouring and filtering. The system is not
applicable to the typically very wide size ranges found in core materials used for volume
filling. The guidance here on gradings takes the user through the following:
!
3
(3.8)
These relationships are also valid for relating characteristic sizes of armourstone, ie they are
valid for any percentage of passing, such as the median value:
CIRIA C683
2
Dimensions of pieces of armourstone
The simplest measurement of an armourstone piece is its mass, M (kg), which can be
determined by weighing. The dimension of the equivalent cube, Dn (m), known as nominal
diameter is used in design. The diameter of the equivalent sphere, Ds (m), is now rarely used
for armourstone. For a rock of density, ρapp (kg/m!), relationships between M, Ds and Dn are:
3.4.3
1
8
9
10
grading widths
107
3 Materials
3.4.3.1
!
standard grading system of EN 13383 for armourstone
!
Rosin-Rammler curves
!
graphical illustration of grading curves
!
fragments and effective mean mass, Mem
!
requirements and compliance of EN 13383 Standard gradings
!
additional useful information on EN 13383 Standard gradings
!
the relationship between M50 and Mem
!
non-standard gradings
!
core materials.
Grading width and common terminology
A sample of natural quarry blocks will display a range of block masses or sieve sizes. The
percentage of total mass lighter or smaller than a given mass or size is often presented as
cumulative curves for assessment of mass and size distributions. The block mass is expressed
by My, where y per cent of the total (or cumulative) sample mass is lighter than M. For
example, M50 is the mass of the theoretical block for which half of the mass of the sample is
lighter.
The overall steepness of the curve is an indication of the uniformity in mass, generally
termed the grading width or gradation. A quantitative indication of the uniformity is the
ratio M85/M15 or its cube root, which reduces to Dn85/Dn15 or D85/D15. Table 3.4 gives the
description of the various grading widths, expressed in above mass and size ratios.
Table 3.4
Armourstone grading width related to the uniformity
D85/D15
M85/M15
Less than 1.5
1.7–2.7
Wide gradation
1.5–2.5
2.7–16
Very wide or quarry run gradation
2.5–5.0
16–125+
Grading width
Narrow or single-sized gradation
For wide gradings, the phrase well graded merely implies that there are no significant gaps in
material sizes over the total width of the grading. Gap-graded material may occur naturally, or
can result when two quite different single-sized products have been blended.
The gradings required by designers and controlled by producers generally become wider as
they become lighter. In most cases, armourstone is narrow graded. Rip-rap or riprap is the
term usually applied to armourstone with a combination of the following characteristics: wide
gradation, generally bulk placed, often placed as a cover layer and frequently used in
estuarial and riverbank applications. Rip-rap has had entire proceedings of an international
workshop devoted to it; see Thorne et al (1995).
Determination of the gradation of the granular material is important for the following
reasons:
108
!
the packing and the volumetric layer (or void) porosity of bulk-placed materials is highly
dependent on the overall slope of the grading curve (see Section 3.4.4.3, Box 3.6)
!
behaviour such as filtering and piping, especially across transitions between different
granular materials, is governed by rules based on gradation (see Section 5.4)
!
wider gradings will tend to segregate during bulk handling and stockpiling. Limiting the
grading width can control this.
CIRIA C683
3.4 Quarried rock – production-induced properties
3.4.3.2
1
EN 13383 system for standardisation of gradings
EN 13383 divides armourstone products into:
!
Heavy gradings (“HM”) for larger sizes appropriate for armour layers – normally
handled individually
!
Light gradings (“LM”) appropriate for armour layers, underlayers and filter layers –
produced in bulk, usually by crusher opening and grid bar separation
!
Coarse gradings (“CP”) often used for filter layers – of such a size that all pieces can be
processed by production screens with square openings (ie typically less than 200 mm).
The system for defining heavy gradings requirements is based on setting limit values with an
associated percentage passing by mass (see Figure 3.19). A set of nominal limits corresponds
to the target size of the armourstone. A set of extreme limits corresponds to tolerances. The
standard grading requirements and associated passing values are summarised in Table 3.5.
2
3
4
5
6
Figure 3.19
System for limits of EU standard gradings – percentages of passing as
given are for heavy grading
7
For heavy gradings, the associated limits are:
!
ELL (Extreme Lower Limit) – the mass below which no more than 5 per cent passing by
mass is permitted
!
NLL (Nominal Lower Limit) – the mass below which no more than 10 per cent passing
by mass is permitted
!
NUL (Nominal Upper Limit) – the mass below which no less than 70 per cent passing by
mass is permitted
!
EUL (Extreme Upper Limit) – the mass below which no less than 97 per cent passing by
mass is permitted.
8
9
In Table 3.5 limits for Mem are also given, defined as effective mean mass, ie the average mass of
a sample of stones without fragments (those below the ELL-value of the grading, see Section
3.4.3.5).
10
CIRIA C683
109
3 Materials
Coarse
Light
Heavy
Table 3.5
Heavy, light and coarse European EN 13383 standard grading requirements
Mem
Class designation
ELL
NLL
NUL
EUL
Passing requirements
kg
< 5%
kg
< 10%
kg
> 70%
kg
> 97%
kg
lower limit
kg
upper limit
kg
10 000–15 000
6500
10 000
15 000
22 500
12 000
13 000
6000–10 000
4000
6000
10 000
15 000
7500
8500
3000–6000
2000
3000
6000
9000
4200
4800
1000–3000
700
1000
3000
4500
1700
2100
300–1000
200
300
1000
1500
540
690
Class designation
ELL
NLL
NUL
EUL
Passing requirements
kg
< 2%
kg
< 10%
kg
> 70%
kg
> 97%
kg
lower limit
kg
upper limit
kg
60–300
30
60
300
450
130
190
10–60
2
10
60
120
20
35
40–200
15
40
200
300
80
120
5–40
1.5
5
40
80
10
20
15–300 *
3
15
300
450
45
135
Class designation
ELL
NLL
NUL
EUL
Mem
Passing requirements
mm
< 5%
mm
< 15%
mm
> 90%
mm
> 98%
mm
< 50%
mm
45/125
22.4
45
125
180
63
63/180
31.5
63
180
250
90
90/250
45
90
250
360
125
45/180 **
22.4
45
180
250
63
90/180 ***
45
90 ***
180 ***
250
NA
Mem
Notes
* = wide light grading, ** = wide coarse grading, *** = gabion grading, NLL = 20% and NUL = 80%.
See Table 3.6 in Section 3.4.3.7 for additional information on standard gradings.
For example, to fulfill the mass distribution requirements for an EN standard heavy grading
designated “3–6 tonnes” (or 3000–6000 kg), up to 10 per cent (by mass) may be below the
nominal lower limit NLL of 3 t, and up to 30 per cent may be above the nominal upper limit
NUL of 6 t. These undersize and oversize tolerances make the grading more practical to
produce. The grading is allowed a further margin for borderline stones at the extremes
using extreme lower (ELL) and extreme upper (EUL) limits. So for the 3–6 t example, ELL
restricts the percentage below 2 t to 5 per cent and EUL limits blocks above 9 t to less than 3
per cent, see also Figure 3.21. Similar definitions with slightly different percentage
requirements are introduced for light and coarse gradings.
The introduction of a system of standard gradings within EN 13383 has brought several
advantages. For the producer, these mostly concern the economics of production, selection,
stockpiling and quality control. The system enables engineers and producers to refer to a
batch or consignment of stones by its designated bottom NLL and top sizes NUL (using
masses or sieve sizes) with a meaning that is consistent to all. Standard gradings are
considered essential for coarse and light gradings as these are selected by mechanical means.
If non-standard gradings are specified, selection by mechanical means requires changing bar
openings, new screen decks or completely new barrels. With only a few grading classes
110
CIRIA C683
3.4 Quarried rock – production-induced properties
recognised within Europe, producers can pre-select armour stones and stockpile the
materials as standard graded products, knowing that designers will specify standard gradings
wherever possible.
1
2
3
4
5
6
7
8
Figure 3.20
Illustration of all EN 13383 standard grading curves using idealised
Rosin-Rammler curves designed to conform optimally to all EN 13383
grading requirements
9
As heavy gradings are selected by eye, it is not difficult to define and produce them in a nonstandard way. Instead of having to select either 1–3 t or 3–6 t, a 2–4 t grading could be
chosen if it was considered that the 1–3 t grading would be too light and specifying the safer
3–6 t range would involve an excessive layer thickness (although there would be fewer blocks
to place). For temporary dedicated quarries supplying single projects, where maximised
CIRIA C683
111
10
3 Materials
utilisation of the blasted rock is the guiding principle, standard gradings are less essential.
The following practical constraints apply to the production of gradings and the specifier
should always consider the cost implication, particularly for dedicated quarries:
3.4.3.3
!
a producer cannot produce overlap gradings of say, 1–3 t, 2–5 t and 3–6 t by any efficient
means, as the mass distributions overlap excessively (see also Section 3.9)
!
a producer cannot afford to supply gap gradings, such as 10–60 kg together with
300–1000 kg, if there is no demand for the 60–300 kg material that will also be created
(see also Section 3.9).
Rosin-Rammler curves for mass and size distributions and idealised gradings
This section on Rosin-Rammler curves is included:
!
to help interpolate between limits of standard gradings and generate complete graphical
curves (see examples given in Figure 3.20)
!
to explain theoretical gradings of core materials (see Section 3.4.4)
!
to predict in situ block size distributions (see Section 3.9.2) and quarry yields (see
Section 3.9.4)
!
to help match demands for materials with predicted quarry yields (see Section 3.9.5).
Derivation of an idealised grading curve
If the M50 is given together with a measure of the grading width, eg NUL/NLL as given by a
standard grading designation, or by M85/M15, theory enables a unique idealised curve to be
drawn for each standard grading. To be able to derive, plot and see the grading curve of the
expected product when specifying or purchasing a standard grading, in addition to knowing
the requirement limits, is a useful tool for designers, contractors and producers.
Theory
The basic form of the typical curve shape is the Rosin-Rammler (Ros-Ram) equation given by:
nRRM 
)+  1   M y nRRM +
)+
 My 
+
y = 1 − exp ln  ( 
 ≅ 1 − exp −0.693 

(
(
 M 50 
+  2   M 50 
+
+
+
(3.12)
or its inverse:
1 / nRRM
)

+ ln (1 − y ) +
+
+
M y = M 50 

1


+ ln
+

(
+  2  +
1 / nRRM
)+ − ln (1 − y ) +
≅ M 50 

+ 0.693 +
(3.13)
where y is the fraction passing value; My, is the mass corresponding to that value using a
percentage subscript to express that fraction, and nRRM the uniformity index, being a
measure for the steepness of the grading curve (see Equation 3.15).
As well as providing idealised standard gradings, the Ros-Ram curve shape can be fitted to
give a useful representation of most sets of grading data measured during production and
processing in the quarry, including core materials. To produce a good fit to real data,
numerical regression or other methods are used to select M50 and the uniformity index
nRRM. The Ros-Ram equation is the most universally applicable of several possible twoconstant models for cumulative mass or size distribution. It is always possible to find real data
for which Ros-Ram is not a good fit.
The Ros-Ram form can be used for distributions of size (using D to replace M in Equation
3.12). Two uniformity coefficients, nRRD and nRRM, are therefore often used, where nRRD =
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CIRIA C683
3.4 Quarried rock – production-induced properties
3nRRM. This relationship between uniformity indices of mass and size is valid for nominal
diameter, equivalent sphere diameter and can also be considered valid for sieve sizes. If a
graded material is represented by Equation 3.12 using masses, it may also be represented by
its equivalent Ros-Ram equation using nominal sizes. Masses may be converted into sizes in
term of nominal diameter Dn or sieve diameter D, which should not be confused. Conversion
of masses to sizes is achieved by dividing by density to give volume, the cube root of which
gives the nominal diameter Dn. To plot particle size obtained as Dn in terms of sieve diameter
D, divide by 0.84.
1
2
Relating theory to NUL/NLL
Given any two fixed points on the Rosin-Rammler curve, M50 and nRRM can be determined.
For example, if the nominal lower limit mass of a grading is NLL and the fraction passing at
that value is yNLL, and similarly the nominal upper limit mass is NUL and the fraction
passing at that value is yNUL, then by solving the following two equations:
 ln(1- y NLL ) 
M 50 ≅ NLL 
(
 -0.693 
-1/n RRM
 ln(1- y NUL ) 
M 50 ≅ NLL 
(
 -0.693 
-1/n RRM
(3.14)
4
to give
 ln(1 − y
)
NUL ( log( NUL NLL )
n RRM = log 
 ln(1 − y
)(
NLL 

3
(3.15)
the full curve described by Equation 3.12 is given.
5
How the idealised standard grading curves are obtained
The position and steepness of each idealised standard grading curve is set up not only to
comply with the limit requirements, but also to lie in the middle of the range of compliant
specifications for that grading. Standard EN gradings (eg 1000–3000 kg) impose
requirements such that y lies between 0 and 10 per cent passing at NLL (1000 kg) and
between 70 and 100 per cent at NUL (3000 kg). To define each idealised grading curve
uniquely and keep the system simple, each standard heavy and light grading has been
constrained using Equation 3.15 at the same two percentage passing points on the curve for
each pair of NLL and NUL values designated in the EN 13383 standards. The values chosen
are yNLL = 6 per cent and yNUL = 90 per cent respectively. Theoretically, these values give
designers maximum reassurance that the M50 plotted lies near 0.5 (NLL+NUL). The more
obvious first choice of 5 per cent and 85 per cent would lead the wider idealised standard
grading curves to miss 0.5 (NLL+NUL) by an unacceptable degree. The values chosen
minimise these differences to within 10 per cent of the target for the full suite of standard
heavy and light gradings. The only exception is the special wide grading of 15–300 kg, where
M50 is 26 per cent lower than the average of the nominal limits. For a more typical example
such as the 1000–3000 kg grading, the idealised curve gives M50 = 2.08 t, ie within 4 per
cent of 0.5(NLL+NUL). For further details see Latham et al (2006).
6
7
8
Plotting grading curves using Rosin-Rammler
Substitute a series of mass values My into Equation 3.12. This will return the series of fraction
passing y values needed to complete the plot. Before doing so, first set the nRRM and M50
values needed in Equation 3.12. To plot any heavy or light standard grading designated with
NUL and NLL, calculate the uniformity index nRRM using Equation 3.15 with yNLL = 0.06,
yNUL = 0.90. To obtain M50, substitute nRRM using either the NLL or NUL form of Equation
3.14. The resulting idealised grading curves are presented in Figure 3.20. These summarise
the expectations of a purchaser of standard gradings.
9
10
CIRIA C683
113
3 Materials
3.4.3.4
Graphical illustration of EN 13383 standard grading curves
To see the difference between different standard gradings as graphs plotted in this manual,
theory based on the Rosin-Rammler equation has been used. Idealised curves (Figure 3.20)
defined by each standard grading pair of NUL and NLL, (see Table 3.5), show the degree of
overlap (to allow for undersize and for oversize in the grading) and the changes in grading
steepness for the families of heavy, light and coarse standard gradings. The figures show, at a
glance, the approximate values that might be anticipated anywhere along the grading curve,
for any standard grading that has been specified. The idealised approximation becomes less
reliable at the more extreme ends of the grading curve.
NOTE: For the optimal curve idealisation, yNLL and yNUL are set at 6 per cent and 90 per
cent respectively for light and heavy gradings, and at 10 per cent and 95 per cent for coarse
gradings.
3.4.3.5
Fragments and effective mean mass, Mem
In the European grading system, fragments is a technical term for stones below the ELL.
Some fragments from crushed corners etc always exist however small their percentage of the
total mass. By excluding fragments from the total mass of a sample of stones, it is possible to
obtain a meaningful average mass simply by bulk weighing and counting all the stones. This
is termed the effective mean mass, Mem, of the sample and it provides a rapid method of
grading control. In the EU standard, it is referred to as “the average mass of the sample
heavier than a fragment”. For cover layer applications, the range of Mem will normally be
specified. Producers are required to keep Mem within this specified range rather than
applying controls on M50 directly. The minimum and maximum allowable Mem (ie lower limit
and upper limit of effective mean mass) are given the symbols Memll and Memul. Guidance on
conversion between Mem and M50 is given in Table 3.6 and Section 3.4.3.8.
3.4.3.6
Requirements and compliance of EN 13383 standard gradings
The exact requirements that define the range of masses users can expect from a heavy or
light standard grading or a coarse standard grading defined by sieve size, are set out in Table
3.6. Note NLL and NUL, for coarse gradings are set at 15 per cent and 90 per cent passing
while the ELL and EUL are set at 5 per cent and 98 per cent passing. The exceptionally
narrow 90/180 mm grading is intended for gabions. The 45/180 mm grading is relatively
wider than the others. In addition to the limit requirements for coarse gradings, there is a
need to constrain the median size further. A minimum value is therefore imposed on D50.
Examples of non-compliance are illustrated in Figure 3.21, which shows test results
producing failing and passing curves according to the combination of limit requirements and
Mem requirements of EN 13383, together with the idealised Ros-Ram grading curve for 3–6 t.
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CIRIA C683
3.4 Quarried rock – production-induced properties
1
2
3
Figure 3.21
3.4.3.7
Illustration of compliance and non-compliance with the grading system requirements
for a 3–6 t standard grading
4
Additional information on EN 13383 standard gradings
Designers require information on the range of M50, especially the minimum M50 that they may
reasonably expect when specifying a given NLL-NUL designated heavy or light grading. To
provide this information it is necessary to understand the relationship between Mem and M50 as
explained in Section 3.4.3.8 and the additional information given in Table 3.6, column (b).
The designer is concerned with the minimum and maximum M50 that can be expected given
compliance with the Memll and Memul limits. These are given in columns (c) and (d) of Table 3.6.
Example: the designer should be prudent in specifying a standard 1–3 t grading when his
design requires a minimum M50 value of 2.3 t; an actual M50 value of 1.87 t can be expected
(see column (c) of Table 3.6) while still complying with the requirements of the standard
grading. Alternatively, he may select a non-standard grading of eg 2–4 t, see Section 3.4.3.9.
Table 3.6 also presents similar information on the five standard coarse gradings. When a
standard coarse grading is specified, the designer may choose to determine stability on the basis
of a Dn50 value calculated from D50 (Dn50 = 0.84D50) specified in Table 3.6, column (b). This is
a conservative approach since in most cases the delivered material will have a greater D50.
NOTE: The coarse gradings may be grouped as three gradings of similar width or three
gradings with differing width.
5
6
7
8
Grading width indicators and Ros-Ram uniformity coefficients can also be compared for all
gradings in Table 3.6.
9
10
CIRIA C683
115
3 Materials
Coarse
Light and heavy
Table 3.6
Additional information on standard gradings
a
b
c
d
e
f
kg
M50/Mem
(Equation 3.18)
M50min =
Memll × (b) kg
M50max =
Memul × (b) kg
Ideal nRRM
Ideal nRRD
10 000–15 000
1.002
12000
13000
8.92
26.76
6000–10 000
1.024
7680
8710
7.08
21.24
3000–6000
1.054
4430
5060
5.22
15.65
1000–3000
1.099
1870
2310
3.29
9.88
300–1000
1.163
628
802
3.00
9.01
60–300
1.243
162
236
2.25
6.74
10–60
1.352
27
47
2.02
6.06
40–200
1.269
101
152
2.25
6.74
5–40
1.386
14
28
1.74
5.22
15–300*)
1.570
70
211
1.21
3.62
a
b
c
d
mm
D50 = 0.5
(NLL + NUL ) mm
Ideal nRRM
Ideal nRRD
45/125
85
1.09
3.28
63/180
122
1.06
3.19
90/250
170
1.09
3.28
45/180**
113
0.80
2.41
90/180***
135
1.61
4.83
Notes
* the 15–300 kg grading is exceptionally wide and values of M50max and M50min are presented that use
Equation 3.16 rather than Equation 3.18; ** wide coarse grading; *** gabion grading.
3.4.3.8
Relationship between Mem and M50, and grading widths including practical experience
Approximate relationship for any grading width
The values of M50 and Mem were measured on numerous projects across a range of standard
heavy and light gradings identical to those in EN 13383. Since M85/M15 can be estimated
with reasonable confidence, Equation 3.16 shown in Figure 3.22 based on field project data
can be used to estimate M50/Mem for any grading. Alternatively, using a direct theoretical
relationship between M85/M15 and NUL/NLL for idealised curves, the relationship can also be
summarised using Equation 3.17, which enables immediate estimates of M50/Mem from
contract specification.
116
M50/Mem = 0.860 (M85/M15)0.296
(3.16)
M50/Mem = 0.860 (NUL/NLL)0.201
(3.17)
CIRIA C683
3.4 Quarried rock – production-induced properties
1
2
3
Figure 3.22
M50/Mem as a function of the grading width, M85/M15, measured from
field project data (see Equation 3.16) (on the basis of invesigations
carried out by J A van Meulen)
4
Recommended relationship for standard gradings
Standard light and heavy gradings of EN 13383 were designed to become systematically
wider with decreasing M50. This fact has been harnessed to develop a prediction Equation
3.18 applicable only to standard gradings. It combines empirical data with theoretically
derived results.
M50/Mem = 1.61 M50-0.05
(3.18)
It is important to note that a better prediction of M50/Mem is to be expected using Equation
3.16 than Equation 3.18 for those cases where gradings are uncharacteristically wide or
narrow for the given M50 such as may occur for certain non-standard gradings.
3.4.3.9
Non-standard gradings
The cost-effectiveness of using standard gradings versus non-standard gradings should
always be evaluated. Standard gradings should be used whenever possible unless the
armourstone is being supplied by a dedicated quarry. The restriction on standard sieve
dimensions and screens that are manufactured means that credible non-standard coarse
gradings are few, although alternative grading requirements to the 90/180 mm could be
devised, eg for gabions.
5
6
7
NOTE: Reference is made in the following sections to Category A gradings when
requirements on Mem apply and Category B gradings when there is no control on Mem.
Category A gradings are normally to be used for cover layers, as these gradings have a
control on the average mass. Category B gradings are not intended for use in cover layers
(see Section 3.7.1 for further information).
8
Mass or size distribution similar to standard gradings – simple approach
A simple approach consists of determining non-standard gradings using the average
characteristics of all the standard gradings. This approach is applicable to Category B heavy,
light and coarse standard gradings by only calculating extreme limits from user-defined
nominal limits as follows:
!
CIRIA C683
set NUL and NLL to the desired values where the design M50 or Dn50 will be close to the
mean of NUL and NLL, ie M50 ≅ 0.5 (NUL+NLL). Note the gradation should be kept
reasonable and that the ratio NUL/NLL should not be taken too small as this may lead
117
9
10
3 Materials
to difficulties for production. The precise ratios should be adjusted by careful
consideration of standard gradings of similar width
!
set ELL = 0.7 NLL and EUL = 1.5 NUL. It is assumed that no further constraints will
be required for the effective mean mass or for maximum Dn50 in such a non-standard
grading specification and that if the grading is to be specified or declared with reference
to EN 13383, it would be of Category B status unless a more detailed approach is
adopted
!
assign the class limits ELL, NLL, NUL, EUL for the gradings family concerned (coarse,
light and heavy) to definitions based on 5, 10, 70 and 97 per cent respectively.
If an equivalent non-standard grading of Category A is to be declared or specified with
reference to EN 13383, the average mass (excluding fragments) should be bounded between:
!
a lower limit Memll = 0.8 (NLL + NUL)/2
!
an upper limit Memul = (NLL + NUL)/2
Mass distribution similar to standard gradings for Category A specification – detailed
approach for light and heavy gradings
The simple approach can be improved upon considerably as there is a number of
relationships that will generally hold for all the standard mass gradings (except 15–300 kg)
and any new non-standard ones with similar grading widths. The width of a standard
grading can be characterised by NUL/NLL, M85/M15 or nRRM. Any non-standard grading
likely to be practical to produce in the quarry and have a similar potential application to the
existing standard gradings can have their specification limit masses, Y (kg), derived relative
to M50 (kg) using coefficients presented in Table 3.7. They are related by the power law:
Y = AM50B
(3.19)
where A and B are coefficients (see Table 3.7).
These requirement values will need to be further adjusted and rounded at the discretion of
the specifier, to generate credible limit masses for quality control.
Table 3.7
Coefficients suggested for non-standard grading requirements for the specification or
declaration of gradings with similar properties to standard gradings
All mass values in kg
Specification
Additional information
ELL
< 5%/
<2%*
Memll
NLL
NUL
EUL
<10% >70% >97% min Mem
Memul
max Mem
M15
factor A
0.027
0.156 2.520 5.160
0.449
1.060
0.160 3.340 0.663 1.515
factor B
1.32
1.160 0.920 0.880
1.080
0.990
1.171 0.918 1.041 0.959
M85
M50
min
M50
max
eg for a standard grading
M50
=35 kg
calculated
2.9
9.6
66.4
117.9
20.9
35.8
10.3
87.2
26.9
45.9
rounded
3
10
65
120
20
35
10
90
27
45
eg for a non-standard grading similar to a standard grading
calculated
M50 =
3000 kg rounded
1050
1685
3984
5923
2556
2935
1893
5180
2768
3279
1000
1700
4000
6000
2500
3000
1900
5200
2750
3250
Note
* for a light grading (NLL <300 kg) the mass indicated is limited to 2%, otherwise the limit is <5%.
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3.4 Quarried rock – production-induced properties
1
Size distribution similar to standard gradings for Category A specification – detailed
approach for coarse gradings
The first three coarse gradings shown in Table 3.5 have ratios characterised by the following:
ELL/D50 = 0.28
NLL/D50 = 0.56
D50min/D50 = 0.79
NUL/D50 = 1.57
EUL/D50 = 2.24
For any user-defined D50, all appropriate limits can be obtained and rounded to available
screen sizes.
2
Mass distribution not similar to standard gradings for Category B – graphical method
If a given design M50 requires specification of a non-standard grading wider (easier to
produce) or narrower (more difficult to produce) than the equivalent nearest standard
grading, the suggested limit requirements in Table 3.7 should be disregarded in favour of
limits governed directly by the grading width chosen. Once the user has set the desired NUL
and NLL masses, the following graphical method, which assumes a log-linear form to the
grading curve, can be used:
!
using a log scale for mass and a linear scale for percentage passing, plot the NUL mass
point at 70 per cent passing and the NLL mass point at 10 per cent passing
!
join the two points with a straight line and interpolate to find the M50 value
!
linearly extrapolate to read off mass values at 2 per cent (if light gradings) or 5 per cent
(if heavy gradings) to obtain ELL. Similarly, read off mass values at 97 per cent to obtain
EUL.
3
4
5
Designating a non-standard grading
The EN 13383 gives specifications for a number of standard gradings with both Category A
and Category B status, but a producer may wish to declare other gradings for sale. Provided
the grading on offer can be tested for conformance using EN 13383 test methods, this is
perfectly acceptable within EN 13383 rules, but it must be declared using a labelling system
compatible with terms used for EN 13383 gradings: “HMA declared NLL-NUL; extreme limits:
ELL-EUL; effective mean mass: Memll-Memul. For example: a 2–4 t grading would be declared by
inserting the correct figures in place of the italics, eg using guidance from Table 3.7:
3.4.4
“HMA declared 2000–4000; extreme limits: 1050–5900; effective mean mass: 2500–3000”.
7
A designer wishing to specify limits different to the standard limits in Table 3.5 (Tables 1 to 5
of EN 13383-1:2002) would designate their requirements in a similar way. Note that the
prefix letters HMA, HMB, LMA, LMB and CP are used to distinguish heavy mass, light mass
and coarse size gradings respectively, where the subscript A refers to Category A, which
imposes the Mem restriction, while for Category B it is omitted.
8
Core materials
Core materials are generally used for volume-filling. As such, they do not have requirements
for a characteristic size such as M50. The top size is generally indicated and bottom sizes may
be controlled. The geotechnical properties required for core materials, typically shear
strength, placed porosity and permeability are identified in Section 5.4. These geotechnical
properties are greatly influenced by the width of the grading and most notably, the content
of fines. The fine material content is closely related to the tail of the quarry yield curve and
the fines removal technique. An approach for the prediction of porosity suitable for core
materials is given in Section 3.4.4.3.
CIRIA C683
6
119
9
10
3 Materials
3.4.4.1
Core materials terminology
Certain terms in general use indicate the degree to which the grading of natural quarry
product in the blast is modified by processing. Core materials with no fines control are
termed “quarry run”, “tout venant” (as used in England) or “brut d’abbatage” (as used in
France). They include all granular material found in the quarry blast-pile that can be picked
up in a typical loading shovel. Essentially, stones too large for easy digging and loading are
left behind.
“Crusher run” includes everything passing through the primary crusher. The top size is
restricted by crusher aperture settings.
“All-in” includes everything passing through a spacing of a grizzly or a screen aperture. All
these materials have an unknown proportion of material below a nominal reference mass
indicating fines, say below 1 kg. For use in the core of structures, the possible occurrence of
significant proportions of fine material, especially if they contain clays, is of concern as this
may be washed away during construction and/or reduce shear strength, leaving the structure
more prone to geotechnical instability.
“Processed core materials” have been processed for fines removal. The use of grizzlies and
other fines-removal methods may introduce profound changes in the grading curve shape
and the uniformity parameter describing the gradation width. These materials, while still
retaining very wide gradations, may be more costly to produce. The removal or inclusion of
fine material, such as that below 1 kg, affects the packing density of material dumped as core.
The limit value, such as 1 kg, is typically a notional value. Usually all that is required is
demonstration that effective procedures are in place for removal of fine particles. It should
be noted that permeability of the core can be greatly enhanced by removal of fines.
3.4.4.2
Core materials in a design context
In many cases where material is to be used for volume-filling, the decision whether to specify
no fines removed (quarry run) or alternative core materials with fines removed, is difficult as
there is a lack of guidance on the subject. The optimal specification requires an
understanding of the performance of the differing types of core materials, key parameters
often being the porosity or the risk of damage to the structure through piping or internal
erosion. For example, in a harbour breakwater, especially where wave transmission is to be
limited, the decision to set the fines cut-off at, say, 10 kg, 1 kg or at no cut-off may need
consideration of:
!
core porosity and, indirectly, permeability
!
percentage utilisation of quarry yield if materials are coming from a dedicated quarry
!
instability because of clay minerals in the fines
!
shear strength and liquefaction potential.
The effectiveness of quarry procedures for limiting smaller particles also deserves
consideration (see Section 3.9.5).
120
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3.4 Quarried rock – production-induced properties
By considering the uniformity coefficient nRRD of the materials in question and their particle
shape, geotechnically significant estimates of the porosity and total mass of material can be
given. The procedure for porosity estimation using Tsirel’s equation (1997) is described in
Section 3.4.4.3. An example is then given in Box 3.6 of how a quarry yield grading curve
may be modified, eg by a particular fines removal process in the quarry, from one RosinRammler curve to another steeper one; the consequent changes in bulk porosity can be
evaluated using an equation developed by Tsirel (1997). Removal of fines significantly
increases porosity and permeability, so where it is desired to reduce wave transmission (as is
the case for most breakwaters) it should only be necessary to remove fines if geotechnical
design factors make it necessary.
Porosity prediction of core materials is also extremely important for the calculation of
material tonnage requirements from the quarry.
3.4.4.3
1
2
3
Calculating the porosity of bulk-placed materials
The formulae and guidance given in this section can be applied to all bulk-placed granular
materials including cover layers, underlayers, filters and core. It provides a prediction of
average porosity for different gradings and different characteristic shapes.
4
The porosity of bulk-placed materials, nv (-), may be predicted using Equation 3.20 (angles in
degrees) adapted from Tsirel (1997) and Equation 3.21:
1
( eo ) arctan ( 0.645nRRD )
90
e
nv =
1+ e
(3.20)
e=
(3.21)
5
where e is the void ratio given by the volume of voids divided by the volume of solids (-) and eo
is the void ratio associated with single-size particles of different shapes (-), as given in Table 3.8.
For any standard or non-standard grading, it is possible to obtain nRRD (see Tables 3.6 and
3.7 and Section 3.4.3.3) and then to estimate eo (from Table 3.8). Once e has been obtained,
the bulk-placed (void) porosity, nv, can be calculated, using Equation 3.21.
Table 3.8
6
Coefficients for porosity prediction using Equation 3.20
Shape of
fragments
Cube-like
Elongated
Single-size
void ratio, e0
0.88–0.92
0.93–0.96 1.00–1.03
Flat
Typical mechanically
crushed
Smooth sand
and pebbles
Steel balls
0.92–0.96
0.65–0.80
0.52–0.61
Caution. Equation 3.20 was derived from rock fragments packing experiments in many
quarries. It has not been widely applied in hydraulic engineering but is likely to be an
improvement on previously available rules of thumb that give wide ranges of possibilities for
porosity. The equation suggests there is no absolute size influence on bulk-placed porosity. In
practice, the typical D50 for the material and the manner of dumping may also affect porosity.
This is because smaller materials more easily retain angularity and are of larger aspect ratio.
An empirical relationship to quantify this effect for M50 (kg) is:
LT = 2.31 M 50-0.02
(3.22)
7
8
9
where LT is the length-to-thickness ratio (see Section 3.4.1.1).
Note also that smaller materials with low abrasion resistance will become more rounded
during bulk handling. There is evidence to suggest that the above equation of Tsirel, which
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10
3 Materials
was calibrated primarily for dumped materials, and Figure 3.23 may tend to overestimate the
porosity for dumped standard armourstone gradings if the uniformity coefficient, nRRD, is
greater than about 5 and where relatively thin layers are considered. Furthermore, Tsirel’s
empirical relationship was not calibrated for the case of dumping or tipping through a water
column.
Various published predictions of porosity of bulk-placed materials are given in Latham et al
(2002a). Predictions based on Equations 3.20 and 3.21 and Table 3.8 are given in Figure
3.23, where equivalent values of average LT (= l/d, see Section 3.4.1.1) and descriptive shape
terms corresponding to Tsirel’s shape classes are suggested.
Example calculations on the change in porosity due to fines removal and oversize cut-off are
given in Box 3.6.
Figure 3.23
122
Bulk-placed (void) porosity, nv as a function of shape and uniformity in sizes
CIRIA C683
3.5 Construction-induced properties
Box 3.6
Example calculation of changes in bulk porosity resulting from fines cut-off and oversize
removal using the Tsirel and Rosin-Rammler equations
1
The effect on porosity of removing fines below 100 mm (mass ~ 1.5 kg) and oversize stones greater than
1 m (mass ~ 1.5 t) may be calculated as follows (see also Figure 3.24):
Characterise the Ros-Ram distribution of the quarry blast pile as, eg, D50 = 300 mm, nRRD = 0.9. For very
efficient quarry processing, set NLL of 100 mm with yNLL at 0.03 (or 0.06 for less efficiency) and NUL of
1000 mm with yNUL at 0.97 (or 0.90 for less efficiency) to represent the fines cut-off and oversize removal
efficiency and recalculate uniformity nRRD and D50 using (the Rosin-Rammler) Equations 3.14 and 3.15
(see Section 3.4.3.3). The processed core materials then have D50 = 455 mm, nRRD = 2.06. Assuming the
quarry run has angular shape, the bulk porosity of the quarry run is about 0.24 (using Equations 3.20 and
3.21) and that of the processed core material about 0.36. There is a significant impact on permeability in
the core and volume of blasted rock left behind in the quarry. Limited documented experience from
contractors suggests quarry run dumped in the sea may have porosity of around 36 per cent and with fines
removal, about 40 per cent, which suggests the Ros-Ram plus Tsirel equation approach to porosity
prediction illustrated above should be used with caution when applied to materials dumped through water.
2
3
4
5
Figure 3.24
3.5
Illustration of change in size distribution resulting from fines removal below 1 kg
and limiting of oversize blocks
6
QUARRIED ROCK – CONSTRUCTION-INDUCED PROPERTIES
Thicknesses of cover layers, filter layers and underlayers including rip-rap that are bulkplaced or dumped and raked to profile, are set by design criteria. The designer sets the
thickness to be a given proportion of a certain characteristic size of the grading in question,
typically as a function of Dn50 . Guidance on mass-to-volume conversions in such thin layers is
rarely given because of unpredictable boundary effects, but for bulk-filling operations
porosity is described in the context of core materials in Section 3.4.4.
For layers designed to be built as single or double layers using individually placed pieces, eg
from heavy gradings, guidance for layer thicknesses and porosities is given in Section 3.5.1.
In addition to particle geometry, a key property affecting thicknesses, packing and volumefilling relationships is the rock density itself. As rock density also affects hydraulic stability,
the consequences to the designer of using material with different density is addressed in
Section 3.5.2.
3.5.1
Layer thickness and porosity of individually placed armourstone
Geometric information on armourstone as a granular material both for bulk-filling and in
layered systems is essential for estimating quantities for design and for billing purposes as
well as for predicting hydraulic properties. Details are given in Gauss and Latham (1995),
Latham et al (2002b) and Stewart et al (2003). To enable prediction of volume-filling
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123
7
8
9
10
3 Materials
properties, the type of placements assigned to granular materials in the works, are classified as:
!
random placement
!
standard placement
!
dense placement
!
specific placement.
These terms are described in detail in Section 9.8.1. All bulk-placed materials are designated
random placement, whereas any type may be appropriate for stones placed individually into
armour layers. In principle, for armour layers, there are two distinct calculations adopted to
obtain bulk volumes (ie rock volume, Vr (m!), plus void volume) in a panel. Vb,d (m!) is the
design bulk volume assumed before construction and Vb,s (m!) the surveyed bulk volume
after construction. Vb (m!) is the bulk volume referring to either method. By following
guidance in Boxes 3.7 and 3.8 their differences should be minimised. The Equations
3.23–3.28 (see also Figure 3.25) define the geometry and related properties of armour layers.
Designed bulk volume (m!):
Vb,d = A td
(3.23)
Surveyed bulk volume (m!):
Vb,s = Acs L
(3.24)
Theoretical orthogonal thickness (m):
td = n kt Dn50
(3.25)
Volume of rock (m!):
Vr = Vb (1-nv)
(3.26)
Total number of stones in panel (-):
Na = n A kt (1-nv)/Dn50²
(3.27)
Bulk (or placed packing) density (t/m!):
ρb = (1-nv) ρapp
(3.28)
where:
A
=
total surface area (m²) of the armour layer panel parallel to the local slope
Acs
=
cross-sectional area (m²)
L
=
panel chainage length (m)
n
=
number of layers (-)
nv
=
(volumetric) layer porosity (-)
kt
=
layer thickness coefficient (-)
ρapp
=
apparent density of the armourstone (t/m!) (see Section 3.3.3).
NOTE: The volume of rock, Vr, should not be confused with the volume of armourstone,
which is Vb. The only practical possible use of Vr is as an input to determine the mass of rock,
ρapp Mr = ρapp × Vr which is also the total mass of armourstone.
The placed packing density or bulk density, ρb (t/m!), can be predicted from Equation 3.28
or, if the mass of armour placed into a panel is known, it may be determined directly from
the surveyed bulk volume. When dealing with wider gradings, a better prediction for the
number of blocks, Na (-), will result if Dn50 in Equation 3.27 is replaced by the nominal size
calculated from the average mass, Mem .
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3.5 Construction-induced properties
1
2
3
Figure 3.25
Armour layer geometry
The terms void ratio and porosity are well established for granular materials. However, in
Equation 3.26 nv is termed the void porosity of the armour layer, or simply volumetric armour
layer porosity to avoid confusion with the term porosity as applied to a specimen of intact rock
(see Section 3.3.3). Furthermore, when using the terms armour layer porosity or void porosity, the
user must be aware that the values depend on the method of surveying the bounding
volume.
NOTE: The armour layer porosity is calculated as an average property for the whole panel
being surveyed. This contrasts with suggested relationships presented by Bosma et al (2003),
who describe the layer porosity as a spatially varying property. The relationships they
propose are more applicable to dumped armourstone. These also have the potential to define
local changes in the average proportion of void space in armour layers near transitions, for
example where armour abuts concrete seawalls or between successive underlayers.
3.5.1.1
5
6
Importance of layer thickness coefficient k t and porosity nv
Designers and contractors must assume a layer thickness, td (m), to prepare drawings and
estimate the bulk volume Vb,d (m!), eg for preparing materials procurement tonnage details.
For individually placed armourstone in single or double layers, this is obtained from
Equation 3.25 (with n = 2 for a double layer), which in turn requires appropriate values for
the layer thickness coefficient, kt (-), and the median nominal stone size, Dn50 (m). Equation
3.26 converts the bulk volume, Vb (m!), to rock volume, Vr (m!), using an appropriate value
for the armour layer porosity, nv.
In addition to preparing rock volume requirements, estimation of armour layer porosity
assists in the prediction of armour layer stability (see Section 5.2.2.2).
7
8
Both kt and nv can vary considerably. Recent research strongly suggests that more accurate
predictions are achieved when blockiness has been used together with length-to-thickness
ratio to characterise armour shape. An important finding is that porosity and layer thickness
coefficients are lower than suggested in previous guideline documents such as CEM (USACE,
2003). General guidance for standard and dense placement is provided in Table 3.9,
illustrating a more blocky armour and a less blocky or irregular armour, defined by the shape
descriptor blockiness, BLc, for an assumed most typical mean value of the length-to-thickness
ratio, LT = 2 (see Section 3.4.1.1). Stones with higher mean LT values tend to form more
porous and thinner layers. Stones with lower mean LT values tend to form less porous
thicker layers. For double layers with random placement, values for porosity and layer
thickness coefficient suggested for standard placement may be assumed, although porosity
values will typically range from 0 to 2 per cent higher than for standard placement. The
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4
125
9
10
3 Materials
porosity of bulk-placed materials can be predicted using methods that specifically account for
the width of grading and aspects of shape; see Section 3.4.4.3.
Table 3.9
General guidance for layer thickness coefficient and porosity for various armour layers,
placement methods (Section 9.6), and survey methods (Section 9.9)
Layer and
placement type
Parameter
Reference (spherical foot staff)
survey method
Highest point survey method
Blocky rock
eg mean
BLc = 0.65
Irregular rock
eg mean
BLc = 0.50
Blocky rock
eg mean
BLc = 0.65
Irregular rock
eg mean
BLc =0.50
Single dense
kt , kthp
0.84
0.77
0.89
0.82
Single dense
nv , nvhp (%)
32
35
36
40
Double standard
kt , kthp
0.91
0.87
0.96
0.92
Double standard
nv , nvhp (%)
32
35
36
40
Double dense
kt , kthp
0.91
0.87
0.96
0.92
Double dense
nv , nvhp (%)
31
32
35
36
Notes
BLc = Blockiness (see Section 3.4.1.2).
Guide values based upon assumption of mean length to thickness ratio LT = 2.0, and deduced from
research study of Stewart et al, 2003.
The subscript “hp” refers to highest point survey method (see Section 9.9).
Guidance presented in Box 3.7 for the standard, controlled method of individual placement
of armourstone further illustrates the blockiness concept. Photographs of measured model
armour layers (Figure 3.26) and full-scale armour layers (see Stewart et al, 2003) show the
sensitivity of packing to block shape. These test panels emphasise the importance of matching
model armour shape and placement methods used in laboratories to those at full scale,
whenever potentially tighter placement procedures are in operation. Full-scale test data that
illustrate the wide range of possible values for kt and nv (and ρb), are presented in Table 3.10
(see also Box 9.3).
Figure 3.26
126
Models illustrating shape effects with standard
placement on 1:2 slope. Top: BLcmean = 75%,
LTmean = 2.4, nv = 34%, kt = 0.87. Bottom:
BLcmean = 46%, LTmean = 2.0, nv = 39%, kt = 0.85
CIRIA C683
3.5 Construction-induced properties
Table 3.10
Examples of as-constructed layer thickness and bulk (or placed packing) density properties
obtained from full-scale structures surveyed using the 0.5Dn50 spherical probe method
1
Test location and armourstone grading (t)
Layer and placement type
Single
Double standard
Double dense
Parameter
Shoreham
Bardon Hill
Immingham
Torr Works
Reculver
8–12
3–6
0.5
3–6
1–3
kt (-)
0.71
0.80
1.03
0.82
-
ρb (t/m!)
1.90
1.84
1.63
1.79
–
nv (%)
30.0
34.3
40.0
34.8
–
kt (-)
0.77
0.88
0.92
0.91
0.94
ρb (t/m!)
1.89
1.89
1.65
1.85
1.77
nv (%)
30.1
32.8
39.2
32.9
34.4
kt (-)
0.76
0.86
–
0.92
–
ρb (t/m!)
1.96
1.93
–
1.86
–
nv (%)
27.6
30.9
–
32.5
–
Figure 3.27 provides guidance for estimating the layer thickness coefficient kt (-), and armour
layer porosity, nv (%), for armour stones placed above water, where placement can be
controlled. It is based on the reference survey method, which uses a spherical-bottomed probe
of 0.5Dn50 for surveying. While such a survey method cannot be employed in practice in all
situations, guidance based on a reference method is required. This guidance can then be put
into practice for more commonly adopted survey methods such as the highest-point method as
presented in Section 9.9.8.1, where surveying technique corrections to kt and nv are explained.
The empirically derived prediction chart in Figure 3.27 for double layers is applicable to 1:2
slopes using controlled placement termed standard placement, as discussed in Section 9.8.1.1. In
Figure 3.27 an example with BLcmean = 0.65 and LTmean = 2.5 gives kt = 0.81 and nv = 0.335.
More general guidance can be found using the equations given in Box 3.7. Comparison of
predicted and measured armour layer porosity is given in Box 3.8.
2
3
4
5
6
7
8
9
Note
Curves are given to predict armour layer porosity, nv, and layer thickness, kt, for a range of values of
d/lmean – this is the inverse of the the length-to-thickness ratio, LT (see Section 3.4.1.1); the blockiness
coefficient, BLc, on the horizontal axis is defined in Section 3.4.1.2.
Figure 3.27
CIRIA C683
10
Prediction chart for nv and kt of individually placed armourstone in double
layers, standard placement
127
3 Materials
Box 3.7
Guidance on layer porosity (packing) and layer thickness for armourstone individually
placed above water
The guidance in this box is based upon extensive study of armour packing (Newberry, 2003; Stewart et al,
2003), which examined the dependency of layer (void) porosity, nv , and layer thickness coefficient, kt , on
method of placement, stone shape and definition of the surface. Nineteen full-scale test panels were
compared with models, and it was found that scale effects on armour layer geometry were negligible,
provided shapes were matched. Ninety-one model revetments were built (see Figure 3.26) to investigate
the effect on nv and kt of LT, BLc, standard and dense placement methods, slope angles, single and double
layers – all for very narrow size ranges associated with standard heavy armourstone gradings. Border and
survey effects were compensated for by using reference methods at laboratory and field scale.
Multivariate linear regression analysis was used to develop the following predictive equations:
nv = A + B BLcmean + C/LTmean
(3.29)
kt = A + B BLcmean + C/LTmean
(3.30)
Mean values of BLc and LT were used as the governing variables for assessing nv and kt values.
Small improvements in the prediction given in the chart in Figure 3.27 can be made when the standard
deviations and range of block masses are also included in the regression equations. Substitution of the
regression coefficients from Table 3.11 into Equations 3.29 and 3.30 will provide guidance on single- and
double-layer geometric parameters for 1:2 slopes when placed with standard placement. Steeper slopes
generate marginally tighter layers.
To calculate variation of armour layer porosity for dense placement, the value calculated as ∆nv using
Equation 3.31 is to be added to nv obtained from Equation 3.29, resulting in a slight reduction.
∆nv = A + B BLcmean + C/LTmean
Table 3.11
(3.31)
Coefficients for determining porosity, nv, and layer thickness coefficient, kt, for a 1:2
slope, using Equations 3.29–3.31
Parameter
A
B
C
Single
nv
0.59
-0.24
-0.22
Single
kt
0.01
0.48
1.04
Double
nv
0.55
-0.21
-0.20
Double
kt
0.21
0.30
1.03
Double
∆nv
-0.11
0.10
0.08
Layer type
Layer thickness can be derived from Equation 3.25 and placed packing (or bulk) density from Equation
3.28 (see Section 3.5.1). Values of void porosity and layer thickness calculated using the methods given
in Equations 3.29–3.31 may be used as input.
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3.5 Construction-induced properties
Box 3.8
1
Predicted versus measured layer porosity
The 90 per cent confidence limits for nv are ±2.4 per cent porosity and ±3.7 per cent porosity for double
and single layers respectively, and for kt they are 0.01 and 0.11 for double and single layers respectively;
see Stewart et al (2003) for further discussion. The quality of fit is shown in Figure 3.28. Both standard
and dense placements (see definitions in Section 9.8.1.1) refer to individually placed blocks. Dense
placement usually reduces the porosity by about 2–4 per cent compared with standard placement.
Materials that are bulk-placed vary considerably in their width of gradation and this has a greater impact
on porosity than the range of shapes as shown in Section 3.4.4.3. For further details of layer thickness
and porosity prediction including values for other slopes, see Stewart et al (2003).
2
3
4
Figure 3.28
3.5.2
5
Predicted versus measured layer porosity, nv, using Equations 3.29
– 3.31 and empirical coefficients
Effect of rock density on design parameters
Where available, rock of alternative mass density to that assumed in the initial design may be
considered for possible use in a project. Typically mass densities of up to 3.5 t/m! can be
obtained for dense rocks such as eclogite, and higher, eg > 4 t/m!, for manufactured
armourstone obtained from recycled copper and steel slags. For an increase in density, an
unchanged design gives a lower stability number Ns = Hs/(∆ Dn50) and hence greater stability
through an increase in ∆ Dn50 (m), where ∆ is the relative buoyant density (-) (see Sections 5.2.1
and 5.2.2). The effect of water absorption can be significant and is discussed in Section 3.3.3,
Box 3.5.
The designer may also wish to examine the various effects of substituting rock of alternative
density ρapp,alt that achieves the same hydraulic stability (ie a constant value of the stability
number, Ns = Hs/(∆ Dn50) as the initial design density ρapp,d. For identical stability, using
subscripts “d” and “alt” for initial design mass density terms and alternative mass density
terms respectively, graphs have been plotted using the Equations 3.32 and 3.33 for the
median mass M50 and the total mass of the armourstone Mt respectively.
M50, alt/M50,d = (ρapp,alt/ρapp,d)/(∆alt/∆d)3
(3.32)
Mt,alt/Mt,d = (ρapp,alt/ρapp,d)/(∆alt/∆d)
(3.33)
6
7
8
9
The equations have been used to generate the contour plots of multiplication factors given in
Figure 3.29, for both freshwater and seawater applications.
10
CIRIA C683
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3 Materials
Figure 3.29
Contour plots of multiplication factors for change in density. Top: Fresh water, ρw = 1.0
t/m³; bottom: Seawater, ρw = 1.025 t/m³
For identical stability, the multiplication factor for the total number of armourstone blocks,
Na (for a narrow grading where M50 ≅ Mem), is proportional to the factor ∆², see Equation
3.34, while for armour layer thickness, ta, the factor is proportional to the factor 1/∆, see
Equation 3.35.
Na,alt/Na,d = (∆alt/∆d)2
(3.34)
ta,alt/ta,d = ∆d/∆alt
(3.35)
In summary, for the same hydraulic stability, substituting rock of greater density allows a
smaller armour block size, reduced total mass in armour layer, reduced layer thickness and
an increased number of units to place (possibly increasing the placing time).
If there are no design changes, an increased density will give increased stability and possibly
increased durability. An advantage of using less dense material for core arises from its greater
volume per unit weight of material transported to site, since it is the bulk volume making up
the design levels that is attractive provided that the geotechnical properties are satisfactory.
Box 3.9
Influence of change of density on median mass, M50 , and total armourstone quantity, Mt
Example: A project considers the use of 10 000 t of armourstone with M50,d = 8 t, with an initial design
mass density of ρapp,d = 2.6 t/m³. An alternative source with a rock mass density of ρapp,alt = 2.3 t/m³ is
locally available. The multiplication factor (= the right-hand side of Equation 3.32) is 1.65 (see Figure 3.29
top) and the alternative M50 value (see Equation 3.32) is then: M50,alt = 1.65 × 8 t = 13.2 t.
Similarly, using Equation 3.33, the total amount of armourstone material is determined to be:
Mt,alt = 1.09 × 10 000 t = 10 900 t
130
CIRIA C683
3.6 Rock quality, durability and service-life prediction
3.6
ROCK QUALITY, DURABILITY AND SERVICE-LIFE PREDICTION
3.6.1
Introduction
1
The information contained here (Section 3.6) is for consideration prior to specification
(Section 3.7). The differences in possible demands on the performance of armourstone from
one aggressive application to another mild one are substantial. Without knowledge of site
conditions and the design application it is therefore not always possible to be confident from
test results alone whether the rock materials will be either suitable or unsuitable. Degradation
models can be used to take these differences into account and in some cases will suggest
unacceptably rapid losses in performance. Fortunately, there are still many mitigating
strategies (eg over-dimensioning, high maintenance etc; see Section 3.1.3) available to the
design team, before finally preparing the material specification.
A key tool for the engineer in this manual is a multi-purpose and generalised look-up table of
intrinsic properties (see Table 3.12). Each property is classified into bands indicative of
excellent, good, marginal or poor armourstone durability considering all conceivable rock
types and quarry sources. Such a classification is independent of design and site conditions,
and therefore cannot provide categorical assurances for suitability or service life outcomes.
Each attribute (each row in Table 3.12) has a direct or indirect consequence for the resistance
to a particular type of loading that may or may not actually be present for the application.
For the same application, relative outcomes for different rock sources can be inferred from
the classes. In this relative sense, the four classes given for each specific attribute or property
have the following tentative interpretation.
Excellent – ideal and sometimes available. This material, with reference to this specific
attribute, can be used without any risk of degradation with time over a typical design life.
Good – better than average. In normal situations, no specific attention need be paid to this
attribute. It will generally not lead to any significant degradation, although it may show
progressive signs of degradation over a typical design life in certain circumstances.
Marginal – lower than average. Without specific attention, the attribute may lead to
significant degradation. It should be studied. If necessary, production, construction or design
should be adapted (see Section 3.1.3.1) by using appropriate blasting techniques (see Section
3.9), increased quality control (see Section 3.10) or by oversizing armourstone size using
appropriate prediction of the degradation (see Section 3.6.4), for example. This may be
associated with short periods where loss of performance is more severe.
Poor – much lower than average. If possible, the material should not be used where
exposure may affect the attribute and lead to rapid degradation. If it is used, specific
attention should be paid, as for marginal attributes. However, a specific survey of the
structure will generally be required and heavy maintenance may be necessary.
key factors in the quarry and the rock material itself
!
project site variables
!
a model to help quantify the effect of degradation factors active at the structure site.
3
4
5
6
7
8
Using such classes for specification purposes without paying due regard for the application
is not recommended. For the designer or contractor to evaluate optimised solutions, it is
important to specify a good match of materials requirements with the degradation
conditions on site. To achieve such a match requires systematic approaches that take
account of:
!
2
9
10
CIRIA C683
131
3 Materials
Prediction of degradation and damage with time can facilitate the use of whole-life cycle
approaches, with further potential added benefits to the environment.
NOTE: Rock degradation prediction is by its nature inexact and burdened with difficult
judgements. This section of the manual provides systematic methodologies for degradation
prediction. Further validation and refinement of these recently proposed degradation
models, eg by back analysis of case histories is required. However, the tools described do
reduce the amount of guesswork that would otherwise be involved, especially in cases where
less than ideal armourstone has to be used.
Section 3.6.2 introduces the concept of durability, modes of degradation in different parts of
a structure and symptoms of rock that may have poor durability. Section 3.6.3 provides a
system for assigning, in numerical terms, the overall armourstone quality designation,
termed AQD, of a source, using quarry evaluation criteria as well as laboratory test results.
The principles common to all degradation models are described in Section 3.6.4. Full details
of a general degradation model and its application are presented in Section 3.6.5.
Degradation specifically caused by breakages is treated in Section 3.6.6.
3.6.2
Durability and degradation
The durability of armourstone on a given project is quantified by the rate of loss of material
performance (such as reduction of mean mass or interlock) attributable to changes in
armourstone property in engineering time. This means that poor-quality materials exhibiting
low resistance to weathering may stand up well in mild energy environments, with low
exposure to climatic conditions, where degradation forces are virtually non-existent, for
example in the permanently submerged part of the core of an impermeable breakwater.
Degradation processes can be broadly classified as wear, fracture and pervasive
disintegration, see Lutton and Erikson (1992), Fookes and Poole (1981). These depend on
the position of armourstone in the structure.
132
!
In the armour layer, armourstone may be exposed to weathering such as freeze and
thaw, salt crystallisation, wetting and drying, temperature cycling when above water.
Dissolution below water is rarely significant. For coastal structures, the intertidal zone is
the area most vulnerable to such physico-chemical effects. In permanently submerged
armour layers, effects are negligible. For structures designed to adjust dynamically,
impacts from armour stones may lead to breakage, attrition and greater overall wear. For
these structures, the resistance to the forces induced by rocking or rolling is important.
The main performance requirement is to minimise any decrease in M50. Prediction of
M50 reduction is therefore sought by demand-based designers wishing to set quality
requirements high enough, or by supply-led designers wishing to build in degradationcompensating measures within the design philosophy.
!
In the underlayer, armourstone is exposed to weathering effects to a lesser degree than
the armour layer. The main concern is that degradation may lead to breach of filter
rules.
!
Core material is less exposed to weathering agents, so the consequences are likely to be
less critical. Dissolution may take place below water or be induced by intermittent water
circulation above water level. This may lead to voids and reduction of the bearing
capacity. The solubility is highly dependent on the water chemistry as well as mineral
content and rock porosity. For example, most types of limestone will not dissolve in the
chemical environment of most sea waters but will dissolve slowly in acidic fresh water.
CIRIA C683
3.6 Rock quality, durability and service-life prediction
1
Indicators of possible poor durability
Petrography, mass density, porosity, mineral fabric strength, armourstone production method
and discontinuity pattern in the quarry, provide a good indication of relative durability when
comparing sources. For any durability concerns, appropriate testing should be performed.
Magoon and Baird (1991), McElroy and Lienhart (1993) and Latham (1992) are
recommended sources for further details.
!
!
!
Petrographic examination, based on visual observation or thin sections, generally
provides a first evaluation of durability. Weathered rocks, breccias and conglomerates are
most susceptible to displaying poor durability when exposed to salt or freeze action.
Specific attention should be paid to schists, phyllites, chalk and marls, to rock containing
clay minerals or with weak cements. Some geologically recent sources of basalt are
known to display a specific weathering degradation mechanism known as
“sonnenbrand”. Rock containing pyrite minerals have been observed to display early
breakage caused by oxidation of pyrite under water and heat action.
Water absorption (WA) is a good indicator of in-service durability. Armourstone with a
low WA, less than 0.5–1 per cent, will display a good resistance to severe cycling stresses
such as salt crystallisation or freeze and thaw. For significantly higher values of WA,
appropriate accelerated weathering tests should be performed to evaluate concerns
about resistance to weathering of the rock. If taken in isolation, WA can be misleading,
since rocks with WA greater than 4 per cent may have a free-draining pore structure and
thus perform well in service for certain applications. A high proportion of microporosity
as a percentage of the absolute porosity is detrimental. Rock that is porous but free
draining is less prone to breakdown by freeze-thaw action and salt crystallisation. In the
USA, the Mississippian-age Salem Limestone (Indiana Limestone) and Berea Sandstone
both have absorptions exceeding 6 per cent. Both have been used in breakwaters on the
Great Lakes where weathering intensities are extreme (MCWI > 300, see Table 3.15).
The Salem Limestone in the Chicago Breakwater is still performing satisfactorily after 80
years. The Berea Sandstone in the Cleveland Breakwater is still in good condition after
almost 100 years.
3
4
5
6
Rock with mass density lower than 2.3 t/m! is considered to have unacceptable durability
for normal use. For rock of low density and high water absorption, the low resistance to
weathering is sometimes less of a problem than the low resistance to breakage.
Armourstone characteristics were introduced in Sections 3.2–3.5. Predicting the future
response of armourstone with given characteristics in the quarry, under the wide range of
possible lifetime loadings remains a subject in need of further research. Presented below are
guidance tables and modelling tools that may be useful in the process of evaluating the
quarry source, the site aggressiveness and the service-life of the armourstone.
3.6.3
2
Procedure for source evaluation of armourstone quality
7
8
Assessment of the attributes affecting quality of the rock source
Table 3.12 provides a summary of the most significant quality-related intrinsic attributes of a
source of armourstone, based on field and laboratory data. The table has three uses:
!
to provide a guide to four classes of quality for each attribute that affect the global
relative durability
!
to provide numerical input data for an overall rating system for comparing
armourstone sources
!
to provide data needed for the application of a degradation model.
9
10
CIRIA C683
133
3 Materials
The criteria recommended in the table are adapted from Lienhart (1998), established
practice, and in some instances are specifically adjusted to maintain compatibility with the
category settings in EN 13383 and recent experience.
When using Table 3.12, it must not be assumed that these rock types have the results shown
in the columns below where mentioned. In addition, the following points should be
considered.
134
!
the table draws on quantitative and semi-quantitative assessment criteria. It is not
designed for specification purposes
!
requirement categories for specific tests that have been selected for specification
purposes in EN 13383 and other national standards may be set with fewer than four
categories and at different values to the above guide
!
national guidance for setting specifications often prefers fewer categories and higher test
performance levels, for simplicity and conservatism
!
the guidance offered in this table is intended for detailed semi-quantitative general
durability evaluation with an option to determine overall quality of a source in terms of
the armourstone quality designation AQD, using the system in Table 3.13. It is
therefore important to provide an appropriately sensitive rating, four classes being
considered reasonable
!
the range of test results in one quality class may not correlate with the range of results of
another test in the same quality class (eg tensile and compressive strength values).
CIRIA C683
3.6 Rock quality, durability and service-life prediction
Table 3.12
1
Guide to quality and durability of armourstone from a quarry source using field and
laboratory criteria
Quality and durability guide (not intended for specification purposes)
Criteria
Lithological
classification
Field evaluation in the quarry
Regional in
situ stress
Reference
EN 932-3
Lienhart
(1998)
Excellent
Good
Marginal
Poor
Unfoliated igneous
and metamorphic
rocks, quartzites and
high silica cement
sandstones, compact
crystalline limestones
Crystalline
dolomites,
crystalline limestone
and moderately well
cemented
sandstones
Argillaceous
limestones, poorly
cemented
sandstones,
dolomite reef rock
with void cavities
Shaly limestones, reef
breccia, shale,
siltstone, slate, schist,
chalk, gypsiferous
carbonates
Low stress, no folds,
no faults
Medium stress,
unloading features
may be present
High stress. Release
fractures parallel to
face may be present
Very high stress.
Faults may be present
in quarry face. Rock
bursts may be
present in floor
II – slightly
weathered (staining
persists through a
greater part of the
rock mass)
III – moderately
weathered (less than
half the rock mass is
decomposed)
Di80 < 1.0 m ****
2
3
Weathering
grade
BS
5930:1999
IA – fresh,
unweathered
IB – faintly
weathered (staining
on major surfaces)
Discontinuity
analysis
(IBSD)
Wang et al
(1990)
Di80 > 2 m ****
Di80 = 1.5–2.0 m
****
Di80 = 1.0–1.5 m
****
Groundwater
condition
Lienhart
(1998)
Dry
Moist
Water flowing from
Seepage from quarry
walls and pooling on
walls
floor
Lienhart
(1998)
Non-blasting
methods: eg
dimension stone
quarry production
methods
Tailored single row
blast, low shock
energy, specific
charge < 0.2 kg/m!,
blast hole diameter
~ 75 mm
Conventional
blasting with ANFO,
specific charge
0.2–0.4 kg/m!,
blast hole diameter
~ 100 mm
Aggregate blasting
with large stone as
by-product, specific
charge > 0.4 kg/m!
Lienhart
(1998)
< 5 per cent of
stones have LT > 3,
95 per cent of stones
are weathering Grade
IA, free of unfilled
cavities and are
extremely high
strength
5–10 per cent of
stones have LT > 3,
95 per cent of
stones are
weathering Grade IB
or better, dense or
free-draining, very
high strength
10–15 per cent of
stones have LT > 3,
95 per cent of stones
are at least
weathering Grade II,
either micro-porous
or with unfilled
cavities, high strength
>15 per cent of
stones have LT > 3,
95 per cent of stones
are at least
weathering Grade III,
argillaceous or
micaceous
Lienhart
(1998)
Armourstone is
stockpiled for three
months for curing
and release of stress
Armourstone is
stockpiled for two
months
Armourstone is
stockpiled for one
month
Freshly extracted
armourstone is
transported directly to
project site for
placement
Armourstone
integrity
(visual)
Lienhart
(1998)
> 95 per cent of
stones are free of
incipient fractures,
flaws or cracks due to
stress relief, rough
handling, overblasting
or other causes after
two months set-aside
in stockpile
90–95 per cent of
stones are fracture
free after two
months set-aside in
stockpile
85–90 per cent of
stones are fracturefree after two
months set-aside in
stockpile
< 85 per cent of
stones are fracturefree after two months
set-aside in stockpile
8
Block integrity
(drop test)
See Section
3.8.5
IM50 < 2%
Bn < 5% *
IM50 = 2–5%
Bn = 5–10% *
IM50 = 5–15%
Bn = 10–35% *
IM50 > 15%
Bn > 35% *
9
Block integrity
(FSST)
Dupray
NOTE: FSST is a design tool to assess the effect of the actual integrity of a source. As such,
(2005) see
classification of CFSST values should be avoided
Section 3.8.5
Production
method
Stone shape
and
weathering
grade
Set-aside
Block integrity
Tourenq et al
(sonic velocity:
(1971)
Ic and Df )
CIRIA C683
Ic > 80
Df < 20
Ic = 80–70
Df < 20
Ic = 70–50
Df < 20
Ic < 50
Df ≥ 20
4
5
6
7
10
135
3 Materials
Table 3.12
Guide to quality and durability of armourstone from a quarry source using field and
laboratory criteria (contd)
Quality and durability guide (not intended for specification purposes)
Laboratory Tests
Criteria
Reference
Excellent
Good
Marginal
Poor
Petrographic evaluation
Trained petrographer
**
**
**
**
Mass density, ρrock (t/m!)
EN 13383-2:2002
> 2.7
2.5–2.7
2.3–2.5
< 2.3
Water absorption (%)
EN 13383-2:2002
< 0.5
0.5–2.0
2.0–6.0
> 6.0
Microporosity/total porosity (%) Lienhart (2003)
<2
2–6
6–20
> 20
Methylene blue adsorption
(g/100g)
Verhoef (1992)
< 0.4
0.4–0.7
0.7–1.0
1.0
Compressive strength (MPa)
EN 1926:1999
> 120
120–80
80–60
< 60
Schmidt impact index (%
rebound)
ISRM (1988)
> 60
50–60
40–50
< 40
Sonic velocity (km/s)
EN 14579:2004
>6
4.5–6
3–4.5
<3
Point load strength (MPa)
ISRM (1985)
>8
4–8
1.5–4
< 1.5
Fracture toughness
(MPa.m1/2)
ISRM (1988)
> 1.7
1.0–1.7
0.6–1.0
< 0.6
Indirect tensile (Brazilian)
strength (MPa)
ASTM D3967-95a
(2004) ISRM (1978)
> 10
5–10
2–5
<2
Los Angeles (% loss)
EN 1097-2:1998
< 15
15–25
25–35
> 35
Micro-Deval (% loss)
EN 1097-1:1996
< 10
10–20
20–30
> 30
MgSO4 soundness (% loss)
EN 1367
<2
2–10
10–30
> 30
Freeze-thaw (% loss)
EN 13383-2:2002
< 0.5
0.5–1
1.0–2
>2
Sonic velocity reduced by
freeze-thaw (% change) ***
Section 3.8.6
<5
5–15
15–30
> 30
Wet-dry (% loss)
ASTM D5313-04
< 0.5
0.5–1
1.0–2
>2
Note
* breakage rate, Bn, may be estimated visually by counting without weighing or derived accurately by
weighing, see Section 3.8.5.1
** no criteria established, see Section 3.3.2
*** provisional criteria needing confirmation from further research
**** Di80 = 80 per cent passing in situ block size.
136
CIRIA C683
3.6 Rock quality, durability and service-life prediction
1
Assessment method for overall rating of quality of a rock source
Table 3.13 shows an example of a completed quality rating assessment worksheet where the
use of integer ratings gives maximum and minimum values of 4 Excellent and 1 Poor. The
objective is to derive an overall rating for the armourstone source. In this manual, Lienhart’s
overall rating applicable to quarried rock is termed “Armourstone Quality Designation” (AQD).
In this example, column (d) provides six precise weighting values (58, 73 etc). These arise
from Lienhart’s (1998) detailed research on armourstone for the Great Lakes (USA).
Designers working with experienced engineering geologists may prefer to assign alternative
weightings for each of the criteria listed separately. For example, keeping to four alternative
weighting values for the criteria importance as follows: essential = more than 90; important
= 80–90; equal = 70–80; minor = 50–70, rounded weighting values could be assigned. In
this way, AQD values pertinent to a specific application could be developed, but care should
be exercised when introducing customised weightings if the AQD value is to be used in
degradation modelling.
Many different implementations of Lienhart’s systems approach are possible depending on
the ease of acquiring data. For example, one based entirely on laboratory results using six
factors is presented in Lienhart (2003), whereas six quarries with overall ratings of between
2.45 and 3.41, using quarry site and laboratory criteria, were described in Lienhart (1998).
The determination of AQD is recommended for comparing the overall intrinsic quality of a
source of armourstone that will be indicative of durability given similar site applications. The
user who understands the basis of the quality criteria, the principles of generating an
importance weighting, and the use of parameter rating systems for rock engineering may use
it and adapt it to good effect. For example, substituting continuously varying ratings instead
of integers within each category would allow greater accuracy and for the range of AQD to
extend below a value of 1 for a poor source and above 4 for an excellent source. These
numerical values of AQD can then be used to compare sources. The application of AQD for
durability prediction modelling is described in Section 3.6.5.
2
3
4
5
6
7
8
9
10
CIRIA C683
137
3 Materials
Table 3.13
Example of a completed quality rating assessment worksheet (after Lienhart, 1998)
a
b
Marginal
Poor
(=4)
(=3)
(=2)
(=1)
√
Lithological classification
√
Field-based indicators
Regional in situ stress
3
{(c) × (d)}/
mean of (d)
3
58
2.12
2
73
1378
2.67
Discontinuity analysis
√
3
95
3.48
2
73
1.78
1
95
1.16
2
80
1.95
3
73
2.67
2
95
2.32
1.5
90
1.65
3
80
2.93
1.67
88
1.79
√
2.67
88
2.87
√
2
88
2.15
3.67
80
3.58
Sum
1229
34.9
n
15
15
Mean
81.9
2.33
√
Groundwater condition
√
Production method
√
Rock block quality
√
√
√
Block integrity test
√
Block integrity visual
Mass density
√
Water absorption
√
Microporosity/total porosity
√
Methylene blue absorption
√
Compressive strength
√
Schmidt impact index
√
√
Fracture toughness
√
Los Angeles
√
Micro-Deval
√
Freeze-thaw loss
6
%
73
Point load strength
5
Average
3
Sonic velocity
4
Weighted rating
√
Petrographic evaluation
2
e
Weathering grade
Set-aside
1
d
Rating value Weighting
Good
Quality rating
Excellent
Criterion
c
MgSO4 soundness
√
Wet-dry loss
√
Notes
138
1
This sheet includes 15 factors (nine field, six laboratory), hence overall rating or armourstone quality
designation (AQD) is mean of column (e) based on all 15 factors. If no data are available for one or
more factors, AQD should be based on the number of included factors. A complete and balanced set
of data is ideal.
2
In addition to engineering geology indicators, each boxed grouping of tests 1 to 6, generates one
average rating value in column (c) from one or more suggested tests. They refer to 1: resistance to
major breakage; 2: mineral fabric physical quality; 3: resistance to minor breakage (compressive); 4:
resistance to minor breakage (tensile, dynamic); 5: resistance to wear (shear and attrition); 6:
resistance to in-service weathering.
3
Test results and field assessments can be used to generate continuously varying ratings from 0.5 to
4.5 rather than integer values. Similarly, AQD results can vary from 0.5 to 4.5.
CIRIA C683
3.6 Rock quality, durability and service-life prediction
3.6.4
1
Principles of degradation modelling
In simple terms, a degradation model is the application of mechanics consisting of:
!
!
!
material properties + loadings (and boundary conditions) = deformation or damage
response
or:
evolution of material properties + history of loadings applied = history of damage
response
or:
2
average material properties + average loading intensity = average rate of degradation.
Degradation models use armourstone properties representative of the armourstone consignment
at the point of leaving the quarry. This may be measured by a specific material property, such as
armourstone integrity or abrasion resistance, or an overall quality index, such as AQD.
The model then predicts the response to future loading intensity of the rock armour with
such properties. These may be short-term loads or long-term in-service loads. The model
output gives the change in the performance parameter (such as M50, or the complete mass
distribution) for any number of handling events or storm/flood events or, alternatively, for
the number of years in service including the design life of the structure.
3
4
The loading intensity or project site aggressiveness can be assessed in terms of:
!
attrition loading intensity: a function of waterborne attrition agents, rocking, sliding and
rolling loads (affected by stone size, wave energy, mobility in design, interlock due to
shape and grading)
!
breakage loading intensity: a function of rocking and rolling loads (affected by stone size,
wave energy, mobility in design, interlock due to shape and grading)
!
physiochemical climatic loading intensity: a function of zone on structure,
meteorological climate, slope angle.
5
6
For static armour designs, mass loss is by both fast and imperceptibly slow or subcritical opening
of cracks, spalling, rounding and by accelerated loss of interlock from wear. A comprehensively
averaged model is currently considered most appropriate in such cases where wear is the
dominant mechanism (see Section 3.6.5).
7
For a dynamic design, attrition and breakage loading intensity will be considerably higher
than climatic loading intensity – a breakage model calibrated using armourstone integrity,
mineral fabric strength and/or resistance to wear properties may be more useful.
Degradation models focusing specifically on wear mechanisms (Tomassicchio et al, 2003) and
breakage mechanisms (Tørum and Krogh, 2000; Dupray et al, 2003) have also been proposed.
Such models consider progressive mass reduction associated with repeated storm events where
storm loading exceeds a threshold energy for start of damage, or where armour movement
velocity is above a threshold value. Such models attempt to deal with mass loss by specific wear
or breakage mechanisms that ignore climatic weathering intensity effects. The fewer the
degradation mechanisms considered in a model, the more rigorous the model calibration
approaches can be, but the less widely applicable is the model to long-term service life prediction.
Probabilistic methods have been proposed to assess accumulated structural damage (eroded
profile area) due to probability of exceedance of the design condition (see Takahashi et al,
2003). Such design approaches also require an estimate of the reduction in M50 of the
armourstone due to rock material degradation. The degradation model tools described here
may be tentatively applied to estimate changes in M50 for such purposes.
CIRIA C683
139
8
9
10
3 Materials
3.6.5
In-service degradation models for general wear of armourstone
Two in-service degradation models for general wear of armourstone are outlined below.
NOTE: Accuracy is not guaranteed, but it is believed to be better than guesswork.
A brief introduction to the principles of the model and possible suggested improvements based
on the work of Lienhart (1998) since its first presentation in 1991 are given here. For practical
implementation of the two models, readers may skip directly to Sections 3.6.5.1 and 3.6.5.2.
These general wear models are designed to introduce a systematic approach to the
forecasting of progressive degradation of armourstone with time. They are, however, based
on the notional assumption that, over the long term, deterioration of armourstone during
service life follows the same progressive form as would the mass loss of stone pieces during a
laboratory wear test. In practice, mass loss locally or even over a large part of a structure may
be episodic and relatively rapid (eg bursts by freeze-thaw, Sonnenbrand, or oxidation of
pyrite etc) following long dormant incubation periods. Deterioration measured by mass loss
may also begin to accelerate after a critical number of years, whereas the laboratory
degradation shows a continuously decelerating degradation trend. Engineering experience
and judgement, such as may be obtained following an examination of degradation and stonerounding processes near the proposed site (eg see Fookes and Thomas, 1986), should always
be taken as a primary indicator of service life. The models are no substitute for the expertise
of a qualified and experienced engineering geologist’s judgement.
With these limitations and provisos, the user is then in a position to incorporate these
predictions into the design. The original 1991 model has been considered in several projects
in Cartagena, Colombia (Assen, 2000); Brindisi, Italy (Tomassicchio et al, 2003); western
Canada (Lienhart et al, 2002; Lienhart, 2003); Iceland (Tørum, 2003); and the Middle East,
to help specify armourstone quality requirements or to improve understanding of
maintenance needs in these coastal structures.
The original 1991 model was based on test results using a wet laboratory mill abrasion test
with constant abrasive environment applied, which were presented as a plot of fractional
mass remaining M/M0 versus laboratory mill time, t, in units of 1000 revolutions. The
gradient generates an index called the abrasion resistance index, ks (-), measured as a
fraction of mass loss per 1000 revolutions.
The Micro-Deval test, termed here the MDE, is another (standard) mill test for wear
resistance by a wet surface grinding action (EN 1097-1:1996). This test value, termed the
Micro-Deval value written MDE , is highly correlated with ks . This test is now the standard
wear test for aggregates and is specified for resistance to wear in the armourstone standard
EN 13383. Test results needed to apply the model are therefore now widely available for rock
used as armourstone. Equation 3.36, which is valid for MDE < 70 (Latham, 1998b), is used to
relate the abrasion resistance index, ks , and the Micro-Deval test value, MDE .
Having established the mass loss versus time curve, laboratory time is then converted to years
on site using the equivalent wear time factor, X (-), which is derived from the product of
nine weighted parameter ratings given in Table 3.14 and which accounts for the site
aggressiveness.
The model can be implemented in two ways, the MDE method (essentially identical to the
1991 model) and the AQD method. Both assume the long-term pattern of mass loss in service
to be progressive and of the same form as a steady abrasion test.
140
CIRIA C683
3.6 Rock quality, durability and service-life prediction
3.6.5.1
1
Micro-Deval (MDE) method
The Micro-Deval method used in the model appears at first to be only relevant to
armourstone that degrades by attrition and surface grinding mechanisms. To extend the
model to other modes of degradation, the experience of researchers was used to score semiquantitatively the strength of interactions between factors perceived to be most important for
all the principal degradation mechanisms including spalling and fracturing. For an
explanation of the coupled terms X4, X6 and X9 where aggressive site factors preferentially
weaken armourstone with certain intrinsic properties, see Latham (1991).
2
Step 1
Use Equation 3.36 to convert Micro-Deval MDE test results to ks values, or use previously
published data for the abrasion resistance index, ks (-), which describes the intrinsic resistance
to mass loss by abrasion.
ks = 4.12⋅10-5 MDE1.485
3
(3.36)
4
Step 2
Plot fractional mass remaining M/M0 versus time, t (in units of 1000 mill revolutions), using
Equation 3.37 and compare result with the abrasion resistance classification chart, Figure 3.30:
M/M0 = 0.05 exp(-30kst) + 0.95 exp(-kst)
(3.37)
where M is the mass remaining after time, t, and M0 is the initial mass (kg).
It has been suggested that this double exponential decay plot may be made more
representative of the mass loss profile of typical armourstone shapes if the pre-factor 30 in
Equation 3.37, governing the initial fast decay, is raised to about 200.
5
6
7
8
9
Figure 3.30
CIRIA C683
Abrasion resistance classification chart based on Micro-Deval test results. MDE values
have been converted using Equations 3.36 and 3.37 to mass loss plots indicative of the
equivalent mill abrasion test results. The quality boundaries for abrasion resistance
have been revised from earlier published positions for compatibility with the European
standard MDE specification categories (courtesy J van Meulen)
141
10
3 Materials
Step 3
To determine the site aggressiveness, calculate X, the equivalent wear time factor using
Equation 3.38:
X = X1 × X2 × X3 × X4 × X5 × X6 × X7 × X8 × X9
(3.38)
where X1, X2 … X9 are a series of site aggressiveness loading parameters obtained from Table
3.14.
Note the slight revisions to the former ratings for the site loading parameters (Latham, 1991)
given here in the light of further research and case history experience. To obtain X6,
substitute the project site weathering intensity factor, MCWI, given in Table 3.15, based on
work of Lienhart (2003). Care is required because of the unusual input parameters, which
yield MCWI units in degrees² × cm / number of days². Also substitute water absorption test
results.
NOTE: The drop test breakage index IM50 , is also used to quantify the block integrity and
how its value is coupled with the wave energy term (X4) and mobility in the design term (X9).
The accuracy of the suggested ratings for these coupling effects is uncertain and could be
low. Breakage rate values, Bn (%) (see Table 3.12), can be used as a guide to IM50 values
required for X4 and X9.
Step 4
Finally, to determine the service life prediction, plot M/M0 curve against time (T in years on
the structure) by multiplying the time scale (t in thousands of revolutions) in Step 2 by X. Or,
equivalently, plot the change in mass, M/M0 (-), against service life time, T (years), using
Equation 3.39. This plot gives the fraction of original mass remaining for any period of
service life or design life.
M/M0 = 0.05 exp[-30(ks/X)T] + 0.95 exp[(-ks/X)T]
3.6.5.2
(3.39)
Armourstone quality designation (AQD) method
The AQD method (suggested here using parameter ratings given in Table 3.13) aims to scale
the rate of loss of performance using an aggressiveness and design application factor that is
totally independent of the global intrinsic property assessed by Micro-Deval method. It
therefore differs from the MDE method.
Step 1
Perform a systematic quarry evaluation with a combination of field and laboratory
assessments and obtain AQD using Tables 3.13 and 3.14. Use Equation 3.40 to convert AQD
to ks, where ks now describes the intrinsic resistance to mass loss of the armourstone quarry
source in question (by consideration of all potential susceptibilities to possible degradation
mechanisms that may be active in any structure over the long-term).
ks = 0.032 AQD-2.0
(3.40)
Equation 3.40 was derived empirically by Lienhart as a simple means to convert AQD values
into plots with fraction of original mass remaining versus time T in years on the structure,
assuming the equivalent wear time factor X = 1. To derive the relationship in Equation 3.40,
AQD values of 1.5, 2.5 and 3.5 were set by curve fitting to correspond with ks values that
separate resistance to progressive degradation at three quality boundaries that are essentially
similar to those given by abrasion resistance classes shown in Figure 3.30. For the AQD
142
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3.6 Rock quality, durability and service-life prediction
1
method, ks has the units of change in fraction of mass remaining per year, assuming the
equivalent wear time factor on the structure X is equal to 1.
Step 2
Use Equation 3.37 to plot reference curves for intrinsic armourstone performance with AQD
= 0.5 to AQD = 4.5. These are given in Figure 3.31 where performance is plotted in terms of
mass fraction remaining against time T on the structure in years, assuming the equivalent
wear time factor X = 1.
2
Step 3
Obtain X using Equation 3.38 and Table 3.14, taking care with X4, X6 and X9 to apply ratings
that specifically apply to the AQD method (rather than the MDE method).
3
Step 4
Plot the change in mass, M/M0 (-), against service lifetime, T (years), using Equation 3.39.
This plot gives the fraction of original mass remaining for any period of service life or design
life.
4
5
6
7
Figure 3.31
Intrinsic armourstone performance classification chart based on AQD, assuming
equivalent wear time factor, X = 1 (courtesy J van Meulen)
8
9
10
CIRIA C683
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3 Materials
Table 3.14
Ratings estimates for parameters in armourstone degradation model, for input to
Equation 3.38 (after Latham, 1991)
Parameter
ks
Rating estimates
Rock fabric strength
Use MDE test value and relationship: ks = 4.12×10-5 MDE1.485
or AQD value and relationship: ks = 0.032 AQD-2.0
Parameter
influence
Xmax/Xmin
Calibration
Reliability*
~500
Excellent
~10
Good
~2.5
Fair
~2
Fair
~10
Fair
~10
Good
~7
Good
~7.5
Poor
Size
Effect given by 0.5(M50)1/3 (M50 in tonnes)
X1
X2
M50
15.0
8.0
1
0.1
0.01
Rating
1.23
1.00
0.50
0.23
0.11
Grading width
(M85/M15)1/3
1.1–1.4
1.5–2.4
2.5–2.4
1.2
1.0
0.5
Rating
Initial shape
X3
Angular/
irregular
Blocky/
equant
Semirounded
Rounded
1.00
1.1
1.50
2.00
Rating
Incident wave or current energy (treat as independent of size of stone)
X4
Rating
Rating
Significant wave height, Hs
(m)
> 8.0
4.0–8.0
< 4.0
If IM50 > 15%
0.3
1.0
2.0
If IM50 = 5.0–15.0%
0.5
1.3
2.3
If IM50 = 2.0–5.0%
0.7
1.6
2.6
If IM50 < 2%
1.0
2.0
3.0
If using AQD method
0.7
1.6
2.6
Intertidal
Supra-tidal
/hot
Supra-tidal
/temperate
Always
submerged
1.0
2.5
8
10
< 100
100–300
300–600
> 600
If WA > 2.0%
0.8
0.6
0.4
0.2
If WA =
0.5–2.0%
1.0
0.8
0.6
0.4
If WA < 0.5%
1.4
1.2
1.0
0.8
If using AQD
method
1.0
0.8
0.6
0.4
Zone of structure
X5
Rating
Meteorological climate weathering intensity
(Use MCWI index of Lienhart – see Table 3.15)
MCWI index
X6
Rating
Rating
Waterborne attrition agents
X7
144
Sediment type
shingle
gravel
sand
silt
none
Rating
0.2
0.5
1.0
1.2
1.50
CIRIA C683
3.6 Rock quality, durability and service-life prediction
Table 3.14
1
Ratings estimates for parameters in armourstone degradation model, for input to
Equation 3.38 (after Latham, 1991) (contd)
Parameter
Parameter
influence
Xmax/Xmin
Rating estimates
Calibration
Reliability*
Concentration of wave attack
X8
Tidal range (m):
< 2.0
2.0–6.0
> 6.0
Rating for slope angle of 1:2.5 or steeper
1.0
1.2
1.5
Rating for slope angle of 1:3.0 or steeper
1.5
1.8
2.0
1–2.4
2.5–3.9
4–6.9
7–20
If IM50 > 15%
1.5
0.6
0.3
0.1
If IM50 = 5.0–15.0%
2.0
1.0
0.5
0.2
If IM50 = 2.0–5.0%
2.0
1.5
1.0
0.5
If IM50 < 2%
2.0
1.8
1.6
1.4
Rating If using AQD method
1.5
1.3
1.1
0.7
2
~2
Fair
Mobility of armourstone in design concept
Hs/(∆Dn50)
Rating
X9
Rating
3
~20
Fair
4
Note
* calibration reliability of the ratings estimates is variable, ranging from a simple reasoning including
qualitative field observations of factor influence (poor) to extensive confirmatory data (excellent).
Table 3.15
Meteorological Climate Weathering Intensity (MCWI)
for rock (Lienhart, 2003)
5
Rock weathering intensity analysis
a
b
c
d
e
f
g
h
Mean (max) – mean (min) temperature range over several years
Mean annual temperature
Mean number of days Max Temp > Freezing
Mean number of days Max Temp ≤ Freezing
Extreme max and min temperature range over several years
Mean number of days with precipitation > 0.25 mm
Annual precipitation, cm
Total normal degree-days, base 18°C *
6
7
MCWI = (a/b) × (d/365) × (e/c) × ((g/f) × h)
Notes
Care is required in calculating MCWI because of the unusual units of the various weather parameters.
Units are degrees² × cm / number of days² as the second term “d/365” is dimensionless (365 = no days in
a year).
* Total normal degree-days, base 18 degrees Celsius = sum of heating degree-days and cooling degreedays, and is measured in degrees. For each day where the outside temperature is such that a building
may require heating, the heating degree-day (in degrees Celsius) = 18 minus the mean outside
temperature for a 24-hour period. For each day with average temperatures above 18 degrees C, the
heating degree-day is recorded as zero. The weather offices total these heating degree-day values for a
specific weather station for a year and provide the “normal” total heating (in degrees C) for the average
year. The cooling degree-day (in degrees C) = the mean outside temperature for a 24 hour period
minus 18 degrees. The “normal” total cooling (in degrees C) is reported like the heating degree-days.
3.6.5.3
Comparison between MDE and AQD methods
An example where both methods are applied to the same dataset is given in Box 3.10. The
remarkable similarity of the result is fortuitous. The AQD method is attractive because it
draws upon many more intrinsic factors of relevance. On the other hand, the MDE method is
probably better calibrated, being based on case history calibrations where abrasion test results
CIRIA C683
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were related to site case histories of degradation with time. It is suggested that in practice,
results of both methods be examined along the lines discussed in Box 3.10 and illustrated in
Figure 3.32. The user is encouraged always to perform a sensitivity analysis considering the
range of parameter values that may be applicable. There is too little case history data to give
guidance on which of the two methods is to be preferred.
Both methods assume the long-term pattern of mass loss in service to be progressive and of
the same form as a steady laboratory abrasion test. After some value that could be anywhere
between 10 per cent and 50 per cent mass loss, an accelerated deterioration may be more
realistic than the assumed continuously slowing rate given by the form of the abrasion test
plot. Increasingly inaccurate predictions are likely for M/M0 below, say, 0.7.
Box 3.10
In-service degradation model for general wear of armourstone: illustrative example of
two methods
This box considers data compiled for intrinsic properties of an armourstone source and site
aggressiveness parameters and compares the results of the degradation model for general wear of
armourstone using two methods. In Table 3.16, the column for the MDE method indicates three test
results. The MDE test result of 20 per cent is used with Equation 3.36 to provide the ks value of 0.00352
(boundary between Marginal and Good in terms of abrasion resistance). The water absorption and
integrity drop test results are also required to more accurately select the coupling of the different
attributes of the source rock with the site aggressiveness parameters X4, X6 and X9, as identified in Table
3.14. All nine parameters are scored according to Table 3.14 and the product X=1.12 is determined using
Equation 3.38. The column for the AQD method takes a more in-depth assessment of the intrinsic
properties of the source material using the assessment scheme in Table 3.12 and 3.13 and in this
example gives an AQD = 2.33, (top of Marginal range), which from Equation 3.40 yields the ks value of
0.00589. The parameters in Table 3.14 this time yield the product X = 1.80, using Equation 3.38. The resulting
service life predictions plotted using Equation 3.39 and shown in Figure 3.32 are similar for both methods.
They suggest that M50, originally of 8 tonnes, will have fallen to 7.2 t (90 per cent) in about 20 years.
Table 3.16
Parameter*
Application of armourstone degradation model for in-service mass loss to cover layers
Site loading information relating to degradation
MDE method eg
MDE = 20%,
WA = 1.2%,
IM50 = 12%
AQD method eg AQD =
2.33 based upon AQD
for quarry source data
given in Table 3.13
0.00352
0.00589
ks
X1
M50 = 8 tonnes
1
1
X2
(M85/M15
)1.3
1.2
1.2
X3
Angular irregular shape
1
1
X4
Significant wave height for design storm Hs = 5.0m
1.3
1.6
X5
Zone of concern is intertidal
1
1
X6
Meteorological climate weathering intensity, MCWI = 700
0.4
0.4
X7
Attrition by silt
1.2
1.2
X8
Steep (1:2) slope with high (7m) tidal range
1.5
1.5
X9
Mobility in design expressed by Hs/(∆Dn50) = 3.0
1
1.3
X
Equivalent wear time factor (Equation 3.38)
1.12
1.80
Note
* Refer to Table 3.14 for selection of appropriate parameters.
146
CIRIA C683
3.6 Rock quality, durability and service-life prediction
Box 3.10
In-service degradation model for general wear of armourstone: illustrative example of
two methods (contd)
1
2
3
4
Figure 3.32
3.6.6
Service life predictions for the general in-service degradation model, using MDE and
AQD methods. The very close agreement shown is somewhat fortuitous and not likely
to be reproduced in practice (courtesy J van Meulen)
5
Modelling degradation due to breakages
Minor and major breakages affect the mass distributions and also, to some extent, the shape
of armourstone. For example, during the survey of a contract using a 6–10 t grading of
armourstone, Laan (1992) observed that degradation related to transport and handling led
to a production of pieces smaller than 3 t whose mass represented 9 per cent of the original
material. In addition, he observed that the M50 decreased from 8.5 t to 7.6 t. In a different
situation, 1–3 t armourstone gradings, from different sources and exposed to different levels
of quality control, were exposed to repeated routine handling events associated with
stockpiling and loading. Dupray et al (2003) observed in each case a mass of small fragments,
say smaller than 100 kg, totalling 5–8 per cent of the initial consignment and that the initial
M50 decreased by 14–21 per cent in certain cases.
6
7
This section discusses the effects of minor and major breakage on mass distribution, their
quantitative contribution to mass distribution changes, and how to assess these changes from
test results.
3.6.6.1
8
Effects of minor breakages and major breakage
Minor and major breakages have different effects on mass distribution of armourstone.
Minor breakage produces small fragments originating from breakage of stone edges or
crushing of armourstone corners (see Figure 3.11). It has a limited effect on the values of
Dn50 or M50 compared with the effect of major breakage. Minor breakage modifies the mass
distribution in the sense that the fragments appear in the form of a tail and a vertical shift of
the lightest part of the grading curve, as shown on Figure 3.33. The amount of fines
generated is expressed by the parameter Fo (%).
Fragments resulting from minor breakage during transport or handling or structural
loadings may be removed by further selection or by wave or current action. In this latter case
CIRIA C683
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3 Materials
the grading curve does not contain the fines, but only displays a general but small shift
characterised by δm (kg) (see Figure 3.33). Note that the steepness of the grading curve does
not change in this case, but the mass of each stone decreases by an average value of δm.
Methods to determine δm and Fo, as well as equations that relate these two parameters, are
discussed in detail in Dupray (2005) and Dupray et al (2007). However, a safe estimate of the
value of Fo (-) or (%) can be determined where the curvature of the post FSST grading
changes (see Figure 3.33) and these parameters can be related by Equation 3.41:
Fo =
δm
M em
(3.41)
where Mem is the effective mean mass (kg).
Major breakage of individual blocks leads to a limited number of large fragments but does
not lead to fines production (see Figure 3.10). If a significant proportion of stones display
major breakage, M50 may be diminished significantly. The M50 decrease and occurrence of
fragments induced by major breakage appears on the grading curve as a shift towards the
smaller sizes and a decrease of its steepness (see Figure 3.33).
Figure 3.33
Effects of minor breakage and
major breakage on the grading
curve (courtesy J van Meulen)
In reality, the degradation induced by both poor integrity (major breakage) and by minor
breakage may take place simultaneously. They can be separated out and Figure 3.34 shows
schematically the combined effects of minor and major breakage. The grading curve to be
expected if only minor breakage alone had taken place is also plotted. When considering a
value of passing x, IMx,m represents the relative mass decrease due to minor breakage whereas
IMx,M represents the part of the relative mass decrease due to major breakage. Similarly, the
bounded areas between initial and breakage curves δAm and δAM represent the effect of
minor breakage and major breakage respectively.
Figure 3.34 clearly shows that the common indicators of resistance to breakage such as IMx
(see Equation 3.4 in Section 3.3.4) are biased by the effect of minor breakage since IMx =
IMx,M + IMx,m , which in fact stands for the effect of major and minor breakage. Hence, using
IMx,m and IMx,M or δAm and δAM is a means of separately assessing the effect of both types of
breakage. Different methods to distinguish the effect of major and minor breakage from the
global modifications of the mass distribution are discussed in Dupray (2005). A point-by-point
method to determine the modification induced by minor breakage alone is given in Box 3.11.
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3.6 Rock quality, durability and service-life prediction
1
2
3
Figure 3.34
Separation of the effect of minor and major breakage from global
modifications of the grading curve (* the effect of minor breakage)
Box 3.11
Point-by-point method to determine the effect of minor breakage
4
The amount of fines generated by minor breakage, Fo, is determined from the mass distribution affected
by combined minor and major breakage at the point of curvature change. δm can then be determined
from Equation 3.41 where Mem is determined on the population before degradation. The mass of each
individual stone, assuming only minor breakage, can be determined from each initial mass, mi, by
retrieving the average mass broken off by minor breakage, δm. Thus, Equation 3.42 gives the mass of
each particle after minor breakage, mf:
mf = mi – δm
5
(3.42)
The mass distribution of the armourstone population after minor breakage can be determined from the
new population of mass, mf, as plotted in Figure 3.35.
NOTE: The total reference mass for the final population should include the mass of all fragments
generated by minor breakage as well as the final mass of stones suffering minor breakages.
6
7
8
9
Figure 3.35
CIRIA C683
Separation of the effect of minor and major breakage from global modifications
of the grading curve using a point-by-point approach
10
149
3 Materials
3.6.6.2
Quantitative effect of breakages on armourstone grading using statistical model
Effects of minor and major breakage on gradings can be modelled using appropriate Monte
Carlo simulation. The model whose results are presented here (see Figure 3.36) is based on a
statistical fragmentation model as initially developed by Grady and Kipp (1985) modified into
a one-dimensional Monte Carlo model to simulate the effect of breakage processes on a
standard 300–1000 kg grading (Dupray, 2005). The model allows minor and major breakage
to be handled separately or in combination. Such a graph allows the designer to estimate the
expected value of IM50, given reasoned assumptions for the expected number of pieces that
would display major breakage, ie a good assumption of Bn, and the amount of minor
breakage characterised by Fo or δm (see Equation 3.41).
Using Figure 3.36 (left), a designer can determine the expected effect of major breakage on
the shift in the value of the original M50 in the quarry and use this information for setting
tolerances in term of IM50 for a given design. This will require the designer to select
reasonable values for Fo and Bn as input to Figure 3.36:
!
Fo in service or during construction may be determined using the double exponential
expression developed for attrition in Section 3.6.5 and applying Equation 3.39, which
will provide M/M0. Fo can then be determined knowing Fo = 1–M/M0
!
Bn can be determined from feedback from actual performance eg using a survey of
breakage during contracts or on existing structures. Alternatively, a mechanically based
field test method presented in Box 3.12 can be used.
Figure 3.36
Top: Values of IM50, as a
function of the breakage rate,
Bn, and the amount of minor
breakage estimated with Fo .
Bottom: Values of δAM/A*, as a
function of the breakage rate,
Bn, and the amount of minor
breakage estimated with Fo
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CIRIA C683
3.6 Rock quality, durability and service-life prediction
Box 3.12
1
Determination of the effect of minor breakage and major breakage
An estimate of the relative number of pieces that may display major breakage during construction or in
service, the Bn value, may be based on the experience of the designer with the armourstone considered
or feedback from performance of the same material in similar conditions. Alternatively, the results for the
field-crushing test introduced by Tørum and Krogh (2000) may be used. This test provides the designer
with characteristics of the material with regard to its breakage resistance expressed by parameters k, α
and β. The energy required to induce major breakage in half of an armourstone population P50 (J) can be
determined with Equation 3.43:
2
α
 M 50 
P50 = k 
(
 ρrock 
(3.43)
where the value of k depends on integrity. In other words, the k-value expresses the energy amount (in
Joules) required to crush 50 per cent of the blocks of 1 m³ volume.
The fraction by number of blocks that display breakage, Bn (-), when exposed to a given level of energy P
can be determined using Equation 3.44:
 P 
Bn = β ln 
( + 0.5
 P50 
(3.44)
Governing parameters have been determined on good igneous rock: the value of α (-) is close to 0.65; the
value of β (-) is within the range of 0.44–0.5; the value of k (-) is within the range of 81 000–99 000. The
reader should refer to the original work for further detail.
The determination of the appropriate energy to which armourstone is exposed, P (J), is a difficult task that
is still the subject of research. Extensive studies would be required to provide detailed guidance for the
selection of the most appropriate value of P. This subject was partly investigated for berm breakwaters by
Tørum and Krogh (2000) and for rubble mound breakwaters by Trmal (2004). To assist the designer,
Equation 3.45 is provided as a means to determine a first estimate of P (J):
 VA 
P = 0.5M 50 Ki gH 
(
 gH (


3
4
5
(3.45)
where H is the wave height (m), VA is the characteristic velocity of armourstone piece during impacts (m/s)
and Ki is an impact parameter whose value may be between 0.6 and 0.9.
NOTE: The total reference mass for the final population should include the mass of all fragments generated
by minor breakage as well as the final mass of stones suffering minor breakages.
3.6.6.3
Prediction of the effect of major breakages using a dedicated degradation model
specific for breakage
This section discusses the use of Full-Scale Splitting Test (FSST) results in combination with
an associated degradation model presented in Equation 3.46. Recent research proposed a
new degradation model that is specific to major breakage. The parameter δAM (kg), which is
the change in area under the grading curve due to major breakage (see Section 3.6.6.1), was
identified as an appropriate indicator for major breakage that is not biased by the effect of
minor breakage and that displays less variability than the usual breakage indicator, IM50
(Dupray, 2005 and Dupray et al, 2007). The key relationship of the degradation model is
given in Equation 3.46:
 E 
A* ⋅  D (
 MD 
δ AM =
CFSST 3
3
ED
=
total degradation energy applied to the material (J)
MD
=
total mass of material exposed to degradation (kg)
CFSST
=
characteristic integrity (J/kg) determined using FSST (see Section 3.8.5.2).
A*
=
characteristic reference area (kg).
7
8
(3.46)
9
where:
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151
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On the use of the degradation model
Starting with an armourstone consignment of known grading, defined by standard NLL and
NUL limits, with a total mass of MD, the designer can then use Equation 3.46 to assess the
projected loss of mass by major breakage for an applied energy, using the term δAM.
The determination of δAM requires values of:
!
A*, which is a characteristic reference area (kg) as required for dimensional consistency
(see Step 1 below)
!
ED, which is the equivalent energy applied to the material that induces major breakage
(J) and consequently the increase of δAM (kg). It is of interest to the designer to
determine ED for both the construction situation and the situation in service. Recent
research provides a way to determine ED for routine handling at the quarry or on site
(see Step 2 below)
!
CFSST, which represents integrity. See Box 3.21 of Section 3.8.5 for a simplified method to
determine its value from full-scale splitting tests in the field. For information, high integrity
tends to correspond to values of CFSST greater than 35 and poor integrity to values smaller
than 27. However, integrity of the armourstone may increase during routine handling
where certain weaknesses are exposed and some breakages occur. It may therefore be
more appropriate to use an updated value of integrity to take into account breakage that
has already occurred, represented by using CH instead of CFSST (see Step 3).
Using Figure 3.36, δAM can be easily converted into the traditional integrity indicator Bn or
IM50. For example, assuming the loss from attrition, Fo , is estimated as 5 per cent, whether
from experience or by using the degradation model due to attrition, and that δAM /A* is
found to be 0.3. This will correspond to a value of Bn of 0.33, ie one-third of the blocks
display major breakage as determined from Figure 3.36 (bottom). Using Figure 3.36 (top),
the relative decrease due to major breakage of the M50, ie IM50,M , is 27 per cent.
Step 1: Determination of the characteristic area, A* (kg)
This term A* is required for dimensional consistency of Equation 3.46. It could be
determined as exact integration of the area below the grading curve. However, by assuming
that the grading is linear (and not a Rosin-Rammler form, see Equation 3.12) A* can be
simply determined using the grading limit masses. Thus, A* = (NLL + NUL)/2.
Step 2: Determination of the equivalent degradation energy associated with routine
handling events
Three field investigations including three different rock types were carried out. They
consisted of measuring CFSST and mass distribution changes induced by routine handling
events. This enabled Equation 3.46 to be calibrated against effective degradation measured in
the field. The sources were tested using standard armourstone gradings of 1000–3000 kg.
The degradation energy, ED (J), was determined from the actual potential energy of the
armourstone consignment (converted into kinetic energy). Thus, the energy loss of the
material during handling events is simply calculated from the height to which the
armourstone material is lifted by the handling machine (see Equation 3.47). In the study, the
wheel loader had an average lifting capacity of 3 m.
ED M D = 1.98 ⋅ gH h
(3.47)
where Hh is the height to which the armourstone material is lifted by the handling machine
(m), and MD is the total mass of material exposed to degradation (kg).
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1
Step 3: Increased integrity during routine handling events
During repeated handling events, major breakage of weak stones has two effects. First, it
affects the mass distribution as discussed in Figure 3.33. Second, it breaks the weakest blocks
that are then no longer available for further major breakage. It therefore tends to increase
the integrity (Figure 3.37 right). In the service environment and over time, it is also possible
that planes of weakness can be opened up that will not be fully revealed by handling events
in the quarry. This risk should normally be covered by accelerated weathering tests
performed on appropriate samples. If there are no concerns about a risk of breakage of
armourstone, for example resulting from freeze and thaw processes, then the parameter CH,
as defined in Equations 3.49 and 3.50, should be a good assumption of the effective integrity
of the consignment. If this is not the case, then the increase in integrity given by Equations
3.49 and 3.50 should not be applied.
The parameter nH may be used as an indicator of the number of handling events (see
Equation 3.49). However, an objective measure of the relative amount of degradation
induced by major breakage with reference to the amount of major breakage displayed
during the FSST is the parameter XH, defined by Equation 3.48. This applies to any type of
loading events or loading history for which the mass distribution is known or given:
*

 δ AM   AFSST
XH = 
(  * ((
 δ AFSST   AH 
2
3
4
(3.48)
where:
A*H
=
value of A* before the first handling events. It can be approximated by (m10
+ m70)/2 where m10 and m70 are the characteristic masses of the consignment
that is handled
δAM
=
total change in area under the grading curve induced by major breakage
from the beginning of the degradation process (kg)
A*FSST
=
value of A* before the full-scale splitting test, equal to (NLL + NUL)/2 (kg)
δAFSST =
total change in area under the grading curve induced by major breakage
during the full-scale splitting test (kg).
5
6
The integrity increase with handling events of this kind can be determined with a simplified
approach (see Equation 3.49):
CH/CFSST = 1 + 11.19(nH/20)1.93
(3.49)
7
where: nH is the number of handling events. Alternatively, XH can be used to assess the
increase of integrity (see Equation 3.50):
CH/CFSST = 1 + 7.28XH4.02
(3.50)
8
9
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3 Materials
Figure 3.37
3.6.7
Variation of integrity as determined with the FSST with repeated
standardised rough handling events; Top: as a function of XH.
Bottom: as a function of the number of handling events (SHE).
A fourfold increase in integrity is seen after between four and
six handling events
Summary of recommendations for degradation modelling
If available, service record observations are the best guide for calibration of degradation
models and validation of predictions. Damage prediction modelling is more complex where
the armour is mobile during storms. Aggregated distances travelled by stones, possibly
producing severe degradation by corner breakage and rounding, as well as by splitting, need
to be considered. Both integrity and abrasion resistance are therefore extremely important.
For dynamic structures such as berm breakwaters and other novel low-cost designs with
expected movements, degradation models (Tørum and Krogh, 2000; Tomassichio et al, 2003)
have advanced sufficiently to warrant application of calibrated stone integrity testing (fullscale splitting test results) and mineral fabric strength tests (eg point load strength index and
MDE) to assess mass losses during stone splitting and rolling. For berm breakwater analysis of
mass losses, breakages and rounding with reshaping storm events, key research papers by
Tørum and Krogh (2000) and Tomassichio et al (2003) should be considered.
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For static designs, especially where marginal and poor armourstone is to be considered, the
general degradation models that attempt a comprehensive average degradation assessment
over the service life are recommended.
NOTE: Armourstone degradation models should only be applied with considerable caution
and backed up by sensitivity analysis that will make clear the degree of uncertainty in the
service life predictions.
3.7
1
2
PREPARING THE ARMOURSTONE SPECIFICATION
This section provides advice on preparing a specification for quarried rock. A specification
template is provided in Table 3.17. Note that this does not include the specification for the
workmanship of placing the armourstone on the construction site that is given in Appendix
A1 and supported by the text in Chapter 9. Quarried rock specifications include
requirements for materials to fall within given values of parameters when assessed using
standard test methods. This section provides the general framework for setting the
requirement levels as defined by European standard EN 13383 (see Section 3.1.4). Section
3.8 provides more detailed information on the test methods.
3
4
The manner in which EN 13383 describes armourstone differs from previous practice in some
parts of Europe and the rest of the world, and in some cases it uses different test methods to
evaluate their properties, but there is no change to the general quality of the armourstone in use.
The effect of the standard is that the specification process for materials has become
considerably simplified. However, those specifying need to understand how to use this
standard and incorporate it into their contract specifications.
5
The key to using EN 13383 is to understand that when selecting an armourstone grading or
property the designer/purchaser must select the appropriate category. It is then the
producer’s responsibility to produce material complying with the requirements for that
category. In all cases, as well as the specific categories laid down in EN 13383, other
categories are possible.
6
It is possible for a specifier to select a “No requirement” (NR) category. Examples of NR
categories are given in Table 3.17.
If properties are outside specified limits, the producer may declare a value, which may be
accepted by a purchaser if these declared values are acceptable for the end use. For example, if
the percentage of armourstone pieces with LT > 3 for a coarse grading is 25 per cent (cf normal
maximum of 20 per cent), the producer would state “LT25”. A client could buy this as an LTNR
core material. Similarly, the producer might prepare for sale a non-standard heavy grading with,
say, upper and lower nominal limits of 2000 kg and 4000 kg respectively. A grading category
could then be declared as “HMA2000/4000” (see also Section 3.4.3.9 on non-standard gradings).
7
8
Where a producer decides not to test for a particular property and still offer it for sale, then he
may declare a category of “No performance determined”. If this matches a “No requirement”
on the part of the purchaser/specifier then the material can be used.
9
Grading categories follow requirements as already described in Section 3.4.3.
10
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3.7.1
EU context
Within the European Union, a large proportion of armourstone projects will be constructed
for public bodies. The Public Procurement Directive requires public bodies to use
harmonised European standards in full and not to specify in other ways or to use other
standards. National regulations in member countries provide the legal basis for enforcement
of harmonised standards.
EN 13383-1:2002, Annex ZA addresses the provisions of the EU Construction Products
Directive (89/106/EEC). Both EN 13383-1:2002 and its Annex ZA have been produced under
a mandate given by the European Commission and the European Free Trade Association to
CEN. Annex ZA is described as “informative”, but its requirements become mandatory to
ensure compliance with the mandate and/or where CE marking is applicable to armourstone.
CE marking is a “passport” enabling a product to be legally placed on the market in any
European member state. This does not necessarily mean that the product will be suitable for
all end uses in all member states, but merely shows that the product addresses the regulatory
requirements set out in a particular European Directive, in this case the EU Construction
Products Directive (89/106/EEC).
Clauses identified in EN 13383-1:2002, Table ZA.1 indicate the characteristics that are subject
to regulatory requirements for the specified application in one or more European member
states. There is no obligation to determine or declare a value for a characteristic in a member
state where there is no regulatory requirement for that characteristic unless it is subject to a
“threshold” value.
Conformity to these identified requirements confers a prescription of fitness of the
armourstone for the intended uses indicated in the scope of EN 13383-1:2002. However, to
meet the provisions of the EU Construction Products Directive (89/106/EEC), armourstone is
also required to conform to any transposed European legislation and national laws relating to
dangerous substances referred to in EN 13383-1:2002.
Within the notes to Table ZA.1 in EN 13383-1:2002, reference is made to the type of
compliance requirement, for example: fail threshold value, categories, declared value. EN
13383-1:2002 Annex ZA also details the allowed levels for attestation of conformity as “2+”
or “4”. If level 4 is selected the producer alone is responsible for factory production control
and initial type testing. If level 2+ is selected then independent certification and surveillance
of the producer’s factory production control procedures are required.
CE marking is a legal requirement for armourstone supplied to or within most EU member
states. The main exception is the UK, but industry in the UK has adopted a voluntary system
of CE marking that makes it as effective as in other member states. In all cases, CE marks
must be translated into the language of the member state supplied. Figure 3.38 illustrates the
information required for CE marking.
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3.7 Preparing the armourstone specification
1
CE conformity marking, consisting of the
“CE”-symbol given in directive 93/68/EEC
01234
Identification number of the inspection body
Any Co Ltd, PO Box 21, B-1050
Name or identifying mark and registered
address of the producer
2
02
Last two digits of the year in which the
marking was affixed
0123-CPD-0456
Number of the EC certificate
EN 13383-1
Aggregates obtained by processing natural, manufactured or recycled materials and
mixtures of these aggregates for use as armourstone
Particle shape
Category
Particle size
Categories
Particle density
Declared value
(e.g. LTA)
3
No. of European standard
(e.g. CP63/180 , LMA5/40
Description of product
and
(Mg/m³)
Information on regulated characteristics
HMB300/1000)
}
Resistance to fragmentation/crushing
Category
(e.g. CS60)
Resistance to attrition
Category
(e.g. MDE10)
Release of dangerous substances
e.g. Substance X 0.2 µm³
Resistance to breakage
4
Durability against weathering
Dicalcium silicate disintegration of
air-cooled blastfurnace slag
Iron disintegration of air-cooled
blastfurnace slag
Disintegration of steel slag
Category
(Visual - Pass/
fail)
(Visual - Pass/
fail)
(e.g. DSA)
Durability against freeze/thaw
Category
(e.g. FTA)
Durability against salt crystallisation
Category
(e.g. MS25)
Durability against weathering
Category
(e.g. SBA)
Figure 3.38
Declared value
Declared value
5
6
Requirements for CE marking and labelling (from EN 13383-1:2002, Annex ZA)
If producers voluntarily or otherwise decide to CE mark their armourstone, the producers
need to comply strictly with the indicated requirements. Where the CE mark identifies
particular characteristics, the supplier is required to indicate the category or declared value
appropriate to the armourstone. The user is responsible for confirming that the declaration
of properties on the CE mark complies with their particular requirements.
7
It should also be noted that where armourstone is placed on the market in a European
member state that has no regulatory requirement for a particular characteristic, the supplier
is not required to determine the performance for this characteristic. In this case “No
performance determined” should be stated in the CE marking information.
Typically all that will be required in a contract is a tabular specification of the format shown
in Table 3.17. If steel slag or other slag types or basalt are specified then additional
requirements will be necessary as set out in Table 3.18.
8
9
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Table 3.17
Property
Selection of categories for armourstone specifications
Category to EN 13383-1:2002
Grading
Selection of gradings should take account of the required grading width and average mass
requirements with reference to guidance in the rest of this manual (see especially Chapters 5 to 8)
Volume-filling materials (see
Section 3.1.2.1), such as
quarry-run or tout-venant used
in the core of breakwaters.
(See also Section 3.4.4 for
further explanation of ways of
controlling such materials)
Where materials are not providing any significant protection or filtration function, the grading
system in EN 13383-1:2002 is not appropriate. This includes the quarry run or tout-venant
materials typically used in the core materials to a breakwater. Any attempt to impose the EN
13383 system on them will lead to waste of resource and substantially increased cost.
Opinions vary as to whether any control at all should be imposed on such materials, but the only control
that has any engineering justification is limiting the fines content at the bottom end of the grading (see
Section 3.4.4), although even this will have a cost and resource penalty associated with it.
Coarse grading – CP
(see Section 3.4.3 for
explanations of gradings)
Insert appropriate categories from EN 13383-1:2002, Table 1, but note that such materials
should not be specified for applications only requiring a volume fill.
Light grading – LM
(see Section 3.4.3 for
explanations of gradings)
As far as possible, standard gradings (see Sections 3.4.3.4, 3.4.3.6) should be used from those
listed in EN 13383-1. Unlike heavy gradings, which can be modified quite easily (as the pieces of
armourstone are generally handled individually), light gradings are produced using standardised
equipment (screens and crushers) and procedures that are difficult to modify without incurring
significant cost. When selecting gradings, every opportunity should be taken to optimise quarry
yields, especially for quarries dedicated to a particular large project (see Section 3.9.5 on quarry
operations and the case history in Box 3.1).
When selecting the appropriate category, it is suggested that EN 13383-1:2002, Table 3 category
B materials be used for all applications except cover layers (see below).
Cover layer applications
EN 13383-1:2002, Table 2 Category A gradings should normally be used for cover layers as these
gradings have a control on the average mass of the grading.
When assessing the size of grading required for hydraulic stability, designers should be aware of
the fact that the value of M50 (and the associated value of Dn50) is greater than the corresponding
average mass Mem. Conversion factors are given in Sections 3.4.3.7 and 3.4.3.8.
The width of the grading LMA15/300 is believed to be unsuitable for cover layer applications.
Heavy grading – HM
(see Section 3.4.3 for
explanations of gradings)
Heavy gradings can be standard gradings or non-standard gradings (see Section 3.4.3.9.) When
selecting the appropriate category, it suggested that EN 13383-1:2002, Table 5 Category B
gradings be used for all applications except cover layers.
Cover layer applications
EN 13383-1:2002, Table 4 Category A gradings should normally be used for cover layers, as these
gradings have a control on the average mass of the grading.
When assessing the size of grading required for hydraulic stability, designers should allow for the
fact that the value of M50 (and the associated value of Dn50) is greater than the corresponding
average mass Mem. Conversion factors are given in Sections 3.4.3.7 and 3.4.3.8.
Shape (as assessed by length
to thickness ratio, LT; see
Section 3.4.1.1)
For cover layers it is suggested that the category LTA should normally be specified. However, where
the armourstone is being used beneath more than two stone thicknesses of other armourstone,
then LTNR will normally be acceptable.
Proportion of crushed or
broken surfaces, RO (see
Section 3.4.1.5)
Unless naturally rounded boulders of riverine or glacial origin are being used, RONR will normally
be acceptable. Where natural boulders may be used in structures in which rounded stones could
lead to instability then category RO5 should be selected.
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Table 3.17
Properties
1
Selection of categories for armourstone specifications (contd)
Category to EN 13383-1:2002
Should be selected in accordance with EN 13383-1:2002, Table 8, which allows the
designer/specifier to select the most appropriate value for the oven dry particle density, x = ρrock
EN 13383-1:2002, Table 8, implies that such densities should not be less than 2.3. However, in
some applications it may be reasonable to use lower densities. This particularly applies to
materials used for volume-filling, which are not explicitly covered by EN 13383-1:2002. It may
also apply to underlayer and cover layer applications in situations where the prevailing climate at
its proposed place of use is sufficiently mild (Fookes and Thomas, 1986).
Designers should note that in calculations for hydraulic stability of armourstone used in cover
layers (see Section 5.2) the apparent density ρapp should be used. Netherlands Ministry of
Particle density, x = ρrock (see Transport, Public Works and Water Management (Laan, 1999) indicates that ρapp can be
Section 3.3.3.2 for definitions) calculated by multiplying the (oven-dry) particle density specified in accordance with EN 133832:2002, Clause 8 by factors:
!
[1 + 0.005WA] where the armourstone is to be used in a structure of which all or part is
permanently submerged. This factor is based on half the pore volume within individual pieces
of armourstone being filled with water
!
[1 + 0.0025WA] where the armourstone is to be used in a structure of which all or part is
temporarily submerged. This factor is based on one quarter of the pore volume within individual
pieces of armourstone being filled with water.
In the above formulae, WA is the percentage water absorption of the armourstone, determined in
accordance with EN 13383-2:2002, Clause 8 (see also Section 3.3.3.3).
Resistance to breakage (as
assessed by compressive
strength, CS, in MPa)
For cover layer applications, it is recommended that category CS80 is selected in order to avoid
excessive breakage of the armourstone through the mineral fabric.
For cover layers where the loadings are limited and for filtering applications, category CS60 will be
sufficient, however.
For volume-filling applications where grading is not critical and the standard gradings in EN
13383-1:2002 do not apply (see “Volume-filling materials” above), it will be more appropriate not
to set any requirements for resistance to breakage.
Armourstone integrity
Although EN 13383 states that armourstone integrity is of particular importance and states that
armourstone should be free from significant discontinuities that could lead to breakage during
loading unloading or placing, the property is very difficult to control. Nevertheless, to gain an
estimate of the degree of breakage likely and whether it can be accommodated within the design,
checks for armourstone integrity are strongly advised as part of initial type testing.
For guidance see Section 3.8.5 and also EN 13383-1:2002, Annex B.
Resistance to wear (as
assessed by abrasion losses
determined as Micro-Deval
coefficient, MDE, in the MicroDeval wear test
For cover layers and dynamic structures such as beaches, specify:
!
MDE10 for very highly abrasive environment (eg frequently stormy seas with shingle-structure
interaction, fluvial torrents, dynamic armour layers including berm breakwaters)
!
MDE20 for highly abrasive environment (eg occasionally stormy seas with shingle or sandy
foreshore)
!
MDE30 for moderately abrasive environment (eg occasional wave or current action with
suspended sediment load).
For most other applications specify MDENR. Such applications include:
!
cover layers where insignificant sediment loads are present in the water
!
filtering and volume filling applications, because there is insignificant wear in such
applications.
Water absorption
It is recommended that water absorption, WA, is determined in accordance with EN 133832:2002, Clause 8. No requirement level needs to be set, but the results are needed for two
reasons:
!
for apparent density calculations for hydraulic stability (see density above)
!
as a screening test for durability against salt crystallisation and/or freeze-thaw attack (see
below).
Resistance to freezing and
thawing, FT (as assessed by
loss of mass in testing)
Where it is relevant to the climate of end use for the armourstone, testing for resistance to
freezing and thawing should be undertaken and category FTA should be selected. However, EN
13383-1:2002, Clause 7.3 explains that where WA is determined not to be greater than 0.5 per
cent (category WA0.5), no further testing is required.
Where armourstone is permanently submerged, freezing and thawing processes are likely to be
limited in effect even in cool climates, and FTNR may generally be selected for such stone. (See EN
13383-1:2002 Annex C for more information.)
Resistance to salt
crystallisation (as assessed by
the percentage loss of mass,
MS, obtained in the
Magnesium Sulphate
soundness test)
Where it is appropriate to test for resistance to salt crystallisation, category MS25 should be
selected. However, EN 13383-1:2002 Clause 7.3 explains that where WA is determined not to be
greater than 0.5 per cent (category WA0.5), no further testing is required.
Where armourstone is permanently submerged, salt crystallisation processes are likely to be
limited in effect and MSNR may be selected for such stone. (See EN 13383-1:2002 Annex C for
more information.)
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2
3
4
5
6
7
8
9
10
3 Materials
Table 3.18
Additional requirements for particular armourstone sources
Source
Property
Recommended EN 13383-1 category
Di-calcium silicate disintegration
Free, when tested in accordance with EN 17441:1998, 19.1
Iron disintegration
Free, when tested in accordance with EN 17441:1998, 19.2
Source: steel slag
Disintegration
DSA (see EN 13383 for details)
Source: basalts
Signs of sonnenbrand
SBA (see EN 13383 for details)
Source: air-cooled
blast furnace slag
3.7.2
Non-EU context
It is recommended that the approaches of EN 13383 continue to be adopted for applications
outside the EU. However, the following important differences in approach need to be noted.
There will be a need for external audit and confirmatory testing, since CE marking or
producer declaration will not apply. It may not always be possible to achieve the level of
quality control that can be enforced in Europe. In this situation there may be much greater
significance for drop testing for integrity (see Section 3.8.5). The drop test will give a useful
indication of the extent of the problem. The full-scale splitting test will enable designers to
allow for the change in grading between initial production and final placement in the
structure.
There is more freedom to use armourstone of lower density than 2.3, eg high-porosity lowdensity rock, which can in fact perform perfectly satisfactorily in certain applications.
In developing countries, it is much more likely than in Europe that dedicated quarries, such
as those for breakwaters, will be opened up. In this case ther will be a far greater need for
non-standard gradings to ensure that the design matches the quarry yield (see Section 3.9.5).
In many parts of the world, local geological maps reveal that the available construction
materials are of types and geological ages (eg Tertiary) that are not normally associated with
armourstone of high quality. It is therefore important to specify armourstone quality using
clauses and categories that recognise the quality that is likely to be economically available. It
may be very expensive to exclude materials of poorer quality from a source of mixed quality.
Supply-based design approaches, using armourstone quality evaluation, durability and
degradation modelling tools (see Section 3.6), together with cost-benefit analysis that includes
greater maintenance options, will be needed. These combined approaches can provide a
rational framework for evaluating the consequences of specifying relatively marginal or poor
quality materials in circumstances where there is no viable alternative.
3.8
TESTING AND MEASURING
This section includes instruction and comment on the tests required by EN 13383. Annex G
of this standard requires that some tests should be performed with a frequency that aims at
delivering CE marking of the production. However, for specific needs within a contract or
specific project, other test schedules may be required and the frequency of testing modified
to fit with the need to assess variability of the deliveries. This section also provides details on
complementary or alternative tests, many of which are identified in Table 3.12. The use of
alternative tests to those in EN 13383 has greater significance for initial source evaluation
and specifications falling outside the scope of CE and other trade-marking schemes for
construction materials (see Section 3.7).
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3.8 Testing and measuring
As discussed in Section 3.1.4, the choice of test methods for armourstone in Europe is quite
tightly prescribed compared with the standard practice for evaluation of armourstone to be
used for erosion control in the USA. In the non-EU context, ASTM test methods referred to
in ASTM D4992-94 (2001) that could be used for evaluation and specification purposes
where there is not a corresponding EN or ISRM (International Society for Rock Mechanics)
standard, are indicated in this section or in Table 3.12. Other US publications that refer to
test details are EM 1110-2-2302 (1990) Construction with large stone and ASTM D6711-01
on stones for filling gabions.
The client should consider the ability of the laboratory to carry out the testing in accordance
with the general requirement. COFRAC, NAMAS, UKAS or other types of laboratory
accreditation schemes will confirm the ability of the laboratory to conduct the testing with the
required confidence and authority. A visit to the testing laboratory may be useful to ensure
that the quality of the equipment and the qualifications of the operators are satisfactory.
3.8.1
1
2
3
Sampling
The aim of sampling in an existing quarry is to obtain material representative of the average
properties available to the purchaser. The properties may be properties of the mineral fabric
of the armourstone (aggregate and hand-sized pieces) or properties of the armourstone itself.
The purpose of sampling for initial evaluation of a greenfield site is mostly directed towards
geological site investigation. Such sampling will differ from that described in this section,
which is concerned with control and verification of the production quality.
Sampling methods are described in EN 13383-2:2002 Clause 4. They include sampling from
stockpiles, bucket conveyors, bucket loaders or grabs, stationary conveyor belts, silos, floating
equipment, wheeled transport and at belt and chute discharge points. Care in sampling,
labelling and transport of the samples is essential if the analysis is to give reliable results. A
variety of equipment is used to avoid sampling bias. The possibility of human bias, most
easily introduced by visual selection, can be avoided by preparing a sampling plan.
This plan should introduce randomisation (see EN 13383-2:2002) for the sampling
increments (ie sub-samples) to cover all parts of the batch that the samples are to represent.
For moving material, it is recommended to sample at regular increments during loading or
unloading. Sampling variation caused by the heterogeneity of the source of samples should
be reduced to an acceptable level by taking an adequate number of sampling increments. In
certain cases, a source supplying armourstone may consist of two or more distinct rock types.
In such cases, the purchaser will require results from sample suites for each rock type. This
enables the purchaser to evaluate the merits of all rock types and the scope offered by
accepting unplanned or planned blends from the one source.
The sampler should be informed of the aim of the sampling. Once a representative sample of
armourstone is obtained, it must be reduced to the relevant test specimen sizes and numbers.
The reduction should be carried out so that no artificial bias is introduced into the test pieces
or test specimens (see EN 13383-2:2002 guidance on sample reduction). Examples of good
sampling practice are given in Box 3.13 and sampling work flow for selecting test portions
for the various tests is given in Figure 3.39 and Table 3.19.
4
5
6
7
8
9
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3 Materials
Shape and broken surface:
Select and test 200 pieces
Coarse grading: 160–500 kg of stone
Light grading: 200 pieces
Heavy grading: 25–140 pieces
Mass distribution:
If rock:
Reuse of
sample
1
2
3
4
5
6
7
Integrity testing: 50 pieces (more stones may be required than for mass distribution)
Mass density and water absorption: 10 specimens of mass from 150–450 g
Compressive strength: 10 drilled cores of 50 mm (or 70 mm*)
Freeze and thaw: 10 specimens of 0.45–10 kg (coarse grading) or 10–20 kg (light or heavy grading)
MDE: 2 kg of 10/14 mm aggregate crushed from six pieces **
Salt crystallisation: 2 × 500g of 14 mm aggregate crushed from six pieces
Methylene blue: 200 of 0–2 mm crushed from six pieces ***
If basalt:
Stability: 20 pieces larger than 1 litre
If air-cooled blast furnace (ACB) slags:
1
2
Fe disintegration: 30 pieces of slag of size 40–150 mm
C2S disintegration: 30 pieces of slag
If steel slags:
Stability: 20 pieces larger than 1 litre
Figure 3.39
Sampling chart identifying possible multiple uses of the same samples and test pieces
leading to economies in the testing programme
Notes
* if UCS is expected to be less than 40 MPa; ** or from representative aggregate; *** not compulsory
in European but recommended when concerned with clay minerals.
Specific national standards relating to use of gabions, eg those in France and USA, may introduce
sampling requirements compatible with this scheme.
Box 3.13
Examples of sampling for moving and static stocks of heavy gradings
Case 1: Sampling for the control of the mass of deliveries for a coastal contract, where HMB3000-6000 is
required (ie, a 3–6 t heavy mass grading of category B and therefore no control of the average masses).
It is loaded on to a barge for further shipment to the construction site. The loading process consists of
20 000 t of material loaded from several stockpiles on the quayside into the barge. Loading takes place
over 24 hours. The sampling of stones is carried out as follows: (i) every 15 minutes the wheel loader ready
to empty its bucket on the barge is asked to empty it at the grading measurement point, (ii) after emptying
its bucket the wheel loader takes the previously weighed sub-sample and places it on to the barge. In
some circumstances, the purpose of such sampling during loading may be achieved equally well by a
client’s representative being present one day before loading is due to start, and weighing from parts of
the stockpile. This may satisfy concerns over possible delays to the loading operation caused by weighing.
Case 2: Sampling of HMA1000-3000 at a static stockpile in the quarry. A sample for mass distribution (EN
13383 requires ≥ 90 stones), shape testing (EN 13383 requires ≥ 50 stones) and initial type testing of
block integrity testing is also required (≥ 50 stones) to be taken. The scope to reuse the same samples
and test specimens for different tests is further illustrated in Figure 3.39. The long and thin layout of most
stockpiles usually makes access practical from only one side. The number of bucket-loads needed to
produce a little over the 90-stone sample is estimated. For example if nine bucket-loads of a 10 m³ wheel
loader are taken: one from each end of the stockpile, one at the centre of the face of the stockpile and
three equally spaced in the middle of each half of the stockpile, the nine loads emptied on the floor of the
quarry consist of about 90 stones or 200 t. If the total sample is still much larger than needed it can be
reduced by dividing the circular heap into eight “cake-portions” and taking the required number of
portions for the near-perfect sample size. The blocks can then be numbered and weighed for input to the
mass distribution test. Systematic and unbiased methods such as removing every nth block in the
sequence can reduce the test portion to give a 50-stone sample for integrity testing and shape testing. The
sample is ideal for providing initial type testing to give the additional shape information for integrity and
blockiness, as all stones have been weighed and stone dimensions can be assessed. Note that for the fullscale splitting test for integrity (see Section 3.8.5), stones below 1 t and above 3 t as well as stones with
more extreme shapes are discarded to produce a test sample of 50 stones.
162
CIRIA C683
3.8 Testing and measuXrxinxgx
Table 3.19
Summary of samples and test specimens required for armourstone testing (see also EN
13383-2:2002 Annex G)
Coarse grading
Light grading
Heavy grading
Drill cores, aggregate from stockpiles or exposed faces of quarries. In the case of a rock sample, the
mass of material delivered for the examination shall be not less than 5 kg.
Petrography
Methylene blue
absorption, MBA
Sample: 200 g of 0–2 mm from representative aggregate. If aggregate is not available, aggregate shall be
prepared by jaw-crushing of six representative armourstone pieces of similar size.
Grading
Sample mass in kg of the test
specimen = NUL (mm) × 2
200 AS
10–15 t: 25 AS; 6–10 t: 30 AS;
3–6 t: 60 AS; 1–3 t: 90 AS;
0.3–1 t: 140 AS
200 AS
Same sample and AS as grading
Same sample and AS as grading
Same sample and AS as grading Same sample and AS as grading
Same sample and AS as grading
Shape, eg LT
Broken surfaces RO
1
2
3
Sample: 10 p; if mass density is expected to be lower than 2.3 t/m! take 40 p in one go
Mass density ρapp
(Sr = 0 and 100%)
Water absorption WA
Test specimen: mass between 150 g and 450 g, sawn or drilled from each different AS
Sample: 2 kg of 10–14 mm representative aggregate. If aggregate is not available, aggregate shall be
prepared by jaw-crushing fragments of 6 AS of similar size. All test aggregate to have removal of
extremely flaky and cubical shaped pieces.
Resistance to wear
MDE
4
Sample: 10 p
Resistance to minor
breakage, eg UCS
Test specimen: drilled cores of 50 mm diameter and length (or 50 mm cubes).
NOTE: 70 mm cubes and cores required if UCS < 40 MPa expected.
Resistance to major
breakage, eg DT or
FSST
DT: 50 AS from ELL-EUL
FSST: 30 AS from NLL-NUL, good
shapes
Dicalcium silicate
disintegration of ACBS
Sample: 30 p
Iron disintegration of
ACBS
30 p of slag, with a nominal size between 40 mm and 150 mm
6
Sample: 20 p larger than 1 litre
Disintegration of steel
slag
Test specimen: pieces with a sawn surface larger than 0.005 m²
7
Sample: 10 p each to produce one p. If low resistance to freeze and thaw is expected,
take 20 AS pieces instead of 10. Laboratory test piece is linked to water absorption test piece,
see EN 13383-2:2002 for details.
Resistance to freezing
and thawing, eg FT
Test specimen: 0.45–10 kg
Resistance to salt
crystallisation, eg MS
5
Test specimen: 10–20 kg
Test specimen: 2 × 500 g of 10–14 mm representative aggregate. If aggregate is not available, aggregate
shall be prepared by jaw crushing of material obtained from 6 AS of similar size.
Sample: 20 p, each to produce one p larger than 1 litre
8
Sonnenbrand SB
Test specimen: pieces with a sawn surface larger than 0.005 m²
Notes
9
ACBS: air-cooled blast-furnace slag, AS: armourstone pieces, p: test pieces or test specimens from
different AS, DT: drop test, FSST: full-scale splitting test.
10
CIRIA C683
163
3 Materials
3.8.2
Testing of physical properties
3.8.2.1
Petrography
EN 932-3:1997 gives guidance on the simplified description of petrography that shall only be
used for simple identification. Detailed petrographic analysis by the ISRM method (Brown,
1981), is always advisable for evaluation of a new source, and should be performed by a
qualified geologist. The methylene blue staining technique for thin sections will further help
to identify minerals that may be deleterious. When clay minerals are evident from thin
section analysis of the rock, the methylene blue test may be performed in accordance with
EN 933-9:1999, to evaluate their significance, see also Verhoef (1992).
3.8.2.2
Aesthetic properties
As mentioned in Section 3.3.1, the colour of natural armourstone should not be defined or
specified more precisely than the shade of the colour. Use of colour charts for specification
purposes is not recommended. Visual observation of the shade may be instructive and
stockpiles should be available for inspection.
3.8.2.3
Rock density, water absorption and porosity
ASTM D5779-95a (2001) on field determination of apparent specific gravity of rock for
erosion control is a means for field-testing using a portable balance and system for weighing
immersed specimens. It is ideal when a rapid appraisal of density and its variation is
required, as no oven-drying is necessary.
The wide variety of terms in use worldwide provides considerable scope for confusion. Care
has been taken to provide details (see Box 3.14) of the calculations of apparent density, ρapp,
water absorption, WA (-), and degree of saturation, Sr (-), as defined in Section 3.3.3.2.
Apparent mass density, water absorption and porosity, p (-), are generally determined
simultaneously. These properties may be determined on aggregate representative of the
armourstone, samples such as cores prior to mechanical testing or pieces of armourstone. Test
methods consist of weighing the test sample in an oven-dry (OD) state and saturated-surface
dry state (SSD) and determining its volume either by direct measurement of a well-defined
geometry or indirect measurement such as by the mass of displaced water (hydrostatic
weighing). As a general rule of thumb, porosity values are about twice the values of water
absorption.
A selection of useful test methods is presented in Table 3.20, see also Figure 3.8. The method
defined in EN 13383-2:2002 Clause 8 is recommended in Europe.
Table 3.20
164
Methods to determine mass density, water absorption and porosity
Test method
Test specimens
Method used
Comments
EN 13383-2:2002
Clause 8
Ten pieces of 150–450 g
Dry and saturated-surface Test specimens can have
dry weighing
irregular shape
Hydrostatic weighing
Volume is determined indirectly
EN 1936:1999
Six prismatic or cylindrical
pieces larger than 25 ml
The standard provides guidance
Dry and saturated-surface
on determining the real mass
dry weighing
density
Geometric determination
Test specimens for resistance
of the specimen volume
to breakage may be used
EN 1097-6:2000
Minimum of 7 kg of
aggregate smaller than 45
mm or minimum of 15 kg
of aggregate smaller than
63 mm
Dry and saturated-surface
dry weighing
Aggregate should be
Hydrostatic weighing or
representative of armourstone
pycnometer method
CIRIA C683
3.8 Testing and measuXrxinxgx
Box 3.14
1
Calculation of mass density and water absorption during testing
Masses of the test specimen, MT, are determined by weighing, which is generally carried out at two
extreme values of water content or degree of saturation, Sr:
!
!
Sr = 0 or oven-dried state, OD; in that case MT(Sr=0) = MM where MM is the mineral mass (see Figure 3.8)
Sr = 100 per cent or saturated surface dry state, SSD; in that case MT(Sr=1) = MM + ρw × Vp,
where Vp is the pore volume (see Figure 3.8).
The volume is either indirectly determined by hydrostatic weighing, VTH, or directly (geometrically)
measured on cores or cubes, VTG, before carrying out other tests such as the compressive strength test.
2
a. Direct measure of the volume of the test specimen: If the volume is geometrically determined and its
value is VTG, then the apparent mass density is defined as:
ρapp(Sr=0) = MT(Sr=0)/VTG
(3.51)
ρapp(Sr=1) = MT(Sr=1)/VTG
(3.52)
b. Non-direct measure of the volume of the test specimen, VTH: Hydrostatic weighing is a useful method
for test specimens or aggregates with irregular shape. Equation 3.53 gives the relationship, based on:
!
!
3
VH is the volume of water displaced by the specimen; VH = VM
MH is the hydrostatic mass of the specimen determined by weighing while suspended
in water
VTH = [MT(Sr=1) – MT(Sr=0)]/ρw + VH
(3.53)
Apparent mass densities are determined as follows:
ρapp(Sr=0) = MT(Sr=0)/VTG ≅ MT(Sr=0)/VTH ≅ ρw × MT(Sr=0)/[MT(Sr=0) – MH]
(3.54)
ρapp(Sr=1) = MT(Sr=1)/VTG ≅ MT(Sr=1)/VTH ≅ ρw × MT(Sr=1)/[MT(Sr=0) – MH]
(3.55)
In natural conditions on site, the actual apparent mass density of the rock depends on its actual water
content as implied by the symbol ρapp(Sr). The designer should make the appropriate substitution of Sr in
Equation 3.56 (see Section 3.3.3.3, and Table 3.17):
ρapp(Sr) = ρapp(Sr=0) × (1-Sr) + ρapp(Sr=1) ´ Sr
(3.56)
The water absorption and porosity are given by:
WA = [MT(Sr=1) – MT(Sr=0)]/MT(Sr=0)
4
5
(3.57)
p = [MT(Sr=1) – MT(Sr=0)]/[ρw × VTG]
for geometric measurement of the volume
(3.58)
p = [MT(Sr=1) – MT(Sr=0)]/[MT(Sr=1)) – MH]
for hydrostatic measurement of the volume
(3.59)
6
3.8.3
Testing properties of individual pieces of armourstone
3.8.3.1
Shape
For shape specification compliance, factory production control in EN 13383 uses the test:
determination of the percentage of pieces of armourstone with a length-to-thickness ratio LT
greater than 3. The method to determine l and d uses two straight laths positioned parallel to
each other at right-angles to the longest dimension l and then to the smallest dimension d. l
and d are measured using a carpenter’s rule, a tape measure or, to achieve greater accuracy,
callipers (see Figure 3.82).
Shape indicators including length-to-thickness ratio, LT, cubicity, (L+G)/2E, and blockiness,
BLc, are discussed in Section 3.8.4.
3.8.3.2
8
Mass and size
9
The mass of individual armourstone pieces is rarely determined alone but rather to
determine:
CIRIA C683
7
!
the mass distribution by combination of individual masses
!
the input and output data for armourstone integrity tests that use destructive testing
!
the blockiness index of armourstone pieces (relevant for individually placed armour
layers).
10
165
3 Materials
For coarse armourstone EN 13383-2:2002 recommends the use of steel rod sieves, with
square openings of 250 mm, 180 mm, 125 mm, 90 mm and 63 mm, fitting on receivers, and
a single opening sieve, 360 mm. Test sieves with apertures conforming to ISO 3310-2:1999
are necessary for openings smaller than 63 mm. As an alternative to the very practical steel
rod sieves shown in Figure 3.40, perforated steel plates of the same sizes as recommended in
EN 933 may be satisfactory for testing.
Figure 3.40
Steel rod sieves in use for determination of size distribution of a coarse grading
(courtesy G Laan)
For light and heavy armourstone weighing of individual pieces is needed both for the
reference and alternative methods of EN 13383-2:2002. For pieces lighter less than 60–100
kg, weighing can be carried out satisfactorily using a laboratory scale. For heavier pieces,
weighing scales may be used on site or in the quarry, provided they meet EN 13383
requirements on the precision (see Figure 3.41). Load cells or spring-type scales may be used
(see Figure 3.42), but, again, specific attention should be given to the measurement precision.
In addition to the standard certification of the equipment, it is recommended to have
available a series of reference blocks of known mass for regular calibration checks during the
weighing or at least for verification before each measure.
Figure 3.41
166
View of high capacity weighing scale made of portable weigh beams, used for blocks
with a mass of less than 6 tonnes (courtesy S Dupray)
CIRIA C683
3.8 Testing and measuXrxinxgx
1
2
3
4
Figure 3.42
View of load cell and fisherman’s spring-type
scale (courtesy G Laan)
3.8.4
Testing geometrical properties of armourstone as a granular material
3.8.4.1
Shape
5
EN 13383 offers two tests to constrain unwanted stone shapes in armourstone deliveries.
Determination of the percentage of pieces of armourstone with a length-to-thickness ratio
LT greater than 3. The standard requires percentage LT > 3 to be controlled for all gradings
but introduces different ways of calculating the percentage so that there is no bias, eg
towards the shape of the smaller particles. The test method requires LT to be estimated
visually and measured only on borderline blocks.
Proportion of crushed or broken surfaces, RO. Clearly, freshly blasted or crushed pieces of
quarried rock are angular and can be said to have greater than 50 per cent surface area that is
joint-bounded or newly crushed or broken. Rounded glacial boulders, cobbles and core stones
from basalt and dolerite quarries have a completely different visual appearance. The test is by
visual assessment and counting of these non-angular stones. The proportion of stones without
crushed or broken surfaces can then be declared by the producer or restricted by the specifier.
Measurement of shape parameters. The measurement of mean length-to-thickness ratio and
mean blockiness is based on the determination of specifically defined dimensions. For
blockiness, in addition to determining the X, Y and Z dimensions of the enclosing cuboid of
the stone, stone masses and rock density are required (see Box 3.15). It is therefore
recommended to carry out shape determination at the same time as the other properties,
such as mass distribution or integrity, are determined. It is advisable to measure X, Y, Z, l and
d of all 50 pieces in the sample. This provides for greater accuracy in the EN 13383 test. It
also generates the additional information for mean and standard deviation of LT and BLc as
may be requested for initial type testing by designers and contractors for the layer thickness
and void porosity prediction (see Section 3.5.1.1). Tape measures are sometimes used, but
the use of a custom-made calliper is greatly preferred if the required accuracies are to be
achieved. The maximum dimension, l, is often given by the long diagonal in more tabular
and blocky rocks. It is sometimes best computed by means of Pythagoras’s Theorem when
callipers are not practical.
CIRIA C683
167
6
7
8
9
10
3 Materials
Box 3.15
Shape assessment including measurement of blockiness
This box provides necessary information for executing assessment of blockiness and includes discussion
of variability of shape measurement descriptors. For definition of blockiness, BLc, and length-to-thickness
ratio, LT, see Section 3.4.1.
For heavy armourstone that cannot be manipulated easily, the determination of dimensions X, Y, and Z
involves subjective judgement. X, Y, and Z are theoretical dimensions corresponding to the axial
dimensions of the minimum volume enclosing box. To the operator, the directions of X, Y, and Z may be
immediately apparent and the dimensions easily estimated, or, for less blocky stones, the directions may
be difficult to visualise. Values of l and d are more objectively defined. LT is still subject to large operator
errors during test conditions for irregular blocks because of uncertainty with d, which can lead to
significant errors in the ratio l/d.
To execute the blockiness assessment test, a representative sample of 50 stones is selected. For each
stone to be assessed in turn, first locate the minimum thickness (bar spacing through which the stone
could just pass) d and record this as the Z dimension and direction. Then view (or imagine viewing) parallel
to the Z dimension. Consider different possible directions for orthogonals X and Y in the plane
perpendicular to Z (and d). Choose the directions for X and Y that enclose the block in an imaginary box
that has a minimum for the product XY and thus for the whole block. Record these as X and Y.
NOTE: The French system for cubicity measurement uses an alternative, though again potentially
subjective, set of orthogonal dimensions to characterise the form of a block. First, the length l (=L) is
measured, then E and G are set orthogonal to the direction of L where L may be the long diagonal on a
blocky rock. It is possible that in practice the requirement that L is set to be the longest dimension is
relaxed in the case of obviously blocky rocks.
Report values of X, Y, and Z (and l if requested) on a spreadsheet, making a descriptive note of the use of
callipers, laths and tapes. Note that to measure BLc also requires mass and density determination, which
is usually available if the testing is combined with grading control or armourstone integrity tests.
Discussion of variability
Blockiness measurement is generally considered more subjective than length-to-thickness ratio, but in a
field study (Newberry, 2003) accuracy was greater than expected. The coefficient of variation of BLc and
LT was determined per typical block from a sample taken from a heavy grading. Each stone was measured
by seven operators using pocket tape measures. For both shape descriptors, the standard deviation
divided by the mean from all seven operators (issued with the same instruction guides and of varying
experience) was determined. Between the seven operators, the coefficient of variation CoV was obtained
and then averaged over the total number of stones. The average CoV for BLc and LT was 0.13 and 0.11
respectively, assuming no influence from variability in weighings and density determination. This suggests
that field conditions may lead to comparable accuracy for BLc and LT determinations even though l and d
are more objectively defined than X, Y, and Z. It appears that variation in assessing the value of d is high.
The average BLc for the sample determined by each operator ranged from 61.0 per cent to 57.2 per cent
and average LT ranged from 2.03 to 2.21. With correct use of callipers and laths as described in EN
13383-2:2002, greater reproducibility for LT would be expected. This sample consisted of only 46 blocks
and a mix of two rock types, suggesting more research is required to examine the apparent similarity in
accuracy of assessing mean LT and mean BLc.
3.8.4.2
Mass distribution
EN 13383-2:2002 specifies the following two methods for determining the mass distribution
of light and heavy gradings:
!
the reference method, which should be used in cases of dispute
!
the alternative method, which is quicker and more suitable for production control than the
reference method but is less precise.
The minimum number of pieces of armourstone, excluding fragments, required to be used
in a test portion depends on the grading category the armourstone material appears to fall
into on initial visual inspection.
The reference method weighs all the stones individually and uses the mass of weighed stones.
In the alternative method, bulk weighing may be carried out on stones visually sorted into
categories. EN 13383-2:2002 describes both these methods. Box 3.16 illustrates the
fundamental methods behind plotting grading results. In Box 3.17, results of these are
168
CIRIA C683
3.8 Testing and measuXrxinxgx
1
shown together with results of another method that can be used for production control,
based on visual comparisons.
Further consideration of methods for testing gradings can be found in ASTM D6092-97
(2003) on standard practice for specifying size of stone for erosion control and the US Army
Corps EM 1110-2-1601 (1994) for rip-rap.
Box 3.16
Guidance on calculations for generating mass grading curves
A sample of natural armour stones will display a range of stone masses or sieve sizes. The percentage of
total mass lighter or smaller than a given mass or size is used to construct cumulative curves in the
assessment of mass and size distributions. My expresses the stone mass for which y per cent of the total
sample mass is lighter. For example, M50 is the mass of a theoretical stone for which half of the mass of
the sample is lighter. The distribution of particle masses or sizes can be represented by cumulative curves
with reference to percentage of (i) total mass or (ii) total number of pieces. These differences have been
a source of confusion. The characterisation of granular materials in geotechnics and coastal engineering
refers to percentage of total mass. It is instructive to give an example showing how the different results
are generated from first principles using real figures obtained for a sample of 25 stones. In the example,
shown in Table 3.21, the results generated by inserting discrete values are also compared with those
produced by grouping similar masses into intervals (bins) before forming the cumulative curve.
Differences in the results are shown plotted in Figure 3.43 and summarised in Table 3.22.
Table 3.21
C1
Stone
masses
(tonnes)
C2
Cum
mass
Calculation of cumulative curves
C3
Cum %
by mass
less than
0.65
0.65
1.26
C4
C5
C6
C7
Cum % by
number less
than or equal
C8
C9
Cum % by
Bin mass Mass in
range
range
Cum
mass less Number
mass
than ref
to stone mass
in range
mass
C10
Cum number
less than ref
mass
C11
0.71
1.36
2.65
8
2.27
4.42
12
1.14
3.42
6.64
16
1.27
4.69
9.11
20
1.39
6.07
11.80
24
1.47
7.54
14.65
28
1.59
9.13
17.73
32
1.67
10.79
20.97
36
1.73
12.52
24.33
40
1.82
14.34
27.87
44
1.89
16.23
31.54
48
1.99
18.22
35.40
52
2.02
20.24
39.33
56
2.09
22.33
43.39
60
2.19
24.52
47.64
64
2.26
26.78
52.04
68
2.39
29.17
56.68
72
2.50
31.66
61.53
76
2.64
34.31
66.66
80
2.74
37.04
71.98
84
3.02
40.06
77.84
88
3.25
43.30
84.15
92
3.42
46.72
90.80
96
4.74
51.46 100.00
100
4
C12
number less
Ref
than ref
mass
mass
0.00-0.49
0.00
0.00
0.00
0
0
0
0.5
0.50 - 0.99
2.27
2.27
4.42
3
3
12
1.0
1.00-1.49
5.27
7.54
14.65
4
7
28
1.5
1.50-1.99
10.68
18.22
35.40
6
13
52
2.0
2.00-2.49
13.45
31.66
61.53
6
19
76
2.5
2.50-2.99
5.38
37.04
71.98
2
21
84
3.0
3.00-3.49
9.68
46.72
90.80
3
24
96
3.5
3.50-3.99
0.00
46.72
90.80
0
24
96
4.0
4.00-4.49
0.00
46.72
90.80
0
24
96
4.5
4.50-4.99
4.74
51.459
100
1
25
100
5
5
6
7
8
C1 are the masses of 25 individually weighed armour stones that have been placed in ascending order.
C2 gives the progressive sum as each new mass is added to the previous one. C3 divides C2 by the total
mass and expresses it as a percentage. C4 gives the proportion of stones with masses lighter than the
one in C1 and therefore goes up by 4 per cent for each new stone as there are 25 blocks in all. For a 90stone sample, C4 entries would go up by 100/90 or 1.1 per cent. C1 to C4 generate data for cumulative
plots that show one data point for each mass. They are therefore the most accurate and are termed
discrete cumulative plots.
CIRIA C683
3
Cum % by
4
0.91
2
169
9
10
3 Materials
Box 3.16
Guidance on calculations for generating mass grading curves (contd)
C5 to C12 show calculation stages to create binned cumulative plots. C5 shows the selected mass
intervals and their upper value represents the reference mass given in C12 required for plotting binned
cumulative lighter plots. C6 to C8 develop data for the binned plots for cumulative percentage by mass,
while C9 to C11 develop data for the binned plots of cumulative percentage by number of stones.
The plots of C1 versus C3 and C4 are shown together with plots of C12 versus C8 and C11 in Figure 3.43.
All four plots are different: binned plots place curves further to the right of discrete plots and curves based
on percentage by number are generally shifted to the left of curves based on percentage by mass. In
summary, binning makes a small but sometimes significant change to the discrete results: the fewer bins,
the larger the significance. Cumulative plots by mass are fundamentally different to cumulative plots by
number. Readers should be warned that graphing software has automatic functions to generate
cumulative plots and these invariably make the assumption that it is the cumulative plot by number (ie
the frequency of occurrence of the mass or other parameter in question) that is required in histograms
and cumulative plots.
Figure 3.43
Examples of different
mass distribution
cumulative plots
obtained from the
same mass values
Having created any one of the four curves, specific percentiles of the cumulative curve such as M50, M85
and M15 can be obtained, eg by graphical linear interpolation from an enlarged plot, by mathematical
linear interpolation of adjacent points spanning the specific percentile, or by curve fitting. Using linear
interpolation, Table 3.22 shows how the percentiles, such as those used for design, can have different
values depending on whether the percentage data is discrete, binned, by mass or by number. For mass
distributions in coastal engineering, the correct values to use are percentage by mass, the discrete data
being more accurate. Note that the arithmetic average mass Mem is the same in each case and the ratio
M50/Mem by mass is considerably above unity and by number it is considerably below unity.
Table 3.22
Variation in design parameters resulting from different calculation methods
Discrete data
Parameter
Binned data
By mass
By number
By mass
By number
M50 (t)
2.23
1.94
2.28
1.93
M15 (t)
1.48
1.09
1.51
1.09
M85 (t)
3.27
3.18
3.08
3.04
M85/M15 (-)
2.21
2.84
2.04
2.78
Mem (t)
2.06
2.06
2.06
2.06
M50/Mem (-)
1.08
0.94
1.11
0.94
For sieve size distributions, particles cannot in general be counted and there is only one possible analysis
method, namely that based on percentage by mass using bins corresponding to available sieve intervals.
The percentage by mass and binning methods are therefore used together to create particle size
distribution statistics and curves. An example of when percentage by number is used is when analysing
the distribution of shape descriptors within a sample of blocks. Percentage by number gives a more
meaningful expression of the occurrence of extreme shapes.
170
CIRIA C683
3.8 Testing and measuXrxinxgx
Box 3.17
1
Alternative methods for the determination of mass distribution
The following box presents the mass distribution (see Figure 3.44) determined in accordance with the
standard method (curve a) and the alternative method (curve b) of EN 13383. Curve c shows the mass
distribution determined without weighing but by sorting armourstone pieces visually into four separate
mass ranges (ie four bins) defined by the five limits: ELL, NLL, (NLL+NUL)/2, NUL and EUL. This task may
be made easier by sourcing five witness blocks with approximately the same limit masses that should
then be prominently displayed for visual comparison and checking.
Bin 1 contains blocks of mass visually estimated to be between ELL and NLL; the number of blocks is
called N1. Similarly, Bin 2 contains N2 blocks from NLL to (NLL+NUL)/2; Bin 3 contains N3 blocks from
(NLL+NUL)/2 to NUL; Bin 4 contains N4 blocks from NUL to EUL. Each bin is supposed to contain blocks
with an average mass equal to the average mass of the bin limits. Bin 1 would then contain N1 blocks of
mass m1 = (ELL+NLL)/2 and have a total estimated mass of N1 × m1. The cumulative proportion in each
bin is given by X1 = m1/MT; X2 = X1 + m2/MT; X3 = X2 + m3/MT , where MT is the total mass of armourstone.
The cumulative mass lighter is determined by plotting Xi as a function of the upper limit of the bin. The
average mass is estimated by (N1 × m1 + N2 × m2 + N3 × m3 + N4 × m4)/(N1 + N2 + N3 + N4). Curve d
shows the mass distribution determined similarly for eight bins.
2
3
4
5
6
Figure 3.44
Mass distributions determined with (a) the reference method and (b) the alternative
method of EN 13383, (c) and (d) by visual sorting in bins with estimation of the mass
of each bin
3.8.5
Mechanical properties
3.8.5.1
Resistance to breakage
7
In EN 13383, tests under the heading resistance to breakage refer only to strength of the
mineral fabric determined on hand-sized specimens or aggregates. As such resistance to
breakage is only appropriate to assess the risk of minor breakage of armourstone and will not
necessarily indicate armourstone integrity as discussed in Section 3.3.4. EN 13383 requires
that the resistance to breakage of the mineral fabric of armourstone shall be determined
using the compressive strength test according to EN 1926 Annex A. This test method differs
only marginally from more conventional rock mechanics test methods for unconfined
compressive strength, termed UCS.
For testing with EN 1926 Annex A, 10 specimens are prepared from separate pieces of
armourstone. They should be cubes with 50 mm edge or cylinders whose diameter and
height are equal to 50 mm. Note that for material with an expected compressive strength
lower than 40 MPa, the use of test specimens with characteristic sizes of 70 mm is allowed.
Test specimens should be tested in their saturated condition that is reached after soaking in
water for (48 ± 4) h. If any existing plane of anisotropy is identified, it shall to be clearly
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indicated on each specimen by means of two parallel lines and mentioned in the test report.
Results from the test on 10 test pieces enables (i) the mean of the best nine and (ii) the
strength of the two weakest specimens, to be compared with the specified requirements.
The point load strength test (ISRM, 1985) is a portable, rapid means to assess the resistance
to breakage of the rock that can be performed on cores, sawn blocks or rough chiselled
lumps. Results are corrected to the equivalent value for 50 mm cores and expressed as the
point load strength index Is (sometimes written Is(50)), which correlates well with UCS, where
UCS ≈ 22Is (EN 1926 Annex B). Since it is easy and cheap to use, this test may be
appropriately used for quarry evaluation and quality control purposes.
Further tests are indicative of the strength of mineral fabric:
!
indirect Brazilian tensile strength (ASTM D3967-95a, 2004; ISRM, 1978), whose ratio to
the compressive strength gives an indication of the rock brittleness
!
fracture toughness (ISRM, 1988), which indicates resistance to crack propagation and is
sometimes recommended but is difficult to perform
!
Los Angeles (EN 1097-2:1998) is currently performed on aggregates for factory
production control and could be used as a quality control means provided a proven and
sure correlation with UCS is given
!
Schmidt impact (ISRM, 1988) and sonic velocity (EN 14579:2004) are indirect nondestructive tests that provide indicators of the existence of cracks.
Values of these various tests are given in the guide to durability (Table 3.12).
3.8.5.2
Armourstone integrity
Standard integrity clauses based on subjective visual criteria alone have often failed to
provide sufficient safeguard against “unfair” rejection by the purchaser as well as “unfair”
acceptance. No standard test for armourstone integrity is currently recommended in EN
13383. Guidance on approaches to assess integrity is given in Annex B of EN 13383. There
are two approaches for the quantification of the likelihood of major breakage that can
improve the subjective visual assessment.
Destructive testing aims at (i) reproducing the characteristic loading to which the
armourstone may be exposed such as for the drop test (DT), or (ii) exposing the test
specimen to standard loading such as for the full-scale crushing test (FSCT) or the full-scale
splitting test (FSST). Whereas the drop test is a routine quality control test to perform at the
quarry, it does not allow prediction of the grading changes. Designers prefer to have FSCT
or FSST results, as they may be used with design tools to predict grading changes. Such
standard loading tests may be performed as an initial type test when selecting a quarry.
Non-destructive testing is based on auscultation of armour stones using sonic waves.
Unexpectedly slow sonic velocities through a piece of armourstone indicate the presence of
open cracks or flaws. Note that the test results are highly sensitive to the test conditions,
notably existence of small cracks in the vicinity of the measuring device and the coupling
media. Test methods are detailed in Box 3.18. Non-destructive testing is appropriate for
quality control during deliveries especially for borderline strength large stones. It is
recommended to calibrate threshold values against destructive test results.
While in principle, non-destructive methods for integrity are preferable and they may
eventually prove superior since they are a suitable means to evaluate the quality of the
material that is used, none is currently more reliable than existing destructive tests.
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Box 3.18
Assessment of armourstone integrity using non-destructive sonic velocity test methods
1
Based on the success of sonic velocity detection of cracks in small specimens, full-scale methods have
been developed in France and in the Netherlands. The principles of each approach are given in this box
together with details of the method to evaluate armourstone integrity using the continuity index, Ic, based
on more than 15 years of French experience with armourstone specification and testing.
2
The continuity index, Ic (%), is defined as:
Ic =
Vp
⋅ 100
V*
(3.60)
where Vp is the P-wave velocity (m/s) measured through the armourstone test piece and V* (m/s) is a
theoretical sonic value determined from the mineral composition of the rock as given in Table 3.23.
For other rock types, V* may be determined from detailed petrographic analysis (Denis et al, 1979). Ic
values decrease with both cracks and porosity and the degree of fissuration, Df (%), is a means of
separating the effect of discontinuities from the effect of natural porosity, p (%), and is given by (Tourenq
et al, 1971):
Df = 100 – 1.4 × p – Ic
Table 3.23
3
(3.61)
Theoretical sonic velocity V* values used for Ic calculation (Denis et al, 1979)
Rock type
Granite
Gneiss
Diorite
Gabbro
Amphibolite
Quartzite
Sandstone
Schist
Limestone
Dolomite
V* (m/s)
6000
6500
7000
6000
5800
6600
7200
4
The characteristic value of Ic to be reported for each stone is the minimum value determined after
measuring in three orthogonal directions. The measurements should be performed on 30 blocks at least.
For a sample to be assigned to an armourstone integrity category such as Ic(60) or Ic(80), two conditions
should be verified: (i) the mean value is greater than x and (ii) less than 10 per cent of the blocks display
a value lower than x, where x is the number in the brackets (expressed as a percentage). Suggested
integrity ranking based on values of both the degree of fissuration, Dp (%), and the continuity index, Ic (%),
are given in Table 3.24.
A Dutch method is presented by Niese et al (1990). It requires 20 measurements of the P-wave velocity,
Vp (m/s), per individual stone (the research used between 17 and 25). The spread of results is then plotted
as the cumulative percentage of stones by number (y-axis) with velocity less than a certain velocity (x-axis).
Both a larger spread and a lower average velocity imply poorer integrity. Thus, a normalised velocity
anisotropy index, Id (-), was defined for each stone as:
Id = (R90/R10)/R50
5
6
(3.62)
where Ry is the velocity represented at y (-) per cent, equal to Vp,y/Vp,max, where Vp is the P-wave velocity
(m/s).
Practical difficulties include: length of time to take each reading, methods are limited to armourstone
gradings below about 6 t, and obtaining technical equipment and trained personnel. Suggested integrity
ranking based on the normalised velocity anisotrophy index, Id (%), is also included in Table 3.24.
Table 3.24
7
Proposed ranking of integrity from non-destructive measurement
Excellent integrity
Good integrity
Marginal integrity
Poor integrity
Df < 20%
Df < 20%
Df < 20%
Df < 20%
Ic(80) ≤ Ic
Ic(70) ≤ Ic ≤ Ic(80)
Ic(50) < Ic ≤ Ic(70)
Ic < Ic(50)
Id ≤ 1.25
1.25 ≤ Id ≤ 2
2 ≤ Id ≤ 3
Id > 3
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Destructive testing is the most direct approach to assess the resistance of the armourstone
population to major breakage. Of the many such test methods reported, the drop test or DT
(Latham and Gauss, 1995), full-scale crushing test or FSCT (Tørum et al, 2000) and fullscale splitting test or FSST (Dupray, 2005 and Dupray et al, 2007) are the only tests to have
descriptions or field results recorded in sufficient detail to permit widespread use.
For the drop test, the degradation process is pragmatically reproduced by dropping
individual pieces of the armourstone population from a height that is representative of the
average loading experienced during construction. For the full-scale splitting test, a better
control of impact conditions occurs: an impactor is released from a standard height on to the
test specimen, leading to a test result that is not directly representative of degradation
experienced but may be used for the prediction of grading changes.
The test configurations are presented and discussed in Box 3.19. The detailed approaches
for testing and analysing for drop test and full-scale splitting test are given respectively in
Box 3.20 and Box 3.21.
It is recommended that the reference test for factory production control of integrity is the
drop test (Box 3.20). When more accurate prediction of the effect of integrity at a new source
is required and a designer wishes to predict degradation caused by breakages, then the FSST
(Box 3.21) is to be recommended as part of initial type testing. FSCT may also be used,
although it is not presented here since the equipment required makes it difficult to perform.
For further details refer to the key report, Tørum et al (2000).
Combining the results of any breakages suffered by each stone tested into a result for the
whole sample provides a characteristic value of integrity for the armourstone population.
Useful indicators to analyse destructive test results but also to characterise degradation
experienced by an armourstone population in the field are summarised below.
!
Bn is the ratio of the number of pieces that display major breakage to the number of
pieces in the population. For an objective determination of Bn, Equations 3.63 and 3.64
are recommended
Bn = (number of stones with Lm ≥ 10 per cent after testing)/(number of stones tested) (3.63)
Lm = (Mi – M*f)/Mi
(3.64)
where Lm is the loss of mass (%), Mi is the mass of the stone prior to testing (kg), and M*f
is the mass of the largest piece remaining after the test (kg)
!
174
IMx is the relative decrease of a characteristic mass with reference to the initial mass prior
to degradation, at a given fraction or percentage passing value on the cumulative plot
(see Equation 3.4).
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Box 3.19
1
Configurations for full-scale destructive tests for integrity
The test configurations are presented in Figure 3.45.
For the drop test (DT), individual armourstone pieces are dropped onto an anvil made of a bed of other
armourstones of similar size. The surface of the anvil should be levelled and laid in a single compact layer
on a 0.5 ± 0.05 m thick layer of crushed rock aggregate.
For the full-scale splitting test (FSST), an impactor is dropped on to the top of the individual armourstone
piece to be tested, which is positioned on an anvil. The anvil consists of one block of the same rock type
and its mass, MA, should be MA = EUL ± 5 per cent. The anvil should be buried within quarry-run rockfill,
compacted and levelled at ground level.
2
3
4
5
Figure 3.45
Comparison of test configurations for drop test and full-scale splitting test
When performing these tests, specific attention should be paid to the height and alignment of the stone
(for the drop test) or of the impactor (for FSST). This may be achieved by using a control chain fixed to the
grab (for the DT) or along the impactor (for the FSST) with appropriate length. For the drop test, spinning
or undesired rotation of the block during the fall should be avoided by using appropriate machinery such
as an orange-peel grab.
NOTE: Performing these tests in a quarry is an unfamiliar activity that may be repeated only every two to
five years. Specific risk assessment and safety procedures must be devised and adhered to. Operators
should be instructed to wear appropriate protection and personnel kept at sufficient safe distances to
avoid flying rock fragments. Machinery will also need to be protected. A suggested template for risk
assessment is included in Appendix A2.
6
7
Both types of destructive test are rather time-consuming to perform and require some
assistance from the quarry, preparation, time and equipment, space and safety attention.
Destructive tests should therefore be specified and performed only where necessary.
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Box 3.20
Determination of the drop test breakage index, Id50
The drop test is used on heavy gradings to reproduce degradation related to construction. Its results are
expressed in terms of the breakage number Bn or drop test breakage index, Id50. The sample should
contain at least 50 pieces, using sampling in accordance with EN 13383-2 from masses above the ELL of
the grading in question. Equipment and other aids consist of a suitable hydraulic grab (the orange-peel type
is recommended), weighing equipment accurate to within 2 per cent of ELL, and an anvil (see Box 3.19).
To execute the test
1
2
3
4
5
6
Before the test, determine the individual masses of each armourstone piece and also the initial mass
distribution using the standard method of EN 13383.
Subject each block in the test sample in turn to a drop on to the anvil, ensuring a fall height of 3 m ±
0.1 m.
Set aside all resulting pieces whose mass is greater than the ELL mass, or whose mass is assessed
to be close to the ELL mass, for further weighing.
Record the result of each drop, noting the number and type of visible flaws in blocks and the number
and type of blocks or broken pieces resulting.
Clear all rock fragments from the anvil, leaving clean surfaces before dropping the next stone.
On completion of the drop test for each stone in the test sample, individually weigh and record the
mass of each stone piece heavier than the ELL. Record the mass of the heaviest of these pieces, mf*,
corresponding to each dropped stone.
Calculate the value of Bn using Equation 3.63 and 3.64.
Calculate the drop test breakage index, Id50 as follows. Plot the cumulative mass distribution curves for
the total (50-block) sample before drop testing and the cumulative mass distribution after drop testing for
all pieces heavier than the ELL. By linear interpolation of the cumulative plot, calculate the median sample
mass before testing Mi50 and the median sample mass of pieces above ELL after testing MfELL50. The drop
test breakage index, Id50, is given by:
Id50 = (Mi50 - MfELL50)/Mi50
(3.65)
NOTE: After the drop test, there is usually only one piece remaining that is larger than ELL, although it is
just possible to have two. Therefore the cumulative mass distribution derived from each largest piece after
each impact, Mf*, is practically identical to that including all pieces heavier than ELL, but may differ.
Particular care should therefore be taken when inspecting the cumulative mass distribution curves using
all pieces larger than ELL or if using Mf*. They will both be different from the actual mass distribution after
testing because they exclude the finer fragments. Thus, Id50 underestimates the expected decrease of M50
during construction.
NOTE: Id50 assesses both integrity and resistance of the mineral fabric to breakage.
Report the following data: the drop test breakage index, Id50; a reference to this box; a description of the
sample including its mass grading; the source of the sample; the date of testing. If agreed beforehand,
the cumulative mass distributions before and after testing shall be provided (it is recommended that this
be on a single graph), together with the value of Bn.
The drop test is a quality control tool that may be performed in two days (including
sampling) with equipment available at the quarry. The drop test result is highly variable,
however, because of the lack of impact geometry control such as block motion, discontinuity
orientation and location of impact on the block.
The full-scale splitting test is a tool for the designer to predict mass distribution changes. The
test takes longer to perform (maximum three days including sampling) and requires an
impactor. However, it provides a good control of the test conditions on impact and yields
results that show up the effects of discontinuities. It provides a means to relate the
degradation during routine handling and during service life to the results of an integrity test
(FSST), as explained in Section 3.6.6.
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Box 3.21
Determination of the full-scale splitting test index, IFSST50, and characteristic integrity, CFSST
The FSST is used to determine the maximum effect of discontinuities on the mass distribution. The test
result yields both an FSST index value, IFSST50, and an FSST strength value, CFSST. The actual mass
distribution change of the grading can be determined using the degradation model of Section 3.6.6. The
test sample shall contain at least 30 blocks sampled in accordance with EN 13383-2, with masses larger
than the NLL mass. Stones with LT above 3 should be discarded during preparation.
Equipment and other aids. The mass of the impactor, MI, is close to the average nominal limits of the
grading considered, MI = (NLL+NUL)/2 ± 5 per cent, and the radius of the impactor should be close to the
radius of the average nominal limits rI = 0.5 (MI /ρapp)(1/3). The release equipment of the impactor should
allow a good control of the height and position of the impactor. The use of tyre and sling to handle the
impactor is a simple but effective method. Alternatively, a dedicated shackle whose opening is controlled
from a crane may be used. Weighing equipment should be accurate to within 2 per cent of ELL.
Test procedure
1
2
3
4
5
6
Each stone is weighed before testing and its mass, Mi, recorded.
Each stone is visually examined to detect any possible planes of weakness. Sonic measurement can
be carried out to quantitatively determine the weakest direction, should any exist in the test
specimen.
The test specimen is placed on the anvil with the plane of weakness as vertical as possible.
The impactor is lifted to the required height, Hd, above the centre of the sample and released.
All fragments (as defined in Section 3.4.3.5) larger than 10 per cent of NLL are individually weighed
and their individual mass recorded.
The total number of FSST sample test stones subjected to impacts, nFSST, is recorded.
1
2
3
4
NOTE: The FSST has been performed and verified in the field for the standard grading 1–3 t, with an
impactor mass, MI, of 2 t and an anvil mass, MA, of 4.5 t. The drop height Hd was 2 m (Dupray, 2005).
Calculate the value of Bn using Equations 3.63 and 3.64.
Calculate the FSST index. Plot the point-by-point cumulative mass distribution curves for the sample prior
to drop testing. Plot the point-by-point cumulative mass distribution after FSST using the total initial mass
as the reference mass for the standard method of EN 13383-2 – ie in Clause 6.5.1 of EN 13383-2.
Calculate the median sample mass before testing, Mi50, and the median sample mass of pieces above
ELL after testing, Mf50. The FSST index, IFSST50 (-), is given by:
IFSST50 = (Mi50 - Mf50)/Mi50
5
(3.66)
NOTE: IFSST50 represents the maximum mass distribution decrease that may be expected from discontinuity
propagation. As with Id50 in the drop test, IFSST50 includes the effect of minor breakage.
Calculate the FSST characteristic integrity, CFSST. Plot both pre- and post-FSST mass distributions.
Determine the vertical of the post-FSST mass distribution curve at mass M = 0.1.NLL to determine the
value of F (see also Section 3.6.6.1). Determine the area below the mass distribution curve pre-FSST, Ai ,
and post-FSST, Af . An approximate value of CFSST (J/kg) can be determined using Equation 3.67.
CFSST =
gnFSST M I H d A f − Ai − F ⋅ ( NLL + NUL ) 2
3
MT
( NLL + NUL ) 2
6
(3.67)
where MT = total mass of the consignment tested; nFSST = number of stones tested. Af and Ai can be
determined by numerical integration of the area below the mass distribution curves. Alternatively, the
reader may refer to Figure 3.34.
7
NOTE: CFSST accounts specifically for the effect of discontinuities. Populations of blocks displaying open
cracks tends to have a value of CFSST smaller than 27 J/kg whereas others with no significant
discontinuities tend to display CFSST larger than 35 J/kg.
Report the following data: the breakage rate, Bn, the full-scale splitting test index, IFSST50, and the full-scale
splitting test characteristic integrity, CFSST; a reference to this box; a description of the sample including
its mass grading; the source of the sample; the date of testing. If agreed beforehand, cumulative mass
distributions before and after testing should be provided, eg to predict degradation. It is recommended
that this be on a single graph.
3.8.6
Durability and accelerated weathering tests
Ideally, cyclic stressing simulation tests (for example, freeze-thaw, sulphate crystallisation,
wetting and drying, thermal cycling), should be carried out on sample stones of the same size
as those to be used on site. This is impractical, however, so a compromise for routine testing
is necessary. Specially designed test procedures using large pieces (eg greater than 20 kg)
may sometimes be recommended in the material evaluation process for a source with no
service history. There is a greater need to use non-standard large test pieces if the
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recommended test piece size will not capture the features of the rock texture that are of
concern. The integrity test on full-scale armourstone is another way of detecting such largescale features, although possible weakening by cyclic stressing leading to opening of macroflaws will not have been reflected by integrity tests. The largest test specimen size in the EN
13383 standard freeze-thaw test uses 10–20 kg pieces. Many specialist tests and investigations
of armourstone degradation were described in the volumes by McElroy and Lienhart (1993)
and Magoon and Baird (1991).
3.8.6.1
Freeze and thaw test
Only very rarely has degradation induced by freeze and thaw occurred in rock with water
absorption, WA, lower than 0.5 per cent. EN 13383 considers that rock with WA < 0.5 per
cent is resistant to freeze and thaw.
The test method (EN 13383-2:2002 Section 9) is based on visual assessment and a threshold
value for the loss of mass of armourstone pieces undergoing 25 freeze and thaw cycles
between +20°C and -17.5°C with a period at 0°C. For the material to be considered resistant
to freeze and thaw, no more than one piece among the 10 tested should display signs of
degradation.
Refinements to this method, based on widespread practice for rock and concrete durability
testing have been proposed, where additional sonic velocity measurements are taken before
and after freeze-thaw cycles (see Box 3.22). They have been suggested by several countries,
eg France and Austria, and should be considered for source evaluation in aggressively cold
environments.
3.8.6.2
Salt crystallisation test
The European test method recommended for resistance to salt crystallisation of armourstone,
EN 1367-2:1998 Clause 8, sometimes referred to as the magnesium sulphate soundness test, is
based on the standard test for 10–14 mm aggregate samples using magnesium sulphate
solution. Repeated immersion in saturated solutions of magnesium sulphate is followed by
oven-drying to partially or completely dehydrate the salt precipitated in permeable pore
spaces. The internal expansive force, derived from the rehydration of the salt upon reimmersion, was originally intended to simulate freeze-thaw action. It is considered more
representative of the precipitation of sea salt from intertidal and splash zones of hot dry
coastal environments than the freeze-thaw test using fresh water. The test uses five
precipitation cycles and may take three weeks. It attempts to measure only the weaknesses in
the armourstone at the mineral fabric grain-scale. If there is a requirement for rock with WA
> 0.5 per cent to have resistance to salt crystallisation, it is to be set at MS < 25 per cent
according to EN 13383-1:2002 Annex C and measured according to the test for thermal and
weathering properties in the EN 1367-2:1998 magnesium sulfate test. In the USA, it is
common to conduct the test using sodium sulphate in place of magnesium sulphate. The
percentage loss in the latter test is usually 1.5 to 2 times higher than in the former, the factor
depending upon rock type.
The equivalent US test, ASTM C88-99a, is more labour-intensive and also takes three weeks
to perform. It uses a range of aggregate sizes up to 125 mm and weights the results of the
test according to size fraction. This permits the effect of possible meso-scale flaws in the
larger pieces to be detected. The EU standard for railway track ballast (EN 13450:2002)
introduces a magnesium sulphate test with 31.5–50 mm aggregates. Such a test would also
give meaningful results for comparing armourstone sources.
The chemical reaction that occurs between carbonate and sulphate in solution is a concern.
The test may not be suitable for all rock types, and reservations have been expressed
elsewhere in respect of some carbonate aggregates and some aggregates having a high
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proportion of magnesium bearing minerals or of cryptocrystalline quartz. There is therefore
always a high variability associated with the sulphate soundness test and usually at least a
three-week reporting time. When the strength of visible microcracks is in question, an
experienced geologist’s visual examination of cored specimens that have been subjected to a
five-cycle sulphate soundness test can be more useful than the numerical result of the
standard test.
Box 3.22
Outline of alternative French freeze-thaw test method using sonic velocity
A representative sample is selected at the quarry consisting of at least five stones. Test specimens are
prepared by coring a cylinder of at least 15 cm diameter and 30 cm length or by sawing so that two sawn
faces are perpendicular and display an area for visual examination greater than 15 cm × 15 cm and 10
cm thickness (see Figure 3.46). Before the test, photographs of the sawn faces are taken and the P-wave
velocity is measured in three perpendicular directions. The size of the sample is small enough to use a
sonic velocity tester of the type used routinely for concrete testing. The samples are exposed to 25 freeze
and thaw cycles as required in EN 1367-1:2000. The armourstone is considered to be resistant to freeze
and thaw if (i) no open crack is observed after the cycles and (ii) less than 20 per cent of the pieces tested
display a decrease of sonic velocity larger than 15 per cent.
1
2
3
4
5
6
7
Figure 3.46
3.8.6.3
Samples before and after freeze-thaw test using sonic velocity. Top: specimen with wet
surface displaying discontinuities and significant decrease of sonic velocity after test.
Bottom: specimen displaying open cracks and significant decrease of sonic velocity.
Before test: Sonic velocity, Vp = 5100 m/s, continuity index, Ic = 76 per cent; after test:
Vp = 2600 m/s, Ic = 40 per cent (Top: courtesy S Dupray, bottom: courtesy J Perrier, CNR)
Test for breakdown by Sonnenbrand
Sonnenbrand is defined in EN 13383-2:2002 as a type of rock decay that can be present in
some basalts and which manifests itself under the influence of atmospheric conditions.
Sonnenbrand starts with the appearance of grey or white star-shaped spots. Usually hairline
cracks are generated, radiating out from the spots and interconnecting them. This reduces
the strength of the mineral fabric, and as a result the rock decays to small particles.
The laboratory sample for testing for Sonnenbrand consists of a single piece of basalt
armourstone, which is cut to give two test portions, each with a sawn surface equal to or
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greater than 0.005 m². One test portion is examined for signs of Sonnenbrand after boiling
for 36 h. A record is made of any formation of grey/white star-shaped spots and cracks (both
hairline and larger) and any breakage of the test portion. As an aid to examining the boiled
test portion, a comparison can be made with the unboiled test portion. The star-shaped
spots and associated cracks of rocks exhibiting deterioration by Sonnenbrand are shown in
Figure 3.47.
Figure 3.47
3.8.6.4
Stones affected by the “Sonnenbrand effect” (courtesy G Laan). Left: pattern on the
surface of basalt rock, leading to severe failure; right: considerable cracking interpreted
as being caused primarily by Sonnenbrand effects
Non-European tests and other source evaluation tests
The geometry of pore spaces contributing to the microstructure of the mineral fabric is
strongly indicative of susceptibility to weathering in engineering time. When the ratio of
microporosity to macroporosity is relatively high, cyclic stressing caused by water penetration
and crystallisation effects is much more severe because the solutions do not drain away
rapidly. This can be discovered by testing using a procedure described in Lienhart (2003).
Tests designed to reveal weakness resulting from the effects of clay minerals may be
particularly appropriate for argillaceous sedimentary rocks, impure micritic limestones, and
many igneous rock showing signs of weathering. Examples of such tests include: wetting and
drying, ASTM D5313-04, and methylene blue absorption, EN 933-9:1999. A novel testing
approach for degradation prediction in hot climates based on thermal cycling is described in
Box 3.23.
3.8.6.5
Chemical analysis, organic matter and leaching tests
Such analysis and tests are not generally relevant for armourstone derived from quarried
rock but may be used where organic matter or significant soluble minerals are thought to be
present in the rock. Organic content may be determined by removing it from the sample by
heating or by chemical means (EN 1744-1). For leaching, EN 1744-3 may be used. Rock
samples from mining areas suspected of having potentially toxic minerals may be sent to
geological laboratories for an elemental analysis of constituents.
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Box 3.23
1
Thermal cycle testing for hot climate applications
The test presented in this box was developed by CNR for riverbanks in the south of France to predict
degradation of fine-grained impure limestones as well as some granites caused by day/night heating/cooling
cycles and rapid cooling during summer storms. The test aims to reproduce these conditions.
The test specimens of 20 × 10 × 10 cm parallelepipeds are prepared by sawing individual pieces. The
bottom of the test sample is locked while the top is heated. A single identified face is regularly exposed
to water spray. The specimen is exposed to 160 cycles of 4 hours composed of:
1
2
3
4
2
3 hours of heating from room temperature to 80°C by putting the specimen in a isolated container
heated by a set of electrical resistors.
10 minutes without heating.
40 minutes of violent cooling by water spray from a series of nozzles.
10 minutes without wetting or heating.
Every 10 minutes, the vertical and horizontal lengths and internal and surface temperature of the specimen
are measured. It is then possible to compare visual observations of the specimens, modes of degradation,
dilatancy and temperature. Temperature variations inside the sample may vary from 25°C to 60°C.
This test is proposed as an important complement to petrographic analysis for projects where the hot site
environment carries a risk of causing thermal degradation. It is relevant for selecting rock sources
displaying a certain degree of weathering or containing minerals that may evolve with time. The test takes
more than a month to perform but can provide an objective understanding of predicted degradation, the
mechanism involved and the selection of alternative rock sources. Example results of indicative behaviour
are shown from micritic limestones in Figure 3.48.
3
4
5
6
Figure 3.48
3.9
7
Trace recording of thermal cycling. The lower trace indicates the inside temperature,
the upper trace the surface temperature; the steps reveal the rock has undergone
degradation (courtesy J Perrier, CNR)
QUARRY OPERATIONS
8
For the purpose of sourcing armourstone, quarries fall into three categories.
Aggregate quarries. In general, activity in these quarries focuses on procedures for
roadstone and concrete aggregates production. Aggregates production and processing is core
business so any armourstone production is undertaken with minimum possible disruption to
normal markets. Quarry operators will however, consider on commercial merit all trading
opportunities and additional costs associated with armourstone production, handling,
storage, quality control and quality certification. Aggregate quarries willing to adjust blasting
and processing to improve armourstone yields are ideal for the contractor and the material
costs may be very reasonable since all excess material from an armourstone blast is processed
along with routine aggregates production. What makes armourstone from a dedicated
quarry expensive is the set-up cost and the amount of materials that cannot be used. By
adapting procedures in an aggregates quarry in this way, the problem is solved.
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Dedicated quarries in greenfield sites. These quarries are set up specifically to be the source
of rock for a particular contract. The rate of production of armourstone can therefore be
geared to the scale of the quarry operation, so there are no delays for the construction team.
The major disadvantage is that a considerable amount of excess material, such as the fines
and sizes not required, will be left over. The cost of producing these excess materials has to
be recouped and is usually reflected in a higher price for the products sold. Furthermore, it
is becoming increasingly difficult worldwide to open a quarry in a greenfield site, particularly
at short notice, considering all the permits and the environmental impact assessment
required. For large breakwater projects, adapting existing quarries is becoming increasingly
favoured.
Dimension stone quarries. Reject blocks from dimension stone quarries are ideal for the
supply of very large armourstone. Typically, dimension stones are cut out or pneumatically
split using a row of closely spaced holes. Many blocks extracted in this way have to be
disqualified from further processing, ie cutting and polishing, either because of visual
appearance or flaws. Similarly, natural blocks that are bounded by several angled joints are of
no use as dimension stone products. If very large, these are further broken up by a breaker.
Such rejects are manoeuvred into big waste heaps from where they need to be recovered if
they are to be sold as armourstone by-product. Where these uneconomic waste blocks of the
dimension stone industry are near coastal waters, they often make excellent sources of heavy
armourstone. The production of smaller gradings generally requires secondary breakage.
The distribution of shapes within a consignment, some pieces being very blocky, may need
careful consideration for certain applications.
Section 3.9 is organised in two parts: Sections 3.9.1–3.9.5 deal mainly with quarry evaluation
and yield prediction while Sections 3.9.6–3.9.9 cover the practical aspects of running
armourstone operations in the quarry.
3.9.1
Exploration and evaluation
The principles of locating and evaluating a quarry are summarised in this section. An
important part of this process is the discontinuity survey and the in situ block size distribution
assessment, which are presented in Section 3.9.2. Blast design specific to armourstone
production is briefly outlined in Section 3.9.3, while in Section 3.9.4 emphasis is given to the
use of Rosin-Rammler curves and the prediction of quarry yield curves. For large projects
requiring dedicated sources of armourstone, quarry yield prediction is a critical part of
design optimisation. To check whether the proposed design will result in higher or lower
utilisation of the quarried rock, yield-matching methods are described in Section 3.9.5.
3.9.1.1
Quarry evaluation of armourstone in general
Analysis of in situ block sizes and analysis of rock quality (covered in Section 3.6) are essential
and distinct tasks. In practice, they are addressed together at the time of the quarry site
evaluation. Information should be gathered and processed in a systematic manner – see for
example the generalised scheme applicable to both greenfield sites and existing quarries
shown in Figure 3.7 in Section 3.2.3. The assessment of data and the analysis tools required
to prepare an armourstone evaluation report for a potential source should draw upon details
found in many parts of this Chapter, eg Sections 3.2, 3.3, 3.4, 3.6, as well as Section 3.9,
which includes in situ and blast size analysis.
3.9.1.2
New armourstone quarry in a greenfield site
The process of exploration and evaluation leading to the decision to set up a new
armourstone resource aims to:
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!
locate a target resource
!
determine the quality and production rate for different sizes of armourstone
!
determine the economics of extraction
!
determine the cost of processing up to the quarry gate
!
assess the planning and environmental costs of extraction, restoration and processing
!
optimise the distance from site or transport facilities
!
ensure the facilities around the quarry have the capacity to transport armourstone to
load-out facilities. This includes considerations such as road capacity and crane capacities
in the local harbour
!
for small quarries, the stocking area might be an issue
!
obtain the quarry production engineer/quarry operator.
3
Many of these points are developed in Smith (1999). The literature search and field
reconnaissance is focused on areas constrained by suitable geology for block size and quality
and by economic distance of the resource from the project site. Opening a new armourstone
resource follows the same basic process as for any mineral resource, irrespective of the scale
of the material requirements, and has much in common with the search for rock-fill and
construction materials in highway and dam engineering works. In most countries, project
engineers should be aware that it is increasingly difficult to obtain planning permission to
open a new quarry or even to open a borrow pit for a small project.
The primary objective is to locate a source with large enough natural blocks (ie one with a
suitable in situ block size distribution, IBSD). Large discontinuity spacings averaging greater
than 1 metre usually indicate an in situ rock mass that will yield sufficient volumes of large
blocks (see Table 3.25). In general, sources that can yield large blocks will also be of
satisfactory physical and durability properties. Exceptionally, this is not the case. Rock sources
are inherently variable and evaluation of rock quality using tests is always necessary. Many
insights into the practicalities of setting up a dedicated armourstone quarry in a greenfield
site and advice on delivering armourstone gradings efficiently for a large breakwater project
can be found in Van Meulen (1998).
3.9.1.3
2
4
5
6
Principles of armourstone yield assessment
Predicting the blasted block size distribution (BBSD) is the key to assessment of
armourstone potential in new temporary (ie dedicated) quarries as well as in the adaptation
of aggregates quarries for armourstone production. Modern approaches to modelling
blasting, increasingly applied to aggregates and ore blasting, require an estimation of the
size distribution of blocks in the rock mass that exists prior to blasting and certainly an
indication of the maximum in situ block size. Such approaches are even more applicable to
armourstone production because large blocks cannot be produced if they are not there in
the first place. Once it is established that a good proportion of large blocks naturally exist in
the rock mass before blasting, many of the in situ blocks will be liberated and remain
unbroken to produce heavy armourstone if the blast is designed correctly. This natural
block size distribution, due to intersecting discontinuities, is termed the in situ block size
distribution, IBSD (sometimes referred to as ISBD).
To assess the top sizes and yield curves of armourstone, the rock engineering investigation
has the following logic, as illustrated in Figure 3.49:
7
8
9
In situ discontinuity analysis # IBSD prediction # blast modelling # BBSD prediction and
assessment.
The range of methods of IBSD assessment and the underlying importance of IBSD were
explained in a recent review of rock mass blastability and fragmentation by Widzyk-Capehart
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and Lilly (2002). While there are many blasting engineers and geotechnical consultants with
expertise in quarrying techniques, experience in armourstone operations remains relatively
scarce. Production methods and yield prediction techniques applicable to armourstone have
proven difficult to find from literature. Various suitable approaches have therefore been
brought together here in Sections 3.9.2–3.9.4. It should be noted that blast design and yield
prediction are not exact sciences and the approaches suggested below are essentially
qualitative, subject to large possible errors and should be supplemented with genuine
blasting experience whenever possible. Nevertheless, they do represent methodologies that
can significantly help a production team constrain the cost of a project and achieve its
objectives.
3.9.2
Assessment of in situ block size distribution, IBSD
The most directly relevant set of initial geotechnical data needed for planning production is a
3D survey of the discontinuities of the rock mass to be blasted, leading to an IBSD
prediction. If such a survey and analysis from surface outcrop is not practical or too
expensive, there are several possible field techniques giving measurements that correlate with
the degree of jointing or the mean size of in situ blocks such as drill core recovery, rock
quality designation and seismic velocity. Palmström (2001) presents a practical overview of
these methods to assess the degree of jointing and the conversion to mean in situ block
volumes. Logging of borehole drilling rate and resistance force or down-hole sonic velocity
measurements (Rat, 1973; Allard and Blanchier, 1980) are alternative indirect approaches.
These are sometimes referred to as measurement while drilling (MWD) techniques (Segui
and Higgins, 2001).
Discontinuities in most rock masses can be classified into sets according to their orientations.
There are usually three sets, because rock masses of orthogonally jointed bedded
sedimentary sequences are common. For a greenfield site investigation, with poor outcrop
exposure, borehole orientation is critical if discontinuity spacing data is to be recovered from
all major discontinuity sets. In many circumstances, vertical drilling is the only practical
approach to sampling the rock mass. Such investigations will focus on the plan-shape
variability of vertical spacings and intact rock strengths deduced from drill core recovery. In
general, a more extensive site investigation yields greater cost savings. Data from core
recovery can be used to assess the average in situ block dimensions using the weighted joint
density method of Palmström (2001) if both spacing and obliquity of the discontinuity to the
core axis is logged. This method is given as the final IBSD method, see below.
In addition to logging discontinuity spacings from recovered solid cores, down-hole
visualisation surveys of joint traces using open-hole drilling can be a fruitful investment.
These provide the data needed to assemble an IBSD prediction as the discontinuity
orientations in space are detected.
With the rapid advances in digital imaging, semi-automated geological face mapping,
including joint mapping, is being developed for input to many rock mechanics application
software packages. These systems may soon enable IBSD to be determined rapidly from
computer software, without manual mapping of joints. Related research and commercial
software can easily be located using internet searches with terms such as services, automated,
joint, “rock slope”, laser, imaging, technology, software. Until these systems become more
robust and can generate joint set and spacing data (an example of such technology
developments is described by Slob et al, 2005), manual, photo-analysis and laser-assisted
scanline mapping offer the best practical means to obtain complete IBSDs.
Assessment of test blasting in a potential quarry area is of limited value unless the 3D
variability of discontinuity spacing, eg to depths and in regions that are of potential interest,
is also evaluated.
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g
e
c
Schematic illustration of quarry yield prediction. a,b,c: before, during and after multi-row
high-fragmentation blast in aggregates quarry; d: in situ blocks in intensely jointed quartzite
showing two discontinuity sets with mean spacing of ~0.4 m, which indicates that this
aggregates quarry cannot produce heavy armourstone (1 m scale bar bottom right); e:
aggregates blast and high fragmentation in aggregates quarry, low armourstone yield
mainly from blocks liberated from stemming section; f: in situ blocks in outcrop of gneiss
from proposed greenfield site for armourstone quarry with mean joint spacing of ~2m; g:
armourstone blast in aggregates quarry, large armourstone yields from loosened blocks
Figure 3.49
b
f
d
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2
3
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4
5
6
7
8
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3.9.2.1
Scanline mapping of discontinuities
IBSD assessment begins with discontinuity data acquisition and analysis. The method
described here in brief is the scanline method (Figure 3.50). Wang (1992) divided the
scanline methods into two kinds.
!
Quick scanline. This just gives the location of each joint intersection along a scanline,
with respect to an origin taken at one end of the scanline. Usually a measuring tape (eg
of 30 m) is stretched out along a direction for which plunge and azimuth are recorded.
It may be possible to generate quick scanline data from photographs, from laser surveys
(eg using quarry face profilers) and also from borehole walls and cores.
!
Detailed scanline. The orientation of each discontinuity plane is measured using a
compass clinometer and noted together with the intersection of that plane (or its
projection into space) along the scanline. Figure 3.51 shows a data entry sheet for such a
survey. It is useful to code the degree to which discontinuities persist, for example less
than 3 m may be assumed as the maximum trace length to indicate non-persistent (n)
and all the rest as persistent (p). Many modern joint pattern analysis programs also
require the discontinuity trace-length and truncation geometry to be recorded. Further
discussion on discontinuity identification is given in Section 3.2.2.
NOTE: The purpose is to represent the IBSD of the 3D volume of the rock mass in its
condition prior to detonation. Blast-induced fractures from backbreak of a previous blast
round may significantly alter the pattern seen in a quarry face from that given by natural
geological discontinuities alone. Blast-induced discontinuities will not generally extend far in
from the surface and may be discounted from the discontinuity survey or have a low
persistence attributed to them.
Using scanline data and simple methods developed in the rock mechanics field (see Box 3.24)
it is possible to apply Wang’s equation method for IBSD assessment.
3.9.2.2
IBSD by Wang’s equation method
Step 1
The principal mean spacing PMS (m) for the three sets is determined as explained in Box
3.24. Alternatively, the Karzulovic and Goodman (1985) algorithm can be programmed to
give PMS values from quick scanline data.
Step 2
Determine the three characteristic angles α (°), β (°) and . (°) that define how far these three
sets diverge from the orthogonal condition. The angles between all three pairs of normals to
sets A, B and C are equal to 90–α, 90–β and 90–.. Therefore, α, β and . can be easily found
from an equal angle stereonet plot of the three poles using the standard method for finding
angles between directions. Because of their interdependence, it is not important which pairs
are assigned to each of α, β and . .
Step 3
Plot the principal spacing data as histograms and assign the most appropriate principal
spacing distribution.
Step 4
Apply Equation 3.68 using values from Table 3.25. This equation was calibrated originally by
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Wang (see Wang et al, 1990) using statistical simulations, hence the so-called “equation
method”:
Vi , p = Ci , p ⋅
PMS A PMS B PMSC
⋅
⋅
cos α cos β cos .
(3.68)
where p = 10, 20 … 100 (%); and Vi,p is the volume of in situ blocks, denoted by the subscript
i, at a particular percentage passing value given by the subscript p.
For example, the in situ block volume at 50 per cent passing, Vi50 (m!), will be given by
Equation 3.68 using the coefficient Ci50 from Table 3.25, depending on the distributions of
the spacings observed. If in doubt, either the exponential or lognormal choice for all three
sets is considered to be a reasonable assumption. For certain sedimentary rock masses, a
uniform distribution, where all spacings are equally common, may be appropriate for
bedding spacings and used together with two exponential sets. Further discussion of the use
of this equation method is given in Lu and Latham (1999).
To illustrate the use of Table 3.25, if all three discontinuity sets are taken to have an
exponential spacing distribution and, for example, PMSA = PMSB = PMSC = 1.0 m and the
mean set orientations are orthogonal, the 50 per cent and 80 per cent passing volumes for
the IBSD are: Vi50 = 2.7 m! and Vi80 = 8.9 m!.
2
3
4
When performing an IBSD analysis based on data where discontinuity persistence has been
recorded (see Figure 3.51), it is often valuable to consider spacing data that:
!
include both p- (persistent) and n-coded (non-persistent) discontinuities (see Box 3.24) to
provide a lower bound for IBSD
!
include only p-coded discontinuities to provide an upper bound to the estimated IBSD,
see Box 3.27, Case History B.
In predicting IBSD for armourstone evaluation, when distributions are not known, the uniform
distribution assumption and the inclusion of both p- and n- discontinuities gives a smaller and
thus more conservative estimate of IBSD for the range of armourstone sizes of importance.
Table 3.25
5
6
Coefficients, Ci,p (-) for use with the equation method of IBSD assessment for a range of
function types
Vi,p (m!)
Exponential for
three sets
Uniform for three
sets
Exponential for two
+ Uniform for one
Lognormal for three
sets
Vi10
0.332
0.375
0.420
0.469
Vi20
0.710
0.700
0.825
0.949
Vi30
1.207
1.052
1.282
1.511
Vi40
1.852
1.460
1.824
2.225
Vi50
2.708
1.939
2.487
3.094
Vi60
3.980
2.548
3.325
4.283
Vi70
5.867
3.343
4.439
5.949
Vi80
8.948
4.495
6.151
8.498
Vi90
15.332
6.623
9.144
13.376
Vi100
38.922
17.772
24.905
38.207
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Box 3.24
Scanline data and discontinuity spacing analysis
This box presents the terminology and methods needed to generate an IBSD prediction using Wang’s
equation method.
Figure 3.50
Scanline mapping showing spacing between discontinuity sets and example
measurements. a: non-persistent discontinuity: length < 3 m; b: persistent discontinuity:
length ≥ 3 m; c: spacing (DS); d: principal spacing (PS); e: Set A; f: Set B; θ is the angle
between the scanline and a line normal to a discontinuity set.
Discontinuity data mapping sheet
General information
Job number 1
Quarry name: Scandanavian
quarry
Rock type: Granite
gneiss
Number of tape: 1
Tape attitude: azimuth Tape plunge angle: (+/-) 15
176
(down)
Sheet number: 1 of 5
Discontinuity data
Intercept
No
Type
(m)
1
2
3
0
Start scanline
0.00
1
Joint set A
2
Joint set A
4
Attitude
Dip direction Dip
Persistence Remarks
4
5
6
2.00
358
48
p
3.90
360
46
p
Joint set A
6.05
348
50
p
6
Joint set A
7.75
10
46
p
7
Joint set A
9.85
340
45
n 1.4
8
Joint set A
10.80
358
42
p
3
Joint set B
4.15
190
73
p
5
Joint set B
7.20
212
68
p
9
Joint set B
12.10
175
65
p
7
Notes: Tabulated data are shown after plotting on a stereonet has enabled sorting into sets and
reordering. Calculation of mean spacing, MS (m), for each set then uses the classified intercept values,
see Figure 3.50. Persistence: p – persistent discontinuity, n – non-persistent discontinuity with length
given in (m). Rock engineers seek an unambiguous way of defining the orientation of a discontinuity
plane. The best way is to refer to the dip direction (0° to 360°) measured clockwise from North, ie an
azimuth direction. For the direction a ball would roll down an inclined plane where the dip or dip angle (0°
to 90°) is the angle measued from horizontal of the ball’s trajectory, ie its steepest path. Note that the
strike direction of a plane is at right angles to the dip direction.
Figure 3.51
Illustration of data shown in Figure 3.50 presented on a modified scanline data entry
sheet and representation of discontinuity sets as poles on equal angle stereonet.
Discontinuity sets are systems of discontinuities that have approximately the same inclination and
orientation. As a result of the processes involved in their formation, most discontinuities form in families
that have preferred directions. In some cases these sets are clearly defined and easy to distinguish, while
in others the structural pattern appears disordered. Rock engineers use stereonet software to assist with
contouring poles and grouping sets. DS is the discontinuity spacing, defined as the distance between an
adjacent pair of discontinuities measured along a straight line of a given orientation within or on the
surface of a rock mass. MS is the mean spacing along a particular scanline calculated from the DS values.
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Box 3.24
1
Scanline data and discontinuity spacing analysis (contd)
If joints have been coded as falling into specific sets, various methods (eg Priest, 1993) make it possible
to define the mean orientation for that set and thereby to refer spacings and mean spacings to the normal
to the mean orientation of a given set. Principal spacings, PS, refer to a given set of discontinuities and
are distances between adjacent pairs from the same set – measured along an artificial scanline that runs
normal to the mean orientation of that set. Using a stereonet, it is simple to determine θ, the angle
between the scanline orientation (recorded as the azimuth and plunge of the tape) and the normal to Set
A (the centre of the cluster of poles for Set A, see Figure 3.51). The highly significant principal mean
spacing, PMS, value for Set A can then be determined using the equation PMSA = MSA cosθ . Given that
there are typically three discontinuity sets, it will be possible to obtain PMSA, PMSB and PMSC. This may
require more than one scanline. For more irregular patterns, an algorithm based on giving each joint a
different set number, measuring the minimum angle between two individual sets and replacing the pair
with a single weighted set can be implemented. Continuing this process until only three sets remain yields
the three principal discontinuity sets with their mean orientation.
The distribution of principal spacings for any set may be plotted and their mean and standard deviation
can be found easily. The frequency of occurrence in certain class intervals against spacing value for that
class interval will produce a histogram of the discrete data and then an overall curve fit to the histogram
can represent a continuous function. The spacing distributions are usually described well by negative
exponential, lognormal or more rarely by a uniform function (Figure 3.52). Good fits to data have also been
found for fractal, ie power law, functions (Lu and Latham, 1999). The function type that best fits the data
should be determined. It can often be judged by eye. When combinations of different distribution types
are encountered for each set, it should be noted that weighted interpolation between pure end members
may not provide an accurate solution when assigning coefficients for use of the Equation Method; see
column 3 in Table 3.25.
NOTE: Spacings associated with individual discontinuity sets can be derived from quick scanline data (only
spacings are noted), provided there are sufficient numbers of scanlines and the mean orientations of each
set have already been determined, eg by extensive sampling of the orientations of all the discontinuities
in the domain of interest (see Karzulovic and Goodman, 1985).
2
3
4
5
6
7
Figure 3.52
3.9.2.3
Illustration of three commonly found principal spacing distributions for discontinuity sets
IBSD by the dissection method
The dissection method (Wang et al, 1991b) requires detailed scanline data, carried out in
directions that intersect the main discontinuity sets and therefore adequately sample the rock
mass structure. Computer programs (see Wang et al, 1992b) and internet searches for modern
alternatives will be helpful. Such programs use the co-ordinates of planes of discontinuities
obtained from full records of detailed scanline data (Figure 3.50) containing intercept and
orientation of planar discontinuities, in order to determine the volumes enclosed between the
planes.
8
9
The algorithm is generally organised as follows:
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discontinuity from the data file
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!
dissect these two blocks with the next discontinuity in the file to give three or four blocks
!
continue dissection to the last discontinuity, storing co-ordinates of all corners of all
natural blocks
!
derive block volumes (maximum length and nominal diameter of each block may also be
given).
IBSD analysis using dissection programs will typically have the following steps:
Step 1
The user defines the BOUNDARY BLOCK enclosing the rock mass to be evaluated,
choosing six discontinuity planes.
Step 2
The input file is read giving each successive discontinuity plane, for one or more scanline
segments, and the dissection program is run.
Step 3
The output is analysed in the form of 3D views of the rock mass, histograms, distribution
curves, stereoplots of discontinuity poles etc, as illustrated in Box 3.27 Case History B.
3.9.2.4
IBSD by 3D stochastic network modelling
Another approach starts by characterising each joint set measured in the field using the best
fit distributions for dip angle, dip direction, spacing and persistence (see Box 3.24 for
explanation). A program is then used to randomly simulate the pattern created by
intersecting discs or other geometries with the appropriate size distribution so that a
stochastic network geometrically resembling the measured joint pattern is created. In relation
to rock-blasting simulation, IBSD results were obtained this way; see Aler et al (1996). Other
programs – see, eg, Dershowitz et al (1998) – can also generate an IBSD that will have a
statistical matching of discontinuity geometries to the measured ones. It is usual to run a
Monte Carlo simulation to obtain many realisations of the IBSD and adopt an average IBSD.
Such approaches are often considered most appropriate where block patterns are very
irregular. See also Thornton et al (2002) for a discussion of stochastic modelling of
fragmentation.
3.9.2.5
IBSD from drill core data
The volumetric joint count, Jv (1/m), is a measure of the number of joints intersecting a
volume of rock mass expressed as the average number of joints per cubic metre. Jv is
generally calculated from the sum of the reciprocals of each principal mean spacing (ie Jv =
1/PMSA + 1/PMSB + 1/PMSC) and can also be calculated for random and irregular jointing.
Palmström (2001) proposed a block shape factor, β (-), typically set to a value of β = 36 when
it is not known, which, when multiplied by Jv-! , gives the estimated average block volume,
Vi50, assuming an orthogonally jointed rock mass. By considering the likely largest and
smallest spacings typical of the various joint sets, upper-bound and lower-bound Jv estimates
can be generated, which similarly can provide an approximate maximum and minimum in
situ block volume.
Palmström also suggested a simple method for obtaining the weighted joint density, JDw
(1/m), which is similar to the volumetric joint count, Jv (JDw ≅ Jv), given either 1D core
recovered data or 2D data obtained from surfaces. The 1D weighted jointing measurements
that can be made on drill cores to give JDw are obtained as follows:
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!
while core logging, measure the angle, α (°), between core axis and the dip (angle) of
each discontinuity and assign weightings to each joint:
−
Joint weighting: f = 1 for α > 60°
−
Joint weighting: f = 1.5 for 31° < α < 60°
−
Joint weighting: f = 3.5 for 16° < α < 30°
−
Joint weighting: f = 6 for α < 16°
!
count the number of joints (n1, n2, n3, n4) within a given core section length of interest, L
(m), having each of the four possible joint weightings f =1, 1.5, 3.5 or 6 respectively,
associated with the obliquity of the joint.
!
calculate the weighted joint density, JDw (1/m!), using Equation 3.69:
3
The value of JDw may be interpreted as having units of per metre cubed. It may then be
used identically to Jv as a means to assess typical in situ block volume, Vi50, representative of a
sampled section length of core. An examination of, say, 5 m lengths of sampled core sections
with the most intact lengths of recovered core might be used to estimate the maximum in situ
block volume, Vi100, for the quarry area as a whole.
4
The potential drawback is that the interpretation is often based on vertical drill cores that, in
spite of the weightings, may not be capable of representatively sampling the discontinuities
that slice up the rock mass. Horizontal drilling and/or drilling perpendicular to major joint
sets, to supplement vertical drilling, is recommended.
Blasting and blast design
This section first provides the reader with a brief introduction to those blasting factors that
concern armourstone and aggregates production (Section 3.9.3.1). The fragmentation
process is briefly described (Section 3.9.3.2). The basic differences between aggregates and
armourstone blast design are presented (Section 3.9.3.3) and practical measures often found
useful to maximise the yield of armourstone are discussed (Section 3.9.3.1).
3.9.3.1
2
(3.69)
JDw = [(n1 × 1) + (n2 × 1.5) + (n3 × 3.5) + (n4 × 6)]/L
3.9.3
1
5
6
Factors affecting blasting for armourstone
Certain aspects of armourstone production require attention to details that are not usually
emphasised in the extensive literature on blasting, eg JKRMC (1996), Jimeno et al (1997),
Persson et al (1993). The focus with armourstone production is on larger stones than for
normal fragmentation blasting. The aim of any blast is to produce more stones of the size
and form that will facilitate subsequent operations and lead to minimum overall costs. The
blast design is a significant process in securing desired fragmentation but there are many
difficulties to overcome, not least because there are many factors affecting fragmentation
beyond the control of the blast engineer.
7
8
Uncontrollable factors
!
discontinuity spacings and orientation (bedding, joints, faults, cohesion across planes)
!
strength and elasticity (rock type, weathering characteristics)
!
density, porosity, permeability
!
presence of water in blastholes, fractures and joints
!
spatial variations of geology and rock types in general.
9
10
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191
3 Materials
NOTE: All of these factors are essentially geological characteristics of the rock mass or due to
weathering. While uncontrollable, these factors may generally be measured and their effect
taken into account in the blast design. In situ block size distributions can be assessed using
the techniques described in Section 3.9.2.
Controllable factors
!
the properties and detonation methods of the explosives used, including delay timings
!
the blast design (configuration and drilling pattern).
Successful blasting engineers work to clearly defined objectives such as the required size
distribution results, ease of blastpile digging and minimum disruption to the next blast. They
apply theoretical understanding of the mass fragmentation process and rock mass
characteristics, knowledge of the effects of using different explosives and detonation
techniques, environmental constraints and, lastly, experience and expertise in combining
these, which may include the assistance of blasting software. The most important
fragmentation objectives for armourstone blasts are:
!
blasting for improved yields of heavy stones in specially set-aside faces of aggregates
quarries
!
blasting for improved or reduced yields of stones blocks in dedicated quarries.
The economics of the second case are constrained by a need to produce, as far as is possible,
only the material demanded by the design. This may require that secondary breakage is
embraced fully as a means of production when setting the blasting objectives (See Box 3.28).
3.9.3.2
Fragmentation processes
In Box 3.27, the manner in which the in situ bedding, jointing and other discontinuities slice
up the natural rock mass into blocks of predefined shape distributions and size distributions
before blasting is illustrated (see Figure 3.60). The concentrated release of energy from
explosives detonated in confined blastholes transforms the IBSD to a BBSD of finer material
(Figure 3.49). The sudden very high gas pressures in the blast causes shockwave
transmission, compressive crushing near the hole, radial tensile fracturing and slabbing
tensile cracking at free faces. Fracturing and fragmentation are accompanied by gas flow into
cracks, extending them further. The explosive gas, assisted by gravity, heaves the blocks away
from the face and into the blastpile. The ability to achieve a desired BBSD depends on
knowledge of the IBSD, the strength and persistence of the natural geological flaws and:
3.9.3.3
!
other uncontrollable factors such as strength, elasticity and density that contribute to the
inherent ease of breakage or blastability of the rock
!
blast energy mobilised through the blast design.
Comparison of armourstone and aggregates blast design
Design of an aggregates blast aims to minimise excess oversize (and expensive secondary
breakage) keeping the average BBSD to < 10 per cent exceeding about 3 t while ensuring
not too much rock is reduced to useless fines by excessive blast energy. Typically, a specific
charge of 0.4–0.7 kg/m! of Anfo (kilogrammes of explosive per cubic metre of in situ rock) is
used in a two- or three-row shot to achieve sufficient breakage.
Blasting engineers working on armourstone operations should be aware of fundamental
differences in fragmentation results compared with aggregates blasts (see Figure 3.53) and in
practical blast design, where Section 3.9.3.4 will be of assistance. For an armourstone blast, a
specific charge as low as 0.2 kg/m! is often used.
192
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3.9 Quarry operatXioxnxxs
1
2
3
Notes
Fs is the shape factor, see Section 3.4.2
nRRD is the uniformly coefficient of the size distribution curve, Section 3.4.3.3
Figure 3.53
3.9.3.4
CIRIA C683
Illustration of theoretical scenarios for an aggregates blast and an armourstone blast
applied to the same rock mass. IBSD and BBSD are represented by Rosin-Rammler curves
4
Suggestions for improving the yields of armourstone
Generally, the proportion of armour stones in the blast increases with increasing tensile
strength, increasing Young’s Modulus and increasing discontinuity spacing. Normal blasting
practice (eg for aggregates and ores) aims to achieve high-fragmentation blasts. By contrast,
greater percentages of armour stones can be achieved by adjusting common practice through
consideration of the following (see Figure 3.55 for definition of blasting terminology).
5
1
A low specific charge. Generally, a specific charge as low as 0.11–0.25 kg/m! can be used.
If possible, the explosive used should have lower velocity of detonation, VOD (m/s). For
such low specific charges, maintaining high drilling accuracy is critical to avoid
insufficient rock break-out.
6
2
The spacing-to-burden ratio should generally be less than or equal to 1, with burden
larger than the discontinuity spacing in a jointed rock mass.
3
If the bench is either too high or too low, armourstone production will be poor. For an
initial estimate, bench height could be selected as two to three times the burden. In
planning bench levels, the rock mass from which most armourstones might be produced,
such as thickly bedded layers, should be located nearly at the top of the bench alongside
the stemming section of the holes.
4
A large stemming length, larger than the burden, is usually recommended.
5
A small blasthole diameter. A diameter of less than 100 mm is recommended.
6
One row of holes is found to be better than multiple rows. If permitted, holes should be
fired instantaneously rather than using inter-hole delaying (this may cause high ground
vibration).
7
A bottom charge of high energy concentration is needed for the bottom to break clean away.
8
A decoupled column charge of ANFO (ammonium nitrate/fuel oil) packed in plastic
sausages is effective when a 300–3000 kg range is recommended – the explosives are
evenly distributed, giving quite even fragmentation.
9
A decked charge, to break up the continuity of explosives, will be necessary in most
situations when armourstone greater than 3 t is recommended. The material for decking
can be either air or aggregates.
7
8
193
9
10
3 Materials
The most common objective of an armourstone bench blast is to achieve a BBSD with the
maximum percentage of the largest stones possible. The aim of such a blast is to cause the
minimum of new fractures while having sufficient energy concentration to loosen the in situ
blocks fully and bring the rock face down cleanly. The best achievable BBSD curve will lie
close to and just to the left of the upper part of the IBSD curve, spreading out considerably
at lower sizes, eg see Box 3.27 Case History B (Figure 3.62). Where the mean discontinuity
spacing gives vast in situ blocks, blast design must ensure sufficient breakage to limit the
proportion of blocks above 20 t, which is about the limit for practical handling. A lower
armourstone recovery can often be more economical, even though more rock is eventually
excavated and therefore more is left behind as over-production. Excavation of the blastpile
and keeping good faces and toes becomes more difficult the greater the yields of heavy
armourstone and the lower the specific charge. The rate of output from excavators, loaders
and selection plant is also reduced (Figure 3.54).
Figure 3.54
3.9.4
The influence of armourstone recovery on output of selection plant (courtesy J van Meulen)
Prediction and assessment of yield curves
Several models that allow yield curves to be predicted are given here, together with additional
references to new blastability models and a simplified look-up table for approximating yields
(Table 3.26). Methods for assessment of sizes in a blastpile are identified and case histories
incorporating use of both IBSD and BBSD for armourstone yield prediction are included.
NOTE: Blast terms are provided in Figure 3.55.
Prediction of blasted block size distributions, BBSDs (fragmentation curves, yield curves), is
the subject of significant research effort as the possible error in prediction remains very high.
Accuracy is limited because the geological conditions cannot easily be determined for every
blast and the implementation of the blast design may suffer from practical constraints. For
dedicated quarries, early prediction of quarry yield curves – whether by trial blasts or by
scanline and borehole discontinuity surveys together with blast modelling – plays a vital part
in breakwater design optimisation; see for example the discussions on berm breakwaters
given in Section 6.1.6. Described below are several approaches to fragmentation prediction:
194
!
Kuz-Ram model, Section 3.9.4.1: implemented in many software applications; may be
useful if IBSD is poorly known; care is needed to check that nRRD is realistic
!
Bond-Ram models (BRM), Section 3.9.4.2: make good use of IBSD assessments and are
therefore favoured for armourstone; uncertainty in Bond Work Index limits reliability;
has two different implementations
!
Kuznetsov-Cunningham-Ouchterlony (KCO) model, Section 3.9.4.3: replaces RosinRammler equation in a promising new approach; good for fines assessment; requires
reasonably accurate maximum IBSD assessment if to be useful for predicting
armourstone yields
CIRIA C683
3.9 Quarry operatXioxnxxs
!
simplified look-up table, Section 3.9.4.4: provides an alternative to models; simplified
guidance is read from a table given a minimum of discontinuity data for typical
aggregate or armourstone blasts.
After a trial or production blast, it is essential to be able to assess the BBSD on the quarry
floor. Methods to assess the yield curves that are outlined in this manual include:
!
image analysis, Section 3.9.4.5: illustrates the basis of commercial software and how the
photographic image can be converted to yield curves
!
photo-scanlines, Section 3.9.4.6: provides a method for assessing size distributions from
photographs; no specialised software tools required
!
direct screening and block measurement, Section 3.9.4.7: illustrates practical methods
for sizing the blasted materials, establishing various points on the yield curve.
1
2
3
Summary guidance on selection of methods for predicting quarry yield curves
Experience to date does not point to a single best prediction method. The best practice is
somewhat clearer for prediction in higher fragmentation blasts for mines and aggregates
quarries because there is a growing number of documented studies with the blastpile
assessment accuracy needed (associated with sieving of a sample of the full-scale blast or wellcontrolled image analysis), together with detailed IBSD and rock mass analysis. It remains a
relatively small database if all the blast design variables are to be investigated. Field data from
low-energy blasts where the objective is often simply to liberate in situ blocks for use as
armourstone are even scarcer. The case histories (Box 3.26 and Box 3.27) are illustrative of
the ongoing search for successful armourstone blast prediction methodologies.
If site investigation data is minimal but is sufficient to provide RQD (rock quality designation,
see Section 3.2.2) or PMS (principal mean spacing (m), see Box 3.24) values for the in situ
rock mass, Table 3.26 can provide a starting-point prediction without the need to implement
a blast model.
If a reasonably good estimate of the rock mass factor, A (-), can be made (Box 3.25), but
discontinuity spacing is poorly known, the Kuz-Ram model will provide a complete
prediction curve, but with a value of uniformity coefficient, nRRD (-), that is most likely to be
too high. For example, see the data in Table 3.29, which suggest that nRRD for armourstone
blasts is typically 0.7–0.9. Typical armourstone blasts have lower uniformity coefficients than
high-fragmentation blasts, so it is vital that the correction identified by Spathis (2004) is
applied to all uses of the Kuznetsov equation (Equation 3.71) in BBSD models for
armourstone production.
4
5
6
7
To take advantage of the known importance of the in situ discontinuities, it is invariably worth
the effort to obtain data to estimate the maximum and typical in situ block volumes. The
weighted joint density method (Section 3.9.2.5) using drill core data is suitable in poorly
exposed greenfield sites when scanline surveys and photographic face mapping are impossible.
8
If a thorough site investigation can reveal the essential variations of the in situ rock mass
properties, the IBSD curve giving 100, 80 and 50 per cent passing values will help the
blast prediction considerably. The Bond-Ram models make good use of the whole IBSD
and if the work index, Wi, is sufficiently well calibrated for the rock mass in question, they
appear promising. An advantage is that they do not rely on an accurate maximum in situ
size, and focus on the 80 per cent passing sizes that have greater significance for
armourstone production.
9
10
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3 Materials
The KCO model approach appears to be suitable for predicting the smaller sizes (below 50
mm) of any blast. It also appears that if IBSD analysis methods are used to constrain Db100
(≈ Di100) accurately it may work very well. At present, one must chose from two approaches
offered for setting the curve undulation parameter, b (-) (see Equations 3.78 and 3.79). Each
one can give critically different proportions of large blocks between Db100 and Db50, where the
subscript b denotes after blasting. Any future results supporting the simpler empirical
Equation 3.77 and the successful setting of rock mass factor, A (-), and Dbmax (m), will help
consolidate the wider use of the KCO model in armourstone blast prediction.
If a breakwater design is to be finalised on the basis of a best prediction of average yield for
the whole dedicated quarry, it is sometimes advisable for the yield curve prediction to be
conservative and not overly optimistic about obtaining large percentages of the bigger block
sizes. To settle for slightly smaller sizes in the prediction gives the blast engineer the option of
using greater fragmentation if and when there is a tendency to over-produce very large
blocks, and hence to keep production closely on track with the prediction. By contrast,
refining the blast to produce more large blocks is only rarely feasible. Once the design has
been finalised upon a predicted yield curve and a maximum quarry utilisation, every effort
should be made by the quarry production team to produce to that curve.
Once the quarry has been opened, blast assessment is essential and weekly yield curves,
indicators of IBSD and production blasting data should be actively analysed. It will often be
possible to use one of the prediction models suggested above and to calibrate it further for
the intrinsic properties of the rock mass (eg Bond Work Index Wi, rock mass factor A) and
methods in question, so that, for example, the specific charge can be adjusted to
accommodate regional variations of IBSD in the developing quarry.
3.9.4.1
Kuz-Ram Model
Cunningham brought Kuznetsov’s (1973) work up to date, introducing the Kuz-Ram Model
in 1983. Later revisions to Kuz-Ram, Cunningham (1987), included improved estimation of
the rock mass factor A based on Lilly’s (1986) blastability index. There are three important
equations that by simple substitution of parameters, give the BBSD curve. The use of the
Kuz-Ram, or similar models, requires caution. Factors of recognised importance such as
detonation delay timing are not included in Kuz-Ram, while the effect of rock mass structure
and the burden-to-spacing ratio need careful consideration (Konya and Walter, 1990).
(i)
Rosin-Rammler equation
This equation (Rosin and Rammler, 1933) provides the basic shape of the BBSD to be
expected in terms of Db50 and nRRD, giving the fraction passing, y, corresponding to a certain
sieve size Dy (see also Section 3.4.3.3):
nRRD
)+  1   D y nRRD +
)+
 D y  +
y = 1 − exp ln  ( 
exp
.
≅
1
−
−
0
693


( 
( 
2 D
 Db50  +
+    b50  +
+
(3.70)
After Db50 and nRRD have been determined from Equations 3.71 and 3.72 below, substitution
of Dy values will return fraction passing values from which the complete BBSD curve can be
deduced. For a BBSD prediction focused on armourstone sizes of say, 0.1 m to 1–2 m, the
Rosin-Rammler equation is considered the most attractive simple choice. It should be noted
that where data from sieved or photo-analysed blastpiles deviate surprisingly from the RosRam fitting function near the maximum sizes, this could be attributable to the inherently
poor sampling of the coarsest fraction, which can throw the measured results out from the
average production in question. Furthermore, various shortcomings of the Ros-Ram equation
were noted including:
!
196
reported as sometimes giving a poor fit to blastpiles with high yields of armourstone sizes
(Lizotte and Scoble, 1994)
CIRIA C683
3.9 Quarry operatXioxnxxs
!
failure to give a clear maximum size because the function is asymptotic to the 100 per
cent passing value
!
commonly unable to describe with reasonable accuracy the fines content below sizes of
about 50 mm in a blast. This is of particular concern for predicting the detailed nature
of the quarry run and the resultant behaviour of core materials derived from the quarry.
1
2
(ii) Kuznetsov equation
The Kuznetsov equation gives the blasted block size at 50 per cent passing, Db50 (in m not
cm) as a function of (A, V, Q, E), which locates the position of the BBSD curve:
V 
Db50 = 100 A  (
Q
0.8
 E 
⋅ Q 0.167 ⋅ 
(
 115 
0.633
(3.71)
where:
A
=
rock mass factor (-); A =1 for extremely weak rock, A = 7 for medium rock,
A = 10 for hard, highly fractured rock; A = 13 for hard, weakly fractured
rock. Several schemes now exist for improved estimation of A eg using Lilly’s
original blastability algorithm, see Cunningham (1987), Widzyk-Capehart and
Lilly (2002), the essential parts of which are given in Box 3.25
V
=
volume of rock broken per blasthole (m!)
Q
=
charge concentration per blasthole (kg)
E
=
relative mass strength of explosive (-); for ANFO: E = 100 and for TNT: E =115)
Q/V
=
specific charge (kg/m!), a general measure of explosive power in the blast.
Spathis (2004) pointed out an implicit assumption in Cunningham’s Kuz-Ram application of
Kuznetsov’s original equation. The assumption is increasingly invalid for lower nRRD values
typical of armourstone blasts because the mean size differs more significantly from the
median size as nRRD decreases. Spathis plotted the correction needed as a function of nRRD,
which indicates that for nRRD as low as 0.8 the characteristic size, Db50, would be 1.8 times too
large if Equation 3.71 is used without the correction. This could in part explain why
uncorrected applications of the Kuz-Ram model often give overly coarse predictions of
armourstone blasts, as they typically have low uniformity indices, eg nRRD of 0.7–1.0.
3
4
5
6
(iii) Cunningham’s uniformity index algorithm
This empirical formula (Equation 3.72) derived by Cunnigham (1987) determines the
steepness of the BBSD curve, nRRD (-), as a function of blast design geometry (see Figure 3.55).
7
NOTE: There is no significant body of evidence from sieved distributions to support
Equation 3.72. Still it remains widely used.
B  
S 

nRRD =  2.2 − 14 ( ⋅ 0.5 1 + ( 
d  
B 

0.5

 W    BCL − CCL 
⋅ 1 − ( ⋅ abs 
( + 0.1
B  
L



0.1
⋅
L
H
(3.72)
8
where:
CIRIA C683
d
=
blasthole diameter (mm), typically minimum of 70 mm
B
=
burden (m), see Figure 3.55
S
=
spacing between blastholes (m)
BCL
=
bottom charge length (m)
abs (x)
=
absolute value of x
CCL
=
column charge length (m)
L
=
total charge length (m), L = BCL + CCL
9
10
197
3 Materials
H
=
bench height or hole depth (m)
W
=
standard deviation of drilling accuracy (m).
Figure 3.55
Blasting geometry terminology
Box 3.25
Guidance for the determination of the rock mass factor A used in blast prediction
This box provides guidance for setting parameters of the rock mass from which the rock mass factor, A (-),
needed for the Kuz-Ram and KCO models, can be estimated. Only very rarely would a rock mass achieve A
values above 14. For a rock to be considered for armourstone, it is considered likely that A would fall in the
range 9–14.
A = 0.06 (RMD+JF+RDI+HF)
(3.73)
where:
3.9.4.2
RMD
=
JF
=
rock mass description = 10 if powdery or friable, = JF if vertically jointed, = 50 if massive rock
joint factor = joint plane spacing term, JPS + joint plane angle term, JPA
JPS
=
10 if average PMS (eg cube root of the product of three principal mean spacings) < 0.1 m,
20 if average PMS is within range 0.1–1 m, 50 if average PMS > 1 m
JPA
=
20 if the main discontinuity set has a dip direction outwards from face, 30 if it has a dip
direction roughly parallel to the face and 40 if the dip direction is inwards from the face of
the rock mass (for explanation see Box 3.24)
RDI
=
rock density influence = 0.025 ρrock – 50 with ρrock in (kg/m³)
HF
=
hardness factor, depending on uniaxial compressive strength, UCS (MPa), or Young’s
Modulus E (GPa), HF = E/3 if E <50, or UCS/5 if E > 50
Bond-Ram Models
Da Gama (1983) applied Bond’s Third Theory of Comminution to blasting using Bond’s
relation (Equation 3.74 below) to fix the 80 per cent passing size in the blast, Db80 (m).
Bond’s relation was applied together with the Rosin-Rammler Equation 3.70, and
Cunningham’s uniformity coefficient in Equation 3.72, by Wang et al (1992b). They called
this combined approach the Bond-Ram model. It is termed BRM(A) in this manual.
BRM(A)
Bond equation: based on Bond’s Third Theory of Comminution, the reduction in the 80 per
cent passing size during blasting is expressed in terms of the blast energy, W (kWh/t), and a
material property the Work Index, Wi (kWh/t), as given in Equation 3.74:
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3.9 Quarry operatXioxnxxs
)+ 1   1  +
W = 10 ⋅ Wi ⋅ 
(( 
(( − 

+ Db80   Di80  +
(3.74)
where Db80 and Di80 are the 80 per cent passing sieve sizes, after blasting and in situ respectively
(in microns) and W is the energy required for fragmentation and is a function of (E, V, Q, ρrock).
The blast energy, W (kWh/t), can be estimated using Equation 3.75:
Q
0.00365 ⋅ E ⋅  (
V 
W=
ρrock
2
(3.75)
where:
3
E
=
weight strength of explosive (%) relative to ANFO
ρrock
=
rock density (t/m!)
V
=
volume of rock broken per blasthole (m!)
Q
=
charge concentration per blasthole (kg)
Q/V
=
specific charge (kg/m!), a general measure of explosive power in the blast.
The Work Index Wi (in kWh/t) is analogous to Bond’s Work Index for grinding, but is here
calibrated for blasting (Da Gama, 1983) as follows:
 Di 50 
Wi = 15.42 + 27.35 
(
 B 
1
4
(3.76)
where B is the burden (m), see Figure 3.55, and Di50 is the 50 per cent passing in situ block
size (m).
5
NOTE: In grinding, Bond’s Work Index values are known from tables for grinding of
different ores, or they are determined by grinding experiments. Such index values may be
misleading if used directly in blast models without a correction factor.
NOTE: The empirical coefficients in Equations 3.74–3.76 have dimensions that take account
of the indicated units, such that W and Wi have units of kWh/t.
To apply this BRM(A) model, W and Wi values together with Di80 from IBSD information are
substituted in Equation 3.74 and Db80 is determined. Substituting y = 0.8 and Dy = Db80,
together with nRRD value as determined from Equation 3.72, in Equation 3.70, then gives
Db50, from which the complete BBSD curve of Rosin-Rammler form can be deduced.
6
7
BRM(B)
Chung and Katsabanis (2000) demonstrated that Equation 3.72 gave nRRD values that were
consistently too high compared to results from sieved blastpiles. They suggested linking Db50
determined from Kuznetsov’s Equation 3.71 with Db80 determined from Bond’s theory, as a
means to obtain nRRD in the Ros-Ram equation (Equation 3.12), thereby providing an
alternative to Cunningham’s Equation 3.72. In doing so, the value of nRRD (-) is given
analytically by 0.842/(ln Db80 – ln Db50). This, together with Db50 from Kuznetsov’s equation
(Equation 3.71), was found to provide better Ros-Ram coefficients in Equation 3.70 for
generating final BBSD prediction curves that are closer to field data. This Bond-Ram
approach presented by Chung and Katsabanis (2000) is a promising yield prediction
approach for armourstone production and is termed BRM(B) in this manual.
8
9
NOTE: Wi values for bench blasting for armourstone
To produce more accurate Bond-Ram predictions, further calibration of an appropriate value
for Wi is recommended for quarry bench blasting for armourstone. Da Gama (1983)
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10
3 Materials
suggested the use of Equation 3.76, a relationship derived from empirical studies on a small
dataset of blasts in a basalt quarry. From a back analysis of case histories, results presented in
Lu and Latham (1998) suggested a somewhat lower range of values, eg Wi = 6.7 ± 1.1 kWh/t
for one particular Carboniferous limestone quarry and Wi = 10 ± 4 kWh/t for host rock
from various ore mining blasts. Lower values of Wi imply greater ease of blasting into small
pieces. Blasting engineers wishing to adopt the Bond equation for blasting are advised to
consult recent research, eg Kahriman et al (2001) to guide the choice from the values
suggested by Da Gama for basalt (~25 kWh/t) and the significantly lower value of 10 kWh/t
as suggested above and recently by Chung and Katsabanis (2000), or calibrate their own casespecific Wi. The range of possible values for Wi for rock masses considered in the Bond-Ram
model appears to extend from about 5 kWh/t to 40 kWh/t.
Approaches that see the blasting process in terms of the work done to overcome the inherent
blastability of the rock mass during a dynamic comminution process are becoming more
widely used.
3.9.4.3
KCO model
In recognition of the poorer fit in the fines region of the two-coefficient Ros-Ram and power
law equations, more complex equations with four or five curve-fitting coefficients have been
introduced. These curve shapes can overcome the underestimate of fines often found with
Rosin-Rammler curves and are designed to account for more complex combinations of
breakage mechanisms such as fine scale crushing near the borehole, fines development
occuring along propagating branching cracks, and the coarser fragmentation by tensile
cracking (Djordjevic, 1999; Kanchibotla et al, 1999). Ouchterlony (2005a) has proposed a
three-parameter cumulative size distribution function, f(y), with no reduction in curve fitting
accuracy, given here as Equation 3.77:
y=
1
  Db max  
 ln 
(( 
  Dy  
1+ 
D

 ln  b max ( 
  Db50  
(3.77)
b
where:
Db50
=
medium size of blasted stone (m). It is given by Equation 3.71
y
=
percentage passing finer (%)
b
=
curve undulation parameter (see Equations 3.78 and 3.79)
Dbmax
=
upper limit to the fragment size (m). It can be taken as equal to the largest in
situ block size, Di100 or either the burden or spacing if smaller than Di100 .
When introducing the correct parameters into Equation 3.77, the equation becomes a BBSD
prediction model. A suitable name proposed for the model is the KCO (KuznetsovCunningham-Ouchterlony) model.
Ouchterlony (2005a) has proposed two methods for predicting the value of the curve
undulation paramater, b (-).
1
The first is to adopt Cunningham’s uniformity index, nRRD (-), from Equation 3.72 and
to also introduce the relationship of Db50 (m) and the size distribution’s slope. A good
approximation for b (-) was found, given here as Equation 3.78:
 Dbmax 
b = nRRD ⋅ 2 ⋅ ln ( 2 ) ⋅ ln 
(
 Db50 
200
(3.78)
CIRIA C683
3.9 Quarry operatXioxnxxs
2
The second is to use an empirical formula (Equation 3.79), derived from sieved results
from many full-scale blasts (Ouchterlony, 2005b):
 Dbmax 
b = 0.5( Db50 )0.25 ⋅ ln 
(
 Db50 
(3.79)
The function presented in Equation 3.77 fits BBSD sieving results from a wide range of rock
types and blast conditions remarkably well and plugs into the Kuz-Ram model with ease,
improving predictive capability in the fines range and the cut-off at the upper limit,
especially if a good Di100 estimate can be substituted for Dbmax .
Its suitability for armourstone blasts also looks promising. It is suggested that the KCO model
offers great potential in most bench blasting operations. For armourstone blast prediction, as
with all prediction models, it should be applied with caution, especially as it has been
developed for blasts with relatively higher specific charges and burden to spacing ratios than
is common for armourstone blasts. It should also be noted that many unconventional blasting
methods such as decoupling and simultaneous detonation are used for armourstone blasts.
Accuracy of the KCO model and the function given by Equation 3.77 has not been examined
as thoroughly in the 80–100 per cent passing size range where it is most critical for
armourstone prediction, as for the medium and smaller sizes.
3.9.4.4
1
2
3
4
Simplified guidance for BBSD prediction
To give a quick prediction of armourstone yields when the above methods cannot be applied,
it may be instructive to make one quick characterisation of the joint spacing in the rock mass
such as the average PMS value . An RQD summary value, if that is all that can be
determined, may give an indication, but with poor reliability. One can then classify the
potential quarry yields into three ranges, I, II and III, assuming the rock mass has three
orthogonal sets, each with the same PMS and negative exponential spacing distribution and
using concepts developed from Wang’s Equation Method given above. Table 3.26 shows a
range of PMS values: from 0.1 m to 1.2 m covering almost all characteristic PMS values likely
to be encountered in natural rock masses. Column 2 of the table shows how the spacing may
appear much smaller if a scanline runs obliquely and cuts all three sets; the figure given is for
the minimum possible mean spacing. Traditionally, discontinuity spacings along a borehole or
from core logging are described in terms of the RQD (rock quality designation value),
defined as the proportion of scanline or borehole core that consists of intact lengths of 0.1 m
or longer. The RQD is highly dependent on the direction of the borehole or scanline and
columns 3 and 4 show the ranges of RQD for the different PMS values of this orthogonal
system.
NOTE: A reduction in the 50 per cent passing size from 0.2 m in situ to 0.1 m blastpile is a
size reduction factor of 2 and a volume reduction factor of 8. Similarly, a uniformity index
such as nRRD given for a quarry material in terms of size is a factor of 3 higher than if given
for volume or mass, ie nRRD = 3 nRRM .
5
6
7
8
9
10
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3 Materials
Table 3.26
Rapid assessment of in situ and blasted block sizes (Vi80 and Vb80) relating
to the principal mean spacings (PMS) (Wang et al, 1991a)
MS (m)
Max
RQD
(%)
Min
RQD
(%)
Vi80
in situ
(m!)
Vb80 = Vi80 /6
armourstone
blast (m!)
Vb80 = Vi80
/20
aggregates
blast (m!)
%
Vi >1.2
(m!)
Range
0.1
0.06
74
48
-
-
-
-
I
0.2
0.12
91
78
0.1
-
-
-
0.3
0.17
96
89
0.2
-
-
-
0.4
0.23
97
93
0.6
0.1
-
7
0.5
0.29
98
95
1.1
0.2
0.1
18
0.6
0.35
99
97
1.9
0.3
0.1
30
0.7
0.40
99
97
3.1
0.5
0.2
40
0.8
0.46
99
98
4.6
0.8
0.2
52
0.9
0.52
99
98
6.5
1.1
0.3
62
1.0
0.58
100
99
9.0
1.5
0.5
70
1.1
0.64
100
99
11.9
2.0
0.6
75
1.2
0.69
100
99
15.5
2.6
0.8
> 80
PMS
(m) (*)
II
III
Notes
Based on Carboniferous limestone and a specific charge of ~0.2 and ~0.4 kg/m! for armourstone and
aggregates blasting respectively.
* PMS in the table can be replaced by the cube root of the product of all three PMS values.
For PMS = 1 m, Vi80 in column 5 indicates the 80 per cent passing volume is 9 m!. Table
3.26 gives the complete percentage passing values. From Vi80, the 80 per cent passing volume
after blasting, Vb80 has been calibrated assuming a volume reduction factor (geared to the 80
per cent passing value) of 6 for armourstone blasting and 20 for high-fragmentation blasting.
These factors are thought to be reasonably general although obtained from full-scale trial
blasts in a limestone quarry; see Case History A, Box 3.26. Clearly, volume reduction factors
must depend particularly on specific charge, rock type and burden spacing details. The
application of a volume reduction factor for armourstone blasting to the case of in situ blocks
of 1.2 m! will result in a block volume of 0.2 m! or block masses of just over 0.5 t for most
rock types. The percentages given in column 8 and assigned for each PMS might therefore
be taken as the maximum percentages of heavy armourstone blocks (ones larger than 0.2 m!)
assuming an effective armourstone blast has been used. Table 3.26 shows three ranges of
PMS values with the following significance:
3.9.4.5
!
Range I: PMS < 0.4 m, virtually impossible to produce more than 5 per cent blocks
heavier than 0.5 t
!
Range II: 0.4 m < PMS < 0.9 m, necessary to maximise the percentage of large blocks
heavier than 0.5 tonnes
!
Range III: PMS > 0.9 m, a very high percentage of large blocks including mammoth
blocks may result from a blast designed to maximise large blocks. These may be
disruptive. An optimum blast designed to produce the maximum percentage of blocks in
the range defined in the contract blocks should be sought.
Mass distribution assessment by image analysis
Automated image analysis methods are becoming more widespread for determining blastpile
size distributions in mining and quarrying operations. Digital photographs taken while piles
are being loaded (so as to represent the full depth of the pile) and taken from above truck-
202
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3.9 Quarry operatXioxnxxs
loads provide input that readily available image analysis software will convert into size
distributions using sophisticated correction algorithms. A blind trial of various commercial
image analysis software packages (Latham et al, 2003) gives a snapshot of their performance.
Figure 3.56 shows images with known size distributions of the type often used to calibrate
image analysis software. Franklin and Katsabanis (1996) compiled a monograph of papers
and references to such methods.
At least half a dozen commercial automated sizing systems are now in widespread use, not
only for blast yield assessment, but also for production control of processed minerals. There
is potential for wider use of such systems in quality control of gradings, eg barge deliveries of
light gradings.
1
2
3
4
5
Figure 3.56
Typical blastpile size distributions with
similar appearance. Scale divisions = 1
m; P44: nRRD = 0.7, D63.2 = 800 mm, D50
~ 460 mm; P41: nRRD = 0.9, D63.2 = 350
mm, D50~240 mm. The same distributions are shown in Figure 3.53. Note that
Kuz-Ram often predicts nRRD > 1.0
3.9.4.6
Photo-scanline methods
An alternative simple method for analysing photographic data (Lu and Latham, 1996) that
can be undertaken without software is to superimpose scanlines directly on the scaled
photographs. Many scanlines are drawn on each photograph with directions chosen to
minimise bias. As with any image method, care is needed to correct for perspective distortion.
A single length distribution from measurements of segment lengths defined by intersections
between the particle edges is created from all the photographs making up a representative
sample. It is invariably found that the cumulative form of this length distribution has a RosinRammler form. The best fit photo-scanline Rosin-Rammler parameters nRRDp , D63.2p , for
uniformity and characteristic length can be obtained from a linearised plot. To convert the
Rosin-Rammler equation to a linear form, substitute the left-hand side of Equation 3.80 as
the variable Y and log Dp as the variable X and apply linear regression of Y on X to obtain the
gradient and intercept, which give nRRDp and D63.2p.
  1 
log ln 
(  = nRRDp ⋅ log D p − nRRDp ⋅ log D63.2 p
  (1 − y ) ( 
6
7
8
9
(3.80)
10
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203
3 Materials
Equations 3.81 and 3.82 are the calibration equations to convert from segment length
distribution coefficients (denoted with subscript p) to nRRD and D63.2:
D63.2 = 1.119 D63.2p
(3.81)
nRRD = 1.096 nRRDp – 0.175
(3.82)
As for any assessment of blastpiles that sample only the surface-visible blocks, the results are
likely to give coarser BBSD predictions than is representative of the entire pile. Taking many
sample photographs during blastpile loading is preferable.
3.9.4.7
Direct screening and stone measurement methods
It may sometimes be practical to count the number of stones N in the entire potential
armourstone oversize material in a blast, and to perform measurements of stone dimensions
from a representative sample of, say, N/5 blocks. The sizes can be converted to masses using
shape factors based on blockiness. Knowing the total rock mass in the blast and estimating
the total mass in the oversize, the upper part of the BBSD can be plotted (see Box 3.27,
Case History B Figure 3.62) and may be merged with photo-scanline or image analysis
results.
In a production with no crushing, it is possible to assess the proportions in a blast if it is all
processed. Yield curve data presented in Ouchterlony (2005a) is exclusively based on such a
sieve analysis of blasts. The sorted material volumes are logged during production through
the selection plant (eg trommel screen, see Section 3.9.7). Provided the coarsest proportion
from the blast can be estimated, for example by counting stones in heavy grading classes or
as described above, a curve based on assessment at three points can be drawn. In Figure 3.57,
three important points on the yield curve were used to chart the change in BBSD while
reducing specific charge.
Figure 3.57
204
Use of a three-point method to characterise fragmentation and demonstrate the
decrease in Db50 with increasing specific charge of ANFO – data from one quarry
(courtesy J van Meulen)
CIRIA C683
3.9 Quarry operations
Box 3.26
1
Case History A: improving armourstone yields in an aggregates quarry
Full-scale trial blasts were conducted in an aggregate-producing quarry with the objective of improving
armourstone yields. Results are summarised in Wang et al (1992b), which includes details of quality
control for gradings, shape and integrity. The limestone quarry has a classical orthogonal pattern with subhorizontal bedding (some healed with many stylolites) and two vertical joint sets seen in the two rightangled faces. Figure 3.58 shows vertical jointing and bedding in the east quarry face, revealing a closely
spaced joint set that was not seen in the main north face of quarry, also partly shown in the far left of the
figure. Data from 13 quick scanlines taken on two faces and the exposed surface of the rock mass at the
top of the quarry were used to generate the statistics for the three sets of discontinuities summarised in
Table 3.27. Wang’s Equation Method was applied using lognormal distribution coefficients from Table
3.25 and the PMS values in Table 3.27. In Figure 3.59, the IBSD is plotted as a zone of possible
distributions considered to represent the extreme possibilities ie by using both all n- and p-discontinuities
and by using only the p-discontinuities. With a rock density of 2.66 t/m³, it may be estimated that about
50 per cent and 70 per cent of in situ blocks are over 2 t and 1 t respectively and that the biggest in situ
blocks may be 15 m³.
2
3
4
5
6
Figure 3.58
Vertical jointing and bedding in the east quarry face of a limestone quarry. The man (in
the centre) indicates the scale
Table 3.27
Summary statistics of measured discontinuity orientation and spacings for each set
Set number
Mean orientation
7
Principal mean spacing (PMS) and standard deviation ( σ)
Persistent and nonpersistent discontinuity data
Persistent discontinuity data
Dip direction
(degrees)
Dip
(degrees)
PMS (m)
σ (m)
PMS (m)
σ (m)
Bedding
261
12
0.598
0.392
0.598
0.392
Joint Set I
90
79
0.399
0.265
0.575
0.301
Joint Set II
185
83
0.659
0.594
1.259
0.969
8
9
Note
For definitions see Box 3.24.
10
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205
3 Materials
Box 3.26
Case History A: improving armourstone yields in an aggregates quarry (contd)
Figure 3.59
In situ and blastpile armourstone size distributions determined from
photo-scanline and oversize stockpile measurements from three
different blast designs in a limestone quarry. Lines based on linking
oversize with photo-scanline determination of Db63.2
Details of three blasts are included in Table 3.28. The oversize stones from each blast were measured in
detail and combined with photo-scanline assessments of Vb50 giving the line plots shown in Figure 3.59.
Blast no 1 was a conventional high-fragmentation blast producing 8 per cent armourstone. The average
volume of these stones was relatively small, with no stone over 10 t. By modifying the blast design with
burden-to-spacing ratio of about 1.5 and a low specific charge of 0.2 kg/m³, a yield of 22 per cent
armourstone was achieved. An important observation was that the directly measured largest stone sizes
in blast no 3 were almost as large as those predicted by the IBSD analysis. Therefore, it was unlikely
further significant improvement in yields of armourstone could be made by blast design. Important
conclusions were: (i) determination of IBSD will help the blasting engineer know when an armourstone
blast has been optimised; (ii) integrity and shape were not significantly changed by the variations in blast
design during this study. Note some results presented above appear contradictory. Db50 for blasts nos 1
and 3 appear similar, whereas the Kuznetsov equation (Equation 3.71) suggests the different specific
charge should have increased it by some 43 per cent in blast no 3. Different spacing/burden ratio or
locally different IBSDs provide the most likely explanations for this apparent inconsistency.
Table 3.28
Details of three blast designs
No 3
Drilled geometry
No 2
Burden, B
(m)
5.00
5.02
5.34
Spacing, S
(m)
4.04
4.35
3.47
No of blastholes
(-)
13
13
13
Total amount of explosive (ANFO equivalent)
(kg)
2584
1767
1383
(kg/m!)
0.358
0.227
0.205
Percentage of armourstone sized blocks > 0.18 m! or 0.48 t
(%)
8.5
11.3
22
Mean size of armourstone
(m!)
0.474
0.449
0.563
Percentage of armourstone containing at least one flaw, F
(%)
22.9
24.2
25.4
Mean value of LT (= l/d)
(-)
2.3
2.31
2.37
Percentage of armourstone blocks with LT > 3
(%)
11.3
14
12.3
50 per cent passing block volume in blastpile using photoscanline methods, Vb50
(m!)
0.0175 0.0172 0.0191
Armourstone
206
No 1
Explosives
Blast round:
Specific charge, Q/V
CIRIA C683
3.9 Quarry operations
Box 3.27
1
Case History B: Assessment of armourstone potential
An aggregates quarry required an evaluation of the armourstone potential of the quarry. The investigation
considered IBSD analysis of four zones in the quarry using the dissect method (Wang et al, 1991b); see
Figures 3.60 and 3.61. The BBSD from an armourstone blast design was assessed with photo-scanlines
across the blastpile surface and by direct block measurement of oversize (> 3 t) material. These blastpile
assessments were compared with predicted yields from blast models (Figure 3.62). Using actual blast
design parameters and IBSD information, the Bond-Ram model, BRM(A), was found to fit the oversized
part given by measured blocks and to predict slightly smaller sizes than the photo-scanline assessment
of the blastpile surface . It was considered unlikely that the blast design could be improved significantly
since the upper part of the predicted BBSD curve and largest blocks assessed in the blastpile were of the
same size as those predicted from the IBSD analysis (3–10 m³). The blast model that produced yield
curves in close agreement with measurements was then used to provide the quarry with suggested blast
designs to maximise armourstone. Yield predictions were provided for various parts of the quarry. This
example is based upon work by McKibbins (1995).
2
3
4
5
Figure 3.60
Computational dissection of rock masses – left: from Zone B (2100 m³); right: Zone D
(975 m³) – using discontinuity location and orientation data from three perpendicular
scanline segments
6
7
8
Figure 3.61
9
IBSD summary from dissect method yielding many thousands of individual block
volumes. Zones A and B are highlighted as being better suited to armourstone
production than Zones C and D
10
CIRIA C683
207
3 Materials
Box 3.27
Figure 3.62
3.9.5
Case History B: Assessment of armourstone potential (contd)
Example of blasting analysis result. IBSD curves, produced by considering only persistent
discontinuities (coarser IBSD) and all discontinuities, define an envelope for IBSD in Zone
B. The BRM(A) Bond-Ram model for BBSD provides the best prediction of yields for this
blast design based on comparison with assessment of the blastpile using the photoscanline method and by direct oversize block measurements. The photo-scanline survey
sampled only the surface blocks in the blastpile
Matching yield curves and demand
The procedure for matching a quarry yield curve with the demand for different tonnages of
the various armourstone gradings is useful for any quarry but is particularly useful in
dedicated quarries to:
!
plan production
!
consider the potential benefits of secondary breakage
!
calculate the amount of quarried but wasted material
!
optimise the design of berm and conventional breakwaters with regard to maximum use
of quarried materials.
Given any predicted average BBSD yield curve for the production in a quarry, an
approximation may be defined by Rosin-Rammler coefficients such as M50 and nRRM. It is
then instructive to present, on the same plot, the proportions required for different
armourstone gradings. For example, berm and conventional breakwater designs may require
very different proportions of the larger stone sizes, which can lead to significant differences
in the utilisation of quarried materials. Judicious use of secondary breakage may sometimes
help to avoid leaving behind vast amounts of material.
Having obtained the predicted BBSD yield curve that will form the basis of the quarry
production assumption, the yield fraction curve is transformed by differentiating the BBSD
curve. Finally, these values are divided by M50 given in tonnes, to make the area under the
new curve equal to 1.
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CIRIA C683
3.9 Quarry operations
1
The yield fraction per tonne plot can be obtained from the Rosin-Rammler coefficients as
follows:
n
RRM
1
 My 
0.693nRRM 
(
M 50
 M 50 
y pt =
−1
nRRM 
)+
 My 
+
exp −0.693 

(
M
50


+
+
(3.83)
For a given mass My in tonnes, the ypt value gives an approximation for the fraction of the
blast that lies within the range My ± 0.5 t. So that complex grading requirements can be
converted, demand and yields are considered within 1 t bands. If, for example, there is a
large order for breakwater armourstone, including 20 per cent of material of 3–6 t, this design
requirement, ie demanded volumes, would be represented by a bar that occupies 0.2 of the
area under the curve or is 0.2/3 units high between mass values of 3–6 t. This can then be
compared directly with the area under the ypt curve between 3 t and 6 t that represents the
proportion of quarry yield falling within this range. A good match means the 3–6 t
requirement is compatible with the rest of the order, but other ranges must also match well if
quarry utilisation is to approach 100 per cent.
The methods of matching yields and demands are illustrated in Box 3.28 and explained
further in Vrijling and Nooy van der Kolff (1990) in the context of comparing utilisation of
quarried material given alternative breakwater designs, and in Latham and Wang (1992) for
consideration of armourstone supply rates. Note the yield fraction per metre curves may also be
formulated using the derivative of any cumulative yield curve function or an equation
equivalent to Equation 3.83 but presented in terms of sizes. Examples of average production
yield curves are given in terms of the best-fit Rosin-Rammler parameters in Table 3.29,
together with supplementary blast design data. These average figures were obtained from
back analysis of materials supplied to breakwater projects over extended production periods
targeting different armourstone size requirements.
Table 3.29
3
4
5
Examples of yield curves in dedicated quarries, after Vrijling and Nooy van der Kolff
(1990) (courtesy J van Meulen)
Is
MPa
Density
t/m!
M50
kg
M80
t
Sieve D50
m
nRRM
= nRRD/3
Q/V
kg/m!
Target
kg
Diorite
-
2.70
39.19
0.435
0.289
0.35
-
-
Greywacke sandstone
-
2.67
5.13
0.042
0.147
0.40
-
-
Granite
-
2.67
347.63
8.192
0.601
0.267
-
-
Granite
-
2.67
295.58
6.965
0.569
0.267
-
-
Basalt
-
2.80
210.45
2.85
0.50
0.323
-
-
Lapilli tuff
-
2.71
5.32
0.088
0.148
0.30
0.175
30-150
Granite
9.7
2.64
4.88
0.115
0.145
0.267
0.325
500-2000
Granite
9.7
2.63
29.91
1.107
0.267
0.233
0.225
2000-5000
Andesite
7.4
2.76
14.12
0.523
0.204
0.233
0.216
60-300
Shelly limestone
1.0
1.89
15.8
0.279
0.241
0.293
0.431
500-2000
Limestone
5.8
2.66
9.89
0.366
0.184
0.233
0.265
1000-3000
Dolomitic limestone
4.7
2.70
95.62
1.586
0.389
0.30
0.133
4000-8000
-
2.65
23.98
0.887
0.247
0.233
-
-
Rock type
Granite
2
6
7
8
9
Notes
Is = point load strength index (MPa)
Q/V = specific charge (kg/m!)
Target = blast design target, ie armourstone mass range to be produced in largest proportions. To
convert from mass to sieve size, express mass in tonnes, divide by density (t/m!), take the cube root to
obtain nominal diameter, Dn (m), then divide by 0.84 to obtain sieve diameter, D (m).
CIRIA C683
209
10
3 Materials
Box 3.28
Matching quarry yield and rock volumes demanded by any given design
A worked example of how production can be planned to reduce costs by maximising utilisation of a quarry
is illustrated using the yield fraction per tonne, ypt, diagram (Figure 3.63) and an example spreadsheet
(Figure 3.64).
Figure 3.63
Example of matching quarry yield with armourstone requirements in a contract
Areas within dotted rectangular bars represent requirements for 1–3 t and 6–10 t armourstone as a
fraction of the total breakwater materials demanded. Similar plots with different scales can be used to
examine the 0–1 t materials. Areas within solid rectangular bars represent ideal fractions for total quarry
utilisation. These rectangles are drawn after obtaining the ypt curve, where in this case BBSD is described
by M50 = 24 kg, uniformity index, nRRM = 0.233 (equivalent to 63.2 per cent passing nominal diameter of
350 mm, and nRRD of 0.70, as given in the spreadsheet presented in Figure 3.64). It is apparent that the
largest shortfall factor of about four times exists for the 6–10 t grading. The detailed armourstone
requirements total 197 500 t and this would require about 800 000 t of material to be quarried, a 25 per
cent quarry utilisation.
Analysis of the ypt diagram illustrates the potential for secondary breakage of > 10 t to make up the
shortfall of 6–10 t and for the unrequired 3–6 t to match almost perfectly the extra 1–3 t needed, assuming
a certain efficiency loss during secondary breakage. The spreadsheet further illustrates the detailed
implementation of the production plan that achieves a much better 61.8 per cent use of quarried rock.
NOTE: This example shows clearly that blasting for large armour stones is required, here 6–10 t, although
an examination of 60–300 kg and 300–1000 kg is also of interest. If the requirement for 6–10 t had been
much lower, obtaining the smaller gradings would have been critical. Blasting could then have been
directed towards a more favourable BBSD for such an order, ie it would have focused on producing slightly
greater fragmentation to generate smaller product.
From a simple estimate suggesting that the unit rate for both routine quarrying and for secondary
breakage was €1.5 per tonne, and with totals from production plus secondary breakage of 352 322 t, the
price per tonne of ordered rock would be 352 322/197 500 × €1.5 = €2.68/t.
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Box 3.28
1
Matching quarry yield and rock volumes demanded by any given design (contd)
Quarry production demands
Quarry yield prediction and matching
Total demand eg for
breakwater contract
Mass (NLL value)
Production
Production from BBSD
prediction
Balance
Secondary breaking of
>10 t (65% efficiency)
Balance
Secondary breaking of
1-10 t (90% efficiency)
Balance excess
Classes of material
Assumptions: BBSD by Rosin Rammler curve with nominal block size
at 63.2% passing, Dn63.2 = 350 mm, nRRD = 0.7 , ρrock = 2.65 t/m!
(t)
(kg)
(%)
(t)
(t)
(t)
(t)
(t)
(t)
> 10 t
10 000
6000
3000
1000
300–1000 kg
60–300 kg
1–60 kg
fines
0
7008
-10 492
12 108
1616
-1616
0
11 728
11 728
11 728
-11 728
0
23 336
836
836
-836
0
30 466
-8909
3260
-5650
5650
0
43 836
-11 789
3260
-8529
8529
0
94 375
31 875
31 875
31 875
90 139
90 139
90 139
90 139
4
5
6
57.7
62 500
1.0
0
71.5
55 625
60
-18 628
81.0
39 375
300
18 628
88.3
22 500
1–3 t
18 628
92.0
0
3–6 t
3
94.2
17 500
6–10 t
2
20.2
197 500
Quarry utilisation = 61.8%
319 514
0
122 014
0
122 014
7
Total secondary breaking = 32 808 tonnes
8
9
Figure 3.64
CIRIA C683
Spreadsheet analysis together with predicted BBSD yield curve for planning the
matching of quarry yield with demand (courtesy J van Meulen)
10
211
3 Materials
3.9.6
Quarry layout
The production of armourstone will influence the organisation and possibly the layout of the
quarry. The purpose of the present section is not to present the details of quarry organisation
but rather to highlight key issues that should be considered by producers of armourstone or
clients when visiting a quarry that may produce armourstone. The impact of armourstone
production on the quarry organisation will in fact depend on the quantity, the grading and
the type of production of armourstone.
3.9.6.1
Extraction face
Extraction of armourstone may not be possible from all extraction faces. The selection of the
appropriate quarry face is heavily controlled by the geotechnical properties of the rock mass,
especially the discontinuity spacing and the natural block sizes for heavy armourstone. This
may limit the number of faces or benches available in the quarry to zones least affected by
discontinuities if heavy armourstone is to be produced (for further discussion see Sections
3.2.3, 3.9.1 and 3.9.2).
3.9.6.2
Sorting and selection
Specific methods for sorting and selection of armourstone are presented in detail in Section
3.9.7. They are generally divided into two categories: fixed heavy equipment and mobile or
semi-mobile equipment. The costs associated with the purchase of heavy equipment are
significant. Moving fixed heavy equipment, such as heavy trommel screens or grizzlies,
around the quarry will incur substantial costs, so it is important to determine their optimum
position. The travel distance of dump trucks from the face to the primary crusher should also
be minimised. For example, a trommel screen close to the primary crusher will enable both
facilities to be fed at their maximum capacity and will reduce the distance that dump trucks
need to travel. Lighter equipment, such as static grizzlies, may be built in-house at lower cost.
3.9.6.3
Secondary breakage
Secondary breakage is an essential technique to adjust the quarry yield to the actual contract
requirement. In other words, the excess of oversized materials can be reduced by breaking
them into smaller required gradings without affecting the total armourstone blasting.
Although, total production of a given grading by secondary breakage is not cost-effective,
when considered in the context of the whole production of the quarry and other required
gradings, it is often the most cost-effective solution (see Box 3.28).
Secondary blasting may be hazardous and should be performed only when no other
technique is possible. Use of black powder may be very efficient. A sufficient area should be
dedicated to ensure safe and productive working conditions for secondary breakage. The
material should be spread out so that the hydraulic excavator equipped with hydraulic
hammer (sometimes called pecker) or other means can reach all the stones easily. It may be
organised in lines between which the breaking, sorting and transport means (from muckpile
to breaking area and from breaking area to the stockpiles) can work without significant
interference. As space management is paramount in armourstone operations, a layout
scheme such as that shown in Figure 3.65 should be adopted for safer working.
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3.9 Quarry operations
1
2
3
4
Figure 3.65
3.9.6.4
Organisation of the working area for secondary breakage
Stockpiling
5
For the organisation of stockpiles, the key principles to follow are to:
!
reduce the travel distance of machines transporting quarried rock from the faces
!
facilitate movement of machines while stocking or loading
!
limit the height of the stock to reduce breakage and spalling if this is of concern (but
note that wide areas will be required).
6
Consequently, stock may be located at different places in the quarry such as:
!
close to the bottom of the extraction face. This may be effective in separating the
armourstone activity from the aggregate activities. It will also limit the number of
handling events and so reduce breakage caused by handling. If the gradient of access
slopes is gentle (say below 5–7 per cent), delivery trucks may even have access for
loading
!
temporary stocks may be laid out in an unused area adapted for secondary breakage or
reselection to take place. Temporary stocks may also be required for the loading of trains
!
when space is available, organising stocks in a dedicated zone of the quarry is a
convenient solution to separate the quarrying activity from the loading activity.
8
Stockpiles are organised to separate the different gradings physically, as shown in Figure
3.66. The organisation of the stockpiling areas should enable machines to circulate easily and
minimise multiple handling when building or when emptying the stockpiles. The area should
have an appropriate floor to avoid the armourstone becoming contaminated with fines and
to enable traffic in all weather conditions. Stockpiles of heavy armourstone may have a
limited number of layers (two or three) if there is concern about breakage. Typical stockpile
capacity may be 100 t in one layer of HM3000–6000 on a 10 m × 15 m area (see Figure 3.67)
or 200 t in two layers. Light or coarse armourstone may be piled to 3 m high and
approximately 1500 t may be stocked on a 10 m × 40 m area. Alternatively, the stockpiling
capacity may be as high as 1.5 t/m² for 6–10 t armourstone, 2.0 t/m² for 3–6 t armourstone
and 2.5 t/m² for 1–3 t armourstone.
CIRIA C683
7
213
9
10
3 Materials
3.9.6.5
Figure 3.66
Armourstone organised in several standard grading stockpiles
Figure 3.67
Stockpiling of armourstone in layer of 3–6 t armourstone. One
layer represents approximately 100 t of stone
Loading areas
Loading by the client generally takes place from the quarry stockpile to minimise handling
costs. Therefore, the quality of the track as well as the slope at the stockpiles should be
appropriate for this type of traffic whatever the weather. Specific attention should be paid to
the simultaneous traffic of on-road and off-road types of truck and the security issues that
this brings. When using reselection for grading control, it should be performed at the time
of loading.
3.9.7
Selection, sorting and processing
This section deals with the production of armourstone and proposes different approaches to
controlling the mass distribution. Aspects related to selection with respect to shape and
integrity are discussed in Section 3.10. When choosing the most appropriate means to select,
sort or process armourstone, the following items should be considered:
214
!
grading to be produced
!
need for secondary breakage and reselection if light or coarse armourstone are to be
produced
!
quantity to be produced
CIRIA C683
3.9 Quarry operations
!
time available before delivery
!
production rate
!
target cost/price.
1
The system generally adopted just after blasting consists of directing suitable excavators to
extract the blocks of heavy armourstone. A wheel loader can then load out the smaller
materials. The purpose is to free the face as rapidly as possible and to avoid having too many
machines congesting the face area. The material should be sent to stations that are best suited
to separate the fractions, eg heavy armourstone to stockpile areas for reselection, light
armourstone to a selection plant (trommel, barsizer, grizzly screen, static grizzly), material
destined to become coarse gradings to a crushing plant.
3
The most appropriate tools should be chosen, from the following three types:
!
fixed heavy equipment – has a high investment and running cost and needs significant
civil work for installation. It can rarely be moved around the quarry once installed.
Examples are high-capacity trommel screen, grizzly sizers or static bars and fixed
aggregate processing plants
!
light equipment – can be moved around the quarry and can sometimes be built inhouse, such as static grizzlies and barsizers
!
non-dedicated equipment may also be used to process armourstone. This can simply be
plant used for aggregate production or other types of machinery that are available at the
quarry for other activities, such as excavators or grabs.
Detailed guidance on machine capacity may be found in any technical documentation of the
manufacturer (see Section 9.3.1 where links to equipment manufacturers’ websites are given).
3.9.7.1
2
4
5
Production technique for heavy armourstone
For heavy armourstone, visual estimation of the mass with marked-up calibrated reference
stones may be sufficient if performed by a trained or experienced operator. The quality of
the operator’s visual estimation should be checked against actual weighing. Specialised
weighing devices are recommended for the largest heavy gradings (greater than ~ 6 t). For
heavy armourstone and the larger light gradings, there are two options:
6
!
for individually handled stones in heavy gradings, armourstone may be selected at the
blastpile and transported directly to the appropriate stockpile
7
!
all oversize stones may be transported to a temporary stockpile that is then reselected.
This may result in higher output rates (see Box 3.29). This is an appropriate way to
ensure quality control of the material during grading preparation.
It is advisable to be aware of grading requirements and whether mass distribution testing will
use the reference method or alternative methods; see Section 3.8.3.2.
8
9
10
CIRIA C683
215
3 Materials
Box 3.29
Reselection of armourstone
Reselection of larger stones can sometimes be at higher outputs than selection at the face because the
material is much more single-sized. It should be spread out for machinery to access stones easily. The
principle of reselection is that a loader fitted with a weighing device and forks instead of a bucket weighs
the stones and transports them to stockpiles of standard gradings. If there is doubt about whether the
stock complies with requirements, sub-class stockpiles may be used and the stones placed into 1–2 t,
2–3 t, 3–4 t, 4–5 t, 6–8 t, 8–10 t, 10–12 t stocks etc. An excavator may also be used, but specific
attention should be paid to the organisation of the stocks to minimise the travelling distances. Table 3.31
provides the appropriate size of machine and experience of outputs.
Table 3.31
Relationship between the appropriate machine capacity (t) and size of stone to be
reselected
Equipment capacity
> 10 t
6–10 t
3–6 t
Front-end wheel loader with fork
(bucket not appropriate) (t)
45.0
30.0
22.5
Excavator (t)
60.0
50.0
37.5
27.5
17.5
10.0
Powerfork (t) (to be fitted to excavator)
3.65
3.05
2.30
1.70
1.10
0.60
Average selection rate (t/h)
250
215
160
95
43
15
1–3 t
0.3–1 t
60–300 kg
Not recommended
NOTE: The average output of a front-end wheel loader is difficult to determine since it depends on many
parameters, eg the travel distance.
The final grading is produced by recomposition during loading at the quarry and not at the delivery stage.
Consequently, the final grading may either be a standard or non-standard grading. The proportion of
stones required from each sub-class to create a good fit to the average target grading curve is determined.
Mixing at the construction site will ensure that the proper grading is available for construction.
Table 3.32 gives an example of how to prepare a quality control guide table for a 6–10 t grading with M50
between 8.5 t and 7.5 t. The last two columns can be used as a grading plan for 1000 t used by the
machine driver when loading the trains, barges or trucks. The operator keeps a record of the number of
pieces loaded from each sub-class and once or twice a day a grading curve is plotted. If sizes are drifting
off target grading curves, future loads can be adjusted.
Table 3.32
Heavy grading quality control plan
Sub-class
Cumulative %
in sub-class
Percentage in
sub-class
Tonnage in
sub-class
Average stone
mass (t)
Number of
stones
< 4.0 t
0.0
0.0
0
4.0–5.0 t
2.5
2.5
25
4.5
6
5.0–6.0 t
5.0
2.5
25
5.5
5
6.0–7.0 t
27.5
22.5
225
6.5
35
7.0–8.0 t
50.0
22.5
225
7.5
30
8.0–9.0 t
67.5
17.5
175
8.5
21
9.0–10.0 t
85.0
17.5
175
9.5
18
10.0–12.0 t
91.0
6.0
60
11.0
5
12.0–14.0 t
97.0
6.0
60
13.0
5
14.0–16.0 t
100.0
3.0
30
15.0
2
Total:
1000 t
126
NOTE: Although permitted according to the standard, at this stage there should not be any piece smaller
than the 4 t. This allows for the fragments to be produced during the handling of the materials during
transport and placing.
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3.9 Quarry operations
3.9.7.2
Production technique for coarse armourstone and lighter gradings of light armourstone
1
It is generally not economical to select large quantities of the smaller grades (smaller than
300 kg) using picking with excavators and grabs because of low production rates. The
following methods are preferable:
!
typical aggregate quarry processing plant such as a crusher with customised settings (see
Box 3.30)
!
vibrating screen and grizzly
!
selection hill (see Box 3.31)
!
trommel screen (Box 3.32)
!
bars or static grizzly (see Box 3.33)
!
barsizer (see Box 3.34)
!
sidekick (see Box 3.35).
3
For all such equipment, the following relationship between the opening dimension and the
mass of the (armour) stone may be used:
1/ 3
 M 
Dsp = f ⋅ 
((
 ρ app 
2
4
(3.84)
where:
Dsp
=
upper or lower opening dimension (m)
M
=
upper or lower selection mass required, ie M70 or M10 (kg)
ρapp
=
the rock density (kg/m!)
f
=
shape factor, used here as a guide to equipment settings, depending on the type
of system used for selection, (-).
5
From experience, values of shape factor, f, to give appropriate settings for a range of
methods are as follows:
!
visual selection: 0.60
!
vibrating screening unit: 0.60 × (length of square holes)
!
vibrating grizzly unit: 0.55 × (opening at the end)
!
barsizer: 0.45 × (opening at the tips)
!
static grizzly: 0.40 × (average opening)
!
trommel screen: 0.35 × (square root of the screen hole area).
6
7
NOTE: These values of shape factor, f, have been determined based on data from a number
of quarries and should be considered as rules of thumb for size determination. Where a
precise prediction is required, specific measurement of the produced size should be
undertaken to confirm that the settings are appropriate.
3.9.7.3
8
Production technique for core material directly from muckpile
The selection technique to produce core material directly from the pile of blasted stone
(muckpile) essentially depends on (i) the quality expected and achievable, (ii) the quantity
needed in the contract, (iii) the equipment available at the quarry or the cost of getting it.
9
As identified in Section 3.4.4, there are two types of core material and these have different
means of production.
10
CIRIA C683
217
3 Materials
Quarry run. This category includes everything from the finest material of the quarry yield
up to a maximum size in the blastpile and is best described as 0–M kg. Consequently, the
production simply consists of removing the oversize. This can easily be done with a wheel
loader or an excavator. When using a wheel loader, the large size of the bucket and the
limited visibility of the driver will make it practically impossible to produce a lighter core
material than 0–1000 kg. Using an excavator with a smaller bucket and digging towards the
cabin could produce a 0–500 kg material. Note that the grading of the muckpile gets finer
when digging deeper into it.
Processed core materials. This material is produced by removing both the oversized and
fines, generally by means of a robust static grizzly (see Box 3.33). Due regard should be given
to the lower cut-off value since it significantly affects the amount of by-product for which an
alternative use should be found. Changing the lower limit from 1 kg to 5 kg may effectively
lead to rejection of an extra 10 per cent of quarry yield (see also Section 3.4.4).
3.9.7.4
Technologies for the different selection or processing methods
This section presents different techniques or tools suitable for armourstone production,
illustrated in Boxes 3.30–3.35 as follows:
!
crusher (Box 3.30)
!
selection hill (Box 3.31)
!
trommel screen (Box 3.32)
!
bars or static grizzly (Box 3.33)
!
barsizer unit (Box 3.34)
!
sidekick (Box 3.35).
Vibrating screens and grizzlies may be used for production of coarse grading armourstone
provided they are sturdier than traditional aggregates screens. They can be located after the
primary crusher with possible adjustment of its characteristics to produced gradings with
nominal upper limit up to 100 kg or 200 kg (see Box 3.30). This may be appropriate for
production of gabion stone, for instance. The vibrating screen decks will need to be adapted
to handle the larger stones. Constraining the maximum feed size and the smallest mesh or
hole opening will generally prevent damage. Typical limitations are given in Table 3.30.
Table 3.30
Limitation of screening device to limit damages
Maximum feed size
Minimum passing size
~ 120 kg
~ 100 mm (1.7 kg)
Holed steel plate
~ 200 mm (13.0 kg)
150 mm (5.6 kg)
Woven wire mesh
~ 125 mm (3.2 kg)
75 mm (0.7 kg)
Grizzly
NOTE: It is easier to make round holes in a steel plate in a workshop than to make square
ones. The diameter should be increased by 1.23 times the width of a square hole needed for
a similar screening result. However, a steel plate with round holes has a lower screening
capacity. Bigger screening areas and decks are therefore required for similar production rates.
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3.9 Quarry operations
The use of sidekicks (Box 3.35) may be an alternative to grizzly screens, which are generally
expensive to use. In practice, to process crusher output with a grizzly screen, an appropriate
barsizer is hung at the end of the conveyor belt. The top size of the grading is thus controlled
by the crusher setting, the bottom size by the setting on the barsizer.
When using traditional aggregate facilities to produce armourstone, special attention should
be given to the capacity of the conveyor belt underneath the crusher outlet. The strength,
width, number of idlers and travel speed of the belt will normally be suitable for larger stones
than usual. A rule of thumb is that the width of the belt should be at least three times the
length of the biggest stone (see Section 3.4.3). The travel speed should generally not be more
than 1.0–1.5 m/s, which may necessitate a reduction in crushing rates.
Box 3.30
1
2
3
Production of coarse armourstone with a crusher
When large quantities of gradings lighter than 60 kg are required, processing the quarry run through
grizzlies and bar spacers may not be the most efficient since (i) the size of the feed material may
damage the smaller screens, (ii) the percentage of product in the feed might not be high enough for this
method to be efficient (say 15 per cent minimum for efficiency). Alternatively, 10–60 kg may be
produced with a standard size jaw crusher such as would be available in an aggregate quarry. However,
the crusher is generally part of the whole quarry process and using it for armourstone production may
be significantly disruptive.
4
Considering a jaw crusher with characteristic dimensions of width, W (mm), between the fixed and the
moving plate and L the length of the crusher opening, (mm), the maximum mass, M (t), for the crusher
feed without risk of blockage/damage is approximately:
M = 2.3 (L/1000 × W/1000)0.17
(3.85)
The product size is controlled by the closed side setting of the crusher, CSS (mm), that can be adjusted
according to the percentage of product required. Wear of the crusher plates should be taken into account
and the range of adjustment is approximately 50 mm. Table 3.33 gives typical values of settings of singletoggle crushers for production of 5–40 kg to 40–200 kg armourstone.
Table 3.33
5
Setting of single-toggle jaw crushers
Size W × L (mm)
Size W × L (inch)
Min CSS (mm)
Max CSS (mm)
Max grading
Power (kW)
360 × 500
14 × 20
40
75
coarse grading
20
500 × 760
20 × 30
50
115
coarse grading
55
760 × 1067
30 × 42
100
175
5–40 kg
110
1067 × 1220
42 × 48
140
210
5–40 kg
160
1220 × 1500
48 × 59
165
250
10–60 kg
215
1500 × 1800
59 × 71
175
300
40–200 kg
300
6
7
The output of a crusher in t/h is about 0.0016 × L × CSS, where L (mm) is the length of the crusher opening
and CSS is the closed side setting of the crusher (mm).
8
9
10
CIRIA C683
219
3 Materials
Box 3.31
Production of coarse armourstone using a selection hill
To produce core material in which fines are not acceptable, a selection hill may be used where segregation
of the material will take place by tipping the quarry run along the hill. For best results, it should be at least
10 m high. Typical core of 5–500 kg may be achieved (see Figure 3.68).
Safety procedures should be strictly applied. The safest way to proceed is by having the dump truck tipping
on the top of the selection hill and then having a bulldozer push the material over the side of the hill.
Alternatively, a banksman can guide the driver of the dump truck to the edge of the selection hill. In
addition, no activity should take place at the bottom of the selection hill while tipping is taking place,
especially when the quarry run contains large stones that may roll down.
The bottom of the selection hill where the larger stones sit is selectively excavated. The larger stones are
excavated and stocked. The upper size of the grading is controlled by excavating at the face and the lower
size of the grading is controlled by excavating at the bottom of the selection hill. As the slope becomes
steeper, slides will occur that bring finer material down that should then be discarded.
The grading quality of the material achieved is highly controlled by the training and the experience of the
operator.
WARNING: safe procedure is to dump first and then doze over the side, not direct tipping as is shown.
Figure 3.68
220
Schematic view of a selection hill in action. Left: dumping of quarry run by dump truck
under guidance from banksman (not shown) and sorting of larger stones by natural
segregation at the bottom. Right: removal of fines after excavation of the coarser stones
(courtesy J van Meulen)
CIRIA C683
3.9 Quarry operations
Box 3.32
1
Production of light armourstone with trommel screen
Trommel screens are an appropriate means of producing light and coarse armourstone. The facility should
be placed where use of loader and trucks can be optimised (see Section 3.9.6). A trommel screen consists
of a hopper, a reciprocating feeder and a trommel constructed out of rings and spacer bars (see Figure
3.69). The material moves forward by gradient and rotation over and through grids of increasing sizes to
the end of the trommel.
Separation should be sufficient to avoid the different gradings becoming mixed after screening. When a
limited number of gradings are required, the production rate may be increased by placing two identical
barrels together in the trommel at the same dropping zone. Should there be concern about the fines
content of the feed material, the first screening section can be doubled, to reduce the input rate from the
feeder to the trommel at the trommel’s normal rotation speed.
2
3
4
5
6
Figure 3.69
Trommel screen. Top: cross-section of a trommel in action, showing the hopper being
fed by a dump truck and sorted material removed by a front wheel loader; bottom left:
side view, showing the wide separation walls; bottom right: trommel screen viewed
from the hopper (courtesy J van Meulen)
7
8
9
10
CIRIA C683
221
3 Materials
Box 3.33
The use of bars or static grizzly
The static grizzly (set of bars) is a versatile type of selection equipment (see Figure 3.70). It can be used
to remove fines from production of core material as well as to produce coarse or fine material. It may be
built, and the spacing of bars adapted, in-house. Attention should be paid to the length necessary to
ensure effective screening and the angle needed to prevent material becoming stuck on the screen. An
appropriate physical separation should always be made to avoid the separated products being remixed.
Figure 3.70
Left: Static grizzly for
processing of core
materials by fines
removal (courtesy A
Moiset) and right:
Static barsizer for
processing of coarse
and light armourstone
(courtesy J van Meulen)
A static grizzly system is relatively simply made from H- or I-beams and, when properly constructed, can
be quite effective. Screening for only one size is possible, for example taking out the material smaller than
5 kg from quarry run to produce core material 5–500 kg. If the structure is built strongly enough it can
perform well when exposed to routine tough loadings.
It is important to achieve the right balance between the speed the material slides over the bars and the rate at
which material falls through the opening between the bars. If the slope is too shallow, the material will not slide
and blockages may occur. On too steep a slope, the material may slide too fast to fall through the openings.
The sliding speed of the material depends on:
!
!
!
!
the type of equipment used to feed the bars: truck, wheel loader, feeder dumping or trickling
the moisture content of the material: wet material tends to be slower
the shape of the material: round particles tend to be faster
the percentage of fines: material with more fines tends to be slower.
Adjusting the angle of the bars is a difficult and time-consuming operation. Alternatively, the speed of the
material can also be controlled by chains placed over the material flux. These chains may be lifted or
lowered or alternatively their mass can be increased or decreased by adding or removing weights on the
chains. The latter option is generally easier.
Figure 3.71
Static grizzly. Left: side view; centre: top view; right: side view of the grizzly bars from the end
(courtesy J van Meulen)
Components and settings recommended for construction of a static screen are as follows:
!
!
!
!
!
bars should slope at approximately 26–28 degrees
the chain curtain may be made of old anchor chain or old bulldozer tracks
the opening between the bars should diverge from M = 0.8 × Sp (at the top) to Sp (at the bottom),
where Sp is the opening between the bars at the end to ensure that a stone will not get blocked
(Figure 3.71)
the flanges of the beam at the underside should be smaller than the flanges on the topside, to ensure
that a stone will not get stuck when falling through (see Figure 3.71 right)
to avoid any blockage caused by the support connection between the beams, the support spacing
should be at least 2.5 × Sp .
The stones falling in between the bars near the end of the bars will hit against the end wall. This wall
should be structurally strong enough to resist repeated impact of stones. If made of concrete, it should be
protected by a steel plate when the falling stones are larger than 1 kg.
If several gradings are produced by static bars, the width between the separation walls should be more
than the width of the bucket of the wheel loader, ie generally larger than 4 m.
The greater the length of static grizzly, the more efficient it is. A reasonable balance may be found if 6 m
bars – a commonly available commercial length – are used, as they allow a machine to pass underneath
the grizzly, promoting a good recovery rate.
222
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3.9 Quarry operatXioxnxxs
Box 3.34
1
The use of a barsizer unit
A barsizer unit is composed of round bars of axle steel, fixed at one end while the other end can oscillate
freely when hit by stones. Simultaneous emptying and feeding of the barsizer should be avoided to limit
impact to the wheel loader working at the bottom of the barsizer.
2
3
Figure 3.72
View of a barsizer from
the end. Note the free
oscillating bars and
chains to control the
material flux (courtesy
J van Meulen)
The bar diameter is generally 100 mm for stones up to 1.5 t and 115 mm for stones up to 3.0 t. For lighter
gradings, say NUL of 8 kg or 85 kg, bars of 70 mm or 85 mm may be sufficient. The angle for the top bar
varies between 23–26 degrees and for the bottom bar between 28 and 30 degrees depending on the
shape and the moisture content of the stones. The bar length is 2800–3000 mm. The connecting brackets
that fix the bars to a main beam are the main weakness. Possible loosening and movement of the
brackets under repeated use may affect the bar openings at the free end. The equipment thus requires
frequent monitoring and adjustment.
As with the static grizzly, the quality of the product is regulated by the speed at which the material moves
across the bars. The angle of the bars is critical, therefore, and the chains should reduce the speed. The
speed with which the material is loaded on to the bars is also of the utmost importance. A trickle gives a
better clarified product but lower production rates.
When sufficient height is available, several barsizers may be mounted one after the other. A wall or block
face may be used for this purpose – see Figure 3.73. Robust separation walls should be built to separate
the different gradings and to resist the impacts. Experience shows that a reinforced concrete wall with
8–10 mm steel plates can be sufficient for stones of up to 500 kg.
The collection bays should have sufficient capacity, notably the bay that receives the most material, ie the
smallest size of material separated. If not, the selection plant may have to stop when material is collected
from the bays. Since material falls into the bays from height, they may be kept partly full to reduce
secondary breaking due to falling.
4
5
6
7
8
Figure 3.73
View of a set of two
barsizers to produce
gradings. Gradings
being sorted are 0–10
kg, 10–60 kg and
over 60 kg (courtesy J
van Meulen)
CIRIA C683
223
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3 Materials
Box 3.35
The use of sidekick for grading selection
The sidekick, which is generally used to discard balls of clay at the quarry, is an ideal machine for the
production of 5–40 kg and 10–60 kg gradings – see Figure 3.74. The sidekick is installed on the conveyor
taking the material from the primary crusher. The wheels, which turn by the material hitting against the
spokes, push the material over the edge of the conveyor belt to a temporary stockpile. The size of the
stones is controlled by the height of the spokes above the conveyor belt. It is a cheap and simple but quite
effective method and, if available, can avoid the need to modify the plant set-up to accommodate other
equipment. The productivity depends on the crusher setting and output.
Figure 3.74
Examples of sidekicks in operation
(courtesy J van Meulen)
3.9.7.5
Secondary breakage of oversized stones
Secondary breakage may be needed to resize oversized stones or stones in excess of an
armourstone grading class. It can also be used for stones that are wrongly shaped. Secondary
breakage may be a significant part of the activity of a dimension stone quarry if armourstone
is to be produced.
Secondary breakage can be performed using:
224
!
secondary blasting, see Box 3.36
!
drop ball attached to a crawler crane, see Box 3.37
CIRIA C683
3.9 Quarry operatXioxnxxs
!
hydraulic hammer attached to an excavator, see Box 3.38
!
drop ball used by a face shovel, see Box 3.39
!
drop hammer attached to a wheel loader or excavator, see Box 3.40.
Box 3.36
1
Secondary blasting
In addition to reshaping or size reduction, secondary blasting may be used on extremely oversized stones.
This method is a known fly-rock hazard and so should be performed with great care and avoided where
possible. Stone to be secondary-blasted should be carried, if possible, to a safe location out of the way of
the daily operations. Splitting oversized stones with carefully positioned drill holes charged with black
powder is less dangerous and more efficient.
Before drilling, the stone should be examined for any signs of weakness that may affect the blast. Small
holes of 33–51 mm are drilled into the stone in a row, triangle or square pattern, depending on the result
expected. In dimension stone quarries, the machines used for production may be used to prepare the
blasting and generally drill 33 mm holes at the rate of 1.4 m per hour. The depth of the drilled holes is
just over half the thickness of the stone. The specific charge is generally about one-third of the normal
blasting ratio, and black powder, high explosives or detonating cord may be used. The stemming should
be carried out with care to avoid fly-rock. Stemming with water in the drill hole is very effective for high
explosives. The control on the result is poor and the pieces produced may not be useable.
Box 3.37
2
3
4
Drop ball and crawler crane
A drop ball attached to a crawler crane (Figure 3.75) is a low-productivity method to break oversize blocks.
Personnel should keep at a safe distance because of flying stones. An old crawler crane is normally
dedicated to this activity.
The ball is made of manganese steel with a mass of generally 3.5 t to 5.0 t. It is lifted and dropped on to
the stone. The ball may not hit its target every time and the control of the fragmentation size is poor. The
fragments produced may not be useable because of inappropriate shape or size.
5
6
7
8
Figure 3.75
Crawler crane with 3.5 t manganese drop ball (courtesy J van Meulen)
9
10
CIRIA C683
225
3 Materials
Box 3.38
Hydraulic hammer for secondary breakage
A hydraulic hammer attached to a hydraulic excavator (sometimes termed a pecker) is readily available
and therefore frequently used for size reduction and correction of shape (see Figure 3.76). For this
technique to perform well, the appropriate size of hammer and excavator needs to be selected – a small
hammer will only produce chipping.
Based on experience, Table 3.34 gives the relationship between the appropriate sizes of hammer,
excavator and the stone to be broken. The grading to be produced is one class of stone smaller than that
indicated in the table.
Figure 3.76
Hydraulic excavator with 3.5 t hydraulic hammer (courtesy J van Meulen)
Table 3.34
Relationship between the appropriate sizes of hammer, excavator and stone to be
broken
Initial grading
Parameter
> 10 t
6–10 t
3–6 t
1–3 t
0.3–1 t
60–300 kg
Excavator size (t)
60.0
50.0
42.5
32.5
22.5
15.0
Hammer size (t)
4.25
3.50
3.00
2.25
1.50
1.00
Production rate (t/h)
275
225
170
115
65
35
NOTE: When the material is spread out and easily reached by the hammer, higher outputs are possible.
Box 3.39
Secondary breakage using face loader shovel and drop ball
A face shovel with a bottom dump bucket can both pick up a manganese drop ball itself and drop it on to
a stone to break. This breaking can be quite effective but the control over the resulting sizes is poor. The
use of this type of machine is optimum since the drop-balling can be done by the face shovel while waiting
for trucks to load. Reselection of the results is generally required. That is best done by individually
selecting the graded stones required using an excavator with an appropriate grab. The wheel loader can
then clean up the smaller unsuitable stones and fragments. A skilled operator may be able to produce
smaller sizes of stones such as 60–300 kg with no further reselection required other than removing the
fines. The results of secondary breakage can then be collected and loaded by wheel loader immediately.
226
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3.9 Quarry operatXioxnxxs
Box 3.40
1
Drop hammer for secondary breakage
The drop hammer system (Figure 3.77) is not very commonly available, but it is an appropriate tool for
breaking large stones into only slightly smaller stones. Inside a tube, a heavy impactor is dropped on to
the pin at the bottom so that the impact energy for each blow is approximately 5.5 times as high as for a
hydraulic hammer with the same weight of hammer. The high impact energy makes it possible to break
the stones in two while the hydraulic hammer has a much more progressive breakage action.
The hammer can be mounted on an excavator of a smaller size or on a wheel loader. When mounted on
a wheel loader, positioning the hammer into the vertical optimum position is more difficult, but the
production rate for big stones is similar to the rate with a hydraulic hammer.
2
3
4
5
Figure 3.77
Example of drop hammer
mounted on wheel loader
3.9.8
Handling and transport at the quarry
This section provides a brief overview of the types of equipment used to handle and
transport armourstone at the quarry. The handling is generally part of the selection process.
Wheel loaders or excavators working at the plant or the pile of blasted material (the muckpile)
are generally used to separate the oversize stones, feed to and empty from static bars or
trommels etc. Thus the machines used may be equipped with appropriate weighing devices
such as load cells in the hydraulics system or in the structure itself.
3.9.8.1
6
7
Choosing loaders and trucks
The key considerations in choosing the equipment are:
8
!
whether the machine is typically to be used for selection only or for loading
!
whether the target grading implies that bulk or individual handling will be necessary
and also the capacity required
!
the travel distance in the stocks or between the stocks and the working area
!
the availability of reinforced transport vessel bodies, which will permit rougher handling,
assuming that breakage is not a concern
!
protection against contamination with fines.
9
Table 3.35 summarises the types of handling equipment generally used, while Table 3.36
summarises the standard forms of transport.
10
CIRIA C683
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3 Materials
Table 3.35
Characteristics of handling equipment
Equipment
Typical grading size
Comment
!
!
Wheel loader with
bucket
Any, depending on the
capacity
!
!
Wheel loader with forks
(see Figure 3.79)
Any, depending on the
capacity
Excavator with bucket
(see Figure 3.78)
Not suitable for selection of heavy stones.
Care needed to avoid fines (gridded buckets rarely
prevent fines).
Excellent short-distance loading of bulk materials and
individual stones on to barge or train from stock.
Can apply sufficient pressure to engage stockpile for
loading several blocks at a time.
!
Good for individual stones larger than 3 t.
Any, depending on the
capacity
!
Excellent for loading bulk materials at the quarry face.
Can pick out oversize and perform some selection.
Excavator with grid
Any, depending on the
bucket (see Figure 3.78) capacity
!
Excavator with grid
bucket
!
Smaller than 1000 kg
!
!
!
!
Excavator with orange
peel grab
More than 60 kg
!
!
!
Excavator with finger
grab (three tynes)
More than 60 kg
!
!
Can select smaller-sized stones below 300 kg.
Requires shaking of bucket to let fines fall through.
Appropriate for loading but may take fines.
Not appropriate for selection.
Not so good for selection of smaller stones, but
suitable for loading selected smaller gradings, eg up
to 1000 kg (several stones at a time) into dump
trucks without damage.
Appropriate for selection of light gradings.
Can apply sufficient pressure to engage stockpile for
loading several blocks at a time.
Good for selection of individual stones, but grabs are
expensive for stones heavier than 5 t.
Can apply sufficient pressure to engage stockpile for
loading several blocks at a time.
May be expensive to maintain.
Excavator with power
fork (three to five tynes)
(see Figure 3.78)
300 kg to 30 t
!
Very good visual selection of individual heavy stones.
Appropriate for loading of train or flatbed wagon since
it easily permits repositioning of the stone.
Crawler crane with
finger grab
More than 60 kg
!
Outdated; good selection tool but slow.
!
Note
The size of the machine and the type of handling bit should be selected with reference to the grading.
Table 3.36
Characteristics of trucks used in quarries
Truck type
Grading
Comment
!
Off-highway dump-truck
Any
depending
on the
capacity
!
!
!
Road truck and trailer with
aluminium or steel body
< 40 kg
!
!
!
Road truck and wagon with
< 2000 kg
steel body
!
!
!
Road truck and flatbed
trailer
228
> 1000 kg
!
!
Rigid axle or articulated.
For stones heavier than 3 t, loading by excavator is preferred.
Excavators can place the stone in the bucket of the truck
whereas wheel loaders always dump the stones and as a
consequence cause more damage to the stone and the truck.
Care needed to limit fines.
Very appropriate for coarse grading.
Careful loading is required to avoid damage to the trailer.
Very appropriate for coarse grading.
For heavy armourstone say 300 kg to 2 t, the wagon should
have a reinforced steel body.
Careful loading is required to avoid damage to the truck body
Appropriate for any heavy armourstone.
Careful loading is required to limit damage to the trailer.
Locking individual stones with chains on to the flatbed may
be time-consuming.
CIRIA C683
3.9 Quarry operatXioxnxxs
For armourstone production, an excavator may perform several roles at the quarry such as
selection and loading trucks for deliveries. Wheel-mounted excavators may therefore be
preferred to the track-mounted excavators, which are more appropriate for clearing the
blastpile. The cost of re-equipping an excavator with alternative grabs is around 10 per cent
of the excavator cost. This should be considered when preparing the business plan for
armourstone production.
1
2
3
4
5
6
7
Figure 3.78
Use of excavator for handling. Top left: mounted on tracks clearing muckpile and
sorting oversize (courtesy S Dupray); top right: mounted on track with grid bucket
selecting stones after secondary breakage with hydraulic hammer (or pecker)
(courtesy S Dupray); bottom: with high-capacity five-tine power fork at the quarry
for individual handling of heavy stones (courtesy J van Meulen)
8
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CIRIA C683
229
3 Materials
Figure 3.79
3.9.8.2
Wheel loader mounted with a fork used to handle heavy grading
armourstone (courtesy J van Meulen)
Placing wire loops in stones
The contractor should liaise with the quarry production for those cases where the blocks of
armourstone need lifting aids to be attached. For example, the site crane may have to place
some stones that are just beyond its lifting capacity if the grab remains on, but when the grab
is taken off, the stone placement work is done only with a crane and hook. A wire loop or eye
bolt should then be placed in the stone, by drilling, inserting the loop or bolt and grouting in
place, so as to be able to lift the stone with the hook. Eye bolts are not considered good
practice if the rock is to be moved around since it may bend and not be accessible to the hook
after some handling.
Personnel placing the stones should indicate where in the stone the loop is required, taking
into account the shape of the stones and the thickness of the layer in which the stones are to
be placed. In the quarry, the stones are generally placed on their flat side (which is easiest
and natural). However, two of these flat stones placed on top of each other will most probably
be less than the required thickness of the layer, which means that the loops should be placed
in the stones in such a way that when lifted and placed on top of each other two stones make
the approximate layer thickness required.
Because the driller has to stand on top of the stone with a handheld hammer, the stones
should be laid out in a stable position. Smaller stones are more difficult to drill because of
their smaller sizes. Using a drill crawler is often not possible because of the small drill-hole
size required. Consequently the labour costs are high. To ensure satisfactory grouting, the
wire should be completely degreased, so either new wire without grease or degreased old
wire should be used. Suitable resins are available on the market. The holes should be clean of
water and dust before pouring the resin into the holes. The hole has to be filled with resin to
approx three-quarters of the depth before the wire is pushed in. The resin has to cure for a
minimum of three days before the stone is lifted. Characteristics of wire loops are presented
in Table 3.37.
Eventually the wires will rust away. The long-term effect of the wires rusting on the stone is
not known. There is also the visual impact of the wires to consider, especially for those stones
placed above low water and in the outer layer.
230
CIRIA C683
3.9 Quarry operatXioxnxxs
Table 3.37
Wire loop characteristics
3.9.9
1
Characteristics of wire loops as a function of the arnourstone grading
unit
<5t
5–10 t
10–18 t
Diameter drill hole
mm
32
42
42
Depth of drill hole
mm
200
200
350
Distance between the two holes
mm
500
500
600
Diameter steel wire
mm
24
32
32
Length of steel wire
mm
1250
1250
1500
Daily output driller (10 h)
number
45
50
40
Stones per 8 kg resin pack
number
24
17
11
2
3
Loading trucks or trains at the quarry
Truck operatives in the quarry should be aware of the safety regulations that are applicable
and of any specific on-site procedures and restrictions. In particular, they should be aware of
blasting times and of the approved routes to follow. Table 3.38 summarises recommended
equipment for loading of trucks as a function of the grading concerned. Figure 3.80 shows
typical loading of a train and chaining of armourstone on to trucks at the quarry.
4
Table 3.38
5
Types of loading equipment for trucks at the quarry as a function of grading size
Grading
Type of loading machine
< 40 kg
Wheel loader
< 300 kg
Wheel loader, excavator with bucket, excavator with closed-tyne grab
< 2000 kg
Excavator with closed-tyne grab, excavator with powerfork
> 1000 kg
Wheel loader with forks, excavator with large closed-tyne grab, excavator with powerfork
6
Care is required to prevent damage to truck bodies or railway wagons, and to the
armourstone, induced by:
7
!
wheel loader dropping the stones
!
excavator with bucket – loading over the back is least likely to damage the body, whereas
loading over the side gives a smaller target and hence a higher chance of causing
damage
!
excavator with grab – care should be taken when swinging the grab not to catch the sides
of the body
!
excavator with grab/powerfork – with large stones care is required to ensure stones
cannot drop out of the grab/fork and on to the truck
!
movement of armourstone during transit – individual stones may be chained down to
prevent movement.
8
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CIRIA C683
231
3 Materials
Figure 3.80
Loading of armourstone on to truck and train (courtesy
A Moiset). Left: armourstone being chained to truck
3.10
QUALITY CONTROL OF ARMOURSTONE
The purpose of this section is to provide the reader with practical information on the
objectives and methods available for performing controls during production and purchase of
armourstone. The reader may also refer to ISO 9000:2000 for information on quality control
or to EN 13383-1:2002 for information on factory production control as defined in Europe.
Practical information on quality control is given in Laan (1995) and Read (1988).
Quality control consists of the procedures used to monitor and maintain properties of
armourstone. It should be seen not as an incidental extra serving only to increase costs but as
an integral part of production and use of armourstone that will invariably save costs in the
long run. It should be performed with reference to a set of requirements to be achieved as
demanded by the design, eg grading, or with reference to results of initial type tests, eg mass
density or integrity.
Quality control of armourstone focuses mainly on maintaining grading requirements but also
addresses all aspects of rock quality and durability requirements. Quality control is necessary
at different stages of armourstone life and is carried out by different bodies with different
aims (see Table 3.39):
232
!
quality control should take place during armourstone production and should routinely
be performed by the producer, sometimes assisted by a laboratory (see Section 3.10.1)
!
at tender stage, a client should evaluate the quality control processes of potential armourstone
suppliers and also assess their ability to produce armourstone (see Section 3.10.2)
!
during supply, the client may subject the material to quality control before it has left the
quarry or at delivery (see Section 3.10.3). Assistance from a third party may sometimes
be called upon.
CIRIA C683
3.10 Quality control of armourstone
Table 3.39
1
Type of quality control
Stage
Producer
Contractor
Client
Third party
Production (see 3.10.1)
***
*
*
*
Bid stage (see 3.10.2)
**
**
***
**
During supply (see 3.10.3)
**
***
*
**
2
Note
* may be involved under certain conditions; ** involved or may be responsible; *** very involved or
responsible.
3.10.1
Production quality control
3
The quarry is responsible for performing sufficient quality control to ensure consistency of
the production with expected properties. In Europe, the concept of Factory Production Control
(FPC) has been extended to armourstone products. It mainly consists of measurement and
feedback adjustment procedures designed to maintain production of aggregates of certified
quality. Annex D of EN 13383 presents guidance on quality control in the quarry during
production (such as testing frequency). It is clearly the producer’s responsibility to obtain
proper documentation of the procedures and results if product certification and client
satisfaction are to be achieved.
4
Quality control focuses on intrinsic properties and production-induced properties,
especially gradings. A good knowledge of the rock source through evaluation of its ability to
produce armourstone (see Sections 3.2.3 and 3.9.1) is necessary to determine the initial
values of these properties and the optimum quality control of the production. Part of the
quality control consists of ensuring that armourstone is coming from the areas designated in
the extraction plan as suitable for armourstone. Significant variation within the rock source
should be detected by quality control that focuses on petrography, density, porosity and
discontinuity content. For armourstone produced in quarry zones known to have significant
geological variability, the schedule of monitoring both intrinsic and production-induced
properties should be increased accordingly. The production method should also be
considered to determine the optimum quality control, eg quality control of gradings should
be more frequent for eye-selected than for mechanically produced armourstone.
CIRIA C683
6
7
The operator performing the quality control should be trained in the characteristics of
armourstone and the methods used to perform and report the controls. A major effort is
required at the beginning of consignment preparation to establish the best procedures to
adopt. Specific training and equipment may be needed to carry out the following.
!
5
Mass distribution control: a weighing device or load cell on the grab arm is needed to
carry out measurement and control. Their accuracy and precision should be regularly
monitored, eg by repeated weighing of a set of stones or concrete blocks of known mass
corresponding approximately to the mean mass or the nominal limits of the gradings in
question. Before every weighing session, the calibration of the device should be
validated. The controller should be trained to assess visually the mass of blocks of
different gradings, eg by comparing their prediction to actual results of weighings, and
to carry out sampling and grading measurement (see Figure 3.81). During eye-selection
production of gradings, the machine operator should be able to see “visual comparison
stones” for evaluation of the nominal lower and upper limits. Additional visual
comparison stones of average mass generally improve the control of the average mass
and, for steeper gradings, stricter controls may need to be in force. Dedicating one
trained operator to the task of selection helps to control the grading. For mechanical
production, part of the quality control is covered by fine-tuning the choice of bar
spacing, active length and feed rate on to the device, to obtain the desired mass or size
233
8
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3 Materials
distribution of the produced material. If significant change of the input material occurs,
variation in the fines content or shape of particles usually occurs. Wear and damage to
grizzlies and screens is a potential source of drift in product properties and must be
checked frequently.
!
Integrity control: for heavy gradings, the control is generally carried out on each stone
by visual inspection. The controller should be trained by an engineering geologist. For
borderline stones, sonic velocity equipment maybe required (see Section 3.8.5) and it
may be necessary to use an external laboratory to determine the appropriate value to
choose for good integrity stones and to carry out the measurement and determine the
acceptance criteria. Routine dropping of the stones in the quarry may be appropriate
when limited to reasonable drop height such as from the machine.
!
Shape control: the control is generally performed during visual selection. For
mechanical production, shape is a characteristic of the product. Quality control then
consists of ensuring that there is no deviation from the target shape, which would imply
a change in the rock mass. A calliper (see Figure 3.82) is required and the controller
should be experienced with measurement of shape. Witness stones are useful for the
controller to verify borderline shapes. If needed, detailed measurements should be made
for borderline stones of LT ≅ 3, especially for heavy and light gradings.
!
Fines removal and coarse grading: for core material where control of the fines is
required, a bar or static grizzly (see Figures 3.83 and Figure 3.84) are simple means of
mechanically removing fines and are preferable to using a gridded bucket. When
producing coarse and light gradings with mechanical systems, attention should be paid
to the control of cross-contamination and appropriate dividing walls should be installed
as necessary (see Figures 3.69 and 3.73).
Figure 3.81
234
Control testing of mass distributions of a 300–1000 kg standard grading during
production using weighbeams (courtesy A Moiset). This set-up enabled 140 stones
to be weighed per hour
CIRIA C683
3.10 Quality control of armourstone
1
2
Figure 3.82
Use of a calliper for LT
testing and quality
control of blocks for
the determination of
strategically positioned
“visual comparison
blocks” used for
control of shape
(courtesy A Moiset)
3
4
5
Figure 3.83
Short-length static bar
grizzly for fines control
loaded with a front
loader (courtesy A
Moiset). Care is
needed to avoid
damage and blockage
6
7
8
9
Figure 3.84
Large static bar for production of different
grading sizes (courtesy S Dupray)
CIRIA C683
235
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3 Materials
3.10.2
Quarry inspection
For many projects, the client and designer may have identified potential rock sources and
need more information about the source and the quarries’ operational capabilities before
concluding the design or the choice of a quarry. On behalf of the designer, there may be a
need for a quarry inspection that includes a visit to the quarry and some Initial Type Testing
(ITT) to obtain detailed information that the producer does not have to hand such as shape
parameters, eg mean LT and BLc, or integrity parameters, eg sonic velocity, drop test or fullscale splitting test (FSST). These tests will normally have been performed well before the
quality control inspection described in this section. For cases where the structure is designed
to match the quarry properties derived from extensive quarry evaluation (see Sections 3.9.1
and 3.6.3), the data described below will already be available.
Before the signing of a contract, the client should organise a visit to the production and
transport facilities, ie quarry and any loading terminals, to assess its ability to provide the
required material in accordance with the specification and to identify at an early stage any
critical issues that may become a risk for the project. In particular, the inspection aims to
ensure that the quantity and quality of materials, the lead-time for production, the
organisation and the facilities of the quarry are in accordance with the needs to complete the
deliveries in an acceptable condition. If there are no stockpiles, control is not possible and
thus the client will normally insist that stockpiles are available. The client should be aware
that the risk of non-compliance with the specification is much higher if the control is done
during the production. Clients often require at least three days of stock production to be
available on site to perform the control.
Suggestions of guidance for the inspection are given below and a typical aide-mémoire data
sheet (Table 3.40) is provided and can be used as pro-forma. Although intended for the
inspector to complete on the visit to obtain a thorough and consistent appraisal of relevant
aspects of the quarry and its facilities, the producer may wish to keep such records. Attention
should be paid to signs in the rock faces that indicate the rock mass and its quality are likely
to change during the period of supply. The main focus of the quality inspection is to establish
integrity and water absorption, which, if unacceptable, may indicate further information
gathering is not necessary. Photographs of the stocks, extraction faces and production
facilities are generally useful later in the project.
Inspection of the stocks aims to ensure that the quantity and the quality of the armourstone
available, notably with regard to the mass distribution and integrity, are in accordance with
the specifications. Assistance of a third-party laboratory may be needed to determine mass
distributions of material available and to carry out relevant laboratory or in situ tests. In
addition, an evaluation of the stockpile volumes and organisation, independent of the
producer, will provide reassurance that estimates of the lead-time for the quarry to deliver
are realistic. In practice, an armourstone provider without existing stocks of identified
gradings needs longer to prepare the required grading. Planning the visual selection and
stock handling, and, if necessary, secondary breakage or even the opening of additional
extraction faces can add considerable time before the necessary supply rate or delivery date
can be established. The accessibility and means of transporting stock should be studied with
regard to the additional handling that may be required to reach the main transport facility.
The extraction process should be inspected to identify blasting characteristics such as specific
charge, drilling and firing pattern, type of explosive and charge in the column. If any details
on quarry yield in relation to the blasting method are available, eg amount of oversize,
quantity of fines and characteristic sizes, then it is useful to integrate these with any
determination of the quarry yield.
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3.10 Quality control of armourstone
Inspection of the extraction face(s) in the quarry aims to identify and assess the quality of the
production faces and their ability to produce the required quantity of stones. The quarry
faces from where the armourstone is due to be produced should be located on a map (1:25 000
scale is preferable) and their characteristic geotechnical properties noted. These zones should
be inspected and close attention paid to the lithological units exposed and their respective
thicknesses, weathering grade, discontinuity content and variations. Simple indicators such as
colour or grain size should be identified since they are generally useful to help match the
origin of the material in the stockpiles that are being inspected during quality control of the
production. Viewing other parts of the quarry may provide information on alternative faces
for possible extraction. Assistance of an engineering geologist may be required during
inspection or for further investigations that may be needed. Samples from the rock mass may
be taken for further characterisation of the mineral fabric in the laboratory. The conclusion
of this face inspection may be to limit extraction of armourstone to certain faces.
Inspection of the production facilities aims to ensure that the methods and equipment, eg
capacity of machines or characteristics of mechanical sorting devices, are adequate to ensure
the required quality and that they can be used in a reasonable manner. It also aims to
determine the lead-time of production. The inspection should be performed during a
production period to ensure a realistic insight into quarry procedures. The focus of the
inspection depends on the grading concerned and the volumes produced, as both of these
influence the techniques and tools involved. For mechanical production, equipment such as
the primary crusher, grizzly, trommel screen and static bars, their active length and the bar
spacing may be checked; the accuracy of weighing devices such as weighbridges and load
cells on grabs may be controlled; while for visual selection, the accuracy of the mass
classification by operators in the quarry may be checked by weighing some stones. It may be
necessary to sample material and perform mass distribution determination on materials
produced during the visit to ensure that the production techniques are suitable or,
alternatively, to determine the actions to take for the requirements to be fulfilled. The
breakage displayed by armourstone during mechanical sorting may be informative of the
material integrity.
A list of the machine types and capacities available for, or involved in, armourstone
production should be made. Critical situations where there may be a conflict on the use of a
machine should be identified and clarified. For example, during simultaneous visual selection
production of heavy grading and loading, the time periods for the machine with the grab to
be on armourstone work should be carefully split throughout the day or additional, even
dedicated, machines may be required to increase the production. Working areas where visual
sorting or loading is planned should be identified and visited to ensure the floor quality is
suitable so that unwanted fines are not likely to be loaded with the armourstone during
handling, stockpiling or reselection at the quarry.
The loading terminal, ie road, train, fluvial or marine harbour, should be inspected and
information gathered on the sizes and capacities of the machinery, eg to ensure that the
capacity of the grab on the quayside is in accordance with the grading handled. Also, the
period of work can be critical. For example, weather conditions may restrict riverborne
vessels from reaching the terminal in winter or seaborne vessels having access at low tide or
trucks being loaded at night in urban areas. When required, measures to mitigate damage to
the terminal should be identified early, eg placing all-in on a quay to limit damage.
1
2
3
4
5
6
7
8
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Table 3.40
Quarry inspection sheet for quality control by the client
General
Name:
Company:
Contact person:
Function:
Address:
City:
Tel:
Fax:
Date of the authorisation:
Duration of the authorisation:
Other:
Principal use of the quarry: Aggregate quarry [_] Dedicated quarry [_] Dimension stone quarry [_]
Rock source
Geological summary (ages and facies of the source, weathering grade etc):
Geometry (thickness used for armourstone production, orientation of layers etc):
Discontinuities (tectonics and main faults, other geological discontinuities etc):
Geotechnical properties (characteristic values, where available):
Water absorption:
[________] %
EN 13383
Category WA
[________]
Compressive strength:
[________] MPa
EN 13383
Category CS
[________]
Micro-Deval:
[________] %
EN 13383
Category MDE
[________]
LT ratio
[________]
EN 13383
Category LT
[________]
Durability: Category FT [________] Category MS [________];
Category SB
[________]
Mass density:
[________] t/m³
Integrity:
Bn [________] %
Sonic velocity:
[________]; m/s (on blocks)
Others such as sodium sulfate – methylene blue – point load – Los Angeles
Equipment and facilities
Stocking zone: Area _______ ha; capacity _________ tonnes; accessibility for delivery trucks [_]
Handling machinery:
excavator [_]; orange peel grab [_]; dedicated grab [_]; wheel loader [_]
others: _____________________________________________________
Transport: main road
at [______] km – name [______________]
fluvial terminal
at [______] km – name [______________] – capacity [______] t/h
coastal harbour
at [______] km – name [______________] – capacity [______] t/h
train terminal
at [______] km – name [______________] – capacity [______] t/h
Restriction on the use of terminals:
Other information:
Blast geometry
Blast [___] tonne; hole diameter [___] mm; burden [___] mm; spacing [___] m; face height [___] m;
Type of explosive [______]; specific charge [_____] kg/m³; delays [____] ms
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3.10 Quality control of armourstone
Table 3.40
1
Quarry inspection sheet for quality control by the client (contd)
Production of the quarry
Average global production of the quarry [________] thousand t per year
Is grading pre-selection performed? [ Y/N ]
Standard coarse gradings (kg)
2
CP45/125
CP63/80
CP90/250
CP45/180
CP90/180
LM5-40
LM10-60
LM40-200
LM60-300
LM15-300
HM0.3-1
HM1-3
HM3-6
HM6-10
HM10-15
Ratio of the production (%)
Available in stock (thousand t)
Standard light gradings (kg)
3
Average mass controlled [Y/N]
Quarry yield (%)
Available in stock (thousand t)
Standard heavy gradings (tonne)
4
Average mass controlled [Y/N]
Quarry yield (%)
5
Available in stock (thousand t)
Other gradings
Production control
visual [_]
bulk weighing on weighbridge [_]
individual weighing [_]
mechanical sorting [_]
other:
6
Quality of the production in the stocks
Integrity
Good [_]
Acceptable [_]
Resistance to minor breakage:
Shape:
Equant [_]
Durability: weathering [Y/N]
Marginal [_]
Good [_]
Tabular [_]
[___] % (by number) of blocks with major breakage
Acceptable [_]
Elongated [_]
Marginal [_]
7
[___] % (by number) of blocks out of spec
Signs of freeze-thaw damage: [Y/N]
Signs of Sonnenbrand: [Y/N]
Other:
Identification
Inspectors:
Quarry rep:
Date: [_______]
Name [__________________________]
Function: [__________________________]
Name [__________________________]
Function: [__________________________]
Name [__________________________]
Function: [__________________________]
Name [__________________________]
Function: [__________________________]
8
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3.10.3
Quality control during deliveries and construction
This section focuses on the quality control of the material that should be undertaken during
construction and especially during deliveries. It is stressed here that most of the control
should be performed at the quarry to minimise transportation of unsuitable materials. An
aide-mémoire sheet for the client’s controller is given for use either at the quarry or on site (see
Table 3.42). The quality control during execution, ie of the armourstone as constructed, such
as to check construction tolerances for layer thickness, is covered in Section 9.8 and
Appendix A1.
This quality control aims at verifying that the material is in accordance with the
specifications. It is necessary to account for the variation of armourstone properties caused by
the natural variability at the rock source as well as the production technique, ie mechanical
or visual. It should take place, whenever possible, before the delivery has left the producer’s
facilities to limit expenses if a delivery is to be refused. Alternatively, it may take place at a
temporary stockpile or at an appropriate stage of transport. It is recommended to carry out a
detailed control on 10 per cent of the deliveries or at least every 5000 t. This frequency
should be adapted to account for the variability of the extraction or the production, eg increased
for rock sources with high variability, decreased for mechanical production (see Table 3.41).
The frequency of testing should be selected to be representative of homogeneous batches of
production. It should be selected by considering the potential range of variability of the
property. It should also be related to the unit of production, eg weekly production or
delivery schedule. Similarly if the material is taken out by barges, trains or trucks, the
frequency should then be related to the size of these unit loads or sub-units of load. For
example, if the total consignment is composed of two barges, the total load may be controlled
using the bucket of a front wheel loader as sub-unit, so the control may consist of the grading
measurement of a bucket every one-tenth of the loading period.
When temporary stockpiles are used in the project, these should be inspected with regard to
the items listed below. The contractor is generally responsible for this control, but some
clients may mandate a third-party control to be involved. The quality control focuses on the
following items.
240
!
the origin of material is controlled to ensure that the agreed rock source and, if
relevant, the faces selected during the initial visit at the armourstone provider are used.
Indicators such as petrography, colour and grain size are useful for this purpose
!
the mass distribution is controlled. The fulfilment of nominal limits may be controlled
visually by a trained inspector. Guidance is given on quantitative methods in the
armourstone standard EN 13383 in Sections 5 and 6 (Part 2) and requirements are given
in Section 4 (Part 1). Detailed explanations are given in Section 3.8.4. For heavy
gradings, the average mass from each bulk weighing should be calculated, while for
transport by train or road it may be convenient to note the number of stones in each
transport unit. Detailed mass distribution may be determined on the first deliveries and
checks may be made less frequently once mass distribution of deliveries has proved to be
in accordance with the mass distribution of the material at the quarry. This is particularly
important if there is a concern about stone breakage or contamination with fines.
Control of mass distribution is illustrated in Figure 3.85. Specific attention should be
paid to contamination from mixing with other gradings or soils during transport and
temporary stockpiling (see Figure 3.86)
!
visual control of the shape is generally sufficient (see Figure 3.85). Quantitative
determination of shape with reference to EN 13383-2:2002 Paragraph 4.3 should only
be carried by a third-party laboratory in cases of disagreement between the producer
and the client. An example of a stockpile with inappropriately shaped armourstone is
given in Figure 3.87
CIRIA C683
3.10 Quality control of armourstone
!
!
controls of integrity and microcracks should be performed and reinforced where
integrity is a concern. For large heavy gradings, eg above 10 t, borderline stones may be
set aside for further inspection or control of integrity. A continuous inspection may be
carried out by a trained inspector during loading, focusing on the various indicators
such as discontinuity type and extent. This has proved to decrease significantly the
quantity of major breakage where integrity was a concern. Sonic velocity is used in
France monitoring integrity of armourstone during deliveries. The sonic velocity value
determined during initial type testing (see Figure 3.88 for device) and calibrated against
the drop-test is used to ensure no significant decrease of integrity occurs
mechanical sorting devices, once the settings or openings through which stones are
sorted are fixed, will provide a well-controlled production if the input fragmentation or
grading is constant enough. These may be inspected at the beginning of the contract (see
Section 3.10.2) and further inspections performed with corrective actions reinforced, if
non-conformity is observed during deliveries or if the input of fines changes significantly.
In this case, attention may be paid to the wear or loosening of equipment parts that are
mobile or exposed to flow of armourstone. As a consequence of wear or to compensate
for variation at the source, adjustment of setting may be required.
1
2
3
4
5
6
7
8
Figure 3.85
Control of grading at the quarry prior to deliveries. Top left: control of coarse
armourstone, overseen by purchaser and producer representatives (courtesy J van
Meulen); top right: control of light armourstone using a portable grab (courtesy J Perrier);
bottom left: control of light armourstone using a portable grab net (courtesy J Perrier);
bottom right: control of heavy armourstone using portable scale (courtesy A Moiset)
9
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242
Figure 3.86
View of a temporary stockpile of 800–2000 kg where contamination by fine material
and soil is visible (courtesy S Dupray). The board in the front clearly indicates the
grading, which allows drivers to deliver to the appropriate stockpile
Figure 3.87
View of a temporary stockpile of 1000–3000 kg with inappropriate quality control
(courtesy S Dupray). Stones with unsuitable shape and mass are in the deliveries.
The different gradings are hardly separated and distinguished on site
CIRIA C683
3.10 Quality control of armourstone
Table 3.41
1
Guidance on frequency of testing armourstone properties during deliveries
Frequency for mechanically
sorted armourstone
Frequency for individually
selected armourstone
Size – coarse gradings
every 3000–5000 t
N/A
Mass – light gradings
every 3000–5000 t
N/A
Mass – heavy gradings
every 3000–5000 t
every 1500 – 2500 tonnes
Core material – mass
every 10 000–25 000 t
N/A
Property considered
Shape – coarse and light gradings
As for size/mass grading testing (see above), but take into
account the type of use, ie armour or underlayer
Shape – heavy gradings
Visual inspection of 50 per cent of the stones
Integrity
Visual inspection of all stones for heavy gradings; further quality
control may be required for borderline blocks or poor integrity
Rock density, water absorption, durability,
strength (using point load at the quarry)
Adapt based on known variability of the source and the risk of
further weathering: at least every 20 000 t
The procedures to follow in the event of non-fulfilment of specification requirements during
quality control of armourstone during construction should be agreed between the purchaser
and the producer, as early as possible to avoid any delay and discussion while trying to
resolve quality issues. The responsibility for the cost associated with corrective actions should
be agreed beforehand to avoid potential disputes and delays. There are generally three types
of action that may be appropriate depending upon the seriousness of the non-fulfilment.
However, every situation is specific and it is usually possible to avoid stopping deliveries by
quick responsive action between the client and the supplier, the aim being to avoid reaching
a deadlock. In nearly all cases the following applies.
!
!
for conformity and non-conformity of minor concern, corrections may be achieved by
removing individual stones with problematic mass, shape and integrity. Additional material
of precise mass may from time to time be required to correct consignments with borderline
mass distribution. When a tested sample from a stockpile just fails on mass or shape, then a
second sample is made. If the two samples (treated as if a single sample) still fail to meet
the criteria then the stockpile part that the two samples represented is disqualified. The
producer is responsible for the cost of reselecting the whole stockpile. If supplier and client
agree beforehand to a tolerance approach, this repetition of the test may be avoided by
defining ranges of tolerance within which the material fulfils its requirement. The width of
the tolerance should be selected with reference to the sensitivity of the structure to this
parameter and to the precision with which it may be determined
5
6
7
for significant non-conformity, which may be defined in the contract, a delivery may be
refused by the client. The client inspection frequency is then generally reinforced and
might even lead to a systematic overseeing of operations until fulfilment has been reached
8
for major non-conformity, deliveries may have to be interrupted if production has to be
halted. The extraction technique, the production technique and the production quality
control may then be adapted; and the contractor and the producer, and perhaps even
the client, may agree to select new faces in the quarry. In some cases, the contractor
and/or the client may decide to source the material from another provider. The
responsibility for the financial costs should be defined and agreed as early as possible.
9
In some cases, the client, the contractor or the provider may mandate a third-party
laboratory to carry out the relevant testing, measuring and quality control documentation, in
order to evaluate the importance of non-conformity and to propose actions to correct the
deviation and to prevent further occurrences.
CIRIA C683
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4
Note: N/A = not applicable
!
2
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3 Materials
Table 3.42
Information sheet for inspection by the client of deliveries to site
Control during construction and deliveries
Contract: [_____________________________]
Armourstone controlled: Grading: [___________]
Provider [_____________________________]
Place of quality control: Stockpiles [_]; Loading area [_]; Transport [_]; Construction site [_]
Size of the sample: [__________] kg
Armourstone origin
conform [_]; significant non-conformity [_]; major non-conformity [_]
If not conforming, nature of the deviation and correction proposed
Mass distribution
conform [_]; significant non-conformity [_]; major non-conformity [_]
If not, nature of the deviation and correction proposed
Shape
conform [_]; significant non-conformity [_]; major non-conformity [_]
If not,
Fraction (by number) of pieces out of spec [__] %
Correction proposed
Integrity
conform [_]; significant non-conformity [_]; major non-conformity [_]
Drop test was carried out [Y/N]
Sonic velocity measurement was carried out [Y/N]
If not,
Fraction (by number) of pieces out of spec [__] percentage observed during full-scale test or [__]
percentage during handling
Correction proposed
Identification
Controller:
Quarry rep:
3.10.4
Date: [_______]
Name [__________________________]
Function: [__________________________]
Name [__________________________]
Function: [__________________________]
Name [__________________________]
Function: [__________________________]
Name [__________________________]
Function: [__________________________]
Third-party quality control
Producer, contractor or client may seek assistance from an external laboratory or materials
consultancy, to assist during the controls by providing some specific knowledge such as
engineering geology, or equipment such as weighing devices, sonic velocity equipment (see
Figure 3.88) or testing facilities. External laboratories may also be required during the
training of quality control personnel for armourstone operations in the quarry.
In some cases, impartial third-party laboratory expertise is required to sort out discussions
between provider and purchaser. In this case, the role of the third-party laboratory should be
clearly stated. The standards or procedures in question also need to be clearly identified, as
well as the acceptance criteria and associated tolerances. The laboratory should be able to
sample the material freely, in general with the assistance of the quarry, which should provide
handling equipment for heavy gradings. The laboratory should be able to inspect the
facilities and the quarry faces as extensively as required for it to carry out its mission in good
conditions. The third party reports to its commissioning client.
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3.11 Armourstone costs
1
2
3
Figure 3.88
3.11
4
Testing of integrity of heavy armourstone using a sonic velocity concrete
tester (courtesy T Wojnowski). Note the different stockpiles in the
background
ARMOURSTONE COSTS
Costing armourstone material is a difficult task since it depends on many factors related to
the quarry but also to the contract itself. Ultimately, armourstone cost covers the costs of
extraction, production and selection and handling of both acceptable and rejected materials,
together with the subsequent disposal of the latter if required. On average, 75 per cent of the
armourstone cost is attributable to machine costs and manpower.
6
The costs can be divided into fixed and variable elements.
!
!
5
The importance of fixed costs will be relative to the type of quarry considered. For
example, armourstone from a dimension stone quarry (see Section 3.9) is waste material
and may contribute very limited fixed-cost elements to the armourstone production. By
contrast, dedicated or aggregate quarries opening up production faces and special plant
for armourstone contracts will need to recoup all the costs associated with evaluation,
extraction and production. In detail, fixed costs are associated with quarry evaluation
and site investigation (see Section 3.9), overburden removal, adjustment of blasts,
establishing a production face, construction of access roads and possible remediation and
environmental measures such as reshaping the area after extraction is finished. The
investment cost in equipment for an average quarry can be in the range of €3–5 million.
The time required for the preparatory activities for such a quarry is in the order of three
months from the time appropriate plant is on site. Should the site have to be bought,
approval from the different bodies involved may take considerably longer.
Running costs are proportional to the volume of material produced and are associated
with extraction and processing operations such as blasting, mobilisation of equipment for
selection, transport and stockpiling. They are closely related to the grading produced.
Total production costs are generally in the range of €5–8/t. The costs may also have to be
increased to cover royalties and taxes.
7
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Total production costs vary considerably with the type of stone quarried and the annual
output. If specialist equipment is required, the producer may wish to stipulate a minimum
throughput per day for a contract in order to minimise per tonne costs. Stocking and
rehandling of pieces of armourstone is considered to have a high cost. It is generally
accepted that almost two-thirds of the costs are associated with machine mobilisation, which
may be divided as follows:
!
20–30 per cent for drilling and blasting and overburden removal
!
30–40 per cent for loading and selecting at the face
!
20 per cent for transport to the stockpile
!
10 per cent for screening or separation
!
10 per cent for loading at the stockpile before transport.
The key factors that may change this breakdown and thereby alter the final cost of the
material may be summarised as follows (Everist, 1991).
!
primary cost factors: an adequate match between the quarry yield and the uses made of
it, ie use of all the sizes produced in a dedicated quarry, or a good match between
oversize demanded for armourstone contracts and material suitable for aggregate
production in an aggregates quarry. Any significant variation of the quarry yield may
affect the cost
!
secondary cost factors: an adequate match between the timing of the project and the
armourstone production; tonnage of pre- or post-production that may be absorbed to
limit left over material; placing schedule to limit rehandling and stocking at the quarry;
anticipated weather; allowable time for production. If insufficient time is allowed, extra
staff and equipment may be required, which may be costly or disruptive to the general
quarry activity and the quarry may be advised to subcontract some of this specific
armourstone activity.
A good match between the quarry yield and the armourstone production (Section 3.9.4) is an
essential factor that reduces the need for secondary breakage and reselection. Consequently,
contracts with designs that demand a series of gradings with significant gaps in sizes between
them create extra production costs associated with handling, disposing or stocking costs. The
unwanted sizes can be reprocessed by secondary breaking and crushing, which may be costly.
For dedicated quarries, costs may be increased significantly if excess material is generated, ie
if some gradings produced are not accounted for at the design stage, or if large amounts of
fines are removed but not used as aggregates, eg to make concrete armour units. Materials
not used in the project will remain stockpiled in the quarry as waste, a figure of 60–70 per
cent quarry utilisation usually being considered a success. A common pitfall is to
underestimate the volumes of unwanted fines.
For heavy gradings that are essentially produced by hand-picking, the grading itself and the
size of machine affects the picking and placing cost per tonne. Assuming that the materials to
be selected are easily reachable and individually handled, the cost for sorting armourstone
heavier than, say, 3 t is approximately €0.25/t (excluding loading the selected and the
excess/waste materials). For smaller gradings, the cost per tonne increases rapidly because of
the increased number of handling operations (see Figure 3.89).
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3.11 Armourstone costs
1
2
3
Figure 3.89
Estimation of the cost associated with selecting different armourstone sizes. Costs
in euros. The differences result after combining the increased cost of the greater
hydraulic excavator capacity needed and the speed of working expressed in terms
of total tonnes selected per hour (courtesy J van Meulen)
4
Where an aggregates quarry is to be modified to produce heavy armourstone, there will be
costs associated with modifying quarry layout and operations. A breakdown of costs for such
a project is given in Box 3.41.
Box 3.41
5
Costing the supply of heavy gradings from aggregates quarries
Costing armourstone production is particularly important for aggregates quarries where this activity may
cause significant disruption to traditional quarrying practices. This requires a detailed study of
armourstone markets generally. Also to be included in the cost are extra wear and damage to the
equipment and machinery, which is more severe for armourstone production than for aggregates
production and proportionally higher for higher strength and abrasive rock types. An example costing is
set out below.
A large aggregates quarry producing several million tonnes of aggregates per year accepted an
opportunity to supply 20 000 t of a 5–7 t armourstone grading. The production process was hand-picking
with orange-peel grab of oversized and some secondary breakage. The cost may be divided as follows:
!
!
!
!
!
!
costs of layout modifications to the aggregate quarry, including costs associated with the aggregate
activity (around 25 per cent)
drilling and blasting (around 11 per cent)
selection at the muckpile (around 12 per cent); secondary breakage (around 12 per cent)
further selection and sorting (around 13 per cent)
quality control and individual weighing (around 11 per cent)
loading of the client’s transport facilities (around 15 per cent).
6
7
The armourstone cost could have been reduced to the optimum if the contract requirements were known
sufficiently in advance to allow stockpiling of appropriate oversize.
8
For coarse or light gradings, the use of mechanical sorting devices (see Section 3.9.7) should
be evaluated carefully since it may greatly improve the cost-effectiveness of armourstone
production. The unit costs are for putting the material on to the selection plant, ie direct
tipping by truck is not greater for armourstone than for other materials. The depreciation of
the plant and machinery through wear and tear has a considerable influence on the cost and
should be carefully assessed. Table 3.43 gives an overview of the costs (2005 values) associated
with various selection methods. These data are based on feedback from experience and
should be adapted for individual situations.
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Installation
cost (€)
Procurement
(wks)
Selection
(steps)
Input life (t)
Product quality
(see note)
Output (t/hr)
Unit cost
(€/t input)
Typical costs associated with selection methods for coarse and light gradings including
some core materials (cost level: 2005)
Purchase cost
(€)
Table 3.43
Selection hill
0
0–2500
0
1
N/A
6
250
0.40
Static grizzly
15 000
10 000
3+1
1
250 000
5
250
0.30
Mobile grizzly
75 000
5 000
13 + 1
1
1 000 000
3
150
0.80
Barsizer excl feeder
50 000
15 000
8+4
2
1 000 000
2
150
0.90
Barsizer incl feeder
175 000
125 000
13 + 4
3
4 000 000
2
300
0.50
Trommel screen small
300 000
75 000
13 + 2
4
6 000 000
1
300
0.60
Trommel screen large
375 000
75 000
13 + 2
6
6 000 000
1
600
0.50
Sidekick
35 000
5 000
13 + 1
1
1 000 000
4
50
0.70
Note
Product quality levels: 1 = best; 6 = worst.
3.12
CONCRETE ARMOUR UNITS
When identifying rock sources and procurement options for cover layer materials, the
required armourstone may not be found or may not be the most cost-effective option. As an
alternative to the use of quarried rock in the marine environment, concrete armour units
(prefabricated concrete elements) can be a competitive option, especially when heavy
armouring is required. A wide variety of types of unit are available – examples are listed and
illustrated later in this section.
Use of concrete armour units can help maximise utilisation of material resources. The most
suitable type of armouring should be selected on the basis of:
!
structural and hydraulic stability, including the risk of progressive damage (see Section 5.2)
!
hydraulic performance – overtopping and reflection reduction (see Section 5.1.1)
!
availability of rock of sufficient quality, size and quantity (see Section 3.9)
!
fabrication, storage, handling and placement of armour units
!
maintenance and repair of armour layers
!
appearance.
Many types of unit are available on the market. Key considerations for selection are:
!
the hydraulic stability of the unit under a given range of packing densities (Equation 3.91)
!
the structural strength of the unit, in particular impact and fatigue stresses and other
potential damage risks. In general, larger concrete armour units are more sensitive to
breakage caused by the larger forces associated with block movements, while the tensile
strength of concrete remains constant
!
the practicality of economic construction of the unit under local conditions
!
the range of application of the unit (including possible limitations based on field
experience and testing).
This information can be gathered from surveys of field performance, laboratory testing or
from unit developers.
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In this section, design information for several types of concrete armour unit is summarised.
Section 3.12.1 deals with the properties of concrete armour units and presents a classification
of units, Section 3.12.2 summarises some of the units that are more widely used and their
characteristics and Section 3.12.3 discusses the production of concrete armour units.
Many armour units are licensed under patent and the licensees have developed standards of
practice and knowledge bases that allow them to provide support in design and construction
monitoring. More up-to-date or comprehensive guidance may therefore be available from
the licensees.
Design methods for calculating the hydraulic stability of concrete armour units are presented
in Section 5.2.2.3.
3.12.1
Properties
3.12.1.1
Historical development of concrete armour units
The first artificial armour units were simple parallelepiped concrete blocks. Further
development of artificial armour units led to two basic armouring concepts:
!
randomly orientated interlocking armour units
!
uniformly placed friction-type armouring.
In the 1950’s the tetrapod unit was introduced, as casting of concrete allowed armour units
to be shaped in ways that increased stability through better interlocking. The economic
advantages of using tetrapods instead of massive units promoted their use in a large number
of breakwaters around the world. Despite wear and breakage of the top-layer units they
continue to be used today, for example in Japan.
The development of concrete armour units continued (see Table 3.44) in the form of highly
interlocking units of more complex shape such as the Dolos, units that improved on the plain
cube such as the Antifer grooved cube, and a generation of uniformly placed hollow or multihole units, such as the Shed.
Armour unit
3
5
6
7
History of concrete armour unit development
Country
Year
Armour unit
Country
Year
–
–
Antifer Cube
France
1973
Tetrapod
France
1950
Seabee
Australia
1978
Tribar
USA
1958
Accropode
France
1980
Modified cube
USA
1959
Shed
UK
1982
Stabit
UK
1961
Haro
Belgium
1984
Akmon
NL
1962
Diode
UK
1984
Tripod
NL
1962
Hollow Cube
Germany
1991
Dolos
RSA
1963
Core-loc
USA
1996
Cob
UK
1969
Xbloc
NL
2003
Cube
2
4
This section mainly focuses on randomly oriented armour units, for which the governing
factors influencing stability are mass and interlocking of adjacent units. Some details of closeplaced regular pattern units are also discussed.
Table 3.44
1
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Safety concepts for armour units were reconsidered after the failure of breakwaters in the
late 1970s and early 1980s in Sines, Arzew, Tripoli and Diablo Canyon. The failure of these
breakwaters was mainly caused by the structural failure of slender elements. Thereafter the
trend was towards the use of more robust, bulky units of increased structural strength, placed
in one layer with high safety margins for the hydraulic design. Armour units had previously
been placed in two layers to cover the uncertainties with respect to hydraulic stability and
structural integrity. The Stabit was the first randomly placed single-layer armour unit,
introduced in 1961. The Accropode was developed in 1980, followed by the Core-loc and the
Xbloc.
The most commonly used types of concrete armour units are:
!
cubic-type blocks used in a double layer
!
interlocking-type units used in a double layer
!
interlocking-type units used in a single layer
!
regularly placed friction restraint units used in a single layer.
PIANC (2005) has given a descriptive inventory of frequently used units. Several of the more
widely used types will be further described in this section. It should be noted that there are
probably in excess of 100 varieties of armour unit, many of which were developed for a
single use, notably in Japan or Korea, and have not been used more widely. Some of the
currently used units are identified in Figure 3.90.
Figure 3.90
Commonly used concrete armour units
New artificial units are coming on to the market every year and the reader should regularly
update his technical database with the most recent information from technical publications.
3.12.1.2
Classification and structural strength of concrete armour units
Several classifications can be found for concrete armour units, see for example CEM
(USACE, 2003) and PIANC (2005). A descriptive classification can be based on placement
pattern (orientation), layer characteristics, shape and stability factor (see Table 3.45, also
discussed in Section 5.2.2.3). The structural integrity of concrete armour units is mainly
controlled by the shape of the unit.
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Table 3.45
Placement
pattern
Number of
layers
Double layer
Shape
Stability factor (main contribution)
Own weight
Simple
2
Stabit, Dolos
Cube
Complex
Cube
Stabit, Accropode,
Core-loc, Xbloc
Complex
Simple
Single layer
Friction
Tetrapod, Akmon, Tripod
Simple
Single layer
Interlocking
Cube, Antifer Cube,
Modified Cube
Complex
Random
Uniform
1
Classification of armour units by shape, placement and stability factor
Haro
3
Seabee, Haro
Cob, Shed, Tribar,
Diode
The Haro is also placed in double layers.
4
The majority of concrete armour units are cast using unreinforced concrete. A few units have
used reinforcement steel, stainless steel, chopped wire or plastic. Reinforcement is seldom
used, mainly because of fears of corrosion. Reinforcement has generally been found to be less
cost-effective and if steel reinforcement corrodes the adverse effect on durability can
outweigh any advantages in using it.
5
Note
Concrete armour units are subjected to various load conditions. Possible reasons for breakage
of armour units are static failure and construction-related breakages. Wave-induced
movements of the units (rocking) are more likely to induce such breakages, however. The
structural integrity of concrete armour units needs to be ensured, as the units’ hydraulic
stability deteriorates when they fracture or disintegrate, causing a reduction of the stabilising
gravitational force and possible interlocking effects. Moreover, if wave action throws broken
armour unit pieces back on to the structure, an increased rate of breakage may occur. Useful
information on the structural integrity of units can be gained from past experience, finite
element stress (FEM) modelling and full-scale integrity (drop) tests (see Section 3.8.5).
The use of fillets is recommended where high-tensile stresses are likely to develop in units
with a complex shape. Such changes have been used on Stabit and Dolos units, and Melby
and Turk (1997) have used FEM analysis on the Core-loc block to show that a 20 per cent
reduction in maximum tensile stress may be obtained with a fillet equal to 10 per cent of the
height of the armour unit.
Particular attention should be paid to known performance of armour units in service. Storms
are generally infrequent events, so it may be necessary to wait for several years before a
structure is exposed to an event close to the design conditions. Information on structural
integrity of concrete armour units and the known range of application (eg maximum size) is
also important, as the intrinsic strength of units decreases with increasing size. If the unit is
used outside its range of application, breakage may occur before hydraulic failure of the
structure is reached. More information on structural integrity of concrete armour units is
presented in CEM (USACE, 2003).
6
7
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3.12.1.3
Description of concrete armour units
A given unit can be defined by the following parameters:
!
name of the unit and variant
!
volume of the unit, V (m³) – the volume of solid concrete (see Table 3.46)
!
specific dimensions – some artificial units have a complex shape, their specific
dimensions have to be described precisely
!
class of concrete and type of reinforcement – the minimum class of concrete should be
indicated in accordance with EN 206-1:2000
!
licence – this indicates if the unit is available through a licence agreement or is free of
any patent or trademark.
Layer systems of concrete armour units
Armourstone is almost always used in a double layer system. Concrete armour units can be
used in single- and double-layer systems depending on the type of armour unit.
The use of specific placement and orientation requirements for concrete armour units was
introduced for particular types of units together with specific placement methods. Examples
are known where the appropriate placement method was not carried out, leading to failure
of the structure within a few years of completion. Most units have a specific placement
method, which is either published or made available through a training programme.
The placement may be random, where there is neither control on the unit position nor on its
orientation. There should, however, always be a target or minimum placement density.
Alternatively, placement may be orderly, where the unit is placed at a given position with
control on the orientation. There is no random placement with an orderly orientation
method.
The geometry of the armour layer, which depends on the type of concrete armour unit used,
is given by the following parameters:
!
armour layer thickness, ta (m), defined as the distance normal to the underlayer surface,
measured from this surface up to the average of the protruding points. This may differ
from the overall thickness, which is defined as the distance from the underlayer to the
most protruding points
!
placement grid – most units are placed according to a predefined placement grid that
defines the location of each individual unit in relation to the other units. In addition,
specific orientation of the units on the horizontal plane may be required. An example is
given in Figure 9.62 in Section 9.7.2.6, where the placement of concrete armour units is
discussed
!
layer porosity, nv (-), defined as the ratio between the void volume and the layer volume
!
packing density coefficient, φ (-), defined as the number of placed units per square
nominal diameter. This should be compared to the maximum packing density that is
geometrically obtainable and the minimum density below which the hydraulic stability is
not guaranteed
!
number of units per square metre of protected slope, N (1/m²), calculated using the
packing density coefficient, φ. The consumption of concrete per square metre of
protected slope, Vc (m³/m²), can be estimated using the number of units, N.
Table 3.46 summarises the basic geometric design formulae and parameters for randomly
placed concrete armour units. Characteristic values for widely used units are presented in
Table 3.47 in Section 3.12.2.5.
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Table 3.46
Basic geometric design formulae and parameters for randomly placed armour units
Parameter
Armour unit volume, nominal diameter
and characteristic length
Centre to centre distance between
armour units
Area covered by one armour unit
Equation
Eq. No
M 
3
3
V =
 = Dn = k s D
 ρc 
(3.86)
∆x = X c D = X Dn ; X = X c / k s1/ 3
2
Aa = ∆x ∆y = X c Yc D 2 = X Y Dn =
n
N
(3.88)
Armour layer thickness
ta = n kt Dn = n kc D;kc = kt k s1/3
Armour layer porosity
nv = 1 −
Packing density coefficient
φ = n kt (1 − nv )
(3.91)
Number of units per unit area
N = φ / Dn 2 = φ /V 2/3
(3.92)
Concrete volume
Vc = NV = ta (1 − nv )
(3.93)
where:
A
Aa
D
Dn
kc
ks
kt
N
Na
n
nv
ta
V
Vc
M
X, Xc
Y, Yc
∆x, ∆y
φ
ρc
k s2 / 3
nV
1
= 1−
= 1−
A ta
X c Yc k t
X Y kt
2
(3.87)
∆y = Yc D = Y Dn ; Y = Yc / k 1s / 3
1
3
(3.89)
(3.90)
4
total surface area (m²) of armour layer panel parallel to slope
area covered by one armour unit (m²), equal to: nA/Na
characteristic armour unit length (m)
nominal armour unit diameter (m), the equivalent cube size
modified layer coefficient (-)
shape coefficient (-)
layer coefficient (-)
number of armour units per unit area (1/m²)
total number of armour units placed on surface area (-)
number of layers (-)
armour layer porosity (-)
armour layer thickness (m)
armour unit volume (m³)
concrete volume per unit area (m³/m²)
armour unit mass (kg)
dimensionless horizontal distance (-)
dimensionless upslope distance (-)
horizontal and upslope centre to centre distance between units (m)
packing density coefficient (-)
density of concrete (kg/m³)
5
6
7
Note
The layer thickness, ta (m), is given here (see Equation 3.89) for completeness and because it is used in
other equations in this table. It is, however, normally not used in design and specifications for construction.
A specific type of unit is then prescribed, together with the lines and levels of the underlayer.
3.12.1.4
8
Intrinsic properties
Density of concrete
For most concrete artificial armour units, the density of concrete used for fabrication should
be not less than the one used in the hydraulic stability calculations and tested in the
laboratory. Usual values are 2350–2400 kg/m³, but some units (chiefly cubic blocks) have been
used with a much higher density, eg 3000 kg/m³. Using high-density concrete armour units
results in a lower volume of each unit and in a reduced layer thickness (see also Section
5.2.2.3). The benefits of high-density concrete may be offset to some extent by additional
costs for heavy aggregates and for the placement of a larger number of smaller individual
units. Attention should also be paid to the methods of obtaining dense concrete in relation to
durability.
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Other properties of concrete
Artificial armour units are usually made of plain concrete of a standard grade. Concrete is
defined according to the European standard EN 206-1:2000. Key parameters to be defined
in accordance with this standard are given below:
!
exposure class: XS3 – tidal, splash and spray zones
!
maximum diameter of aggregates, Dmax, which generally varies from 20 mm up to 40 mm
!
workability of concrete – slump class S2 (ie 50–90 mm); the workability can be increased
by the use of plasticisers to keep the water/cement ratio, W/C (-), not greater than 0.45
!
characteristic compressive strength and possibly the characteristic tensile strength
(N/mm²) for slender units (EN 206-1:2000 table 7 and 8). This data is to be made
available by the unit developer according to their feedback from experience. Usual
ranges of compressive strength are in the range of C20/25, C25/30 and C30/37, where
the first number is the minimum characteristic strength of a 150 mm diameter by 300
mm cylinder, and the second is the minimum characteristic cube strength. For slender
unreinforced units the tensile strength is more relevant, and tensile strength should be
indicated by the developer (EN 12390-6:2002). The moulds are generally stripped as
soon as practicable. A minimum strength for stripping should be indicated and the use of
maturity tests is recommended to confirm strength. Water/cement ratio should be
minimised to avoid porosity and further durability concerns. A recommended value is 0.45
!
density of concrete (see above)
!
aggregates – common aggregates are generally used and should be selected in
accordance with national standards such as European standard EN 12620:2002.
Aggregates are generally easy to obtain if no durability problem is encountered since
they can be considered as quarry leftovers. Use of lightweight aggregates is not
recommended as stability formulae show that very large units are required. Use of high
density aggregates is recommended for hydraulic stability but the concrete durability
must be carefully assessed
!
cement – for works in the marine environment cement should be according to the
standard EN 206-1:2000, which defines a cement content of 350 kg/m³ for a 20 mm
aggregate concrete. Common French practice is to recommend a cement content, C
(kg/m³), for marine works of C = 700/(Dmax)1/5, where Dmax is the maximum size of the
aggregate (mm). Information on how to choose the cement depending on the
aggressiveness of the environment can be found in the French standard P 18-011.
The reader is referred to EN 206-1:2000 for further details. A useful guidance on concrete in
the marine environment is also given in Allen (1998).
Durability of concrete
Durable concrete should maintain not only its mechanical strength but also its good
appearance and should not develop cracks or change surface texture.
Durability of concrete depends primarily on good fabrication processes, but the cement’s
chemical composition is also of great importance. It is recommended to use ASTM type II or
III, sulphate-resisting cements. If OPC (Ordinary Portland Cement) is to be used, a maximum
C3A content of 8 per cent should be allowed.
Attrition by shingle moved by waves and sometimes by wind-blown sand may damage
concrete armour units. Attrition may also occur when the armour units are rocking. Fooke
and Poole (1981) give some guidelines on the selection of concrete components to limit
attrition. Attrition of armour units may lead to loss in hydraulic stability both in terms of
packing density and interlocking. Survey of existing structures with cubes, tetrapods and
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Accropode units shows that attrition and wear of angles and corners under wave attack can be
serious, particularly on active shingle beaches, and should be considered at design stage. It is
recommended to check that the units have been tested for attrition and that consequences of
wear have been identified and the design developed accordingly. If attrition is expected, the
mass of the units should be increased to account for probable loss of mass. In very severe cases
it is advisable to use very bulky units. In France, a specific method for testing the resistance of
concrete samples against abrasion was developed in the BHP 2000 project (ENPC, 2005).
3.12.2
2
Widely used units
In this section several of the most commonly used concrete armour units are presented using
the classification as given in Sections 3.12.1.1 and 3.12.1.2. A summary of their characteristics
is presented in Section 3.12.2.5.
3.12.2.1
1
3
Cubic-type blocks
Cubic block/cube (see Figure 3.91)
The cubic block or cube is the simplest substitute to natural stone and its main stability arises
from its mass. Stability is also influenced by friction between the blocks.
Cubes are fabricated with unreinforced concrete on a simple horizontal surface, often at a
rate of one block per day per mould. The formwork is made of four faces joining at the
corners. The recommended concrete grade is C25/30 with slump S2 and cement with a low
hydration heat.
Cubes are traditionally placed in two layers, where the lower layer acts as a separator for the
blocks of the upper layer. This can help prevent the tendency for cubes to reorientate during
settlement to form a more regular placement pattern with lower roughness and permeability.
Recent research (Van Gent et al, 2000 and 2001, and Van Gent, 2003) suggests that singlelayer cubes may exhibit some advantages over double-layer armouring in certain cases (see
also Section 5.2.2.3).
The method of placement of cubes is important for the hydraulic performance and structural
response of the armour layer. Randomly placed cubes lead to better hydraulic performance
because wave overtopping and reflection may be reduced. More uniformly placed cubes may
lead to a lower porosity and subsequently to a higher risk of cubes being lifted by excess pore
pressures that develop inside the breakwater. Also, the material consumption rates of more
uniformly, and hence more densely, placed cubes can add significantly to costs. Cubic blocks
are commonly gripped with clamps for placement.
4
5
6
7
8
9
Figure 3.91
Example of cubic blocks
being placed by cable
crane during Barcelona
breakwater construction
(courtesy S Dupray)
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Antifer cube (see Figure 3.92)
The Antifer cube is a development of the simple cube. It has one groove on each of the four
lateral sides of the unit. These grooves improve the interlocking and the hydraulic stability
while decreasing the risk of face-to-face rearrangement.
Units are made of unreinforced concrete on a simple horizontal surface at a normal rate of
one unit per day per mould. Formwork is made of four faces joining at the angles. No formal
standard dimensions exist. The recommended concrete grade is C25/30 with slump S2
concrete with a low hydration heat because of the thickness of the unit.
Antifer cubes are generally used in two layers. The lower layer acts as a separator for the
blocks of the upper layer. Antifer cubes are commonly placed using clamps. The unit
orientation is usually not specified, although most Antifer cubes are placed with the smallest
face upwards. Although the risk of unwanted face-to-face placement is still possible, it is less
probable than with the cube. The placement of Antifer cubes in accordance with the
recommended standards is important so as to guarantee the porosity of the armour layer.
Figure 3.92
Example of Antifer cubes
– Antifer breakwater
(courtesy S Dupray)
Other related units
Parallelepiped units have been used. Some cubes and Antifer cubes with a central hole to
decrease the consumption of concrete have also been used to decrease the risk of internal
stresses due to overheating during hydration of the concrete.
3.12.2.2
Hollow units
Cob, Shed, Seabee, Haro and Diode (see Figure 3.90)
This family of units is derived from the massive cubic block. By providing a void in the
centre of the unit, concrete volumes (and mass) are reduced and a good hydraulic
performance due to energy dissipation is achieved. The units are placed as if in a pavement
with the faces of adjacent units touching one another. The armour layer resists wave action
by the friction between the blocks and wave forces are reduced by the high armour porosity
of these units.
The units are either fabricated without structural reinforcement, or may include noncorrodible integrity reinforcement. The formwork for producing these units is made of
several inner and outer shells.
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3.12 Concrete armour uXnxixtxs
Specific attention should be paid to placement of the units to ensure that they are closely
placed in parallel lines. This operation may be difficult and slow and will require special care
at roundheads and curves. If such close placement is not achieved, the stability of the entire
layer is compromised. Accurate placement of the bottom row is also essential to ensure good
organisation of the subsequent rows on the slope, and toe details should be specially designed
to provide a regular, smooth surface for support.
3.12.2.3
Interlocking units used in a double layer
1
2
Dolos (see Figure 3.93)
The Dolos unit is characterised by a relatively light body and long members that allow a very
high degree of interlocking. The slenderness of this unit can vary, with different relative waist
thicknesses defined as ratio of the width of the octagonal central stem relative to the longest
dimension of the unit. The waist ratio (diameter in centre part to height) is typically r = 0.32
and an increased waist ratio is recommended for larger units (r = 0.34 for units of 20 t and
0.36 for units of 30 t). The waist ratio for larger Dolos units (≥ 20 t) can be assessed by using
Equation 3.94:
1/ 6
M 
r = 0.34  
 20 
(3.94)
3
4
where M is the unit mass (t).
The Dolos unit was initially developed with unreinforced concrete until damage was
observed, attributable to the slenderness of the members. In response to the observed
damage, steel reinforcement has been used at some sites. Design of such reinforcement may
be difficult because of the dynamic loading. Potential problems are corrosion of the
reinforcement, which can lead to cracks, and the increase in cost due to the reinforcement.
The formwork for producing the Dolos unit is made of several shells and may allow a
production rate of one unit per day per mould with experience.
5
6
7
Figure 3.93
Example of Dolos used
on slope with heavy
basalt armourstone on
crest (courtesy S Dupray)
The Dolos unit was a step forward in terms of interlocking between units. Its shape gives
good hydraulic stability of the armour layer as tested in the laboratory. Dolos units are placed
randomly in two layers with a given packing density. The second layer is necessary to create
interlocking.
The good hydraulic stability has not always been supported by good structural strength, and
cases of severe damage and the need for repair have been reported. Extensive research to
minimise integrity problems of the Dolos unit and to understand its structural weakness has
been reported (Lin et al, 1986; Hall et al, 1987; Howell et al, 1989; Luger et al, 1995).
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For existing structures, regular monitoring, at least after storms, should be carried out and
broken armour units may need to be replaced. Rather than repairing a Dolos armour layer
the US Army Corps of Engineers has developed the Core-loc, which can fulfil this role.
Tetrapod (see Figure 3.94)
The tetrapod unit was the first concrete unit with a special shape. This unit has been used
extensively and projects with units up to 50 m³ can be found. The tetrapod has recently been
used mostly in Japan in multi-layer systems.
Analysis on the structural resistance of the unit and its hydraulic stability led to
comprehensive guidance (Sotramer-Sogreah, 1978) for manufacturing of the formworks, the
fabrication of the units, their storage and placement of the units in two layers. The formwork
for producing tetrapods is composed of a bottom shell and three lateral shells.
Wear and breakage have been experienced in several structures caused by rocking of the
units in the top layer. The placement of the units as per the recommended standards is
essential to guarantee the interlocking and the required porosity of the armour layer.
Figure 3.94
Example of Tetrapods used as
armour on breakwater with
crown wall (courtesy Sogreah)
3.12.2.4
Interlocking units used in a single layer
Accropode (see Figure 3.95)
The Accropode unit was developed from experience of the tetrapod and the observation that
double-layer systems may allow unwanted movements of units in the upper layer. This unit
has been used extensively and blocks up to 20 m³ have been employed in some projects.
Analyses of structural resistance of the block and of its hydraulic stability has led to
comprehensive standards for manufacturing of formworks, fabrication of blocks, storage and
placement of units in one layer (Sogreah, 1988). Formwork is made with two lateral shells,
allowing a production of one unit per day per mould.
Accropodes are placed in a single layer in a predefined grid whereby the orientation of the
blocks has to be varied; the latter is typically specified. Various sling techniques are
recommended for placement. The best interlocking of Accropodes can be achieved on steep
slopes (3:4 or 1:1.5). For further details see also Sogreah (2000).
For situations where a natural rock appearance is required, the Ecopode (a unit closely
related to the Accropode) has been developed.
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3.12 Concrete armour units
1
2
Figure 3.95
Example of Accropode
and Ecopode used in
combination (courtesy
Sogreah)
3
Core-loc (see Figure 3.90)
The Core-loc unit was initially developed by the US Army Corps of Engineers for the repair
of damaged structures armoured with Dolos units. The shape of the legs is a true copy of the
Dolos so Core-locs can be applied as repair units for Dolos armour layers, or as is more
usual, for complete armouring systems. The hydraulic stability of Core-loc armour units is
better than that of Accropodes (see Section 5.2.2.3), but the recommended stability
coefficients for design are close to those for Accropodes. The Core-loc is more slender, so its
structural integrity may be less than that of Accropodes.
4
5
The placement procedures for Core-locs and Accropodes are similar; various sling techniques
are applied for both types of armour units. For further details see also Melby and Turk (1997).
Xbloc (see Figure 3.96)
6
The Xbloc is a compact armour unit with high structural strength (similar to the Accropode
unit). The hydraulic stability of Xbloc armour layers is similar to that of Accropode and
Core-loc armouring.
Xblocs have to be placed on a predefined grid. The orientation of individual blocks is
allowed to vary randomly and so is not prescribed. This is the main difference between Xbloc
and other single-layer interlocking armour units. For further details see also DMC (2003).
7
8
9
Figure 3.96
Example of Xbloc during
handling (courtesy Delta
Marine Consultants b.v.)
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3.12.2.5
Layer placement dimensions
Table 3.47 presents values for the characteristic geometric and armour layer parameters
defined in Section 3.12.1.3 for some of the most widely used concrete armour units.
Shape coefficient
Distance
between units
Horizontal
Slopeparallel
Porosity
Packing density
coefficient
Modified layer
coefficient
Recommended
slope
Characteristic geometric and armour layer parameter values of randomly placed
concrete armour units
Layer coefficient
Table 3.47
kt
(–)
ks
(–)
∆x/Dn
(–)
∆y/Dn
(–)
nv
(–)
φ
(–)
kc
cot α
(–)
Cube (two layers)
1.10
1.0
1.70
0.85
0.47
1.17
1.10
Tetrapod
1.02
0.280
1.98
0.99
0.50
1.02
0.667
4/3 to 1.5
Dolos (r = 0.32) 1)
0.94
0.16
2.19
1.10
0.56
0.83
0.51
2 to 3
1.77
0.86
0.491
0.656
1.82
0.91
0.531
0.605
0.9012
4/3 to 1.5
> 12
1.86
0.93
0.552
0.578
<5
1.83
0.91
0.606
0.598
1.85
0.92
0.613
0.587
1.85
0.93
0.618
0.580
0.9201
4/3 to 1.5
> 12
1.87
0.94
0.624
0.569
<5
1.87
0.92
0.587
0.578
1.92
0.94
0.606
0.552
0.97
4/3 to 1.5
1.96
0.97
0.623
0.528
1.33
1.00
0.25
0.75
1.70
0.85
0.31
0.69
Armour unit type
Size
(m³)
<5
Accropode
Core-loc
Xbloc
5–12
5–8.5
8.5–12
5–12
1.29
1.516
1.40
0.341
0.2236
0.333
> 12
Cube (one layer)
high ²)
low ²)
1.0
1.0
1.0
Notes
1 r = waist-to-height ratio (waist diameter of central section and total height of unit).
2 Packing density.
3.12.3
Production and placement
The production process for concrete armour units is similar to that for any precast concrete,
and reference should be made to the national concrete production standards in every case.
In Europe, the European standard EN 206-1:2000 applies. The conditions of fabrication may
vary significantly from northern Europe to the Arabian peninsula or south-east Asia. It is
therefore impossible to define a single specification for the fabrication of the units. However,
this section gives general good practice and guidelines for most of the units and describes their
fabrication and placement. Further information on unit placement is given in Section 9.7.2.6.
3.12.3.1
Formworks and moulds
Most armour units are cast in steel or glass-reinforced plastic moulds. Only cubes and other
parallelepiped blocks are made using simpler wooden or steel formworks. The moulds
should be easy to use and are made of two or more shells depending on the type of unit.
Appropriate measures are required to ensure perfect sealing between half-moulds such as
rigid frames at joints and short spacing between connecting bolts.
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CIRIA C683
3.12 Concrete armour units
Tolerances for all formwork dimensions should be ± 2 mm to ensure good fitting of the
shells and consistency with the volume specification for the armour unit. The volume is the
most important parameter that controls, with the mass density, the mass of the unit and its
stability.
Complex armour units require precise formwork drawings from the unit developer. Usually
sheet steel 5–8 mm thick can be used for the fabrication of the moulds. Maximum deflection
produced by the thrust of fresh concrete should not exceed 1/1000 of the span measured for
any dimension. Stripping angles should be provided for easy form removal without excessive
tensile strength.
Forms can be erected on either a compacted platform or a concrete platform. If using a
compacted platform, particular attention should be paid to the stability of the forms and of
the cast units. Differential settlement of the soil may lead to tilting of the units and may be a
health and safety issue. Appropriate stiffeners should be installed to avoid any deformation of
the forms and to ensure safety of the workers during the fabrication process. Working
platforms should be provided for pouring operations and to ensure complete safety.
Insulated moulds are required in very cold conditions where frost may damage the freshly
poured concrete.
3.12.3.2
1
2
3
4
Casting of concrete armour units
Production of concrete
Concrete is produced in standard batching plants. Daily production can vary from a few
cubic metres up to several hundreds of cubic metres. The output rate and the characteristics
of the batching plant need to be adapted to the project size. It is recommended to use
batching plants with automatic recording of the material mass, using equipment as described
in EN 206.1:2000 Appendix G with a class III automatic recording device.
The batching of concrete needs to be synchronised with the pouring operations. A new batch
should never be started if a risk exists of delays in the pouring activity. A cold joint in
unreinforced concrete is not tolerated, since it will undoubtedly lead to breakage of the unit.
Transport of concrete
Concrete should be transported by special trucks to prevent segregation. Distance from the
batching plant to the fabrication yard should be kept to a minimum to ensure there is no risk
of initial setting of the cement and should never exceed 45 minutes.
Pouring concrete
Concrete is usually poured in layers not exceeding 50–60 cm. Each lift is vibrated up to the
previously poured layer until air is completely removed from the fresh concrete. Cold joints
between layers are not permitted. The number and size of the internal vibrators should be
adequate for immediate vibration of the concrete introduced into the mould. External
vibration units may also be used in addition to internal vibration, but performance should be
checked in each case. External vibration cannot be used alone and must be associated with
internal vibration.
5
6
7
8
9
Stripping formwork and curing
Production is often set up with the intention of reusing a mould each 24 hours, implying that
the formwork is stripped after 18–20 hours.
CIRIA C683
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3 Materials
Thermal shock during the hydration process in mass concrete can be expected with massive
and bulky units. Thermal shocks can occur when the difference in temperature between the
centre of the block and the skin is too high. Thermal protection of the unit at the time of
stripping the mould is required when cold, windy conditions are encountered.
For units with protruding non-self-supported elements, stripping of the formwork can be
done only when a minimum structural strength is obtained. Tilting of units may become a
safety hazard on non-stabilised platforms. Supporting devices should be placed after
stripping of the formwork.
The exposed surfaces of newly placed concrete should always be kept damp or protected by
applying a curing product. Curing should start as soon as possible after pouring of the
concrete for non-shuttered parts and immediately after removal of formwork in other cases.
Similarly, insulation against frost or cold wind effects should start immediately after stripping.
See Figure 3.97 for illustration of pouring and stripping.
Figure 3.97
Example of concrete armour unit prefabrication site with preparation
of moulds (front left); pouring and vibrating (front right); curing and
stripping (back view) (courtesy Port du Havre)
Repairing defects
Three types of defects are found in concrete armour units.
262
!
mass defects can be honeycombs, laitance losses, bubbling, and surface bubbling. Repair
of such defects should be carefully assessed when the unit is made of unreinforced
concrete. There is a severe risk that the repair will be less durable than the original
defective concrete. If the unit is made of reinforced concrete, repairs are possible and
particular attention should be paid to the risk of seawater ingress at the repair and
future corrosion of the steel. When the volume of the defective concrete is less than 5
per cent of the volume of the unit, the unit should be registered as a defective unit and it
may be used in the armour layer provided that it is separated from any other defective
unit. If units displaying mass defects are widely spread in the armour layers, this should
not affect the hydraulic stability. If the volume of the defective concrete is more than 5
per cent the unit should be declared as unsuitable and should either be carefully
repaired or used as a lower mass of unit
!
cracking can take the form of either shallow hairlines or deeper cracking. Shallow
hairline spread surface cracking of a few millimetres depth is tolerated. Deeper cracking
may be a source of breakage if concentrated along a zone typically exposed to high
tensile stresses and should always be avoided. Causes of such cracking should be
CIRIA C683
3.12 Concrete armour units
investigated and eliminated. Cracking should be investigated by core drilling across the
crack. Repairs with epoxy grout, or a similar agent, are not considered a valid
alternative. Cracks should preferably be avoided at the source. Units with deep cracking
have to be rejected or can be used in areas of lesser wave action
!
3.12.3.3
surface defects such as bubbles or bleeding cannot be considered as defects and do not
need repair, because they do not affect the units’ structural resistance. Such defects are
really a sign of poor fabrication methods or concrete mix design and so should alert the
contractor to the need to improve the fabrication methodology.
1
2
Control of the production
Concrete materials
Concrete control methods for the mix design and the production of concrete are described in
EN 206-1:2000. This standard is valid in European countries, but should also be used in
other countries where appropriate local guidance is not available. Proper specifications
should be developed for the concrete production plant in accordance with the standards.
The variability of the cement and other concrete constituents should be taken in account
when preparing a design mix.
3
4
Standards for the quality control of aggregates, cement, water, fresh concrete and hardened
concrete can be directly derived from EN 206-1:2000.
Casting armour units
Each unit is given a unique identification number from stripping time to the placement of
the unit. This identification allows reference to be made to the day of fabrication and any
other data related to the concrete production.
Quality control implies verification of unit volume (or mass) and concrete density. At the start of
the fabrication process, the volume of the unit can be checked by measuring the inside volume
of the mould. Alternatively the unit can be weighed and the concrete density measured with
accuracy. During day-to-day production, the concrete density should be checked regularly at
the batching plant. A minimum of 2 per cent of the units produced should be individually
weighed. The actual mass should be within +2/-1 per cent of the expected mass.
Structural integrity, including cracking and defects, is the second aspect of the armour unit
acceptability. All the units should be scrutinised. Armour units can be damaged during
fabrication or during placement. Any unit with more than 10 per cent loss of mass should be
discarded. A loss in mass is defined by an effective loss after breakage or by a potential loss
due to default in integrity produced by honeycombs or deep cracks. Units with nonconforming mass, ie a loss of mass between 1 per cent and 10 per cent should be rejected.
Units with mass loss less than 5 per cent might potentially be used in the armour layer,
providing damaged units are not concentrated in a single area.
3.12.3.4
6
7
8
Storage
Areas available and the ability to stack units for storage will have been considered early in the
design and construction planning process. The units are either stored at the place where
they were cast or moved to a storage yard (see Figure 3.98). Storage can be in one or several
layers, vertically on their base or on three points. Most units can be stored in two or more
layers, depending on their stability. The number of layers can be decided after analysis of the
safety conditions for the handling of the unit for storage and removal. A key parameter is the
stability of the soil platform for long-term storage.
CIRIA C683
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263
9
10
3 Materials
Figure 3.98
3.12.3.5
Example of units yard in Barcelona with dedicated high capacity
handling frame. Note that units are casted alongside the yard and
cylinder moulds for concrete quality control (courtesy S Dupray)
Placement
Most concrete armour units are placed according to a predefined placement grid that defines
the location of each individual unit in relation to other units. In addition, specific orientation
of units may be required. The placing or packing density needs to be specified and strictly
maintained during placement of the units and every effort should be made to achieve
maximum interlocking. During placement, the packing density can be maintained by
specifying a mean and allowable deviation for the centre-to-centre distance between units, or
it can be maintained by counting the units in a specified area.
Placement grids for interlocking units are generally specified, with each subsequent row of
armour units offset laterally from the previous lower row to avoid failure planes. Single-layer
armour units are placed on a staggered grid – see Figure 9.62 in Section 9.7.2.6. The
horizontal and vertical upslope grid dimensions (centre-to-centre distances ∆x and ∆y, see
Equation 3.87) can be specified with values presented in Table 3.47.
Special attention is required for armour unit placement on exposed points and at junctions
and transitions. Experience in detailing is available from licensees and in many cases threedimensional model tests need to be carried for detailed design. Further discussion on
transitions is given in Section 6.1.4.3.
Placement rates can vary depending on armour unit size, placement tolerance, visibility,
water depth, and the type of crane and platform. At Sohar, Oman, 80 000 units were placed
at six units per hour, although at more difficult sites two to three units per hour may be
more realistic. Placement of concrete armour units is discussed further in Section 9.7.2.6.
3.13
RECYCLED AND SECONDARY MATERIALS
In civil engineering works, a vast range of granular materials are viable alternatives to
natural aggregates. In road foundations, for example, many materials are utilised that have
already been used or are recovered from the waste stream of other activities. These are
normally named secondary materials or residues (Masters, 2001). Substantial energy savings
accrue from using locally available secondary materials instead of primary production. The
terms used in this section (alternative materials, secondary materials, recycled materials,
reuse) are defined in the glossary at the front of this manual.
264
CIRIA C683
3.13 Recycled and secondary materials
Waste materials are used to only a very limited extent in hydraulic engineering because of
the difficulty in estimating the environmental risk they represent. An example of such use is
shown in Figure 3.99 and a case study is given in Box 3.42. This section provides a summary
of available information to enable granular material alternatives to primary quarried rock to
be assessed for use in hydraulic structures. More information can for example be found in
CIRIA publication C590 Potential use of alternatives to primary aggregates in coastal and river
engineering (Brampton et al, 2004).
1
2
3
4
Figure 3.99
Example of the use
of crushed concrete
in a dike
To investigate the possible use of various secondary materials in hydraulic structures, their
setting and function in the structure should be considered (see Table 3.48). The use of such
materials, if enclosed in a membrane or bound by a matrix of bitumen or cement grout, will
lower the environmental impact. Direct use as loose granular material requires
environmental characterisation for which documented previous experience will be most
helpful. Fine unbound material, whether of natural or secondary origin, may be considered a
pollutant if it makes clear waters cloudy or causes a build-up of fines.
Table 3.48
6
Setting and function of materials
Setting within structure
Function
Granular components enclosed in
geotextile/geomembrane, clay liner, or
bound by bitumen or cement grout (low
leaching potential)
!
Loose granular components in contact with
circulating water (high leaching potential)
!
!
!
!
7
Volume-filling (core and reclamation fill)
Armouring (fixing secondary armourstone gradings by
grouting – Section 3.15)
Armouring (absorbing waste as filler in the cement or
bitumen grout)
Armouring (surface layers)
Volume filling, filtering (core and underlayers)
Combining recycled materials with binders will considerably reduce overall leaching potential
and permeability thereby hindering the ingress and egress of water to and from the structure
(Hill et al, 2001).
Depending on the type of binder, the mobility of the different pollutant species will be affected:
!
potential pollutants can be physically trapped within the binder structure
!
potential pollutants can chemically interact with one of the binder components leading to
changes in chemical composition and solubility. This interferes with their expected mobility.
The potential for extra biological impacts caused by using alternatives to primary aggregates
will need to be assessed, and these impacts can arise because of the chemical and physical
CIRIA C683
5
265
8
9
10
3 Materials
effects discussed above.
The aesthetics of coastal and river environments can be very important, particularly if
tourism, recreation and related activities depend upon them. There is already some
resistance to the use of novel types of structures in river and coastal engineering works, for
example rock groynes, because of the perceived aesthetic effects, and in areas designated
because of their scenic qualities there are often guidelines on appropriate forms and types of
structure. These sensitivities may limit the use of secondary and recycled construction
materials in coastal and river engineering, particularly the use of waste tyres, or of
construction and demolition waste, if these materials become visible. For most applications
and alternative materials, however, any aesthetic impact may be more perceived than actual.
In Cornwall in the UK, for example, many beaches formed largely of mine waste are
regarded as not only acceptable but also as an asset to the landscape and tourism.
Both primary and alternative aggregates require processing to ensure their consistency and
quality, for example removing contaminants. These are likely to be very similar for primary and
secondary aggregates but may be higher for recycled materials, for example demolition waste.
3.13.1
Types of alternative material
The recycled aggregates (made of waste materials) most commonly used in civil engineering
are listed in Table 3.49.
Table 3.49
Different types of recycled materials (characteristics and existing uses)
Type
Characteristics
Construction and
demolition waste
Recycled concrete
!
Dredged
materials
!
Steel slag
Blast furnace (BF)
slag
!
Foundry sand
!
!
Main existing uses in civil engineering
solid waste resulting from the construction,
remodelling, repair, or demolition of
structures (ODPM, 2001)
such wastes may include any of the following:
scrap lumber, bricks, concrete, stone, glass.
!
sediments collected from the bed of a river,
lake, harbour or sea by dredger, dragline or
scoop.
!
!
!
!
!
!
!
Municipal solid
waste incinerator
(MSWI) residue
!
!
!
266
Used tyres
!
Other materials
!
the steel industry has traditionally produced
by-products, which have been successfully
used in many fields of application.
Note: because of the swelling risk inherent to
low-density steel slag, its use can be limited.
!
clean, uniformly sized, high-quality silica sand
or lake sand that is bonded to form moulds
for ferrous and nonferrous metal castings
the iron and steel industries account for
approximately 95 per cent of foundry sand
used for castings.
!
most significant by-product from municipal
solid waste incineration
has been used in civil engineering structures
for more than a decade (the first experiments
were carried out in the 1970s)
their effective geotechnical and
environmental characteristics as well as their
long-term behaviour have been well studied
so that the limits of their uses can be
described.
Note: the long-term behaviour of MSWI
bottom ash is not yet fully understood.
increasing numbers of tyres are being used and
even more are expected over the next 25 years.
!
!
!
!
!
!
!
roads structures
embankments
other earthworks.
road construction
beach/nearshore nourishment
habitat creation or restoration
landscaping
topsoil creation or enhancement
roads structures
embankments.
roads structures
embankments.
roads structures
road embankments
subgrade.
drainage systems
roads structures.
colliery spoils, minestone, phosphogypsum, glass bullets, fly-ash.
CIRIA C683
3.13 Recycled and secondary materials
Existing experimental data and recommendations will limit the direct use of certain materials.
1
Typically, recycling of materials like MSWI residues or foundry sands in a water environment
will require the addition of a binder to stabilise their leaching potential. Fly-ash or BF slags
can be used as a binder.
2
Up-to-date information on different types of recycled materials can also be found at the
following websites:
3.13.2
!
<http://ofrir.lcpc.fr>: contains the OFRIR database (Observatoire Francais du Recyclage
en Infrastructure Routiere)
!
<www.ciria.org/cwr>: CIRIA construction waste and resources website
!
<www.wrap.org.uk>: WRAP is a not-for-profit company supported by funding from UK
government. It works to promote sustainable waste management by creating stable and
efficient markets for recycled materials and products.
3
Mechanical and chemical properties
In this section, parameters required for the design of hydraulic structures are compared with
parameters likely to interfere with the use of recycled materials.
4
Required parameters for design
As mentioned in Section 3.1.2, the main property according to the function of the material in
the structure is as given in Table 3.50.
Table 3.50
5
Material properties versus function in hydraulic structures
Function
Volume-filling
Piping control/filtering
Armouring
Main property
Mass density
Porosity
Mass distribution
6
It is not possible to present the range of values of the property parameters, as these will
depend not only on the type of materials but also on the complexity of the processes to be
performed. The general considerations are summarised in Table 3.51.
Table 3.51
Usual texture of the main recycled materials
Type
7
Usual texture
MSWI residue
Gravel
Construction and demolition
waste
Gravel
BF slag
Sandstone
Steel slags
Gravel
Foundry sand
Sandstone
Used tyres
Various (unprocessed,
granulated, bales etc)
8
9
10
CIRIA C683
267
3 Materials
Weathering
Weathering may result from physical disintegration, chemical decomposition or a
combination of both. Physical weathering causes existing discontinuities to open, new
discontinuities to form and the grain boundaries to separate. Chemical weathering results
from changes in the chemical composition of the materials and is usually a slower process
(Skarzynska, 1995a and b). This parameter should be taken into account in recycled materials
because of their complex chemical composition. Weathering can be evaluated by the changes
in particle size. Note that for some materials weathering can also result in carbonation,
leading to binding.
In a research project, Gardner et al (2003) developed the hypothesis that weathering
reactions in industrial by-products will change the environmental and physical behaviour of
the by-product materials. It is expected that weathering reactions will improve the
environmental performance of the material, although it remains unclear in what way the
physical performance will be changed.
Resistance to chloride corrosion
When considering materials for marine environments, the use of recycled concrete is limited
because of its limited resistance to chloride corrosion. Specifications concerning
compositions and properties of concrete in saline environments are defined in the European
standard EN 206-1.
Swelling
Various studies and experiments have confirmed the swelling capacity of many artificial
materials (eg demolition waste), which should be taken into account when considering their
use. No standard yet exists for characterising swelling capacity for these materials.
Resistance to freeze and thaw
Particular attention needs to be paid to the frost susceptibility and frost-heaving values of
alternative materials intended for use in hydraulic structures in cold regions. These values
depend greatly on their porosity and have to be tested when required (see European
standard EN 13383).
Municipal incinerator bottom ash has already shown little resistance to freeze-thaw (Arm,
2003). Test results show that the resistance to freeze-thaw of municipal solid waste incinerator
(MSWI) bottom ash can be good, as reported by François et al (2003).
Chemical characterisation
In Europe, the relevant hazardous properties of the materials processed from waste that are
under consideration should be identified in relation to the European Council Directive on
hazardous waste 91/689/EEC.
For the other materials (not originating from waste), chemical characterisation should be
investigated in the literature (such as Al-Masri et al, 2004, for phosphogypsum and Chen et al,
2002, for glass).
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CIRIA C683
3.13 Recycled and secondary materials
3.13.3
1
Experience from existing uses in hydraulic structures
The different technical and environmental properties mean that use of recycled and
secondary materials varies between 10 and 100 per cent. The greatest volumes are currently
used in earthworks applications such as road bases, structural fills, embankments and general
fills, as reported in Table 3.49. Very few reported cases focus on the use of waste materials in
hydraulic structures.
2
Motz and Geiseler (2001) reported the following uses of steel slags in hydraulic structures:
!
dams and dikes
!
stabilisation of river beds
!
refilling of erosion areas on river beds
!
stabilisation of riverbanks.
3
Recycled aggregates from steel slags – typically larger than 10 mm – are commonly used to
prevent the erosion of fine particles. Steel slags are charaterised by a high density, a high
level of strength and abrasion resistance and a rough texture that ensure long-term
resistance to dynamic forces from waves and river flow.
In the mid-1990s a large quantity of copper slag produced in Hamburg, Germany, was
routinely used as riverbank protection rip-rap and fine gradings. These materials can still be
used within the framework of EN 13383 for mechanical and grading properties. Local
regulations should be taken into account for the environmental assessment (see Figure 3.100).
4
5
The properties of steel slag armourstone have been investigated and are comparable to those
of natural stone such as basalt.
Skarzynska (1995b) mentions existing applications of minestone wastes in the following
scenarios:
6
!
as the core of river embankments without any previous characterisation of the materials
!
as bed protection
!
as impoundment dams and dikes.
Skarzynska (1995b) tested the influence of minestone hydraulic structures on the adjoining
environment and made the following recommendations:
!
hydraulic structures made of minestone waste should be constructed so that the water
will quickly run off the surface of the crest and slope
!
they should be covered with turf so that the surface will allow ecological colonisation.
It was also pointed out that the intensity of the washing-out of harmful substances by surface
water infiltrating through the body of the structure depends on the quantity of the water
flow. The following cases should be considered when evaluating environmental risk:
!
flood embankments: the groundwater movement usually occurs below the embankment
!
surface embankments: constant water filtration takes place through the body of the
embankment
!
river embankment functioning simultaneously as a dike for sediment ponds: filtration
can be towards the river or towards the nearby pond
7
8
9
10
CIRIA C683
269
3 Materials
!
embankments or dikes for water reservoirs: the water in the reservoir is always above
the groundwater level and the infiltration occurs through the dike or body of the
embankment.
Skarzynska (1995b) suggested incorporating polyethylene sheeting or clay screens together
with drainage to remove the infiltrating water.
Skarzynska and Michalski (1998) have investigated model embankments made of colliery
spoil and fuel ash and established the following recommendations:
3.13.4
!
it is best to choose material with a high content of fine fractions and with a high value of
uniformity coefficient to achieve a low permeability coefficient
!
the geometry of the embankment cross-section must be designed such that the
maximum drop of water level produces a hydraulic gradient not higher than 0.3
!
the use of appropriate sealing such as fuel ash or other clay materials can allow the use
of materials presenting a higher water permeability.
Environmental risk analysis
A methodology for environmental risk analysis is presented in Figure 3.100 based on the
prestandard ENV 12920:1998 Methodology for the determination of the leaching behaviour of waste
under specified conditions.
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CIRIA C683
3.13 Recycled and secondary materials
1
MAIN QUESTIONS
!
!
What is the flux of leached (specified) contaminants from a (specified) material in a (specified) utilisation
scenario under (specified) climatic conditions as a function of time (cf long term)?
How can the relationship between the resulting concentration of contaminant in the water at a certain
distance downstream of the application and the results of laboratory leaching tests on the material used
in the application be established?
ENVIRONMENT
PROBLEM
FORMULATION
!
!
MATERIAL
!
RISK
EVALUATION
Construction scenario
−
!
geometry of the structure and role of the material
Hazard identification: in accordance with the European Waste Catalogue
−
Chemical and physical characterisation
−
European/local regulation linked to the solid waste
−
Identification of the hazardous properties in the materials that are relevant in the scenario in
relation to Council Directive on Hazardous Waste 91/689/EEC
Geotechnical conditions, hydrogeological conditions, biological conditions, use of the site over
time, exceptional conditions
−
Exposure assessment: source (release) + path (transport) + target points (exposure)
Representivity of the materials tested (visual inspection…)
−
Selection of the correct leaching methods to investigate the leaching properties as a function
of liquid-to-solid ratio L/S and pH as well as the influence of various internal material properties and external factors on the release of contaminants. Chemical analysis depending on the
chemical characterisation of the waste as collected from the European waste catalogue or
from the literature
!
Choice/development of a suitable model describing the problem under investigation
If possible validation of the model with on-site chemical analysis
Comparison to standards or reference values when existing
Assessment of health risks (ingestion, inhalation)
Assessment of the risk to the environment (ecotoxicity): see local regulations
!
!
RISK
MANAGEMENT
!
7
Decision-making based on risk assessment (authorities, municipalities, companies or organisations)
Risk communication
Insufficient information:
No solutions because:
The project does not go
forward
Material not appropriate.
No mitigation found
5
6
CONCLUSION
!
4
Sampling
−
Data required by regulation (when existing): turbidity
!
3
Environmental and climatic scenario
−
!
!
2
8
Solution found:
May include monitoring
9
Feedback
Figure 3.100
CIRIA C683
Environmental risk assessment methodology, based on ENV 12920 (1998)
10
271
3 Materials
3.13.4.1
Status of knowledge
The engineering properties of many waste materials are often comparable or even better
than traditional aggregates and armourstone. The contamination risk implied by the use of
these elements is characterised through a quality control process during the processing of the
material or can be assessed following a relevant evaluation method, such as that presented in
Figure 3.100.
Even if the use of certain waste materials in a water environment is unsuitable (eg hazardous
industrial wastes), an adaptation of the design of the hydraulic structures can lead to an
increase in the use of many of the alternative granular materials. Certain recycled materials
can also be stabilised by the addition of a hydraulic binder before being integrated into a
project. This operation extends the possible uses of recycled materials in such structures.
It is anticipated that further full-scale experimentation to examine specific scenarios will
extend the body of experience and provide further evaluation of performance. Potential
users of these novel environmental engineering solutions are encouraged to both consult and
submit case histories to this important growing field. A typical case study demonstrating the
use of colliery spoil as beach fill is given in Box 3.42.
Box 3.42
Betteshanger Colliery, Kent: colliery spoil used as bulk fill in beaches for sea
defence/flood prevention (after Hamilton, 1984, in Brampton et al, 2004)
Colliery spoil has been utilised as bulk fill for quite substantial flood and coastal defence structures. When
the sea defences failed in front of the Betteshanger colliery, near Deal in Kent, during a winter storm and
high tides in January 1978, about 2 000 000 m³ of water flowed inland overtopping secondary defences,
flooding structures and covering 300 ha of farmland. The Betteshanger tip (approximately 500 ha in area,
10 m high) was within 3 km of the site and closer than any quarry or borrow site. This convenient resource
was used as a large-volume beach core material, displacing the equivalent volume of shingle for
redeployment on the seaward face. It also supported a new road of crushed rock laid slightly to
landward on the top of the bank (see Figure 3.101) to provide access for machinery involved in
replenishment and other maintenance schemes in the future. The whole scheme used 85 000 m³ of
colliery spoil and 20 000 m³ of rip-rap.
Figure 3.101
3.14
Typical cross-section of the Betteshanger Sea Defence, Deal, Kent
GABIONS
Gabions are robust, versatile composite structures generally comprising double-twist wiremesh baskets filled with hard, durable stone. They can perform a variety of functions within
coastal, estuarial and fluvial environments. Applications are well documented in river
engineering, where the flexibility, permeability and durability of gabion structures have been
exploited to provide robust, sustainable and aesthetically pleasing solutions. Gabions are
routinely used to construct retaining structures, for scour protection, channel linings and
weirs for hydraulic structures, and for erosion protection on riverbank revetments.
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3.14 Gabions
Like many other construction technologies, gabions require proper engineering, design, and
installation to perform at their best and this is particularly so in high-energy hydraulic
environments. The selection and placing of suitable stone fill and the specification of
appropriate wire mesh size, wire diameter and corrosion protection are important steps in
this process. Figure 3.102 summarises key gabion elements, their required properties and
some typical applications. Much useful guidance is available in manufacturers’
documentation, but some of the important properties of hexagonal double-twist wire gabions
and the hard durable stone used to fill them are presented below, together with some
examples of where gabion structures have been used successfully.
Gabion stone
!
Durability
!
Grading
1
2
3
Gabion structures
Gabion basket
!
Retaining walls
!
Strength
!
Revetments
!
Flexibility
!
Scour protection
!
Durability
!
Channel linings
!
Weirs
4
Geotextile filter
!
Filtration
!
Flexibility
!
Durability
Figure 3.102
3.14.1
5
Key features and applications of gabion structures
6
Classification of gabions
Gabions can be classified into box gabions, gabion mattresses and sack gabions, as defined below
(definitions based on ASTM A975-97, 2003):
!
box gabions are double-twisted wire-mesh containers of variable sizes, uniformly
partitioned into internal cells, and filled with durable stone (see Figure 3.103). A typical
box gabion would have dimensions of 2 m (length, l) × 1 m (width, w) × 1 m (height, h)
and comprise mesh type 80 mm × 100 mm
!
gabion mattresses are gabions with relatively small height dimensions compared to
length and width and would usually be of smaller mesh type (see Figure 3.103). A typical
gabion mattress would have dimensions of 6 m (length) × 2 m (width) × 0.15–0.30 m
(height) and comprise mesh type 60 mm × 80 mm. Gabion mattresses rarely exceed 0.5
m in height for practical reasons
!
7
8
sack gabions, rock rolls or tubular gabions are names adopted to describe sausage-like
gabions that are used mainly in fluvial engineering for the toe protection of a bank.
These types of gabions are not specifically discussed in this section.
9
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Figure 3.103
A typical box gabion (top) and
gabion mattress (bottom)
3.14.2
Gabion components
3.14.2.1
Properties of gabion mesh
Most gabions are manufactured using double-twisted wire mesh, which enables the
completed structures to deform significantly without failing and also prevents unravelling in
the event that the mesh is cut (see Figure 3.104).
Figure 3.104
274
The advantage of double-twisted over chain link mesh
CIRIA C683
3.14 Gabions
The double-twisted wire mesh and the lacing wire or split rings used to construct the gabions
should conform to the relevant standards. Current European standards refer only to the
mechanical and corrosion protection properties of the wire and the mesh, and none exists
for the factory manufacture of gabions. The most relevant existing standard for gabion
manufacture is ASTM A975-97 (2003), which has been adopted in the United States. A
summary of the relevant European standards and their scope is presented in Table 3.51.
Table 3.51
European standards for double-twisted wire mesh
Wire properties
Steel wire composition
European testing standards
EN 10218-2:1997
2
Content
Steel composition, strength
Steel mesh composition EN 10223-3:1998
Wire diameter, d (mm), depends on mesh size:
mesh 60 × 80 mm
" wire: d = 2.2 or 2.4 mm
mesh 80 × 100 mm
" wire: d = 2.7 mm
mesh 100 × 120 mm " wire: d = 2.7 or 3 mm
Corrosion protection
(galvanising)
EN 10244-1:2001
EN 10244-2:2001
Thickness of the coating conforms to class A, mass of
coating, mc, depends on wire diameter, d (mm):
d = 2.2 and 2.4 mm:
mc = 230 g/m²
d = 2.7 mm:
mc = 245 g/m²
d = 3.0 mm:
mc = 255 g/m²
Corrosion protection
(polymer coating)
EN 10245-1:2001
EN 10245-2:2001
EN 10245-3:2001
Requirements for organic coatings, PVC or PE:
thickness, composition, strength, durability, flexibility
3
4
5
The most common mesh types and wire diameters used in river and coastal works are
summarised in Table 3.52.
Table 3.52
1
Common mesh types
Mesh type (mm)
Wire diameter
(mm)
Ultimate tensile strength
(kN/m)
60 × 80
2.2
35
80 × 100
2.7
43
80 × 100
3.0
51
100 × 120
3.0
43
6
7
Corrosion protection for the mesh is provided in two ways: first by the process of galvanising
the wire and second by an additional polymer coating, typically PVC.
For river and coastal works the wire should be of heavy galvanised type (Class A, EN 10244)
and may comprise conventional zinc galvanising or, more commonly in recent years, a Galfan
alloy comprising 95 per cent zinc, 5 per cent aluminium and traces of rare earth mischmetal.
The Galfan technology was developed by the International Lead and Zinc Research
Organization (ILZRO) in the mid-1990s, and laboratory tests showed that a Galfan coating is
three to four times more durable than the same amount of conventional zinc protection,
particularly in aggressive saline conditions. The galvanised wire is often further protected with
an additional polymer coating, usually PVC, manufactured in accordance with EN 10245:2001.
Conventional galvanised zinc PVC-coated gabion mattresses have been in place and shown to
be durable in chemically aggressive hydraulic environments for more than 40 years to date.
Where problems have occurred in coastal works, these have been shown to be the result of
physical attrition from stones thrown up by waves or caused by poor construction where
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wave action has caused internal abrasion of the wire as stone moves within the gabion.
Successful examples exist where properly engineered gabion mattress revetments have been
constructed to protect eroding sandy beaches and problems are rare in river and estuarine
environments, where wave and scour energy levels are significantly lower.
3.14.2.2
Specification for durable gabion stone
Gabion stone should be strong and durable and typically it will be convenient to specify
quality using EN 13383. Mudstones and other argillaceous weak rocks should be avoided if
possible, primarily because they tend to degrade once placed. A suitable grading is the EN
13383 standard coarse grading 90/180 mm, (see Table 3.5, Section 3.4) specifically designed
for gabion use. In France, stones used for gabion filling should conform to NF P 94-325-1
(2004).
Guidance on the stone quality to be used in gabions is given in Table 3.53.
Table 3.53
Suggested requirements for stones used in gabion boxes and mattresses
Property
European standard reference
Suggested requirements
Compressive strength (EN 1926:1999)
EN 13383–1:2002
Class EN 13383-1:2002: CS60
(see Section 3.7.1)
Los Angeles, LA (EN 1097-2:1998)
Fragmentability, FR (EN 1097-2 :1998)
LA < 45
or LA > 45 and FR < 7
Resistance to attrition
Micro-Deval (EN 1097-1:1996)
Fragmentability FR (EN 1097-2:1998)
MDE < 45
or MDE > 45 and FR < 7
Resistance to freeze and thaw
EN 13383-1:2002
Category for FTA:
Loss of mass < 0.5 per cent
Density of rock
EN 13383-2:2002
Apparent density > 2.2 t/m³
Armourstone grading
EN 13383-1:2002 2
CP90/180 or equivalent (see
Section 3.4.3.2)
(or CP90/130 for mattresses)
Shape
–
No specific requirement
Type of rock
Petrography
Calcareous, siliceous,
metamorphic or igneous rock
Mechanical strength of rock 1
Notes
1 Either test may be considered.
2 In France, NF P 94-325-1 also applies.
3.14.3
Properties of gabion stone
3.14.3.1
Physical properties of gabions
The void porosity of gabions varies depending upon the type of rock fill and the nature of
the filling operation. Values can vary from 25 to 35 per cent. Values of 25 per cent would be
appropriate when stone fill is carefully hand-placed, while 35 per cent would be typical of
gabions filled for the most part by mechanical means. For the design of retaining structures a
conservative value of 40 cent is often adopted. A consequence of their high porosity is that
gabions are highly permeable.
Tests have been undertaken on gabions to assess their compression and shear strength
characteristics. The compression strength of a gabion depends on the type of mesh, wire
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3.14 Gabions
diameter and rock used to fill the baskets. Currently there is no standard for testing the
compression strength of gabions, but testing on gabions with 80 × 100 mm mesh and 2.7 mm
wire diameter, filled with 80/200 mm stone fill, has indicated an ultimate compression stress
of 4.5 MPa at failure, with strains of 50–60 per cent, highlighting the flexible but robust
nature of gabions (see Figure 3.105).
The shear strength of gabions also depends on the type of mesh, wire diameter, and type of
stone used to fill the baskets and experience has suggested that gabions have a shearing
resistance very similar to an equivalent soil with a relatively high friction angle (35–45°) and
an apparent cohesion (up to 40 kPa) provided by the confining effect of the wire basket.
Currently there is no standard for testing gabion shear strength.
1
2
3
4
5
6
Figure 3.105
3.14.3.2
A compression strength test on a gabion, showing failure of the gabion
Hydraulic properties of gabions
The response of gabions and gabion mattresses to hydraulic loading has been studied by a
number of commercial and research organisations. For gabions under current attack, this
research has led to critical and limiting flow velocities and design equations that take into
account effects of turbulence. The critical velocity is defined in literature as the velocity
required to initiate movement of the stones within the gabion mattress and the limiting
velocity is the velocity at which the gabion mattress reaches the acceptable limit of
deformation. For gabion mattresses under current attack it was found that mattresses with a
thickness of 150 mm have a limiting velocity of 2–3.5 m/s, while mattresses with a thickness of
300 mm can resist velocities of 4–5.5 m/s. Box gabions can be suitable for the protection of
river beds and banks subject to heavy current attack and can be stable at flow velocities of the
order of 5–6 m/s (or more, depending on the quality of construction and assembly).
7
Section 5.2.3.1 presents two design equations, developed by Pilarczyk (1995) and Escarameia
and May (1992) for gabions under current attack that take into account effects of turbulence.
9
8
For gabions under wave attack, design equations are presented in Section 5.2.2.7. These
equations developed by Pilarczyk (1990, 1998) can be used to determine the required gabion
thickness, D′ (m), and stone size of the filling material, Dn50 (m), for moderate wave conditions.
More information on hydraulic properties of gabions can also be found in Escarameia (1998).
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3.14.4
Applications of gabions
Applications of gabions and gabion mattresses in fluvial applications are discussed in Chapter 8.
Typically in these applications gabions will be exposed to currents and vessel-induced waves.
Examples of gabion applications in rivers are shown in Figures 3.106 and 3.107.
Figure 3.106
Gabion riverbank protection
Figure 3.107
Gabion protection to a river channel – the bank is exposed to
current attack only under high flows during flood conditions
In the marine environment, waves repeatedly strike the shore all year round and are much
more aggressive than vessel-induced waves. Because of the aggressiveness of the marine
environment arising from wave and salt action, the following precautions should be followed
if gabions are to be used:
278
!
gabions should not be exposed directly to sea waves (waves tend to make stones move
within the gabions and the wire mesh can be eroded and cut). The solution is to place
heavy armourstone as the primary defence to dissipate a large proportion of the wave
energy (see Figure 3.108)
!
in the event of exposure to sea waves, bituminous grouting may help prevent stone
displacements in the gabions
!
the most highly corrosion-resistant galvanisation process should be used, together with
plastic coating.
CIRIA C683
3.15 Grouted stone materials
1
2
3
Figure 3.108
3.15
Gabion baskets used as retaining wall behind primary armour
4
GROUTED STONE MATERIALS
The stability of loose granular materials (gravel or crushed stone) or open blockwork
elements in new or existing rock structures can be improved by grouting. The grouting binds
smaller grains, stones and elements together. Stone or element sizes may therefore be
reduced, making more economic use of available granular materials. The grouting can be
executed with cement- or bitumen-based materials. Cement-based grouting, which is most
commonly used in association with hand pitched stone, is discussed in Section 3.15.1,
bitumen-based systems are discussed in Section 3.15.2.
3.15.1
Concrete grouts
The main cement-bound material that is used for stability improvement in hydraulic
engineering is colloidal concrete grout. Concrete grout for stone pitching requires good flow
behaviour and optimal resistance to segregation. This last factor is very important for
underwater applications, particularly when exposed to currents and wave motion. Normal
concrete is susceptible to segregation and washing out of fine aggregates in these situations.
Colloidal concrete has been specially developed to meet this requirement.
The colloidal character of concrete grout is achieved by addition of modified natural
polymers. The mix is optimised to meet specific requirements depending on the penetration
depth and coarseness of the stone layer to be grouted, or the spacing between stone pitching.
Colloidal concrete has good flow behaviour, although it is relatively stiff compared with
normal concrete mixes. Because of the low workability and the desired density the optimal
slump is usually 180–200 mm, although the water/cement ratio is relatively high because of
the inclusion of special additives.
Two types of colloidal concrete are used: dense and open-textured. The dense variety is
mostly used for grouting applications, while the open variety is also used in open layer
revetment construction (where a thickness of at least 150 mm is required to ensure sufficient
strength). The dense variety has a (system) density of 2200–2350 kg/m³ and the permeability,
k, is less than that of normal concrete. Open-textured colloidal concrete uses very little fine
aggregate and has a (system) density of 1700–2000 kg/m³. The penetration is limited and the
permeability, k, is between 3 × 10-3 and 5 × 10-3 m/s. Grouting depths achievable with the
open-textured variety are less than with the dense mortar.
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Dense colloidal concrete is available in the same crushing and tensile strengths as normal
concrete, but open colloidal concrete is only available in lower crushing strengths. The
modulus of elasticity, E (N/mm²), of colloidal concrete is about 20 per cent lower than normal
concrete and shrinkage is greater. The usual tests for normal concrete, such as slump, air
content and density, are applicable to colloidal concrete, but a special test has been developed
for resistance to washing out.
The stiffness (low workability) of colloidal concrete means that although it has the advantage
of not segregating during transport, the potential for pumping of the dense variety is less
than for normal concrete and the open variety cannot be pumped at all. Despite the
colloidal character, special methods need to be introduced for underwater grouting, to avoid
washing out of fines and to ensure accurate placing. Before application of the concrete, the
stone to be grouted should be cleaned if there needs to be a good adherence between the
grout and stones.
For a more extensive discussion of cement-bound materials reference is made to CUR Report
156 (CUR, 1992).
3.15.2
Bituminous bound materials
Asphalt mixtures are used extensively in hydraulic engineering, including as revetments to
protect dikes, dams and groynes, as bottom or foreshore protection, as a water-sealing layer
in canals, reservoirs and dams and as a core material in bunds. Some asphalt mixtures are
used as a component for rock revetments, other mixtures are used directly as a revetment.
The most commonly used asphalt mixtures are:
!
asphaltic concrete
!
asphalt mastic
!
asphalt grout
!
open stone asphalt
!
lean sand asphalt.
In the following paragraphs a description is given of mixture-specific properties, the most
commonly used compositions and uses by type of asphalt mixtures. More information can be
found in the TAW Technical report on the use of asphalt in water defences (TAW, 2002).
3.15.2.1
Asphaltic concrete
Asphaltic concrete is a continuously graded mixture of crushed stone or gravel, sand and
filler in which the pores (voids) are almost entirely filled with bitumen. The mixture usually
consists of crushed stone or gravel (50 per cent), sand (42 per cent), filler (8 per cent) and
bitumen (6.5 per cent).
The high stone content makes the mixture very stable and it is watertight and sandtight
because of the small proportion of voids (3–6 per cent), resulting in a very durable material.
Asphaltic concrete is therefore extremely suitable for use in revetments. It is preferably
constructed in one layer (even when the required layer is very thick) and compacted
mechanically. Asphaltic concrete is only applied above the high tide level.
After it has been applied, asphaltic concrete forms a rigid slab, which is particularly resistant to
hydraulic loads such as wave impacts. Nevertheless, because of the high bitumen content, the
slab is still flexible enough to be able to follow some settlement of the ground. An asphaltic
concrete revetment is accessible to vehicles and pedestrians, for example tourists. It is common
to apply a seal coat of bitumen emulsion and grit to increase durability.
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3.15 Grouted stone materials
3.15.2.2
1
Asphalt mastic
Asphalt mastic is a continuously graded mixture of sand and filler with an excess of bitumen.
The mixture usually consists of sand (66.5 per cent), filler (16.5 per cent) and bitumen (17.0
per cent in). Due to the excess of bitumen, at the application temperature (100–190 °C) it is a
pourable and dense mixture that is not compacted mechanically (indeed it cannot be
compacted). After cooling, it is a stable, flexible and dense mixture, as a result of which it is
particularly durable.
Asphalt mastic is used as a flexible bottom and toe protection (slab) and as a penetration
material, both above and underwater. It is also used for grouting joints of stone pitching, as a
repair agent and as a sealant.
3.15.2.3
Asphalt grout
Asphalt grout is a mixture of gravel and an excess of asphalt mastic. The mixture usually
consists of gravel 4/16 (30 per cent) and asphalt mastic (70 per cent). The gravel serves as a
filler to prevent sagging and segregation of the mixture and sometimes to limit the depth of
penetration. The gravel also reduces the expensive bitumen content. The excess of asphalt
mastic means that, at the application temperature (100–190 °C), it is a pourable and dense
mixture that is not compacted (like asphalt mastic, it cannot be compacted). After cooling, it
is a stable, flexible and dense mixture, and so is particularly durable.
Asphalt grout is primarily used as a penetration material for rock revetments (only above
water) and also as a flexible bottom and toe protection (slab) and as a repair agent for
damaged revetments. It is also extremely suitable for making temporary repairs to damaged
rock revetments (even under extreme conditions).
Asphalt grouting can be applied in different ways (see Figure 3.109). With full penetration all
the voids in the stone layer are filled with asphalt grout, while with pattern penetration the
stone layer is partly penetrated following a set pattern. Pattern penetration can be done in
strips or dots. TAW (2002) recommends not to use surface penetration, a method where the
grouting is uniformly spread over the whole surface, as this may lead to a build-up of
hydraulic pressures beneath the impermeable surface layer.
2
3
4
5
6
7
8
Figure 3.109
Grout penetration methods for a rock revetment
In Section 5.2.2.7 design guidance is given for using asphalt grouting on slopes under wave
attack.
3.15.2.4
Open stone asphalt
Open stone asphalt is a mixture of coarse and gap-graded crushed stone that is coated with
asphalt mastic. The mixture usually consists of 80 per cent crushed stone and 20 per cent
CIRIA C683
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asphalt mastic. Because of the high crushed stone content, the asphalt has a large number of
voids, making it permeable to both water and soil. A soil-tight filter (geotextile or lean sand
asphalt) ought therefore to be placed below an open stone asphalt revetment. Open stone
asphalt is used as a porous cover layer and its stability (resulting from the high stone content)
means that it can be applied on steep slopes.
For open stone asphalt to be durable, the stone needs to be coated with a thick, bitumen-rich
asphalt mastic. Materials that prevent sagging are sometimes added to the asphalt mastic,
making it possible to apply a thicker cladding that does not drip off the stone. Open stone
asphalt can also be applied as a prefabricated mattress.
Vegetation can develop easily on revetments made of open stone asphalt because the material
has a high proportion of interconnecting pores. Animal organisms such as barnacles, mussels
and oysters can also attach themselves easily to the material, which thereby can combine
water defence with other functions such as the enhancement of nature and landscape.
3.15.2.5
Lean sand asphalt
Lean sand asphalt (bituminous sand) is a mixture of sand and a small amount of bitumen.
Usually sand extracted at the site is used, which is clad with 3–5 per cent bitumen. The small
amount of bitumen barely fills the voids, so the material is very porous and water-permeable.
The void rate of this very underfilled asphalt is 30–40 per cent.
The high sand content means that the stability of this material is comparable with the sand
that has been used. However, this only applies if the load has a long duration; for loads of
short duration, the bitumen makes lean sand asphalt far more stable than sand. Because of
the open structure and the small amount of bitumen, lean sand asphalt is less durable than
mixtures such as asphaltic concrete and asphalt grout. The bitumen coats the sand with an
extremely thin layer and is therefore concentrated at the contact points.
Lean sand asphalt is used in bulk underwater and above water as a core material for bunds
and breakwaters. Its lasting cohesion makes this an attractive material for use in a bund. It is
also used as a filter layer and sometimes as a (temporary) revetment. In general, lean sand
asphalt is not compacted; this is recommended only if it is used as a (temporary) revetment.
Non-compacted lean sand asphalt has the same permeability as the sand from which it is
made. Adding a filler to the mixture and compacting increases the durability of the material
but reduces its permeability.
3.16
GEOTEXTILES AND GEOSYSTEMS
Geotextiles are often underestimated in their contribution to the stability of a hydraulic
defence structure partly because their unit cost is so small compared with armourstone. The
consequences of not designing and specifying them correctly can be disastrous and can
jeopardise the stability of the whole structure. With proper specification and installation they
can provide, in some instances, enormous savings to a project and increase the life of the
structure significantly. Material specification is discussed in Section 3.16.5 and guidance on
construction specification is given in Appendix A1.
Design information on geotextiles is presented in Section 5.4.3.6. Further details can be
found in Pilarczyk (2000), Van Herpen (1995), Van Santvoort et al (1994), Koerner (1990)
and PIANC (1987 and 1992). Reference is also made to the proceedings of the EuroGeo
conferences and the proceedings of the International Conferences on Geosynthetics.
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3.16 Geotextiles and geosystems
3.16.1
Functions of geotextiles
1
Geotextiles are permeable sheet materials commonly made from synthetic polymer-based
materials. They are used in hydraulic engineering in conjunction with granular materials as
an integral part of hydraulic structures. Geotextiles are part of a family of sheet materials
known as geosynthetics that are used in many geotechnical applications. There are five main
categories of geosynthetic – geotextiles (non-woven and woven), geogrids, geonets,
geomembranes and related products such as erosion control mats and engineering cuspates
(void spacers). There are many grades of each type and these basic types can be combined in
many ways to form specially enhanced geocomposites. In some instances the materials can be
formed into gabions or bags of different shapes. Geotextiles are generally supplied in roll form.
2
Geosynthetics perform five basic geotechnical functions:
3
!
separation
!
filtration
!
transmission
!
reinforcement
!
protection.
4
The most common functions used in hydraulic engineering are:
!
filter/separators. A geotextile is placed on lower permeability beach material to prevent
the escape of fine particles while allowing the free passage of water. The geotextile
provides a stable and consistent bedding layer, often saving the need for one of more
layers of armourstone and potentially resulting in cost savings.
!
reinforcement. Each geotextile has tensile properties and in some instances the
reinforcing function is dominant when used either to reinforce the toe of a structure or
to secure breakwaters placed on soft, low-load-bearing soils. The geotextile prevents
deep-seated slips in the embankment and allows the embankment to be built without the
need for removal or reconsolidation of the soft soil.
The most commonly used geosynthetics in hydraulic engineering are non-woven and woven
geotextiles. These are delivered to site on thick cardboard tubes up to 6 m wide up to 200 m
long and sheathed in a plastic, light-resistant sleeve to protect the material from sunlight
while it is being stored before use.
3.16.2
Types of geotextile
3.16.2.1
Non-woven geotextiles
Non-woven geotextiles are textile structures produced either mechanically (needle-punching)
or by thermal bonding; see example in Figure 3.110. They can be categorised by the fibre
types and bonding method used.
CIRIA C683
!
needle-punched staple fibre fabrics are made from short (staple) fibres, which are
carded (combed), layered into various thicknesses and then needle-punched to
mechanically interlock the fibres into an even, thick fabric
!
needle-punched continuous-filament fabrics are laid in an even pattern to form a sheet
and then needled-punched. Needle-punched fabrics are usually made from
polypropylene (PP), high-density polyethylene (HDPE) or polyester (PETP)
!
thermally bonded continuous-filament fabrics are hot-extruded into even layers and are
hot-rolled together, causing fibres to bond together by surface contact to form a sheet.
They are made either from a mix of polymers, one having a lower melting point than the
283
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other, or from sheathed fibres where the outer coating has the lower melting point.
Typical polymers used are polypropylene (PP) or high-density polyethylene (HDPE).
Figure 3.110
3.16.2.2
Non-woven geotextile (courtesy Geofabrics)
Woven geotextiles
Woven geotextiles are flat structures of at least two sets of threads woven at right angles; see
Figure 3.111. The sets of threads are referred to as the warp running lengthwise and the
weft running across. Woven geotextiles can be categorised by the type of thread and the
tightness of the weave.
!
monofilament fabrics are gauze meshes that offer small resistance to through-flow. The
mesh size must be adapted to the grain size of the material to be retained. Monofilament
fabrics are principally made from HDPE or PP
!
tape fabrics are made form very long strips of stretched HDPE or PP film, which are laid
untwisted and flat in the fabric. They are laid closely together, resulting in limited
openings in the fabric
!
split-film fabrics are made from fibrillated yarns of PP or HDPE. The size of the
openings in the fabric depends on the thickness and form of the cross-section of the
yarns and the fabric construction. Split-film fabrics are generally heavy. Tape and splitfilm fabrics are often called slit-films
!
multifilament fabrics are often described as cloth because they tend to have a textile
appearance and are twisted or untwisted multifilament yarns. These fabrics are usually
made from polyamide (PA 6 or PA 6.6) or PETP.
These thread types can also be mixed to form other families of wovens.
Figure 3.111
284
Non-woven geotextiles (courtesy Ten Cate)
CIRIA C683
3.16 Geotextiles and geosystems
3.16.3
1
Geotextile properties and testing
Measurement of the various basic properties of geotextiles is carried out in the laboratory
using specially designed tests to give the designer index values for comparison of one
geotextile to another and to ensure consistency of product delivered to site. The European
(CEN) and International Standards (ISO) committees have devised tests and the relevant
tests should be used to define the properties required for the application in question. In
Europe generic recommendations are given in the standard EN 13253:2001: Geotextiles and
geotextile related products: Characteristics required for use in erosion control works (coastal protection,
bank revetments).
The relevant index tests should be used to ensure acceptable performance both from an inservice and an installation perspective.
2
3
For a filter/separator the following requirements should be considered in order of priority.
Permeability
Classic filter rules state that each layer of a filter system must be more permeable than the
layer beneath (see Section 5.4.3.6). Similar rules developed for geotextiles suggest a
coefficient of permeability 10 to 100 times greater than that of the filtered soil, especially in
wave environments. It is important that the geotextile should maintain or exceed its index
permeability while under load, ie any reorientation of the fines should not decrease
permeability. When considering drainage elements such as in dams, filtration systems and
slope protection in rivers where single directional flow is likely, the permittivity of the
geotextile should be considered. The permittivity is the discharge perpendicular to the
geotextile per unit pressure head difference and per unit area, expressed in units of 1/s.
Blocking and clogging in single directional flow resulting from biological or chemical buildup (residues) can reduce the permittivity considerably. As a general rule, the correct
geotextile is used where there is no significant pressure drop over the geotextile (taking into
account possible blocking or clogging).
4
5
6
Filtration
The characteristic pore size of the geotextile has to be less than the average grain size of the
soil to be filtered to prevent loss of material through the geotextile. Established design rules
for reversing flow applications and for a typical geotextile state that the pore or opening size,
O90, of the geotextile should be less than the sieve size, D50, of the soil to be filtered. There
are variations for different geotextiles, however, so this should be checked against
recommendations made in EN ISO 12956.
Extensibility
The load imposed on a geotextile by overlying armourstone is not evenly distributed. The
highest stress concentrations will be at locations where the stones are in contact with the
geotextile, which will impose high localised strains. The geotextile needs to have a high strain
capacity to allow it to deform around the stones without rupturing and without loss of
hydraulic properties. Although design drawings show the geotextile in a single plane, in
reality it is forced to take up a highly deformed shape.
7
8
9
Puncture resistance
The geotextile must be able to withstand puncturing loads imposed both during installation
and then during service. The mass, angularity and drop height of the armour stones being
placed directly on the geotextile, together with the haste with which the contractor has to
work in the short tidal windows available, all contribute to the puncturing load the geotextile
CIRIA C683
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10
3 Materials
will experience. Wave action causing movement of overlying armour stones may cause
puncturing or wear of the geotextile while in service. Differential settlement in the subsoil
may also locally increase strain on the fabric.
Thickness
Thickness is required to cushion penetrating loads under the angular points of the overlying
rock and also to provide a lateral drainage path where the surface is occluded by the
overlying armourstone. The lateral drainage capacity is defined by the geotextile’s
transmissivity under load.
Durability
Strength and puncture resistance reduce over time by oxidation and in some instances
hydrolysis. Durability may be influenced by temperature, UV radiation, pollution in the
water, air or soil.
The relevant index tests that most closely match these requirements are:
!
water flow normal to the plane (EN ISO 11058) – closely linked to permeability. Water is
passed through the geotextile under a constant head of water
!
pore size (EN ISO 12956) – defines the opening size of a geotextile and its ability to trap
particles and prevent their passage through the geotextile. The geotextile is clamped
and measured sand particles are washed through the fabric and the percentage passing
is calculated
!
minimum tensile extension (EN ISO 10319) – defines the total extension or elongation
at break in all directions allowing differential movement without break under the
armour stones
!
tensile strength (EN ISO 10319) – simulates the geotextile’s ability to be handled on site
using heavy excavators or equipment. The geotextile is clamped between two jaws and
stretched until break and the tensile strength and elongation (above) is recorded
!
cone drop perforation (EN 918) – simulates the dynamic impact of stones dropped on to
the surface during installation. A metal cone is dropped on to a sample clamped in Orings and the resultant hole is measured
!
static puncture test (CBR) (EN ISO 12236) – simulates the biaxial strain of a rock
attempting over time under heavy load to push through the fabric. A sample is clamped
in O-rings and a plunger is pushed through it. Break strength and displacement are
recorded
!
thickness and thickness reduction under load – this simulates heavy localised
compression of a thick geotextile that has been designed to retain some in-plane flow to
relieve pore water pressures. Thickness is measured under loads of 2 kPa and 200 kPa.
Specification of geoxtiles in accordance with these test requirements is discussed in Section
3.16.5.
The ultimate test for a geotextile is a simulation of site conditions in either an on-site
performance test or a trial installation. To prove the efficacy of the installation method the
designer can specify a site damage test such as a rock drop test where a pad of geotextile is
laid on prepared beach material and held taut by at least nine stones around its perimeter. A
rock similar to those used in the revetment is dropped on to the surface from a maximum
construction height likely, say 2 m, as a worst case and then the armourstone is carefully
removed. There should be no damage holes occurring. This can be carried out at the site of
the quarry which ever is easiest to set up simulation conditions.
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3.16 Geotextiles and geosystems
Different characteristics are important where a geotextile is primarily used as reinforcement,
for example as base reinforcement to the underside of a breakwater constructed on soft silts.
Where the geotextile is expected to be experience high load and prevent spreading or slip
failure of the embankment, there is a requirement for high tensile strength with low
extension. When a geotextile is subjected to high load over a period of time, especially in
saline conditions, the long term creep (elongation over time under constant load) should be
considered.
Most index tests are short-term, low-cost and repeatable and ensure consistency of product in
production. Each manufacturer must have a recognised and independently audited quality
control system. Tests relevant to the application should be carried out at agreed regular
intervals on batches of geotextile. Certificates should then be produced to confirm
consistency of the supplied product. The laboratory, either in house or external, should be
regularly monitored by a recognised standards regulator. In addition, the designer should
request samples taken from materials delivered to site for additional testing if required.
In most European countries, geotextiles are required to be CE marked for the application.
This will, for example, certify the geotextile for “F” filtration applications and “R”
reinforcing applications specifically for coastal and river applications. A CE mark certificate is
supplied, which guarantees that the geotextile meets published values. Independent
laboratories monitor testing carried out by any manufacturer with CE marked products.
To establish durability requirements there are a series of abrasion, UV resistance, oxidation
and chemical immersion tests defined in EN and ISO standards, that should be selected based
on the specific site conditions. One of the most common issues regarding durability is
exposure to UV light and the designer is advised to specify a proven method of protecting the
fibres, such as a certain percentage of carbon black in the fibres. Properties of the polymers
used in the geotextile will depend on the immediate environment, in particular temperature
and whether water is saline or polluted. Properties may also differ in the short and long term.
Tests to prove the stability of geotextiles in the short and long term should be undertaken.
3.16.4
2
3
4
5
6
Construction issues
In addition to the general properties of the geotextile, special attention should be made to
transitions including seams between geotextile elements, overlaps, transitions to other
elements and connections to anchoring systems. Geotextiles are usually jointed with a handsewing machine using the prayer seam in a double line of durable thread. Overlaps should
take account of subsoil movement, placement methods and visibility.
7
Careful consideration should also be given to the placement method for the geotextile.
Geotextiles can be placed in the structure separately from the other materials. This can be
quite complicated, however, if done underwater, especially with waves and currents.
Therefore, in some cases the geotextile may be connected to other materials or prefabricated
elements which can be placed more easily, for example:
8
!
enclosing sand in a large sandbag (geocontainer or geotube) or other geosystem
!
connection to mattresses of other materials such as wooden fascines, concrete blocks,
steel or (open) asphalt, gabions (Reno mattresses).
9
Further discussion on construction issues for geotextiles is given in Section 9.7.1. Appendix 1
covers specification requirements for the installation of geotextiles. There is significant
specialist experience in design and construction techniques. Many manufacturers and
specialist installers have developed and published techniques that aid the performance and
installation of geotextiles in the hydraulic environment.
CIRIA C683
1
287
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3 Materials
3.16.5
Geotextile specification
Geotextile filter fabric should be an approved proprietary geotextile. The common material
property parameters that need to be specified are form (woven or non-woven), type of
polymer, weight, thickness, tensile strength, CBR puncture resistance, pore size, O90 (mm),
and permeability (see Section 3.16.3). Tables 3.54 and 3.55 provide material specification
templates for non-woven and woven geotextiles respectively. The typical values should be
inserted for the specific application in question. Design guidance is given in Section 5.4.3.6.
Detailed design guidance for geotextiles is given in BAW (1993).
The following clauses may typically be used to specify the properties of the geotextile
material:
Non-woven geotextile, for example as a filter/separator beneath rock armour
The geotextile shall be a non-woven fabric manufactured by needle-punching virgin, staple
fibres of polypropylene incorporating a minimum of 1 per cent by mass of active carbon
black. Geotextiles manufactured from fibres of more than one polymer will not be permitted.
The geotextile shall have the properties as given in Table 3.54.
Table 3.54
Specification template for a non-woven geotextile
Unit
Typical value
(see note)
Allowable tolerance
for typical value
Water flow normal to the plane of the
EN ISO 11058
geotextile @ 50 mm head
l/s/m²
………
-10%
Coefficient of permeability
EN ISO 11058
m/s
………
-10%
Apparent pore size – 90% finer, O90
EN ISO 12956
mm
………
+10%
Tensile extension
EN ISO 10319
%
………
-10%
Tensile strength
EN ISO 10319
kN/m
………
-10%
Cone drop perforation hole diameter
EN 918
mm
………
–
Static puncture strength, CBR
EN ISO 12236
kN
………
-10%
Push-through displacement
EN ISO 12236
mm
………
-10%
Thickness reduction for pressure
increase from 2 kPa to 200 kPa
EN 964
%
………
+10%
Thickness @ 2 kPa
EN ISO 964-1
mm
………
-10%
Test description
Approved test method
Note
Typical values to be inserted for specific application.
Reinforcing geotextile used beneath bedding stone for reinforced toe
The geotextile to be used as a reinforcement beneath the bedding stone as a reinforced toe
structure shall be a woven fabric manufactured using virgin, high-tenacity fibrillated yarns of
polypropylene incorporating a minimum of 1 per cent by mass of active carbon black.
Geotextiles manufactured from fibres of more than one polymer will not be permitted.
The geotextile shall have the properties as given in Table 3.55.
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3.16 Geotextiles and geosystems
Table 3.55
1
Specification of a woven geotextile
Approved test method
Unit
Typical value
(see note)
Allowable tolerance
for typical value
Tensile strength
EN ISO 10319
kN/m
………
-5%
Tensile extension
EN ISO 10319
%
………
+5%
Creep over 10 000 hours of testing
EN ISO 13431
%
………
+1%
Apparent pore size – 90% finer, O90
EN ISO 12956
mm
………
+10%
Water flow normal to the plane of the
EN ISO 11058
geotextile @50 mm head
l/s/m²
………
-10%
Test description
Static puncture strength, CBR
EN ISO 12236
kN
………
5%
Push-through displacement
EN ISO 12236
mm
………
+5%
Thickness @2 kPa
EN ISO 964-1
mm
………
-5%
2
3
4
Note
Typical values to be inserted for specific application.
In addition to the minimum characteristics given in Tables 3.54 and 3.55, the Contractor
should ensure that the geotextile (woven or non-woven) is sufficiently robust to withstand,
without being damaged, the working method of placing the geotextile and the subsequent
placing of the rock layer on top.
Samples of the proposed geotextile, typically of minimum size 300 mm × 300 mm, should
be submitted for approval together with a material property data sheet. The data sheet
should be supported by an index and performance compliance certificate issued by an
accredited geotextile filter fabric testing organisation, eg the German Bundesanstalt für
Wasserbau (BAW).
5
6
7
8
9
10
CIRIA C683
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3.17
REFERENCES
3.17.1
Publications
Aler, J, Du Mouza, J and Arnould, M (1996). “Measurement of the fragmentation efficiency
of rock mass blasting and its mining application”. Int J Rock Mech Min Sci and Geomech Abstr,
vol 33, no 2, pp 125–139
Allard, P and Blanchier, M (1980). Estimation prévisionelle de production d’enrochement. CETE
d’Aix-en-Provence
Allen, R T L (ed) (1998). Concrete in coastal structures. Thomas Telford, London
Al-Masri, M S, Amin, Y, Ibrahim, S and Al-Bich, F (2004). “Distribution of some trace metals
in Syrian phosphogypsum”. Appl Geochem, vol 19, no 5, pp 747–753
Arm, M (2003). “Mechanical properties of residues as unbound road materials –
experimental tests on MSWI bottom ash, crushed concrete and blast furnace slag”. PhD
thesis, KTH Stockholm, 148 pp
Assen, R L (2000). “Durability assessment of armourstones along the coast of Cartagena,
Colombia”. Memoirs of the Centre of Engineering Geology in the Netherlands, no 191, Delft, p 84
BAW (1993). Code of practice: use of geotextile filters on waterways Bundesanstalt für Wasserbau
[Federal Waterway Engineering and Research Institute], Karlsruhe
Blyth, F G H and de Freitas, M H (1984). A geology for engineers, 7th edn, International Students’
Edition. Edward Arnold, London, 325 pp
Bosma, C, Verhagen, H J, d’Angremond, K and Sintnicolaas, W (2003). “Void porosity
measurements in coastal structures”. In: J McKee-Smith (ed), Proc 28th int conf coastal engg,
Cardiff, 7–12 Jul 2002. World Scientific. ASCE, Reston, VA, pp 1411–1423
Bradbury, A P, Latham, J-P and Allsop, N W H (1991). “Rock armour stability formulae –
influence of stone shape and layer thickness”. In: Proc 22nd int conf coastal engg, Delft, 2–6 Jul
1990. ASCE, New York, pp 1446–1459
Brampton, A, Wallis, M and Holliday, E (2004). Potential use of alternatives to primary aggregates
in coastal and river engineeering. C590, CIRIA, London
Brown, E T (1981). Rock characterization testing and monitoring – ISRM suggested methods.
Pergamon Press, Oxford
Cassar, J and Vella, A J (2003). “Methodology to identify badly weathering limestone using
geochemistry: case study on the Lower Globigerina Limestone of the Maltese islands”. Q J
Engg Geol and Hydrogeol, vol 36, pp 85–96
Chen, G, Lee, H, Young, K L, Yue, PL, Wong, A, Tao, T and Choi, K K (2002). “Glass
recycling in cement production – an innovative approach”. Waste Management, vol 22, no 7,
pp 747–753
Chung, S H and Katsabanis, P D (2000). “Fragmentation prediction using improved
fragmentation formulae”. Fragblast, vol 4, no 2, pp 198–207
Crossman, M, Segura-Domínguez, S and Allsop, N W H (2003). Low cost structures for beach
control and coast protection: practical design guidance. R&D Technical Report CSA 6020 (SR 631),
Defra, London and Environment Agency, Bristol
Cunningham, C V B (1987). “Fragmentation estimations and the Kuz-Ram model – four years
on, for prediction of fragmentation from blasting”. In: W L Fourney and R D Dick (eds), Proc
2nd int symp rock fragmentation by blasting, Keystone, CO, 23–26 Aug. SEM, Bethel, CT, pp 475–487
CUR (1992). Cementbetonnen plaatbekledingen op dijken en oevers [Cement concrete slab revetments
used on dikes and banks]. Report 156, Research Committee C58, Civieltechnisch Centrum
Uitvoering Research en Regelgeving (CUR) [Centre for Civil Engineering Research and
Codes], Gouda
290
CIRIA C683
3.17 References
Da Gama, C D (1983). “Use of comminution theory to predict fragmentation of jointed rock
mass subjected to blasting”. Proc 1st int symp rock frag by blasting, Luleå, Sweden, 22–26 Aug,
Balkema, pp 563–579
1
Denis, A, Panet, M and Tourencq, C (1979). “Rock identification by means of continuity
index”. In: Proc 4th cong Int Soc Rock Mech, Montreux, Sep. AA Balkema, Rotterdam, pp 95–98
Dershowitz, W, Lee, G, Geier, J E, Foxford, T, LaPointe, P and Thomas, A (1998). “FracMan.
Interactive discrete feature data analysis geometric modelling and exploration simulation”.
User documentation version 2.6, Golder Associates, Redmond, WA
2
Djordjevic, N (1999). “Two-component model of blast fragmentation”. In: Proc 6th int symp
rock frag by blasting, Johannesburg, 8–12 Aug. Symposium series S21, SAIMM, Johannesburg,
pp 213–219
DMC (2003). Xbloc, effective wave protection for breakwaters and shores. Delta Marine Consultants,
Gouda
3
Dupray, S (2002). “Survey of feed-back from users of armourstone focussing on integrity
issues”. PhD progress report no 1, Imperial College, London and LRPC, Lyon
Dupray, S (2005). “Integrity of rock blocks for armouring of hydraulic works – towards fullscale test to predict mass distribution changes”. PhD thesis, Earth Sciences and Engineering
Department, Imperial College Royal School of Mines, London, 325 pp
4
Dupray, S, Latham, J-P and Durville, J L (2004). “Proposal of a full-scale destructive test
method to assess integrity of natural armourstone”. In: J Melby (ed), Proc 4th int conf coastal
structures, Portland, OR, 26–30 Aug 2003. ASCE, Reston, VA, pp 150–162
Dupray S, Latham J-P, Durville J-L, Trichet J-J and Simm J (2007) Engineering materials in
flood and coastal defences: integrity of armourstone, Environment Agency R&D Technical Report
TR3, WAS-069, Defra/Environment Agency Flood and Coastal Defence R&D Programme
5
ENPC (2005). Synthèse des travaux du projet national BHP, 2000 sur les bétons à hautes
performances. Presses de l’Ecole Nationale des Ponts et Chaussées, Marne la Vallée, 298 pp
Escarameia, M (1998). River and channel revetments: a design manual. Thomas Telford, London
Escarameia, M and May, R W P (1992). Channel protection: turbulence downstream of structures.
Report SR 313, HR Wallingford, Wallingford
6
Everist, R A (1991). “Pricing armor rock for rubble mound breakwaters”. In: O T Magoon
and W F Baird (eds), Proc workshop on durability of stone for rubble mound breakwaters, USACE,
Cleveland, OH, 22–23 May. ASCE, Reston, VA, pp 160–169
Fookes, P (1980). “An introduction to the influence of natural aggregates on the performance
and durability of concrete”. Q J Engg Geol, vol 13, pp 207–229
7
Fookes, P and Poole, A (1981). “Some preliminary considerations on the selection and
durability of rock and concrete materials for breakwaters and coastal protection”. Q J Engg
Geol, vol 14, pp 97–128
Fookes, P G and Thomas, R D (1986). “Rapid site appraisal of potential breakwater rock at
Qeshm, Iran”. Proc Inst Civ Engrs, vol 80, Oct, pp 1297–1325
François, D, Gaggl, W and Holnsteiner, R (2003). “Essais en chambre climatique sur des
mâchefers d’incinération d’ordures ménagères – appréciation du gonflement au gel et du
relargage/Climate chamber tests on municipal solid waste incinerator bottom ash –
assessment of frost heave and leaching” [in French and English]. Article 4435, Bulletin des
Laboratoires des Ponts et Chaussées, no 244-245, May-Aug, pp 113–129
Franklin, J A and Katsabanis, T (eds) (1996). Measurement of blast fragmentation. AA Balkema,
Rotterdam, p 315
Gardner, K H, Carter, R K and Shimaoka, T (2003). “Long-term leaching behavior changes
in granular waste materials due to chemical weathering processes: implications for beneficial
use”. In: T T Eighmy (ed), Beneficial use of recycled materials in transportation applications. Air
and Waste Management Association Press, Pittsburgh, pp 335–344
CIRIA C683
291
8
9
10
3 Materials
Gauss, G A and Latham, J-P (1995). “The measurement of layer thickness and the estimation
of as-built bulk density and void porosity in a rock armour revetment at Beesands, South
Devon”. Proc Inst Civ Engrs, Water, Maritime and Energy, no 112, Dec, pp 326–335
Goodman, R E (1993). Engineering geology: rock in engineering construction. John Wiley & Sons,
New York, 432 pp
Grady, D and Kipp, M (1985). “Geometric statistics and dynamic fragmentation”. J App Phys,
vol 58, no 3, pp 1210–1222
Hall, R L, Bevins, T L and Howell, G L (1987). “Drop test of Dolos armor units”.In: B L
Edge (ed), Proc 20th int conf coastal engg, Taipei, 9–14 Nov 1986. ASCE, New York
Hill, A R, Dawson, A R and Mundy, M (2001). “Utilisation of aggregate materials in road
construction and bulk fill”. J Resources, Conservation and Recycling, vol 32, no 3-4, pp 305–320
Howell, G L, Rhee, J P and Rosati, J (1989). “Stresses in Dolos armor units due to waves”. In:
D D Davidson and O T Magoon (eds), Proc seminar stresses in concrete armor units, Vicksburg, MS,
7–8 Nov. ASCE, Reston, VA, pp 164–179
ISRM (1978). “Suggested method for determining tensile strength of rock materials”. Int J
Rock Mech, Min Sci and Geomech Abstr, vol 15, pp 99–103
ISRM (1985). “Commission on Testing Methods. Suggested method for determining point
load strength (revised version)”. Int J Rock Mech, Min Sci and Geomech Abstr, vol 22, pp 51–60
ISRM (1988). “Commission on Testing Methods. Suggested method for determining the
fracture toughness of rock”. Int J Rock Mech, Min Sci and Geomech Abstr, vol 25, pp 71–96
Jimeno, C L, Jimeno, E L and Carcedo, F J A (1997). Drilling and blasting of rocks. AA
Balkema, Rotterdam
JKRMC (1996). Open pit blast design – analysis and optimisation. Julius Kruttchnitt Mineral
Research Centre, Indooroopilly, Australia, p 338
Kahriman, A, Özkan, Þ G, Sül, Ö L and Demirci, A (2001). “Estimation of the powder factor
in bench blasting from the Bond Work Index”. Mining Technology. Trans Inst Materials, Minerals
& Mining and Aus Inst Min & Metall, vol 110, no 2, Aug, Sec A, pp A114–A118
Kanchitbotla, S S, Valery, W and Morell, S (1999). “Modelling fines in blast fragmentation
and its impact on crushing and grinding”. In: C Workman Davies (ed), Proc Explo ’99. A conf
on rock breaking, Kalgoorlie, 7–11 Nov. Aus Inst Min & Metall, Carlton, Vic, pp 137–144
Karzulovic, A and Goodman, R E (1985). “Determination of principal joint frequencies”. Int J
Rock Mech, Min Sci and Geomech Abstr, vol 22, pp 471–473
Koerner, R B (1990). Designing with geosynthetics. Prentice-Hall, Englewood Cliffs, New Jersey
Konya, C J and Walter, E J (1990). Surface blast design. Prentice-Hall, Englewood Cliffs, New
Jersey, p 303
Kuznetsov, V M (1973). “The mean diameter of fragments formed by blasting rock”. Soviet
Mining Sciences, vol 9, no 2, pp 144–148
Laan, G (1981). The relation between shape and weight of pieces of rock [in Dutch]. Report MAW-R81079, Rijkwaterstaat, Delft
Laan, G (1992). “Quality assurance of armourstone in practice”. In: J-P Latham (ed), unpub
report on proc seminar on armourstone, London, pp 77–95
Laan, G (1995). “Quality and quality control for stone for hydraulic structures”. In: C R
Thorne, S R Abt, F B Barends, S T Maynord and K W Pilarczyk (eds), River, coastal and
shoreline protection: erosion control using riprap and armourstone. John Wiley & Sons, Chichester,
pp 441-458 in Thorne et al
Laan, G (1999). Water absorption of armourstone used in hydraulic engineering – study of basanite
and general regulations. Report P-DWW-99-001, Rijkswaterstaat, Delft, The Netherlands
292
CIRIA C683
3.17 References
Latham, J-P (1991). “Degradation model for rock armour in coastal engineering”. Q J Engg
Geol, vol 24, no 1, pp 101–118
1
Latham, J-P (1992). “Seminar on armourstone: production, evaluation, specification and
use”. Unpub, Queen Mary and Westfield College, University of London, 194 pp
Latham, J-P (1993). “A mill abrasion test for wear resistance of armourstone”. In: C H
McElroy and D A Lienhart (eds), Rock for erosion control. Special Technical Publication 1177,
ASTM, West Conshohocken, PA, pp 46–61
2
Latham, J-P (1998a). Advances in aggregates and armourstone evaluation. Engineering Geology
Special Publication no 13, Geol Soc, London, 197 pp
Latham, J-P (1998b). “Assessment and specification of armourstone quality – from CIRIA/CUR
(1991) to CEN (2000)”. In: J-P Latham (ed), Advances in aggregates and armourstone evaluation.
Engineering Geology Special Publication no 13, Geol Soc, London, pp 65–85
3
Latham, J-P and Gauss, G (1995). “The drop test for armourstone integrity”. In: C R Thorne, S
R Abt, F B Barends, S T Maynord and K W Pilarczyk (eds), River, coastal and shoreline protection:
erosion control using riprap and armourstone. John Wiley & Sons, Chichester, pp 481–499
Latham, J-P and Poole, A B (1988). “Abrasion testing and armourstone degradation”. Coastal
Engg, vol 12, pp 233–255
Latham, J-P and Wang H (1992). “Constraints on armourstone production rates. In: J-P
Latham (ed), Armourstone – production, evaluation, specification, use. Queen Mary and Westfield
College, London, pp 95–104
Latham, J-P, Munjiza, A and Lu, Y (2002a). “On the prediction of porosity and packing of
rock particles”. Powder Technology, vol 125, no 1, pp 10–27
Latham, J-P, Newberry, S, Mannion, M, Simm, J D and Stewart, T (2002b). “The void
porosity of rock armour in coastal structures”. Proc Inst Civ Engrs, Water and Maritime Engg,
vol 154, no 3, pp 189–198
Latham, J-P, Kemeny J, Maerz, N, Noy, M, Schleifer, J and Tose, S (2003). “A blind
comparison between results of four image analysis systems using a photo-library of piles of
sieved fragments”. Fragblast, vol 7, no 2, Jun, pp 105–132
Latham, J-P, Van Meulen, J, Dupray, S, (2006). “The specification of armourstone gradings
and EN 13383 (2002)”, Q J Eng Geol Hydroge, 2006, vol 39, pp 51–64
4
5
6
Lee, S G and de Freitas, M H (1989). “A revision of the description and classification of
weathered granite and its application to granites in Korea”. Q J Engg Geol, vol 22, pp 31–48
7
Lienhart, D A (1998). “Rock engineering rating system for assessing the suitability of
armourstone sources”. In: J-P Latham (ed), Advances in aggregates and armourstone sources.
Engineering Geology Special Publication no 13, Geol Soc, London, pp 91–106
Lienhart, D A (2003). “A systems approach to evaluation of riprap and armour stone
sources”. Env & Engg Geoscience, vol 9, no 2, May, pp 131–149
Lienhart, D and Stransky, T (1981). “Evaluation of potential sources of riprap and armor
stone – methods and considerations”. Bull Int Assoc Engg Geol, vol XVIII, no 3, pp 325–332
8
Lienhart, D A, Sayao, O J and Gerdsen A W (2002). “Predicted service life of armourstone: a
case history”. In: O T Magoon and J D Prehn (eds), Proc Breakwaters ’99, 1st int symp
monitoring breakwaters, Madison, WI, 8–10 Sep. ASCE, Reston, VA, pp 145–159
Lilly, P A (1986). “An empirical method of assessing rock mass blastability”. In: J R Davidson
(ed), Proc large open pit mining conf, Oct 86. Aus Inst Min & Metall, Carlton, Vic, pp 89–92
9
Lin, W, Rau, C and Su, R (1987). “The structural responses of Dolos armor units under
dynamic loading”. In: B L Edge (ed), Proc 20th int conf coastal engg, Taipei, 9–14 Nov 1986.
ASCE, New York
Lizotte, Y C and Scoble, M J (1994). “Geological control over blast fragmentation”. CIM
Bulletin, vol 87, no 983, pp 57–71
CIRIA C683
10
293
3 Materials
Lu, P and Latham, J-P (1996). “Estimation of blasted block size distribution of a blastpile
combining photo-scanline technique with Ros-Ram and Schuhmann models”. In: Y Guo and
T S Golosinski (eds), Proc ’96 int symp mining science and technology, Jiangsu, China. AA Balkema,
Rotterdam, pp 683–688
Lu, P and Latham, J-P (1998). “A model for the transition of block sizes during blasting”.
Fragblast, vol 2, pp 341–368
Lu, P and Latham, J-P (1999). “Developments in the assessment of in situ block size
distributions of rock masses”. Rock mech and rock engg, vol 32, pp 29–49
Luger, S A, Phelp, D T, Van Tonder, A and Holtzhausen, A H (1995). “Increased Dolos
strength by shape modification”. In: B L Edge (ed), Proc 24th int conf coastal engg, Kobe, 23–28
Oct 1994. ASCE, New York
Lutton, R J and Erikson, R L (1992). “Problems with armour-stone quality on Lakes
Michigan, Huron, Erie”. In: C H McElroy and D A Lienhart (eds), Rock for erosion control.
Special Technical Publication 1177, ASTM, West Conshohocken, PA
Magoon, O T, and Baird, W F (eds) (1991). Proc workshop on durability of stone for rubble mound
breakwaters, USACE, Cleveland, OH, 22–23 May. ASCE, Reston, VA, p 277
Marcus, D (1995). “Problems and improvement of armor stone quality for coastal structures”.
In: C R Thorne, S R Abt, F B Barends, S T Maynord and K W Pilarczyk (ed), River, coastal
and shoreline protection. John Wiley & Sons, Chichester, pp 532–542
Masters, N (2001). Sustainable use of new and recycled materials in coastal and fluvial construction: a
guidance manual. Thomas Telford, London, 204 pp
McElroy, C H and Lienhart, D A (1993). Rock for erosion control. Special Technical Publication
1177, ASTM, West Conshohocken, PA
McKibbins, L D (1995). “An assessment of armourstone potential at Hulands Quarry”. MSc
thesis, Queen Mary and Westfield College, University of London, p 222
Melby, J A and Turk, G F (1997). Core-loc concrete armor units: technical guidelines. Technical
Report CHL-97-4, US Army Corps of Engineers, Washington DC
Motz, H and Geiseler, J (2001). “Products of steel slags: an opportunity to save natural
resources”. Waste Management, vol 21, no 3, pp 285–293
Newberry, S D (2003). “An experimental investigation into the influence of geometric
properties and construction technique on the packing density of rock armour layers for
coastal engineering structures”. PhD thesis, Imperial College, University of London
Niese, M, Van Eijk, F, Laan, G and Verhoef, P (1990). “Quality assessment of large
armourstone using an acousitc velocity analysis”. Bull Int Assoc Engg Geol, vol 42, pp 57–65
ODPM (2001). Survey of arisings and use of construction and demolition waste in England and Wales,
2001. Office of the Deputy Prime Minister, London,
<www.odpm.gov.uk/stellent/groups/odpm_planning/documents/page/odpm_plan_606333.hcsp>
Ouchterlony, F (2005a). “What does the fragment size distribution of blasted rock look like?”.
In: R Holmberg, Ed, I Proc 3rd EFFE World conference on explosives and blasting, European
Federation of Explosive Engineers, UK, pp 189-199
Ouchterlony, F (2005b). “The Swebrec function: Linking fragmentation by blasting and
crushing”, Mining technology (Trans. Inst. Min. Metal A) 114 (2005) pp a29-a44
Palmström, A (2001). “Measurement and characterization of rock mass jointing”. In: V K
Sharma and K R Saxena (eds), In situ characterisation of rocks. AA Balkema, Rotterdam, pp 49–97
Perrier, J, Mathurin, J-L, Lacroix, H and Grandjean, P (2004). “Méthodes de diagnostic des
protections de berge en enrochements de la vallée du Rhône”. Article 4508, Bulletin des
Laboratoires des Ponts et Chaussées, no 252-253, Sep-Dec
Persson, P-A, Holmberg, R and Lee, J (1993). Rock blasting and explosives engineering. CRC
Press, Boca Raton, FL
294
CIRIA C683
3.17 References
1
PIANC (1987). “Guidelines for the design and construction of flexible revetments
incorporating geotextiles for inland waterways”. Supplement to Bulletin no 57, report of
InCom WG04, PIANC, Brussels
PIANC (1992). “Guidelines for the design and construction of flexible revetments
incorporating geotextiles for marine environment”. Supplement to Bulletin no 78/79, report
of MarCom WG21, PIANC, Brussels
PIANC (2005). Catalogue of prefabricated elements. Report of MarCom WG36, PIANC, Brussels
2
Pilarczyk, K W (1990). Coastal protection. AA Balkema, Rotterdam
Pilarczyk, K W (1995). “Simplified unification of stability formulae for revetments under
current and wave attack”. In: C R Thorne, S R Abt, F B Barends, S T Maynord and K W
Pilarczyk (eds), River, coastal and shoreline protection: erosion control using riprap and armourstone.
John Wiley & Sons, Chichester
3
Pilarczyk, K W (ed) (1998). Dikes and revetments: design, maintenance and safety assessment. AA
Balkema, Rotterdam
Pilarczyk, K W (2000). Geosynthetics and geosystems in hydraulic and coastal engineering. AA
Balkema, Rotterdam
4
Powers, M C (1953). “A new roundness scale for sedimentary particles”. J Sedimentary
Petrology, vol 23, no 2, pp 117–119
Priest, S (1993). Discontinuity analysis for rock engineering. Chapman & Hall, London, 467 pp
Rat, M (1973). “La reconnaissance géologique des tracés routiers, articulation des études et
méthodes de prospection”. Bulletin de Liaison des Laboratoires des Ponts et Chaussées, vol 68, NovDec, pp 33–46
5
Read, J (1988). “The control of rubble-mound construction with particular reference to
Helguvik breakwater in Iceland”. In: Proc conf Breakwaters ’88 – design of breakwaters. Thomas
Telford, London
Rosin, P and Rammler, E (1933). “The laws governing the fineness of powdered coal”. J Inst
Fuel, vol 7, pp 29–36
Segui, J B and Higgins, M (2001). “Blast design using measurement while drilling
parameters”. In: Proc Explo 2001, Hunter Valley, 28–31 Oct. Aus Inst Min & Metall, Carlton,
Vic, pp 231–236
Skarzynska, K M (1995a). “Reuse of coal mining wastes in civil engineering. Part 1:
Properties of minestone”. Waste Management, vol 15, no 1, pp 3–42
6
7
Skarzynska, K M (1995b). “Reuse of coal mining wastes in civil engineering. Part 2:
Utilization of minestone”. Waste Management, vol 15, no 2, pp 83–126
Skarzynska, K M and Michalski, P (1998). “Filtration through hydraulic embankments made
of colliery spoil: model tests”. Waste Management and Research, vol 16, no 3, pp 233–243
Slob, S, Hack, H R G K and Turner, K (2002). “An approach to automate discontinuity
measurements of rock faces using laser scanning techniques”. In: C Dinis da Gama and L
Ribeiro e Sousa (eds), Proc symp Int Soc Rock Mech EUROCK 2002, Funchal, Portugal, 25–28
Nov. Sociedade Portuguesa de Geotecnia, Lisbon, pp 87–94
8
Slob, S, Hack, H R G K, Van Knapen, B, Turner, K, Kemeny, K (2005). “A method for
automated discontinuity analysis of rock slopes with 3D laser scanning”. In: Proc
Transportation Research Board 84th annual meeting, 9–13 Jan. TRB, Washington DC, 16 pp
9
Smith, M R (ed) (1999). Stone: building stone, rockfill and armourstone in construction.
Engineering Geology Special Publication no 16, Geol Soc, London
Smith, M R, Collis, L, Fookes, P G, Lay, J, Sims, I and West, G (2001). Aggregates – sand, gravel
and crushed rock aggregates for construction purposes. Engineering Geology Special Publication no
17, Geol Soc, London
10
CIRIA C683
295
3 Materials
Sogreah (1988). Technical specifications for fabricating and placing Accropode blocks. Port and
Coastal Engineering Department, Grenoble
Sogreah (2000). General specification for Accropode armour. Port and Coastal Engineering
Department, Grenoble
Sotramer-Sogreah (1978). Tetrapods. Technical note, Sogreah, Grenoble
Stewart, T P, Newberry, S D, Latham, J-P and Simm, J (2003). Packing and voids for rock
armour in breakwaters. Report SR 621, HR Wallingford, Wallingford
Takahashi, S, Hanzawa, M, Sugiura, S, Shimosako, K and Van Der Meer, J (2004).
“Performance design of maritime structures and its application to armour stones and block of
breakwaters”. In: J Melby (ed), Proc int conf coastal structures, Portland, OR, 26–30 Aug 2003.
ASCE, Reston, VA, pp 14–26
TAW (2002). Technical manual on the use of asphalt in water defences [in Dutch]. Technical
Advisory Committee on Flood Defences, Rijkswaterstaat DWW, Delft
Thorne, C R, Abt, S R, Barends, F B, Maynord, S T and Pilarczyk, K W (1995). River, coastal
and shoreline protection: erosion control using riprap and armourstone. John Wiley & Sons,
Chichester, 765 pp
Thornton D, Kanchibotla, S S and Brunton, I (2002). “Modelling the impact of rockmass and
blast design variation on blast fragmentation”. Fragblast, vol 6, no 2, pp 168–188
Tomassichio, G R, Lamberti, A and Archetti, R (2003). “Armour stone abrasion due to
displacements in sea storms”. J Waterway, Port, Coastal and Ocean Engg, vol 129, no 5, Sep/Oct,
pp 229–232
Tourenq, C, Fourmaintraux, D and Denis, A (1971). “Propagation des ondes et discontinuités
des roches/Wave propagation and discontinuities in rock”. In: Proc rock fractures: symp Int Soc
Rock Mech, Nancy. Paper I 1
Trmal, C (2004). “Study of mechanical loadings applied to natural armourstone in cover
layer of breakwater under wave action”. MSc thesis, Faculty of Technology, University of
Plymouth, 88 pp
Tsirel, S V (1997). “Methods of granular and fragmented material packing density
calculation”. Int J Rock Mech Min Sci, vol 34, no 2, pp 263–273
Tørum, A (2003). Abrasion mill test results in relation to stone movements on berm breakwaters.
Report no IBAT/MB R2/2003, Norwegian University of Science and Technology (NTNU),
Trondheim
Tørum, A, and Krogh, S (2000). Berm breakwater – stone quality. STF22 A00207, SINTEF Civil
and Environmental Engineering, Trondheim
USACE (1990). Engineering and design: construction with large stone. EM 1110-2-2302, US Army
Corps of Engineers, Washington DC
USACE (1994). Engineering and design: hydraulic design of flood control channels. EM 1110-21601, US Army Corps of Engineers, Washington DC
USACE (2003). Coastal engineering manual [CEM] Engineer Manual 1110-2-1100, US Army
Corps of Engineers, CHL-ERDC, WES, Vicksburg, MS
Van Gent, M R A (2003). “Recent developments in the conceptual design of rubble mound
breakwaters”. In: Proc COPEDEC VI, Colombo, Sri Lanka, 15–19 Sep. Lanka Hydraulic
Institute, Colombo, Sri Lanka
Van Gent, M R A, Spaan, G B H, Plate, S E, Berendsen, E, Van der Meer, J W and
D’Angremond, K (2000). “Single-layer rubble mound breakwaters”. In: I Losada (ed), Proc
3rd int coastal structures conf, Santander, 7–10 Jun 1999. AA Balkema, Rotterdam, vol 1, pp
231–239
Van Gent, M R A, D’Angremond, K and Triemstra, R (2001). “Rubble mound breakwaters;
single armour layers and high density units”. In: N W H Allsop (ed) Proc int conf coastlines,
structures and breakwaters, ICE, London, 26–28 Sep. Thomas Telford, London
296
CIRIA C683
3.17 References
Van Herpen, J A (1995). Geotextielen in de waterbouw [Geotextiles in hydraulic engineering]. Report
174, Civieltechnische Centrum Uitvoering Research en Regelgeving (CUR) [Centre for Civil
Engineering Research and Codes], Gouda
Van Meulen, J A (1998). “Opening and operation of the Pasir Panjang quarry: a dedicated
armourstone quarry in the Malaysian jungle”. In: J-P Latham (ed), Advances in aggregates and
armourstone evaluation. Engineering Geology Special Publication no 13, Geol Soc, London, pp
107–120
1
2
Van Santvoort, G and Veldhuijzen van Zanten, R (1994). Geotextiles and geomembranes in civil
engineering: a handbook. Netherlands Geotextile Society, AA Balkema, Rotterdam
Verhoef, P N W (1992). The methylene blue test applied to geomaterials. GEOMAT.02, Delft, 85 pp
Vrijling, J K and Nooy van der Kolff, A H (1990). “Quarry yield and breakwater demand”.
In: Proc 6th cong Int Assoc Engg Geol, Amsterdam, 6–10 Aug. AA Balkema, Rotterdam, vol 4, pp
2927–2934
3
Waltham, T (2001). Foundations of engineering geology, 2nd edn. Spon Press, London, 104 pp
Wang, H (1992). “Predictions of in situ and blastpile block size distributions of rock masses
with special reference to coastal requirements”. PhD thesis, Queen Mary and Westfield
College, University of London
Wang, H, Latham, J-P and Poole, A B (1990). “In situ block size assessment from discontinuity
spacing data”. In: Proc 6th cong Int Assoc Engg Geol, Amsterdam, 6–10 Aug, pp 117–127
4
Wang, H, Latham, J-P and Poole, A B (1991a). “Blast design for armourstone production”. J
Quarry Management. Part I (Jul), pp 17–21, Part II (Aug), pp 19–22
Wang, H, Latham, J-P and Poole, A B (1991b). “In situ block size distribution for quarrying”.
Q J Engg Geol, vol 24, pp 91–99
5
Wang, H, Latham, J-P and Matheson, G D (1992a). “Design of fragmentation blasting in
surface rock excavation”. In: J A Hudson (ed), Proc symp Int Soc Rock Mech EUROCK ’92. AA
Balkema, Rotterdam, ch 41, pp 233–238
Wang, H, Latham, J-P and Poole, A B (1992b). “Producing armourstone within aggregate
quarries”. In: O T Magoon and W F Baird (eds), Proc workshop on durability of stone for rubble
mound breakwaters, USACE, Cleveland, OH, 22–23 May. ASCE, Reston, VA, pp 200–210
6
Widzyk-Capehart, E and Lilly, P (2002). “A review of general considerations for assessing
rock mass blastability and fragmentation”. Fragblast, vol 6, no 2, pp 151–168
Zhang, L and Einstein, H (2000). “Estimating the intensity of rock discontinuities”. Int J Rock
Mech and Min Sci, vol 37, pp 819–837
7
8
9
10
CIRIA C683
297
3 Materials
3.17.2
Standards
3.17.2.1
ASTM
ASTM A975-97 (2003) Standard specification for double-twisted hexagonal mesh gabions and revet
mattresses (metallic-coated steel wire or metallic-coated steel wire with poly(vinyl chloride) (PVC) coating)
ASTM C88-99a Standard test method for soundness of aggregates by use of sodium sulfate or
magnesium sulfate [superseded]
ASTM D3967-95a (2004) Standard test method for splitting tensile strength of intact rock core specimens
ASTM D4992-94 (2001) Standard practice for evaluation of rock to be used for erosion control
ASTM D5313-04 Standard test method for evaluation of durability of rock for erosion control under
wetting and drying conditions
ASTM D5779-95a (2001) Standard test method for field determination of apparent specific gravity of
rock and manmade materials for erosion control
ASTM D6092-97 (2003) Standard practice for specifying standard sizes of stone for erosion control
ASTM D6711-01 Standard practice for specifying rock to fill gabions, revet mattresses, and gabion
mattresses
3.17.2.2
British standards
BS 5930:1999 Code of practice for site investigation
3.17.2.3
Euronorms
EN 206-1:2000 Concrete. Specification, performance, production and conformity
EN 918:1998 Geotextiles and geotextile-related products. Dynamic perforation test (cone drop test)
EN 932-3:1997 Tests for general properties of aggregates. Procedure and terminology for simplified
petrographic description (AMD 14865)
EN 933-9:1999 Tests for geometrical properties of aggregates. Assessment of fines, methylene blue test
EN 1097-1:1996 Tests for mechanical and physical properties of aggregates. Determination of the
resistance to wear (Micro-Deval) (AMD 14864)
EN 1097-2:1998 Tests for mechanical and physical properties of aggregates. Methods for the
determination of resistance to fragmentation
EN 1097-6:2000 Tests for mechanical and physical properties of aggregates. Determination of particle
density and water absorption (AMD Corrigendum 14306)
EN 1367-2:1998 Tests for thermal and weathering properties of aggregates. Magnesium sulfate test
EN 1744-1:1998 Tests for chemical properties of aggregates. Chemical analysis
EN 1744-3:2002 Tests for chemical properties of aggregates. Preparation of eluates by leaching of
aggregates
EN 1926:1999 Natural stone test methods. Determination of compressive strength
EN 1936:1999 Natural stone test methods. Determination of real density and apparent density and of
total and open porosity
EN 10218-2:1997 Steel wire and wire products. General. Wire dimensions and tolerances
EN 10223-3:1998 Steel wire and wire products for fences. Hexagonal steel wire netting for engineering
purposes
EN 10244-1:2001 Steel wire and wire products. Non-ferrous metallic coatings on steel wire. General
principles
298
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3.17 References
EN 10244-2:2001 Steel wire and wire products. Non-ferrous metallic coatings on steel wire. Zinc or
zinc alloy coatings
1
EN 10245-1:2001 Steel wire and wire products. Organic coatings on steel wire. General rules
EN 10245-2:2001 Steel wire and wire products. Organic coatings on steel wire. PVC finished wire
EN 10245-3:2001 Steel wire and wire products. Organic coatings on steel wire. PE coated wire
2
EN 12390-6:2002 Testing hardened concrete. Tensile splitting strength of test specimens
EN 12620:2002 Aggregates for concrete
EN 13253:2001 Geotextiles and geotextile-related products. Characteristics required for use in erosion
control works (coastal protection, bank revetments)
EN 13383-1:2002 Armourstone. Specification
3
EN 13383-2:2002 Armourstone. Test methods
EN 13450:2002 Aggregates for railway ballast
EN 14579:2004 Natural stone test methods. Determination of sound speed propagation
4
EN ISO 10319:1996 Geotextiles. Wide-width tensile test
EN ISO 11058:1999 Geotextiles and geotextile-related products. Determination of water permeability
characteristics normal to the plane, without load
EN ISO 12236:1996 Geotextiles and geotextile-related products. Static puncture test (CBR-Test)
5
EN ISO 12956:1999 Geotextiles and geotextile-related products. Determination of the characteristic
opening size
ENV 12920:1998. Methodology for the determination of the leaching behaviour of waste under
specified conditions
3.17.2.4
French standards
NF P 94-325-1 (2004) Exécution des travaux géotechniques spéciaux – Ouvrages en gabions – Partie
1: ouvrages hors site aquatique
6
P 18-011 (1992). Bétons – Classification des environnements agressifs
3.17.2.5
ISO
ISO 3310-2:1999 Test sieves. Technical requirements and testing. Test sieves of perforated metal plate
7
ISO 9000:2000 Quality management systems – Fundamentals and vocabulary
3.17.2.6
EC Directive
Council of the European Communities, 1991. Council Directive 91/689/EEC of 12 December
1991 on hazardous waste. Official Journal L 377 , 31/12/1991 pp 20–27
8
9
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4
1
Physical site conditions and data
collection
2
3
4
5
6
7
8
9
10
301
4 Physical site conditions and data collection
CHAPTER 4 CONTENTS
4.1 Bathymetry and morphology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306
4.1.1
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306
4.1.1.1 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306
4.1.1.2 Interaction between morphology and bathymetry . . . . . . . . . . . . . . . 307
4.1.2
Bathymetry and morphology related to marine structures. . . . . . . . . . . . . . . . 309
4.1.2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309
4.1.2.2 Sandwaves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310
4.1.2.3 Muddy shorelines: mudflats and saltmarshes . . . . . . . . . . . . . . . . . . . 310
4.1.2.4 Beaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
4.1.2.5 Coastal dunes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312
4.1.2.6 Cliff and shore platforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313
4.1.3
Bathymetry and morphology of rivers and estuaries . . . . . . . . . . . . . . . . . . . . 314
4.1.3.1 General points. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314
4.1.3.2 Types of estuary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314
4.1.3.3 Types of river . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315
4.1.3.4 Regime theory for rivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318
4.2 Hydraulic boundary conditions and data collection – marine and
coastal waters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319
4.2.1
Wind and pressure conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320
4.2.1.1 Use of wind data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320
4.2.1.2 Use of atmospheric pressure data . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322
4.2.2
Marine water levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323
4.2.2.1 Mean sea level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324
4.2.2.2 Tide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324
4.2.2.3 Storm surges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326
4.2.2.4 Wind set-up. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326
4.2.2.5 Wave set-up. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327
4.2.2.6 Seiches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330
4.2.2.7 Long-period waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331
4.2.2.8 Tsunamis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332
4.2.2.9 Flood waves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333
4.2.2.10 Sea level rise resulting from climate change . . . . . . . . . . . . . . . . . . . . 334
4.2.2.11 Sources of water level data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335
4.2.2.12 Design extreme water levels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336
4.2.3
Marine and estuarine currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340
4.2.3.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340
4.2.3.2 Components of marine and estuarine currents. . . . . . . . . . . . . . . . . . 340
4.2.3.3 Estuarine flow conditions, including basin model and density
currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342
4.2.3.4 Numerical modelling of marine and estuarine currents. . . . . . . . . . . 346
4.2.4
Wind-sea and swell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347
4.2.4.1 General definitions related to waves, sea-states and wave climate . . . 347
4.2.4.2 Representation of regular/random and long-crested/short-crested
waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349
4.2.4.3 Characterisation of wave conditions and wave kinematics . . . . . . . . . 351
302
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4.2.4.4 Statistical properties and distribution of waves in a sea-state . . . . . . . 354
4.2.4.5 Spectral description of waves and wave spectra . . . . . . . . . . . . . . . . . 360
1
4.2.4.6 Generation of waves in the ocean and on inland waters. . . . . . . . . . . 367
4.2.4.7 Transformation of waves in the nearshore and coastal zones . . . . . . . 374
4.2.4.8 Short-term or daily wave climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385
4.2.4.9 Long-term wave climate – analysis of extreme waves . . . . . . . . . . . . . 387
4.2.4.10 Numerical and physical modelling of wave conditions . . . . . . . . . . . . 393
4.2.5
2
Joint probability of waves and water levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397
4.2.5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397
4.2.5.2 The independent and dependent cases. . . . . . . . . . . . . . . . . . . . . . . . 399
4.2.5.3 Desk study methods of analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399
4.2.5.4 Other methods of analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402
3
4.2.5.5 Design with joint waves and water levels . . . . . . . . . . . . . . . . . . . . . . . 404
4.3 Hydraulic boundary conditions and data collection – inland waters . . . . . 405
4.3.1
Hydraulic parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405
4.3.1.1 River geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405
4
4.3.1.2 Hydraulic data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406
4.3.2
River discharges and currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409
4.3.2.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409
4.3.2.2 Hydrology and design discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . . 410
4.3.2.3 River discharge and velocity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412
5
4.3.2.4 Structure of currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419
4.3.2.5 Turbulence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425
4.3.2.6 Bed shear stress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 426
4.3.2.7 River confluences and bifurcations . . . . . . . . . . . . . . . . . . . . . . . . . . . 428
4.3.3
Flood waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429
6
4.3.3.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429
4.3.3.2 Hydrographs (duration/exceedance and rating curves) and stage
relationships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429
4.3.3.3 Flood waves and translation waves . . . . . . . . . . . . . . . . . . . . . . . . . . . 431
4.3.4
Ship-induced waves and water movements . . . . . . . . . . . . . . . . . . . . . . . . . . . . 434
4.3.4.1 Return current, water level depression, front and stern waves . . . . . 436
7
4.3.4.2 Secondary ship waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 440
4.3.4.3 Propeller jet velocities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 440
4.3.5
Modelling of water levels and currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 443
4.3.5.1 Modelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 443
4.3.5.2 Numerical modelling of water levels and currents . . . . . . . . . . . . . . . 443
8
4.3.5.3 Physical modelling of water levels and currents . . . . . . . . . . . . . . . . . 446
4.3.5.4 Hybrid modelling of water levels and currents. . . . . . . . . . . . . . . . . . 448
4.4 Geotechnical investigations and data collection . . . . . . . . . . . . . . . . . . . . . . 448
4.4.1
Objectives of geotechnical investigations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449
4.4.2
Procedures for geotechnical investigations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449
9
4.4.2.1 Preliminary geotechnical investigations . . . . . . . . . . . . . . . . . . . . . . . . 450
4.4.2.2 Geotechnical investigations for design. . . . . . . . . . . . . . . . . . . . . . . . . 450
4.4.2.3 Controlling and monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451
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4 Physical site conditions and data collection
4.4.3
Key elements of geotechnical investigations. . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
4.4.3.1 Desk studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
4.4.3.2 Ground investigations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
4.4.3.3 Site visit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 458
4.4.3.4 Specific issues related to structure types . . . . . . . . . . . . . . . . . . . . . . . 458
4.4.3.5 Investigation techniques and equipment. . . . . . . . . . . . . . . . . . . . . . . 460
4.4.3.6 Interpretation of results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460
4.4.3.7 Ground investigation report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460
4.4.4
References and standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460
4.5 Ice conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464
4.5.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464
4.5.2
Ice growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464
4.5.3
Ice formations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464
4.5.4
Typical winter ice action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 466
4.5.5
Data collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467
4.6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 468
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Flow chart
4
1
Physical site conditions and data
collection
2
Chapter 4 explains how to derive hydraulic and geotechnical design input conditions and
how to undertake data collection.
Key inputs from other chapters
!
!
Chapter 2 " project requirements
Chapter 3 " material properties.
3
Key outputs to other chapters
!
!
!
hydraulic and geotechnical input conditions " Chapter 5
physical site conditions for construction " Chapter 9
physical site conditions for monitoring " Chapter 10.
NOTE:
4
The project process is iterative. The reader should revisit Chapter 2 throughout the
project life cycle for a reminder of important issues.
This flow chart shows where to find information in the chapter and how it links to other
chapters. Use it in combination with the contents page and the index to navigate the manual.
2 Planning and designing
rock works
5
Chapter 4 Physical site conditions and data collection
4.1
Bathymetry and
morphology
survey methods
4.2
Marine and
coastal waters
4.3
Inland waters
4.4
Geotechnical
data
6
4.5
Ice conditions
wind data
discharge and flow
site investigation
ice formations
water levels
turbulence
ice action
tides
flood waves
tests, interpretation of
results
storm surges
translation waves
waves
ship-induced waves
sea level rise
currents
7
reporting
design water levels
8
3 Materials
5 Physical processes and
design tools
6 Design of marine structures
9
7 Design of closure works
8 Design of river and canal structures
9 Construction
10
10 Monitoring, inspection,
maintenance and repair
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4 Physical site conditions and data collection
4.1
BATHYMETRY AND MORPHOLOGY
4.1.1
General
4.1.1.1
Definitions
Topography is the description of the geometrical characteristics of the ground surface above
water. Three methods are commonly used.
1
Conventional levelling.
2
Photogrammetry. In this technique aerial photographs are analysed and the geometry of
objects in the photographs is quantified relative to a fixed co-ordinate system. It can
normally only be applied to a portion of the ground or a structure visible above the
waterline. To maximise the benefits, aerial surveys can be conducted when the water
level is low. Conventional levelling checks have suggested that the resolution of
photogrammetry is better than ±90 mm. The initial costs of a photogrammetric survey
of an area or a structure can be high relative to a conventional survey, but it may be
more economical if several zones are flown together.
3
3D laser scanning. Laser scanning allows rapid acquisition of 3D data (10 000 points
per second) at a relatively high density (approximately 0.1 m point spacing and better).
The speed of data acquisition is particularly useful, as the working window within the
intertidal zone is relatively limited. The scanner may also be able to provide highdefinition digital photographs of the site. Fixed markers, linked to a GPS control
network, provide control of the scan. With further filtering and processing of the
registered point cloud data, digital terrain models (DTMs) of the structure and profiles
can be generated. An additional method of presenting and analysing the data involves
combining the 3D scan data with the 2D photography to generate rectified
orthophotography.
A wide range of techniques are available, but detailed discussion of this subject is beyond the
scope of the manual.
Topographical data are necessary for design and construction. In addition, repeat surveys
can be used to inform maintenance requirements (see Section 10.3.4).
Bathymetry is the description of the ground surface below water. It is a major boundary
condition for geometric and structural design of rock structures and has a significant
influence on the volume of dredging, the volume of rock needed and on the hydraulic
loadings. At coastal sites, for example, the water depth can limit wave heights. On charts for
navigation purposes the seabed level is defined in relation to the Chart Datum, commonly
taken to be the Lowest Astronomical Tide level (LAT) at the site.
The bathymetry of a zone is normally determined by means of a boat equipped with an
acoustic sounder, which may be either single-beam (point-by-point process) or multi-beam
(profile-by-profile process). A description of bathymetric survey techniques is given in Section
10.3.5.
Bathymetric data comprise series of points, each determined with three co-ordinates:
horizontal (x, y) and vertical (z).
Surveying is generally conducted from a boat except in the intertidal and shallow-water
zones, where topographical methods may be used. Four parameters are sought:
!
306
the horizontal location (X, Y) of the boat, which is generally obtained by conventional
topographic equipment such as differential global positioning system (DGPS), laser
and optics
CIRIA C683
4.1 Bathymetry and morpholXoXgXy
!
the water depth (d), measured by the sounder
!
the vertical location (Z) of the level of water, which is obtained by standard topographic
equipment (such as DGPS, laser or optics), by tide measurement or by referenced scales.
Nowadays, data are digital and particular attention should be paid to the density and spacing
of survey lines. They should be sufficiently close to give a fair representation of the bed
features and level without excessive cost. Check lines should be run, at right angles to the
main survey lines, to highlight any survey errors. Careful quality control of data and daily
calibration of equipment are essential.
1
2
Morphology is the description of sedimentation and erosion processes occurring at the bed.
Erosion and deposition may cause the bathymetry to change with time. These changes can
create difficulties when attempting to determine the bathymetry for design or construction
purposes. The rate of morphological change of the bed depends on the rate of sediment
transport. High transport rates generally result in relatively rapid changes of the bed.
However, these morphological changes are very slow compared with changes in the hydraulic
boundary conditions and, except for local scour near structures, may occur over several years
or even decades.
The presence of very soft sediments and/or layers of high concentrations of suspended
sediments (fluid mud, clay) can cause additional survey problems. Indeed, these softer
materials make it difficult to obtain accurate bathymetric measurements because a large part
of the signal emitted and reflected is scattered.
Structures covered in this manual generally require data about bathymetry and morphology
for their design and construction. For example, the construction of a closure dam, river
control works or river-training structures requires overall data about bathymetry and
morphology of the estuary or river as well as local data for the construction site. The data
should provide information about short-term (eg seasonal) fluctuations and long-term
changes and influences. The quantification of these fluctuations will require data from several
surveys conducted over an appropriate period of time. Typical seasonal features are:
4.1.1.2
!
monsoons and storms in a marine environment, including estuaries
!
flood and dry season for rivers.
4
5
6
7
Interaction between morphology and bathymetry
Morphological and bathymetric studies should include expected long-term changes of the
bed level such as those associated with structures along the coast or in an estuary or a river.
Local data are required at the construction site itself as well as from the surrounding area.
These local data should be more detailed than the overall data. The bed level, for example,
should be known with sufficient accuracy before construction can start. Nevertheless, during
construction further bathymetric and topographic survey may be necessary to assess
modifications to local bathymetry. The interactions between overall and local bathymetry,
morphology and hydraulic conditions at a site are shown in Figure 4.1.
The data needed ought to be available from existing maps and charts. Surveys undertaken
for the project can provide specific sounding data. Historical records or data collected in
earlier surveys may also be used, but their reliability should first be critically examined.
Satellite images are another possible source of information. They can be very useful for
mapping purposes, for example in identifying the former course of a river or dune frontage,
which can give an invaluable insight into the area’s morphology.
Special emphasis should be given to morphological data. The characteristics of the sediment
need to be studied, as do the type(s) of sediment transport. Samples of the bed material
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307
8
9
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4 Physical site conditions and data collection
should be taken to provide data about the size distribution. It is important to take samples at
several locations, since the particle size of the bed material may vary considerably from place
to place. The bed samples should also help in establishing whether the bed material is
cohesive. Cohesion depends on the amount of fine particles, particularly clay, and increases
resistance to erosion.
Construction
ie change of local hydraulic boundary conditions
at the construction site
boundary conditions: Sections 4.2, 4.3
hydraulic performance and structural response: Sections 5.1, 5.2.2, 5.2.3
!
!
!
!
!
!
Overall bathymetry
Local bathymetry
Section 4.1
Section 4.1
Overall hydraulic conditions
ie water levels and velocities
Local hydraulic conditions
ie water levels, velocities and
turbulence
sea: Sections 4.2.2, 4.2.3
rivers: Section 4.3.2.3
modelling:
– sea: Section 4.2.4.10
– rivers: Section 4.3.5
!
!
!
!
!
Overall morphology
!
!
!
sea: Section 4.1.2
rivers: Section 4.1.3.3
estuaries: Section 4.1.3.2
Figure 4.1
No
Yes
Is construction
completed?
modelling: Section 5.3
sea: Section 4.2.3
rivers: Section 4.3.2.4
closures: Section 5.1.2.3
turbulence: Section 4.3.2.5
Local morphology and scour
!
!
!
modelling: Section 5.3
scour: Sections 5.2.2.9, 5.2.3.3
erodibility: Section 5.2
Interactions between morphology and bathymetry with reference to hydraulic conditions
and construction
Sediment transport can take place as a bedload, suspended load or both. The type of
sediment transport depends on the size of the bed material and the flow conditions. In
general, coarse material such as gravel and coarse sand is transported as bedload, whereas
fine material such as fine sand and silt is transported as suspended load. To predict the
morphological behaviour of the sea bed, river bed and riverbanks, it is necessary to collect
data about:
!
types of sediments, ie fine or coarse, cohesive or not
!
amount and type(s) of sediment transport, ie suspended or bedload transport or both
!
bed-level changes
!
erodibility of bed and bank material.
In general, the balance between erosion and deposition of bed material and the balance
between entrainment and sedimentation of suspended sediment determine the expected
morphological development. Such development can take place naturally, but it may also be
due to discharge during dredging activities. A simple rule to assess the outcome of this
balance and the expected depth-averaged velocities may be used. The graph presented by
Hjulström (1935) (see Figure 4.2) distinguishes erosion and sedimentation based on
thresholds applied to the average flow velocity. This approach gives only limited results,
however, and further reference should be sought when appropriate in Sections 5.2 and 5.3.
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4.1 Bathymetry and morpholXoXgXy
In addition to morphological characteristics, it is necessary to determine river discharges and
velocities and/or wave climate. Together with morphological data, they control bathymetry
changes. Reference to the wave climate for marine structures is made in Section 4.2.
Discharges and associated water levels for rivers or dams, stage-discharge curves and stageduration curves for rivers are discussed in Section 4.3 and may need interpretation within
the context of the hydrology of the catchment area of the river. Morphological, bathymetric
and flow field data should be collected at an early stage of a project and should be surveyed
during construction. Especially for the design of toe structures and bed protection, the joint
probability of overall morphological changes and local scour may have to be evaluated (see
Sections 5.2.2.9 and 5.2.3.3). In addition, a proper morphological analysis usually requires a
high level of experience and expertise.
1
2
3
4
5
Figure 4.2
Velocity chart as a preliminary decision tool for erosion or
sedimentation (Hjulström, 1935)
4.1.2
Bathymetry and morphology related to marine structures
4.1.2.1
Introduction
6
Knowledge of seabed bathymetry and its morphology at the structure site is fundamental to
the design of coastal and shoreline structures, for example regarding wave heights limited by
water depth (see Section 4.2.4.7). In many cases knowledge of morphological changes of the
bed with time are as critical as the mean bed level to the design, since the lowest bed level in
front of a structure is determined for use in the design. Thus, where a sea bed is either in
dynamic equilibrium or is morphologically unstable, it is essential to determine the range of
bed level changes that should be allowed for in the design.
The stability of the shoreline and its adjoining hinterland depends on the physical character
of the shoreline, which, in turn, is determined by its geology, its geomorphology and the
actions of winds, waves and tides. The assessment of the various types of physical shoreline is
therefore a key issue for effective planning of rock structures.
The geomorphology has a major effect on the project planning and should be characterised
with regards to the loading forces and materials. Essential information required includes:
CIRIA C683
!
for loading forces: the marine forces factors such as wind, waves, tides, sea-level change
and wave- or tide-generated currents characterised by their intensity, direction and
variability with time
!
for materials: the coastal zone geology for both the nearshore, inshore and onshore parts,
including rock and softer sediments, its topography and its bathymetry, the type of mud,
sand, gravel or carbonate and the distribution of mobile and non-mobile sediments.
309
7
8
9
10
4 Physical site conditions and data collection
The interaction of material and loading forces at the land-sea interface is important. This
includes the type of processes, ie erosion or sediment transport or deposition, and their
spatial and temporal changes. Additionally, possible structure-related local scour should be
considered (see Section 5.2.2.9).
The coast morphology and bathymetry are controlled by the balance between the
aggressiveness of the sea and the resistance of the land. They change over time: build-up
takes place where sediment accumulates; the coastline moves landward where areas are
eroded and sediment is removed offshore or alongshore. The morphology of a coast changes
if the applied forces and energies change. The forces are induced by waves, tides, winds,
currents and surges. Their impact on the landform depends on the type, magnitude and
direction of the forces in combination with the materials strength. If the applied forces result
in a change to the shape, to the composition of a landform or both, then a new relationship
develops between the forces and the new landform. This relationship continues to evolve
until a new dynamic equilibrium is reached. Sediment transport causes morphological
changes and maintains this balance between landform and hydrodynamic forces. Typical
seasonal morphological changes in a marine environment, including estuaries, are related to
monsoons, typhoons or both in tropical regions and other seasonal storms in high latitudes.
For example, erosion and build-up of beach alternate during winter and summer respectively
in Europe.
If no data on bed levels are available at all, a first indication of the impact of variability can be
obtained by comparing assumed depth velocities (current or orbital), wave characteristics
(height and period) or both with threshold values for the initiation of sediment transport
(Shields, 1936; Komar and Miller, 1974). Appropriate models should be used for sediment
transport for currents or wave actions and known or predicted values of currents or waves
may be used (see also Sections 5.2, 5.3 and 6.3). The prevailing local current, wave and
sediment conditions may lead to bed variations exhibiting typical mean dimensions and timescales. To collect representative data on bed changes, measurements should cover at least one
sandwave length per section. In case of repeated measurements at one single position, a
minimum sampling frequency of twice the typical frequency of the natural changes of the sea
bed should be chosen.
4.1.2.2
Sandwaves
The sea bed exhibits a variety of bed patterns, like ripples, mega-ripples, sandwaves and tidal
sand banks. The most changing of these bed patterns are sandwaves.
Sandwaves can be described as elongated depositional bedforms with an undulating surface.
The dominant current direction defines the sandwave orientation on the sea bed. The crest
of the sandwave is orientated almost perpendicular to the dominant current direction. In
general the height of sandwaves varies from 1 m to 10 m and their wavelength varies from
100 m to 1000 m. Sandwaves are present in large parts of the southern North Sea, with
lengths in the order of 100 m and heights about 10 m, and related sandwave return periods
of 1–10 or even 100 years (Van den Brink, 1998). The movement of a sandwave along the
sea bed can vary from a few metres to more than 20 m a year. Progressing mudwaves
observed along the coast of Guyana also exhibit long-periodic morphological changes.
Where sandwaves may occur, the bathymetry of the site area should always be surveyed to
determine existence of sandwaves and to estimate their height. Attention should be paid to
sandwave movements when designing a structure in their vicinity (see Section 6.4.3.3).
4.1.2.3
Muddy shorelines: mudflats and saltmarshes
Muddy shorelines occur along the upper levels of the intertidal zone of estuaries, tidal
embayments and on open, barrier coasts. In these locations, the tidal current velocities are
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too low to resuspend completely the mud that settles during the time of slack high water.
Consequently, the net accretion is observed to form intertidal mudflats and saltmarshes.
There is a great diversity in the morphology of mudflats that relates to the changing balance
of physical, sedimentological and biological forces on the sediment. In general terms, the
width of a mudflat is greater in areas of high tidal range than in areas of small tidal range.
However, considerable deviations exist which indicate that there are additional control
phenomena. Mudflats are exposed to cycles of erosion and deposition. It is generally
considered that mudflats under erosion have a low and concave upward profile while
mudflats under deposition have a high and convex upward profile. Modification of the
mudflat profile causes change in the exposure to wave attack, altering the rates of erosion
and deposition, possibly leading gradually to a new equilibrium.
As the upper mudflats build higher through vertical accretion of sediment, the number and
duration of tidal inundations decreases. There is therefore a critical height at which the
mudflat is out of the water long enough for vegetation to establish. The elevation at which
vegetation can colonise a mudflat mostly depends on the availability of plant species able to
withstand this environment. These plants help to reduce flow, encouraging further
deposition of mud. Once a saltmarsh has become established, biological activity,
sedimentation and geomorphological phenomena depend on the pattern and extent of tidal
inundation at that level. Neap tides merely enter and are confined to the creeks, leaving the
saltmarsh dry, whereas spring tides generally rise above the creek banks, drowning the
saltmarsh for a period.
Higher intertidal mudflats and saltmarshes are generically linked. They have complex and
interrelated physical and biological controls. Three broad categories of muddy shoreline
morphology can be distinguished:
4.1.2.4
!
a smoothly sloping surface on which there is a gradual upward and landward
appearance of vegetation. Such shorelines are generally in accretion, growing seaward as
well as building vertically
!
a cliffed saltmarsh with an edge indicative of erosion
!
a ramp of moderate slope angle, carved transversely into finger-like spurs and narrow,
wave-scoured furrows. This shoreline denotes a regime of net erosion, perhaps less
severe than the saltmarsh cliff coast, and it may represent a transitional stage between
slope and cliff.
Beaches
2
3
4
5
6
7
A beach is an accumulation of loose sediment. Its shape changes in response to changes in
wave energy. The mobility of its sediments therefore allows a beach to maintain itself in a
state of dynamic equilibrium with its environment. Beaches behave differently according to
their sediment size and can be subdivided into sand, shingle, mixed (ie poorly sorted mixture of
sand and gravel) and composite beaches (ie a sandy lower foreshore with a shingle-dominant
upper foreshore and backshore with relatively little mixing between the two). The dynamics
and transports of beach materials are not covered in this manual and details can be found in
the Beach management manual (Simm et al, 1996).
8
Although beaches are three-dimensional features, the analysis of their morphology can be
conveniently broken down into the study of cross-shore profile and longshore profile.
9
Cross-shore profile
Even though a wide variety of troughs and ridges may be present on the beach profile, the
most important morphological feature is the average slope between seaward and landward
limits. The backshores of steep beaches usually display a flat-topped ridge or bar known as
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the berm that forms at the limit of wave swash. The removal of the berm and the deposition
of a longshore bar beneath the breaker zone marks the transition from a steep beach profile
to a shallow beach profile.
When a wave breaks at the shore, sediment is pushed up the beach face by the swash and
dragged back down by the backwash. Because of water percolation into the beach, the
backwash tends to be weaker than the swash. Consequently, there is a net onshore movement
of sediment up the beach. The rate of percolation is mainly controlled by the mean sediment
size and the beach porosity or the size sorting of the beach sediment. Water percolates much
more easily into a shingle beach than into a fine sandy beach, and the backwash intensity is
therefore greatly reduced, setting up an onshore movement of sediment, which steepens the
beach.
Small waves tend to build up beaches whereas storm waves tend to lower and flatten them.
The main factor is the steepness of incident waves, which controls the shoaling, the
transformation of shape profile (eg asymmetry) and the wave breaking processes in shallow
water (see Section 4.2). When a steep wave breaks on to the beach, its energy is dissipated
over a relatively narrow area and the swash does not move far up the beach. Thus there is
less opportunity for percolation to occur and less energy is lost in moving sediment up the
beach face. Consequently, the backwash is strong and significant amounts of sediment can be
moved seawards to build a longshore bar. When a less steep wave (ie collapsing or surging)
approaches the foreshore, significant movement of water takes place up the beach face, as the
wave front either collapses or surges up the beach. In this case the swash is strong and less
sediment is moved up the beach face to form a berm.
Longshore profile
The large-scale longshore shape of beaches can be divided into:
!
beaches that are attached to the shoreline, ie pocket beaches
!
beaches that are detached from the shoreline, such as spits, barrier islands, tombolos.
The most basic coastal configuration is an indented coast with bays and headlands. Refraction
means that wave attack concentrates wave energy on the headlands and reduces wave energy
in the bays, which may lead to headland erosion and bay deposition. This process continues
until the coast consists of a series of smooth curved beaches, reaching the ultimate stage of
wave-dominated coastal development.
For coastlines that turn abruptly landward, such as a bay or a valley opening on to a coast, a
finger-like extension of the beach, also called a spit, may appear across the indentation.
Generally spits are connected to the beach end by a narrow neck and are fed by sand eroded
from further up the coast and provided by the longshore transport. Spits are usually linear
features widening at their distal (outer) end, but their form depends on the physical
processes such as longshore transport and supply of sediment.
An island situated immediately offshore has a significant effect on the wave conditions at the
beach. Sediment is swept into the sheltered area behind the island, which can either form a
salient in the beach plan shape or it can allow a neck of sediment, called a tombolo, to
deposit, which then connects the island to the beach.
4.1.2.5
Coastal dunes
Coastal dunes form where there is a sufficient supply of dry sand and sufficient wind to move
it. Dune systems are usually fronted by sand beaches that function in close relation with the
dunes. They undergo periods of growth and erosion, both of which contribute to their
dynamic evolution.
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Deposition processes
Coastal dunes accumulate sand blown inland from beaches by onshore winds. The basic
requirements for the formation of coastal dunes are:
!
a plentiful supply of sand over a wide drying foreshore
!
a backshore area of low relief
!
predominant onshore winds capable of entraining sediment
!
presence of vegetation as a dune-form fixer.
2
An ideal condition for the transport of sand from a beach to the dunes is after waves have
deposited sand on the upper part of the beach and on the intertidal foreshore. At low tide
the sand dries and onshore winds can carry substantial volumes of sand on to the dunes.
Dunes usually begin to form at the crest of a beach where wind-blown sand accumulates
around small objects or debris cast up on the strandline. After the dunes have started to
form, embryonic dunes are low hills of loose sand that are colonised by pioneer plants, which
both increase the resistance of the surface layer of sand to wind erosion and reduce wind
speeds over the surface. These embryonic dunes may keep growing in both height and width
to form a dune ridge parallel to the coastline or foredune. Embryonic dunes are highly
unstable depending on the wave and wind energies they are exposed to. They may resist
wave action when they reach a position on the beach that corresponds to the Mean High
Water Spring Level (MHWS).
Erosion processes
surface erosion by wind action or deflation
!
marine erosion of the toe and seaward face of the dunes.
Deflation is a vertical wind-driven erosion resulting in a lowering of the dune crest or blowouts on dune sides. If the vegetation is seriously damaged, it no longer stabilises the sand;
and wind action then rapidly removes the exposed loose sand, forming a blow-out.
Marine erosion of the dune may occur when the fronting beach is lowered as a result of wave
action. This allows the high tide to reach the toe of the dunes. Waves can then directly attack
the dune toe, causing removal of the sand and undercutting of the dune face. The front face
of the dune collapses on to the beach and the sand is carried away down to the beach. As a
consequence, the front face of the dune retreats, leaving a steep unvegetated surface and the
beach receives an additional volume of sand. Hence, the dunes act as a temporary reservoir
of sand, accumulating it during mild weather, typically during the summer, and releasing it
back to the beach during storms.
4.1.2.6
4
5
Dune erosion is governed by two processes:
!
3
6
7
8
Cliffs and shore platforms
Cliffed coasts are defined as high and steep-faced coasts, consisting of consolidated or
unconsolidated materials from granites to softer glacial till. In areas of low sediment supply, a
shore platform commonly fronts the cliff. Shore platforms are near horizontal and similar in
composition to the lower layers of the cliff.
9
Cliff erosion processes
Landsliding is a primary cause of cliff erosion. Cliff recession is defined as the onshore
movement of the cliff and is controlled by wave attack at the cliff toe that may induce
landslide. Wave action on cliffs has two effects:
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4 Physical site conditions and data collection
!
direct undercutting and erosion of the face that is related to the onshore wave energy
!
removal of debris that is related to the longshore wave energy.
Shore platform erosion processes
Shore platform lowering is a three-stage process involving detachment of particles of
material, transport of this material away from the foreshore and its deposition elsewhere.
The global process depends on the aggressiveness of the environment and the erodability of
the platform materials. Both weathering and marine processes contribute to the erosion of
shore platforms. Weathering processes can directly break up cohesive material or weaken
material that is more easily eroded by marine processes.
4.1.3
Bathymetry and morphology of rivers and estuaries
4.1.3.1
General points
The construction of a closure dam or river control and training structures requires
morphological data covering a large area upstream and downstream of the project. Other
hydraulic data such as water levels, flow velocities, sediment transport etc have to be collected.
Typical seasonal effects are storm surges (especially in estuaries), flood waves and low river
discharge. They are reasonably predictable when attributed to characteristic local
precipitation patterns such as monsoons. The corresponding variations in river discharge
and sediment transport may cause variations in local bed levels of channels or shoals.
Seasonal variations may also be of particular importance for the planning of construction.
Some recommendations for the collection of morphological data are presented in Box 4.1.
Box 4.1
!
!
!
!
!
!
!
!
4.1.3.2
Recommendations for morphological data collection for rivers and estuaries
bed geometry in the entire estuary: cross-sections every 1–5 km for general survey and cross-sections
every 10–1000 m for detailed survey
bed geometry in a river: cross-sections every 5–10 km along the entire river for general survey and
cross-section every 10–1000 m for detailed survey, which should be adapted to the length of the river
measurements should be carried out at different times of year to determine significative differences
in bathymetry for various conditions
the sediment transport in rivers should be measured at one or more locations during low and high
river discharges to enable the relationship between water discharge and sediment transport to be
determined. This can be used for selecting the appropriate model and equation for sediment transport prediction
transported sediment should be sampled to determine its characteristics
sediment transport in an estuary is difficult to measure. Because tide, waves and differences of water
density cause quite rapid changes in transport, extensive measurement campaigns are needed
along a river, bed material sampling should be done every 5–10 km. The bed should be sampled in
at least three positions over each cross-section
in an estuary, bed material should be sampled according to a survey that has a grid of between
1 km ⎛ 1 km and 5 km ⎛ 5 km, which should be adapted to the width of the estuary.
Types of estuary
An estuary is a complex system of channels, shoals and flats. The tidal flow is concentrated in
the channels, whereas the shoals and flats mainly serve for water storage. The channels run
more or less in the longitudinal direction of the estuary with their cross-sectional area
decreasing with the distance from the sea because of the reduction of the tidal discharge. If
an estuary is fed by more than one channel, secondary connection channels may exist,
especially where there are phase differences among the various channels. The sediment may
have different origins, incorporating either marine or riverine material. The tidal motion also
produces a complex pattern of sediment transport. It results in local erosion or areas of
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sedimentation, causing continuous migration of channels and shoals that are observed in
almost all existing estuaries with movable beds.
Section 4.2.3 shows how the hydraulic response characteristics of estuaries can be calculated.
Three types of estuaries are distinguished:
!
short estuary with respect to the length of the tidal wave
!
long estuary with respect to the length of the tidal wave
!
tidal river.
2
As the flow is essentially concentrated in the channels, construction of dams on the shoals and
flats hardly affects the tidal motion. The descriptors used for the river geometry may also be
used for estuaries (see Section 4.1.3.3).
4.1.3.3
3
Types of river
General
Mobile river beds can change rapidly and may display significant variations, sometimes after
only a single flood. Their geometry tends to adapt to hydraulic loadings, which in turn also
change. Four main types of river bed can be distinguished (see Figure 4.3): straight,
meandering, braided and interlaced or anastomosed rivers. The classification of river types is
based on the shape of the channel pattern (Leopold and Wolman, 1957).
SINGLE PATTERN
STRAIGHT
MULTIPLE PATTERNS
STRAIGHT
4
5
BRAIDED
6
7
MEANDERING
Figure 4.3
MEANDERING
ANASTOMOSED
Classification of river types using criteria of sinuosity and number of
patterns (after Rust, 1978)
8
Meandering (see Figure 4.4) and braided rivers (see Figure 4.3) can be observed in the
middle and lower reaches of the river. The sediment regime is dominated by settlement and
floodplains are common. In the higher reaches, erosion takes place and the river flows with
steep gradients in a relatively narrow bed. The bed, as well as the banks, consist of rock. The
following parameters are generally used to characterise the river shape:
≤ = wavelength (m)
9
L = length of the thalweg (see Section 4.3.2.4 for the definition of thalweg) between two
inflection points (see Figure 4.4) going in the same direction (m)
B = width of the open channel (m)
10
Is = sinuosity index defined as L/≤ (-).
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apex
L
inflexion point
B
Figure 4.4
≤
Typical shape parameters of a meandering
river (after Bravard and Petit, 2000)
Two essential parameters of a river, referred to as external parameters or independent parameters,
are the discharge Q (m!/s) and the bedload. Other controlling variables of the river are:
!
the slope of the valley, which governs the energy of the river
!
the grain size of its bed and banks as well as the vegetation of the riverbanks, both of
which influence the lateral movement.
For a catchment area, these parameters are specifically governed by climate (rain,
temperature), geology (topography, lithology), ground characteristics and vegetation. The use
of the land for human activities is a factor that may have an impact on the river morphology.
Dependent parameters, also called degrees of freedom, adjust themselves to the variations of the
independent parameters described above. They are shown in Figures 4.4 and 4.54 and
consist of:
!
channel width, B (m)
!
main channel average water depth, h (m)
!
bed slope, ib (m/m)
!
wavelength of the river bends, ≤ (m)
!
sinuosity index, Is (-)
!
current velocity, U (m/s)
!
maximum water depth, $
h (m).
Any variation of the bedload or the discharge affects the longitudinal profile, the cross-section
profile and the alignment of the river. Consequently, the design of a project in a river should
maintain the fluvial continuum of the river and its equilibrium relations (see Section 4.1.3.4).
Determination of the type of the channel pattern
The type of a river can first be determined by examining topographic charts (scale 1:25 000)
and aerial photographs. Comparison of charts from different periods will show the river’s
evolution over time. Sinuosity, number of channels and position of the banks should be
studied over the entire longitudinal profile of a river to identify changes in the river type and
to correlate them with slope or sudden bed level changes.
Brice (1964) and later Morisawa (1985) propose the use of morphology, sinuosity, type of
sediment transport and the width/depth ratio to characterise the different river types. The
width to depth ratio depends on the bed material. A similar geomorphological approach is
also valid for floodplains. Table 4.1 summarises some characteristics of the four types of river.
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Table 4.1
1
Classification of channel patterns (adapted from Morisawa, 1985)
Type of river
Characteristic aspects
Sinuosity, Is
Morphology
Load type
Width/depth, B/h
Straight
Single channel with pool and
riffles, meandering thalweg
< 1.05
Suspension mixed or
bedload
< 40
Meandering
Single channel
> 1.5
Suspension mixed load
<4
Braided
Two or more channels with bars
and islands
< 1.3
Bedload
> 40
Anastomosed
Two or more channels with bars
and islands
> 1.5
–
2
–
To distinguish between meandering and braided rivers, many definitions were suggested.
Leopold and Wolman (1957) (see Figure 4.5), Ackers and Charlton (1970), Ackers (1982)
proposed relationships between the bed longitudinal slope ib and the discharge Q. This
discharge corresponds either to the bankfull discharge or to the dominant formative
discharge. The bankfull discharge is the discharge with the highest value of h before flows
inundate the floodplain and the dominant formative discharge is the equivalent permanent
flow that would create the actual river.
bed slope i
b
-0.44
i = 0.013 Q
b
(m/m)
3
4
Braided river
Meandering river
0.01
5
0.001
0.0001
10
Figure 4.5
100
1000
Bankfull discharge Q (m3/s
6
10000
)
Distinction between braided and meandering rivers
(after Leopold and Wolman, 1957)
Alternatively, Richards (1982) distinguishes meandering from braided rivers by considering
the stream power index ⋅ (m!/s) defined by ⋅ = Q · ib, with Q (m!/s) = bankfull discharge and
ib (m/m) = channel bed slope. The threshold value ⋅lim is obtained by Equation 4.1. A
braided river has a stream power index higher than ⋅lim. By contrast, a meandering river
has a stream power index smaller than ⋅lim:
⋅lim = 0.011 D500.77
(4.1)
where ⋅lim = threshold of stream power index (m!/s), D50 = median sieve diameter of the
bed material (m).
The unit stream power φ (W/m²) is defined by φ = ∈w g⋅ /B (Van den Berg, 1995). It can be
used to distinguish straight rivers from braided rivers. The threshold φ0 is given by Equation
4.2. Straight rivers have a unit stream power greater than the threshold value φ0, whereas
braided rivers have a unit stream power smaller than φ0:
φ0 = 900 D500.42
7
(4.2)
8
9
where φ0 = threshold of unit stream power index (W/m²), D50 = median sieve diameter of
the bed material (m).
According to Brookes (1988), for values of the threshold φ0 greater than 35 W/m², rivers
tend to readjust their external parameters (discharge and bedload) as a result of anthropic or
natural modifications.
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4 Physical site conditions and data collection
However, all these methods are based on empirical data. River hydraulics manuals (eg
Jansen, 1979; Bravard and Petit, 2000) can provide further information on, for example,
particular characteristics of the river types, such as meander lengths and sinuosity.
4.1.3.4
Regime theory for rivers
The need for design guidelines for stable irrigation canals in the Indian subcontinent led to
the formulation of regime theory. Subsequently, the derived relationships were also used for
other rivers. However, the empirical equations are strongly related to local circumstances and
are not generally applicable to all situations. The various relationships enable a prediction of
the width, water depth, flow velocity, hydraulic radius, hydraulic perimeter and bed gradient
from overall hydraulic parameters. Regime equations have been derived for many areas in
the world, among others by Lacey (1930), Simons and Albertson (1960) and Henderson (1966).
Regime theory is the classic procedure for the design of stable channels when sediment
transport occurs. Its physical basis and historic development have been described in some
detail in several publications on fluvial hydraulics (eg Chang, 1988; Yalin, 1992). Many
authors have studied the topic and proposed equations – see Lacey (1930), Mahmood and
Shen (1971), Simons and Albertson (1960), Chitale (1966) and Mahmood (1974).
The regime equations are supported by regime theories and, in this respect, the following
definition of a river or flow regime seems to apply. A river regime is the range of river
discharges, corresponding water levels and their respective (yearly or seasonally) averaged
values and characteristic fluctuations around these values. Regime theories may be applied
even if very little information on a river is available. It is recommended that the selected
regime equations be calibrated using reliable local data. Most of the regime equations relate
cross-sectional and longitudinal parameters to the discharge.
Many empirical formulae provide the width of the river B according to various morphological
flows, which may be defined as equivalent permanent flows that would create the actual river
morphology. These flows have a return period lower or equal to two years and are called
morphologically dominant formative flow regimes. However, whatever the flow taken into account,
the wavelength of the river bends ≤ (see also Figure 4.4) varies schematically according to the
square root of the discharge (Dury, 1955, 1976; Carlston, 1965; Ackers and Charlton, 1970;
Schumm, 1963, 1968, 1977). The bankfull discharge proves to be the best approach to
characterise geometry and evolution of meandering rivers.
Lacey’s regime equations (see Equations 4.3 to 4.8) are applied most widely to alluvial river
channels and man-made canals with a low sediment transport, ie for sediment concentration
of 100–2000 mg/l and grain size of bed material of 0.1–0.5 mm.
P = 4.87 Q1/ 2
(4.3)
Ac = 2.38 Q5 / 6 / f 1/ 3
(4.4)
R = 0.47 Q1/ 3 / f 1/ 3
(4.5)
1/ 2 1/ 2
(4.6)
U = 0.64 R
f
ib = 0.00030 f 5 / 3 / Q1/ 6
(4.7)
f = 1.59 D501/ 2
(4.8)
where:
318
P
= wetted perimeter (m)
ib
= average gradient of bed slope (-)
Ac
= cross-sectional area (m²)
Q
= discharge (m!/s)
R
= hydraulic radius (m), R = Ac/P
f
= Lacey’s silt factor (-)
U
= average flow velocity (m/s)
D50 = median diameter of bed material (mm)
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Suggested values for the Lacey’s silt factor, f (-), are given in Table 4.2.
Table 4.2
Lacey’s silt factor, f
Sediment
Silt
Sand
Gravel
Stones
Lacey’s silt factor, f
0.3–1.0
1.3–1.5
2.0–4.5
6.0–40
2
Lacey’s equations do not distinguish between bed and bank material. Simons and Albertson
(1960) extended the equations to include the effect of the soil properties of the banks.
Regime equations have also been developed for rivers with gravel beds. Hey and Heritage
(1988) give a summary. Further details on these equations and other regime theories are
given in Henderson (1966).
4.2
3
HYDRAULIC BOUNDARY CONDITIONS AND DATA COLLECTION –
MARINE AND COASTAL WATERS
The principal relationships between the relevant hydraulic boundary conditions are shown in
the diagram of Figure 4.6. The diagram also indicates relevant design parameters that
should be determined.
Marine boundary conditions are caused either by meteorological forcing (eg wind, waves,
storm surges) or by astronomical forcing (tides), or by seismic effects (tsunamis).
Consequently, the mechanisms generating them are different, which should be considered
when combinations of conditions are examined.
4
5
Global climatological conditions
Meteorological conditions
Rough indication for storm (gale);
depression with horizontal pressure
gradients reaching magnitudes of the
order 10 mbar/100 km
Astronomical forces
Deterministic and sitespecific water movements with
fixed periods and amplitudes
Water levels
Wind
Parameters:
speed, direction, duration
6
Precipitation in
catchment area of
river system
Seismic forces
Earthquakes, eg expressed
on Richter scale
Currents
Mean sea level
Surface and circulation
currents
Tide (vertical)
Tide (horizontal)
Storm surge
River discharge
short wave
Waves
long wave
Tide
Wind set-up
Wave set-up
Deep-water waves:
breaking due to wave
steepness
Wave propagation out of
storm area energy
transfer to lower
frequencies: “sswell”
Seiches
Currents (secondary)
Tsunami
Seiches
Tsunami
Water level boundary conditions
Design parameters:
joint water level with exceedance
probability
7
Wind waves
Generated on deep-water
“ssea”
Currents boundary conditions
Design parameters:
current velocities at structure with
exceedance probabilities
8
Shallow water waves:
wave shoaling,
wave refraction,
depth-induced
wave-breaking,
local wave generation
due to wind
9
Wave boundary conditions
Design parameters:
height, period with exceedance
probabilities, angle of incidence
Joint probability design conditions
Figure 4.6
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4 Physical site conditions and data collection
Combinations of two or more parameters together often determine the design loading of a
structure. In these cases not only do the separate design values have to be known but also
any combined design loading associated with the chosen probability of exceedance. The most
elegant way, but often impractical, is to use joint probability analysis to find the probability
that any combination exceeds a target design level.
Examples of combined loading include:
!
water level and wave conditions, which determine the required crest level of a seawall
!
current and orbital velocities, which determine the stone weight of a scour protection.
Joint probabilities of such combinations are discussed further in Section 4.2.5.
4.2.1
Wind and pressure conditions
4.2.1.1
Use of wind data
Wind is the underlying cause of most sources of coastal flood risk, but wind data are rarely
used as direct input to the design of coastal structures. Wind is directly relevant when
determining safe operating limits for marine construction and access to areas exposed to
severe overtopping, but it is most commonly used as input to prediction models of waves (see
Section 4.2.4.6) or of wind set-up and of storm surge (see Sections 4.2.2.3 and 4.2.2.4).
Where wave data are not available, or for some reason are not adequate for the intended
purpose, hindcasting from wind records may be the only way to estimate the wave climate.
Around most of the European coast, sequential wind records in digital format have been
available from meteorological institutes since 1970. It should be noted that on-land records
may easily show a 10–20 per cent reduction in wind speeds attributable to increased surface
roughness compared with values measured over water. As a result, land-based wind speeds
may need to be corrected (ie increased) before use in wave or storm surge models.
Other adjustments may be necessary before using wind data in numerical models, including:
!
standardisation of the wind speed at 10 m above sea surface
!
use of the international metric system (speeds expressed in m/s)
!
selection of wind data, ie duration of 10 minutes as a minimum (peak wind velocities
should not be used)
!
proper consideration of stable or unstable stratification of the atmosphere at the
interface with the ocean. Data obtained in unstable conditions will have to be corrected if
formulae or models based on neutral air-sea interface conditions have to be employed.
Wind velocities over water are available from ships’ observations or from the archives of
weather models. In both cases, individual records may be unreliable but the large volume of
data makes them a good source of site-specific ocean wind climate data.
Wind climate data can be conveniently depicted as a wind rose (see Figure 4.7) or
summarised as a scatter table of wind speeds against directions (see Figure 4.8). Typically,
wind speeds are divided into Beaufort speed ranges and 30° direction sectors.
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1
2
3
4
Figure 4.7
Typical wind rose
350°–
010°
050°–
070°
Mean wind speed
Knots
m/s
020°–
040°
080°–
100°
Fraction of time (%) with wind speeds from
110°– 140°– 170°– 200°– 230°– 260°–
130°
160°
190°
220°
250°
280°
290°–
310°
320°– All directions
340°
Total
DECEMBER
Calm
5
2.5
1–3
0.52–1.55
4–6
2.06–3.09
0.4
0.7
1.2
2.6
3.2
1.4
9.7
1.6
1.3
0.5
0.4
0.7
0.9
14.9
7–10
3.61–5.15
0.2
0.9
1.2
1.6
2.5
2.6
3.1
2.5
2.1
1.1
1.8
0.9
20.5
11–16
5.67–8.24
0.1
0.8
1.6
1.5
2.5
2.1
4.3
4.0
5.4
3.7
2.4
0.6
29.0
17–21
8.76–10.82
0.1
0.2
0.3
0.6
1.3
0.5
1.1
1.9
2.6
2.5
0.9
0.2
12.2
22–27 11.33–13.91
0+
0+
0.2
0.4
0.7
0.2
0.2
1.1
2.0
1.9
0.5
0.2
7.4
0.1
0.1
0.1
0.3
0.6
0.1
0+
1.3
0+
0+
0.1
0.1
0+
0.2
28–33 14.42–17.00
34–40 17.51–20.60
41–47 21.12–24.21
0+
6
0+
48–55 24.72–28.33
7
56–63 28.84–32.45
> 63
> 32.45
Total
0.8
2.6
4.5
6.8
10.3
6.8
10.3
10.9
12.9
10.3
6.5
2.8
Fraction of time (%) missed
97.7
2.3
YEAR
Calm
6.1
1–3
0.52–1.55
17.2
4–6
2.06–3.09
0.6
1.2
1.7
2.0
2.3
1.6
1.5
1.4
1.9
2.0
1.7
1.3
19.2
7–10
3.61–5.15
0.4
1.3
2.1
1.8
1.9
1.9
2.5
2.5
3.6
2.9
2.8
1.4
25.1
11–16
5.67–8.24
0.2
0.7
1.7
1.3
1.2
1.4
2.6
2.6
3.7
2.9
2.5
0.8
21.6
17–21
8.76–10.82
0+
0.1
0.4
0.4
0.4
0.3
0.7
0.8
1.1
1.1
0.6
0.1
6.0
22–27 11.33–13.91
0+
0+
0.1
0.2
0.1
0.1
0.1
0.3
0.6
0.5
0.2
0.1
2.3
0+
0+
0+
0+
0+
0.1
0.1
0+
0+
0.2
0+
0+
0+
0+
0+
0+
0+
0+
0+
0+
28–33 14.42–17.00
34–40 17.51–20.60
41–47 21.12–24.21
8
9
0+
48–55 24.72–28.33
56–63 28.84–32.45
> 63
> 32.45
Total
1.2
3.3
6.0
5.7
5.9
5.3
7.4
7.6
11.0
9.5
7.8
3.7
Fraction of time (%) missed
Figure 4.8
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2.3
10
Example of wind speed/direction scatter table
321
4 Physical site conditions and data collection
The parameters needed for the simple conversion of stationary wind condition into an
equivalent wave condition are the wind speed, the wind direction, the wind duration and the
stability of the air-sea interface. In practice, the wind speed and direction vary over a period
of 10–20 hours long and average values should be computed. Any direct information on
wind duration or persistence that may be available from the original records is lost when the
data are summarised in scatter diagram or rose format.
Wind data can be prepared for use in wave prediction after three main types of treatment.
1
Fit to a standard distribution of wind speeds. A standard probability function, for
example the Weibull distribution, can be fitted to the hourly wind speeds either within
one direction sector or overall. It is often preferable to retain for this analysis only those
values that exceed a predefined threshold for wind speed and to use the POT (peaks
over threshold) method presented in Section 4.2.4.9. The fitted distribution can then be
extrapolated to hourly extreme values. The hourly values can then be converted to
equivalent speeds for different durations, as necessary, using the speed conversion
factors listed in Table 4.3. This method is appropriate for design wind conditions but not
for prediction of overall wind climate.
2
Scatter diagram of wind speed and direction. Wind information in scatter diagram or
wind rose format can be broken down into percentages of data within certain classes of
speed and direction (see Figure 4.8). To be conservative, a long duration can be assigned
to each category of data. In effect, the wave predictions are fetch-limited. This approach
is reasonable when estimating the directional wave climate, but neglecting the wind
duration may lead to over-prediction of wave heights.
3
Time series of wind speed and direction. Sequential – eg hourly, three-hourly or sixhourly – wind speeds and directions can be used as input to wave hindcasting or
forecasting models. If suitable wind data and the appropriate wave model are available
this approach is the most accurate method of converting wind data into equivalent wave
data. Most hindcasting models account for the actual variability of the wind records hour
by hour, as well as time-averaged values. For the design of rockfill reservoir dams such
numerical models are used as forecasting, which is often the only tool that can be used
to derive design conditions for this case.
Table 4.3
4.2.1.2
Wind speed conversion factors related to duration of wind speeds
Time base (hours)
1/4
1/2
1
3
6
12
24
Factor (–)
1.05
1.03
1.00
0.96
0.93
0.87
0.80
Use of atmospheric pressure data
Although atmospheric pressure may be a key source variable for meteorological modelling,
pressure data are rarely used directly in coastal engineering. Probably the only time they are
used is as partial input either to modelling the coastal impacts of hurricanes or to estimation
of storm surges in the absence of more direct sea level data (see Section 4.2.2.3).
In normal conditions the mean air pressure at sea level is approximately 1013 hPa
(1 hPa = 0.1 kPa = 1 millibar). The central pressure in a storm, a typhoon, hurricane or
cyclone is one of the key indicators of its strength and potential to cause damage. Hurricanes
or typhoons very rarely affect European coasts, although severe storms can occur,
characterised by low central pressures. In the storm zones of higher latitudes (above 40°) the
central pressure may reach values down to 970 or 950 hPa, while in tropical storms
(hurricanes, typhoons, cyclones) pressures may drop to 900 hPa. In hydrodynamic modelling
of hurricane or storm effects on the sea surface, it is necessary to set up a propagating
pressure field representing conditions in and around the moving storm (Holland, 1980).
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Pressure and wind are the driving forces behind the development of storm surges. One
component of surge comes from the inverse barometer effect in which lower than average
atmospheric pressure causes a rising of the sea surface. In the open ocean or on exposed
deep waters, coastal pressure statistics can provide a reasonable estimate of the likely
distribution and magnitude of surge. However, at most coastal locations pressure alone gives
a poor indication of surge elevation where local shallow-water effects can cause a significant
amplification of surge relative to deep water (see Section 4.2.2.3).
4.2.2
1
2
Marine water levels
Water level is important because:
!
most instances of flooding and/or structural damage occur during high water level
!
wave overtopping and wave transmission depend on the Still Water Level (SWL)
!
the force on a seawall partially protected from waves by a shallow foreshore depends
on SWL
!
a structure may be exposed (and possibly vulnerable) to different risks for different
water levels, in turn dependent upon SWL
!
the wave height may be limited by breaking before arriving at a structure
!
construction and maintenance is generally affected by the overall water level regime.
3
4
Various components of water level should be considered. Apart from astronomical tides and
very rare seismic (tsunami) effects there are several meteorological components of the water
level to be considered, known as residuals. These residuals comprise storm surges, wind setup, wave set-up and seiches.
Along the Atlantic coasts of Europe, in the English Channel and the North Sea the major
phenomenon that determines the water level is the astronomical tide, which can be predicted
accurately and well in advance. By contrast, meteorological effects, ie residuals, are not
predictable more than, at best, a few days in advance and even then the predictions are
uncertain. Seismic effects (tsunamis) are almost unpredictable or at best can be predicted a
couple of hours before their arrival in areas that are generally very far from the location of
the seism.
Some components of water level are partially correlated, meaning that a higher or lower
value of one component tends to occur at the same time as a higher or lower value of
another component. Correlations often arise between components of meteorological origin,
such as storm surge, wind set-up, wave set-up and even seiches. Depending on tidal levels,
these components may be affected, notably in shallow areas. For example, surges may
propagate differently according to the water depth and current conditions.
Usually the two most important components of the water level at any moment are the
astronomical tide and the storm surge. The former is cyclical with a period that depends on
the relative significance of astronomic forces at a particular location (see Section 4.2.2.2). For
example, along the Atlantic coasts of Europe the dominant period of tide is 12.42 hours (ie
12 hours and 26 minutes) on average. Storm surges occur randomly, typically as individual
events with durations of approximately half a day to one day, peaking about mid-way
through the period (see Section 4.2.2.3). The variation with time of the water level due to
astronomical tide and storm surge is illustrated in Figure 4.9.
5
6
7
8
9
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4 Physical site conditions and data collection
Figure 4.9
4.2.2.1
Variation in water level due to storm surge
and astronomical tide
Mean sea level
For coastal waters open to the sea the mean water level (MWL) can in most cases be taken as
a site-specific constant related to the mean sea level (MSL) of the oceans. In some areas, for
example the eastern Mediterranean Sea, the mean sea level varies slightly, according to the
time of year, in a more or less predictable manner. Observed seasonal sea level changes are
between 5 and 15 cm, whereas in the rest of the Mediterranean Sea differences up to 30 cm
may be observed in some locations.
Most countries have a national datum level, which is often approximately equal to the MSL:
examples are Ordnance Datum in the UK, IGN69 datum level in France and NAP in the
Netherlands. Chart Datum, as used by the British Admiralty in the UK and by the Service
Hydrographique et Océanographique de la Marine (SHOM) in France, represents the lowest
astronomical tide (LAT), which varies significantly from one place to another.
4.2.2.2
Tide
The basic driving forces of tidal movements are astronomical, so are entirely predictable,
which enables accurate prediction of tidal levels and currents. Since tides are long waves,
phenomena of resonance and shoaling effects caused by geography and bathymetry can lead
to considerable amplification of tidal levels in shallow seas and estuaries. Coriolis force plays a
considerable role in explaining the large tidal amplitude differences along European coasts.
Locally (see Figure 4.10), at amphidromic points, the amplitude of the tide is zero. The tidal
wave propagates around amphidromic points clockwise in the north hemisphere.
The tidal range, approximately equal to twice the tidal amplitude, is generally less than
1 metre in open oceans but increases slightly towards the continents and may increase
considerably in shallow seas, for example the continental shelf. Large amplifications are
found, for example, in bays along the coasts of England and Wales (spring tidal range of up
to 12 m), in the Bay of Fundy, Canada (spring tidal range of up to 13 m) and around SaintMalo in Normandy, France (spring tidal range up to 14 m), while a 3–4 m spring tidal range
is common for the southern North Sea.
Tides are predominantly generated by the fundamental gravitational attractions of the Moon
and Sun, which are proportional to their masses and to the inverse square of their distances
from the Earth. Although the Moon is much smaller than the Sun, it has a greater influence
on tides because it is much closer to the Earth. In particular, the timing of the tide is
associated with the relative position of the Moon rather than with the time of day and
advances at about 50 minutes a day. Another consequence of the Moon’s orbit relative to the
Earth is that the tide-generating forces of the Sun and Moon are continuously moving in and
out of phase. Near full moon and new moon, the Sun and Moon act in the same direction to
give larger tides, ie spring tides. Smaller “neap” tides are produced at around first and third
quarter moons when the Sun and Moon’s attraction forces oppose each other. The springneap cycle lasts about two weeks.
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2
3
4
5
Figure 4.10
Propagation of the tidal wave in the North Sea
The orbits of the Moon around the Earth and of the Earth around the Sun are not circular.
Thus tides also vary seasonally, with the largest tides of the year occurring at the spring and
autumn equinoxes, when the Sun crosses the equator and night and day are everywhere of
equal duration. Minor variations also occur over an 18.6-year cycle due to the variable
angular disposition of the Sun and Moon. The major planets have small additional effects.
Along the Atlantic coasts of Europe, the dominant tidal components have periods of
approximately half a day (semi-diurnal tides) and a full day (diurnal tides).
!
Dominant semi-diurnal tidal components include:
– principal lunar (M2, period = 12.42 hours)
– principal solar (S2, period = 12.00 hours).
!
Dominant diurnal components include:
– principal lunar diurnal (O1, period = 25.82 hours)
– luni-solar diurnal (K1, period = 23.93 hours).
7
8
Specific coastline geometry, for example that of channels or bays or estuaries, and bottom
friction can generate phase shift of the dominant tidal components and frequencies equal to
the sum or difference of basic frequencies. The contributions of these secondary frequencies
may locally be significant.
The predictive character of tides can be useful when scheduling critical operations, such as
manoeuvring during construction. When planning to construct, inspect or maintain a
structure it is important to keep in mind that Mean High Water Spring tide (MHWS) at a
given location always occur at about the same time of the day. The MHWS timing at another
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9
10
4 Physical site conditions and data collection
place will be different and the typical neap tide (MHWN) timing is about six hours earlier or
later than the MHWS timing. When planning work on structures it is useful to know the
timing of the most extreme low waters and whether or not they occur during daylight.
For a detailed description of sea level fluctuations and tidal phenomena, see Pugh (1987).
4.2.2.3
Storm surges
Meteorological phenomena, namely atmospheric pressure and wind, may also affect the sea
level in particular during storm events. This section focuses on atmospheric pressure effects
while wind effects are considered in the next section. Pressure and wind effects are often
combined during storms generating long waves, called storm surges, with a characteristic
time-scale of several hours to one day and a wavelength approximately equal to the width of
the centre of the depression, typically 150–800 km. These storm surges produce significant
variations of the sea level, up to 2–3 m at the shore depending on the shape of the coastline
and the storm intensity. In practice, the term storm surge level is sometimes used loosely to
include the astronomical tidal component and other meteorological effects.
Local low atmospheric pressures (depressions) cause corresponding rises in water level.
Similarly, high pressures cause drops in water levels. This is the so-called inverse barometer
effect.
For open water domains, Equation 4.9 gives the relationship between the static rise in water
level za (m) and the corresponding atmospheric pressure:
∗Δ
1
=
≠w
∗x ∈ w gd
(4.9)
where pa = atmospheric pressure at sea level (hPa) and 1013 hPa is the pressure in normal
conditions (see Section 4.2.1.2).
NOTE: Equation 4.9 results from simple equilibrium between the atmosphere and the ocean
in static conditions. Where the atmospheric pressure is higher than the mean value of
1013 hPa, the sea level decreases, provided that it can increase at another place where the
atmospheric pressure is lower than the mean value. This simple relationship does not apply
for closed domains of small dimensions such as lakes. Indeed, if the atmospheric pressure is
the same over the whole water domain there is no change in static water level.
Dynamic effects can cause a significant amplification of the rise in water level, however. When
the depression moves quickly, the water level rise follows the depression. The height of these
long waves may increase considerably as a result of shoaling in the nearshore zones. Along
the coasts of the southern North Sea, storm surges with a height of 3 m have been recorded.
4.2.2.4
Wind set-up
Shear stress exerted by wind on the water surface causes a slope in the water surface (see
Figure 4.11), as a result of which wind set-up and set-down occur at downwind and upwind
boundaries, respectively.
Figure 4.11
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1
For a bottom profile with straight and parallel bottom contours (1D situation), the windinduced gradient of the still water surface, Δ (m), along the x axis (taken normal to the
shoreline) can be computed with Equation 4.10:
∗Δ
1
=
≠w
∗x ∈ w gd
(4.10)
where d = h + Δ = actual water depth, including the wind-induced set-up (m), ∈w = mass
density of the seawater (1025–1030 kg/m!) and ≠w = wind shear stress acting on the water
surface in the direction normal to the coast (N/m²).
The wind shear stress, ≠w , can be evaluated with Equation 4.11 from a specific wind velocity,
U10 , that may be computed from the wind conditions, Uw:
≠ w = ∈ air CD U10 2
Particular solutions can be obtained by integrating Equations 4.10 and 4.11 analytically for
some simple cases. For example, for a closed water domain (eg lake, lagoon) of length, F (m),
with a constant water depth, h (m), and a constant wind speed, U10 (m/s), blowing over the
water domain, the resulting maximum wind set-up, Δw (m), at the downwind coast or shoreline
is given by Equation 4.12, derived by linearising Equation 4.10 by considering that d ( h.
U 2
1 ∈ air
CD 10 F
2 ∈w
gh
Operational systems used for the prediction of storm surges from meteorological forecasts are
based on numerical flow models (either 2D or 3D) of the area considered. The model takes
into account the stress at the sea surface due to the wind and the gradient of atmospheric
pressure (see Section 4.2.2.3). Running such a numerical model with inclusion of tidal forcing
is the recommended way to predict or model storm surges in real cases. This also applies to
the dynamics of the meteorological forces, the effects of the bathymetry in shallow-water
areas and the interactions between the tidal wave and the storm surge. The intensity of
meteorological effects on the variation of MSL can be obtained by comparing the results of a
simulation considering both tidal and meteorological forcings with the results of simulation
considering tidal forcing only. Very often the tide and storm surge model is also run in
combination with a numerical wave model. The flow model gives the water levels, for which
the wave heights generated by wind are calculated.
Wave set-up
Wave set-up is localised near to the shoreline. It is mainly caused by energy dissipation caused
by depth-induced breaking of the incoming waves (see Figure 4.12). For a bottom profile
with straight and parallel bottom contours (1D situation), the gradient of wave set-up, Δ (m),
along the x axis (taken normal to the shoreline) should be computed by solving Equation 4.13:
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5
(4.12)
In the absence of calibration data, simplified results such as those following from Equation
4.12 can only provide a guide to the likely wind set-up, because of uncertainties about the
value of CD and the choice of representative values of h and F. Other analytical and nonlinear solutions can be found in Dean and Dalrymple (1991). If possible, site-specific
measurements of surge, from which wind set-up can be estimated, should be made on a few
windy days. This would enable site-specific calibration of the equations for use in subsequent
predictions.
4.2.2.5
3
(4.11)
where U10 = wind speed at an elevation of 10 m above MSL (m/s), ∈air = mass density of air
(1.21 kg/m!) and CD = air/water drag coefficient with typical values of 0.8 · 10-! to 3.0 · 10-! (-),
the value of which increases with wind speed (eg Abraham et al, 1979; Wu, 1980).
Δw =
2
327
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8
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4 Physical site conditions and data collection
∗Δ
1 ∗S xx
=−
∗x
∈ w gd ∗x
(4.13)
where d = h + Δ = actual water depth, including the wave set-up (m), and Sxx = component
of the radiation stress tensor normal to the coast (N/m).
The component Sxx (N/m) of the radiation stress is evaluated with Equation 4.14 according to
the linear wave theory:
S xx =
1
1
2kd 
∈ w gH 2  +
(
8
 2 sinh(2kd ) 
(4.14)
where k = wave number (rad/m), = 2) /L (rad/m) to describe the spatial periodicity, with
L = wavelength (m) (see Section 4.2.4.2).
For non-linear waves, Equation 4.13 has to be solved by a numerical model together with the
appropriate equation (Aristaghes and Aristaghes, 1985) that governs the evolution of the
wave height H along the bathymetric profile, including breaking dissipation.
NOTE: Both equations are coupled, ie a change of water level affects wave propagation.
Consequently, the variation of wave height, in turn, modifies the set-up, and the system of
equations should thereafter be solved iteratively.
Figure 4.12
Wave set-up
Using linear wave theory for normally incident regular waves, Battjes (1974) derived a first
estimate of wave set-up at the shoreline. Equation 4.15 gives the relationship between the
wave set-up, Δmax , and the wave conditions at the breaker line:
Δmax = 0.3 ο br H b
(4.15)
where οbr = breaker index or maximum wave height to water depth ratio H/h (-) and
Hb = wave height at the breaker line for regular waves (m). The value of Hb can be found by
applying a wave model to the local bathymetry using deep-water waves as a boundary
condition.
For the case of a planar beach, Bowen et al (1968) used the shallow-water linear wave theory
for the radiation stress Sxx and made use of the approximate relationship H = οbr (h+Δ) in
the surf zone to derive Equation 4.16 for the wave set-up:
Δ − Δb =
1
( hb − h )
K
where the subscript b again denotes values at the breaking point and K = 1 +
328
(4.16)
8
2
3ο br
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4.2 Hydraulic boundary conditions and data collection – marine and coastal waters
According to Equation 4.16, the wave set-up on a plane beach increases linearly in the surf zone.
1
For non-uniformly sloping profiles, Equation 4.13 should be solved numerically and coupled
with a wave model. Examples of wave set-up profiles on barred beaches are given in Izumiya
and Horikawa (1984).
On the basis of field measurements and numerical simulations, some relationships have been
established for irregular wave conditions. For example, Hanslow and Nielsen (1992) fitted the
relationships given in Equations 4.17 and 4.18 to their measurements for the shoreline set-up:
Δ = 0.38 H orms
(4.17)
Δ = 0.0488 H orms Lo
(4.18)
2
3
where Horms = incident (deep-water) root-mean-square wave height (m) (see Section 4.2.4.4)
and Lo = deep-water wavelength calculated from the wave period T as Lo= g T²/(2)) (m).
Equation 4.18 results in a slightly better fit of measurements than Equation 4.17, although a
significant scatter of experimental points is still present.
Goda (2000) proposed a chart (reprinted as Figure 4.13) where the shoreline set-up can be
estimated for uniformly sloping beaches (slope = tan+ ranging from 1/100 to 1/10) as a
function of the fictitious wave steepness HΨ0 /Lo , where HΨ0 is the equivalent deep-water
significant wave height. This equivalent wave height is a hypothetical wave height obtained
from the actual significant deep-water wave height Hso (see definition in Section 4.2.4.4)
corrected for the effects of refraction and/or diffraction from offshore to the shoreline. It is
obtained as HΨ0 = Kd.KR.Hso where Kd and KR are the diffraction and refraction coefficients
respectively (see Section 4.2.4.7). Figure 4.13 shows that the shoreline set-up increases as the
beach becomes steeper and as the fictitious wave steepness decreases.
4
5
6
7
8
Figure 4.13
Wave set-up at the shoreline for uniformly
sloping beaches (Goda, 2000)
For the design of coastal structures the important question to address is whether wave set-up
should be included in the design water level or not. If the design formula to be used already
includes this wave set-up in its formulation, then this effect should not be added. This is the case
for formulae that were derived for shallow water. Similarly, if a structure is tested in a wave basin or
a wave flume and the foreshore is modelled, ie deep-water conditions are generated by the wavemaker offshore of the surf zone; consequently the wave set-up is “automatically” modelled in the
experimental tests. So the design water level should then be considered without the wave set-up.
For the other cases, in particular the design formulae that do not include wave set-up, the set-up
should be added to the still water level to obtain the design water level, as stated by Hamm (2001).
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4 Physical site conditions and data collection
4.2.2.6
Seiches
Seiches are standing wave oscillations caused by some excitation mechanism and trapped by
the general form and bathymetry of a water domain such as a harbour, a basin or a lake.
Their periods correspond to the natural periods of oscillation for that water body. Thus
when a long wave crosses the water body, it is reflected from the end and the interference
with the original wave results in a standing wave pattern. If the body of water, such as a bay
or estuary, is open at one end reflection may again occur at the open end and standing waves
can be observed.
Possible excitation mechanisms are:
!
meteorological phenomena, like squalls, impulsive winds and gusts
!
tsunamis from earthquake motions
!
storm surges (see Section 4.2.2.3)
!
long-period wave phenomena such as surf-beat (induced variations in shoaling wave
groups, see Section 4.2.2.7)
!
and even current-induced vortices.
Typical time-scales are of the order of minutes (between 2 and 40 minutes); this corresponds
to a frequency lower than 0.01 Hz in the energy spectrum of the sea surface. One famous
location for seiches is in the Adriatic Sea where the water level at Venice can display
oscillations for considerable periods. Recently de Jong (2004) investigated the origin of
seiches for the port of Rotterdam. He showed that all significant seiche episodes coincided
with the passage of a low-pressure area and a cold front approaching from the sea and 90
per cent of these events occur during the storm season. He developed a method for
predicting the occurrence of seiches based on a criterion for the occurrence of convection
cells. This criterion is expressed in terms of a minimum temperature difference between the
water at the sea surface and the air at higher altitudes in the atmosphere.
Seiches are normally observed in completely enclosed water bodies such as lakes and closed
seas. The simplest case corresponds to a rectangular closed basin of width, l (m), and
constant water depth, h (m). As illustrated in Figure 4.14 the standing wave conditions are
obtained when the ratio of the basin width, l, to half of the wavelength, L, is an integer, as
written in Equation 4.19.
l = n L/2
with n = 1, 2, 3, …
(4.19)
In other words, a seiche may occur when the wavelength of the incident wave is equal to
certain specific wavelength Ln = 2l/n.
If the shallow-water approximation is used in the dispersion relationship between the
wavelength L and the wave period T (see Table 4.6), the periods of seiches, Tn (s), are
obtained by Equation 4.20.
Tn =
2l
n gh
with n = 1, 2, 3,…
(4.20)
Similarly, for a semi-enclosed basin the standing wave conditions are obtained when
Equations 4.21 or 4.22 are fulfilled.
l = L/4 + n L/2
Tn =
330
4l
( 2n + 1) gh
with n = 0, 1, 2, 3,…
(4.21)
with n = 0, 1, 2, 3,…
(4.22)
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(a) Closed basin
1
(b) Open-ended basin
(I) Fundamental Mode (n=1)
(I) Fundamental Mode (n=0)
L1
2
Lo
4
2
Node
Antinodes
(2) Second Mode (n=2)
L1
2
L2
(3) Third Mode (n=3)
L3
3
(3) Third Mode (n=2)
L2
l
Figure 4.14
(2) Second Mode (n=1)
l
4
The three first modes of seiches for closed
and open-ended basins with a flat bottom
(adapted from Carr 1952)
Wilson (1972) and Dean and Dalrymple (1991) consider various other geometrical shapes for
the bottom (for a closed basin of constant width) and also the inclusion of frictional damping.
For real cases it is very difficult to estimate the amplitude of a seiche because it depends in
general on how close the forcing frequency is to the natural oscillation frequency. If they are
close then large amplitudes may occur (eg the tidal amplitude in the Severn estuary, UK). If
an oblong lake is suddenly exposed to a steady wind along its long axis, then the maximum
rise in water level is considerably higher than the one that would be obtained by a simple
balance between water slope and wind force (ie as computed from Equation 4.12). The
maximum can be twice as large as the increase in level caused by wind set-up alone (see
Section 4.2.2.4).
In general, analysis of local water level recordings is the only way to account properly for
seiches for design purposes. Where measurements have to be carried out, the minimum
sampling frequency should be at least twice the expected maximum frequency of the
phenomenon of interest.
4.2.2.7
6
7
Long-period waves
Even in a stationary sea-state individual wave heights vary and it is common for groups of
large waves to occur especially where some swell wave activity is present. Beneath these wave
groups the mean sea level is lowered (set-down) around the breaker line. Between the
groups, where the wave activity is less intense, the mean sea level is higher (less set-down).
This varying level of set-down produces a long-period wave motion, with a period typically of
between 30 seconds and several minutes. The oscillations give rise to bound long waves (ie
bound to the wave groups in the wind-sea). These long waves typically have a modest height,
of about 10–30 cm for most common situations.
The long waves propagate with the wave groups and become more important as they reach
the shoreline. While the primary waves, ie the wind-sea and swell, are largely destroyed by
breaking and frictional effects, the long waves are not and are therefore liberated when the
primary waves break. Much of the long wave energy is reflected, leading to a partial standing
wave pattern known as surf beat. Collectively, these bound and free long waves are also
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referred to as infra-gravity waves. If the waves approach a beach obliquely the long waves can
modify the longshore currents and also form edge waves that travel along the beach and are
often trapped within the nearshore zone. Long waves also produce variations in both the setup and the run-up in the surf zone caused by the primary waves. The long-period oscillations
in these effects can cause both greater damage to, and overtopping of coastal structures.
An order of magnitude of the surf-beat amplitude in shallow water and in the surf zone can
be obtained by using Equation 4.23, an empirical formula derived by Goda (2000):
H' )
ς rms
h 
= 0.01  0 ++1 +
(
H '0
H '0  (
 Lo 
−1 / 2
(4.23)
where ςrms = root-mean-square amplitude of the surf-beat profile (m). It is a function of the
equivalent deep-water (significant) wave height HΨo defined in Section 4.2.2.5 (m), the deepwater wavelength Lo (m) computed from the significant wave period Ts (see Section 4.2.4.4)
as Lo = g (Ts)²/(2)), and the local water depth, h (m).
Bowers (1993) also provides formulae to estimate the amplitude of bound long waves for
intermediate depths and also for surf beat significant wave height. For the case of coastal
structures exposed to long waves, Kamphuis (2001) proposed the use of Equation 4.24 to
estimate the zero moment wave height of the long waves, Hm0LW , at the structure as a function
of the breaking significant wave height Hs,b and the peak wave period Tp (see Section 4.2.4.5).
( H m0 )LW
H s ,b
H 
s ,b
= 0.11  2 (
 gT p (


−0.24
(4.24)
Equation 4.24 can be approximated as a rule of thumb by (Hm0)LW = 0.4 Hs,b . Kamphuis
(2000) also addresses the problem of reflection of these long waves on coastal structures,
showing that the long wave profile (with distance offshore) may be described as the sum of an
absorbed wave and a standing wave. The long wave reflection coefficient was about 22 per
cent during the set of experiments.
4.2.2.8
Tsunamis
Tsunamis are seismically induced gravity waves characterised by wave periods that are in the
order of minutes rather than seconds (typically 10–60 minutes). They often originate from
earthquakes below the ocean, where water depths can be more than 1000 m, and may travel
long distances without reaching any noticeable wave height. However, when approaching
coastlines their height may increase considerably. Because of their large wavelength, these
waves are subject to strong shoaling and refraction effects. Approaching from quite large
water depths, they can be calculated using shallow-water theory. Wave reflection from the
relatively deep slopes of continental shelves may also be an important consideration.
Some theoretical work is available (eg Wilson, 1963), as well as numerical models to describe
tsunami generation, propagation and run-up over land areas (eg Shuto, 1991; Yeh et al,
1994; Tadepalli and Synolakis, 1996) and also some large-scale experiments (eg Liu et al,
1995). More information on tsunamis can be obtained from the Internet, for example at
<www.pmel.noaa.gov/tsunami>.
Tsunamis are as unpredictable as earthquakes. Figure 4.15 presents observations for height
and period of tsunamis from Japanese sources observed at coasts within a range of about 750
km from the epicentre of sub-ocean earthquakes.
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1
2
3
Figure 4.15
4
Heights (left) and periods (right) of tsunamis related to earthquake magnitude
Tsunamis are an important issue in some parts of the world, particularly along the coasts and
islands of the Indian and Pacific oceans. Tsunamis occur more frequently and at greater
intensity in these areas than elsewhere in the world. This risk should be carefully addressed
in the design process for coastal structures. In some countries, eg Japan, tsunamis are a
major concern and are dealt with during the design of any marine structure.
The rarity of tsunamis in northern Europe makes it unlikely that this component of water
level would be important for that region, except where a very high standard of service is
demanded of sea defences, such as those for sensitive installations. For example, the British
Tsunami Initiative allowed 10 organisations to pool their knowledge on tsunami occurrence
and impact. The main results are available at <www.nerc-bas.ac.uk/tsunami-risks>. The
website includes information on actual occurrences of tsunamis and tentative predictions of
maximum tsunami run-up for different ocean areas. Tsunamis are more common around
Italy and in the eastern Mediterranean, where significant events occur at intervals of
approximately 100 years. Consequently they should not be dismissed as unimportant in the
design of structures in this region. For the eastern Mediterranean, the website gives 50-, 100and 200-year values of tsunami run-up of approximately 4 m, 6 m and 8 m respectively.
However, these values appear to refer to occurrence of tsunamis anywhere in the eastern
Mediterranean and not necessarily to a specific location of interest.
4.2.2.9
5
6
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Flood waves
Water levels in rivers are governed by the river discharge, with extreme levels being
associated with flood waves (see Section 4.3.3). Flood waves may contribute to the overall
water level in rivers. However, as a contribution to marine water level their impact is small
compared with tide and surge and is limited to river mouths. Moving upstream from the
river mouth, the tidal influence decreases and only after a certain distance upstream, in the
order of 10–30 km, depending on river discharge and tidal intensity, the flood wave
component may become dominant. In Section 4.3.3 the propagation of flood waves is
discussed as well as the use of rating curves, as a means of relating water levels to river
discharge, and stage relationships to correlate water levels at different locations along the
river. Unless local tide gauge measurements are available, numerical river modelling should
be undertaken during the design stage to quantify the possible effect of flood waves on the
overall water level in river mouths.
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4.2.2.10
Sea level rise resulting from climate change
Observations of sea level rise
Mean sea level rise over the last century is a well-documented phenomenon (IPCC, 2001).
Long-term measurements show a rate of rise of 1–2 mm/year over the last century. In
addition gradual slight changes in land level produce apparent regional variations in the rate
of rise. For example, in the UK, the sea level rise in the south-east of England is higher than
the average rate, while in northern Scotland it is lower than average.
Direct and indirect effects of sea level rise
In the absence of any evidence to the contrary, any increase in mean sea level would be likely
to cause an equal increase in all other water levels, including extreme water levels. In many
cases sea level rise may become an issue certainly if the wave heights are depth-limited. Sea
level rise will then increase the wave attack on the structure.
However, future climate change may also influence weather patterns, which in turn may
influence the size and frequency of storm surges, in turn influencing the total water level and
risk of flooding. Some climate change projections (UKCIP, 2002) suggest that changes in
storm surge could have a significant impact on extreme water level and flood risk. As well as
a change in mean sea level, there is the possibility of a change in tidal range. Long-term tidal
measurements show slight past trends in this respect, which may continue into the future.
What will be the sea level rise in the future?
Many institutions are involved in research on sea level rise and its implications. Since about
1980 there have been consistent predictions of an imminent increase in the rate of mean sea
level rise. A certain proportion of the predicted rise is already thought to be committed
regardless of any corrective action that may be taken, but there is some sensitivity to future
actions in pollution control etc.
The present consensus is that in future the rate of rise will probably increase to about
5 mm/year, with some regional variations, although as yet there is no evidence that this
acceleration has started.
In the Netherlands three scenarios for the future have been adopted:
!
present trend
0.20 m rise per century
!
increased trend
0.60 m rise per century
!
extreme trend
0.85 m rise per century.
How to deal with the sea level rise?
The response to possible sea level rise depends on the activity considered, for example,
whether conducting a safety assessment, considering design or reconstruction of a structure,
or planning reservation of areas for future safety improvement. Each of these activities is
described in more depth below.
Safety assessment. What is the effect of sea level rise on an existing structure? The answer
depends on the design life of the structure and the frequency of monitoring while in service.
In the Netherlands safety assessments on all flood defence structures (dikes, dunes, seawalls
etc) have to be performed every five years. As the time horizon is limited to five years the
actual sea level rise is taken into account. This actual sea level rise is not a future scenario, so
for existing structures it is possible to observe the trend of the sea level and take measures
when necessary.
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Design of structures. If a new structure has to be designed, or an existing structure has to be
repaired or upgraded, the expected sea level rise plays a role in the design process.
Examples of responses to this point from the UK and the Netherlands are given below.
!
!
In the United Kingdom. The Department for Environment, Food and Rural Affairs
(Defra) advises coastal engineers to take account of expected sea level rise when
designing or assessing sea defences. However, predictions of future changes in sea level
are uncertain and are frequently updated and any such changes will be gradual. As a
result, depending on the particular situation, sea level rise may sometimes be considered
on a contingency basis rather than as a firm commitment. For example, rather than
designing sea defences now for a 0.5 m rise in sea level over the next century which may
never occur, designers may instead prepare contingency responses for review when
evidence of accelerated sea level rise is more definite. MAFF (1999) recommends rates of
sea level rise that should be assumed for different Environment Agency regions in
England and Wales: 6 mm/year for the Anglian, Thames and Southern regions, 4 mm/year
for the North-West and Northumbria regions, and 5 mm/year for the remainder.
In the Netherlands. Until 2000 the Dutch government included the present trend of sea
level rise into the design process. This means 0.20 m for a design lifetime of 100 years
and 0.10 m for a design lifetime of 50 years. The design lifetime depends on the
situation, ie whether it is relatively easy to improve the structure again or not: a dike is
easy to upgrade, flood defence structures in urban areas are difficult to upgrade. In
2000 the Dutch government decided that the increased trend of 0.60 m per century was
the scenario that should be taken into account during design of flood defence structures.
But what will happen to the structure after its design life? If the crest height of a structure
plays an important role, as is the case for dikes and seawalls, a time will come when the
height will have to be increased to match the rise in sea level. Whether it is an easy task or
one that demands a completely new structure depends largely on how the structure was
designed initially. What is important during the design is the robustness of the technical
solution. A designer should therefore choose those options that make it reasonably easy to
cope with higher design conditions (water levels, wave forces) than are expected, or that are
expected after the design life of the structure.
Reservation of area for future improvement. By law the owner of a flood defence structure
in the Netherlands has to reserve an area around the structure that will enable it to be
improved in the long term. Use of these reserved areas by other people is highly restricted.
Construction of houses or offices is prohibited, as are activities that may hamper future
improvement of the flood defence structure. The boundary conditions for decision-making
about reservation areas depend heavily on the expected sea level rise. They are based on the
most extreme scenario – a sea level rise of 0.85 m per century – and on a time horizon of 200
years. This equates to a total sea level rise of 1.7 m. Climate change means that a 10 per cent
higher (design) wind speed also has to be taken into account, which converts to an extra 0.4
m of storm surge in the North Sea (specifically for the Netherlands!) and an increase of 5 per
cent in the wave conditions. With these extreme conditions an approximate design of a flood
defence structure has to be produced and the space required for the reservation area will be
established based on that design.
4.2.2.11
2
3
4
5
6
7
8
Sources of water level data
Low-cost software programs to predict astronomical tides are available from hydrographic
suppliers and can be used for sites at which the tidal harmonic constituents have been
established from measurements. However, this is not necessary for most situations. In
practice, the user rarely needs to carry out tidal predictions because tables are composed on
a routine basis and issued yearly by port or coastal authorities and by national authorities.
For example, the US and British admiralties have extensive data files that provide high water
(HW) and low water (LW) levels and times for major ports, usually one year ahead. These data
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should be used to derive site-specific tidal constants needed for prediction at intermediate
sites. Charts and tide tables also include typical tide curves to enable predictions to be made
for intermediate water levels between high and low water.
In most cases, only the astronomical tide (as given in tide tables) and the overall still water
level (as measured by tide gauges) is considered. Where storm surges and seiches are
significant they should automatically be included in tidal measurements and for most
practical purposes they need not be separated out. In most situations it should not be
necessary to commission tide gauge recording or any “new” research into water levels but
simply to review existing data.
Some sources of tidal and water level data are listed below:
!
Admiralty tide tables and charts in the UK (for astronomical tidal ranges)
!
Proudman Oceanographic Laboratory in the UK (for measured or predicted water level
data, for the A class tide gauge network and for the UK on a 35 km grid)
!
Service Hydrographique et Océanographique de la Marine (SHOM) in France
!
open literature on extreme water levels (see Section 4.2.2.10)
!
others such as consultants, universities, port authorities, local authorities, specialist
literature.
Tidal level records go back over 100–150 years at a few stations around European coasts. In
most cases a breakdown into separate astronomical and surge components has already been
performed. This type of data should be checked for unusually high total water levels or surges.
Where water level recording is necessary, one should consider the following points:
!
the gauge location should be permanent, accessible and not subject to interference by
vandals or wave action
!
for measurement of surges and/or sea level trends, the instrument should operate for an
indefinite period
!
for reliable derivation of local tidal constituents, it is recommended to have continuous
tidal observations for at least a year. However, reasonable estimates can be made from as
little as 14 days of data if there are constituents from a site nearby based on a longer
record.
NOTE: Analysis of tidal data is not trivial: extraction of surges requires knowledge of the
astronomical tide and analysis of tidal constituents requires specialist software.
4.2.2.12
Design extreme water levels
Usually the design extreme water level corresponds to the SWL, defined as the average sea
surface elevation over an area at any instant. To determine the extreme design water level, all
components of the water level must be determined as a function of the (average) probability
of exceedance, alternatively expressed as average exceedance frequency or return period.
Such exceedance curves, for example that shown in Figure 4.17, are based upon a long-term
distribution curve, obtained by fitting water level data to a standard statistical distribution
(see Box 4.10). Unfortunately, the lack of data for low frequencies (long return periods)
means that extrapolation is usually necessary. The extrapolation should be checked or
supported by numerical modelling of the underlying physical processes to give a better
understanding of the results.
In most cases the design water level includes tidal elevations, storm surges (caused by
atmospheric pressure effect and/or wind set-up) and long-period seiches, if any, but excludes
localised variations caused by waves. The inclusion of wave set-up and long wave oscillations
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(such as surf beat) in the design water level depends on the application and on the design
formula or model to be used subsequently for the design (see discussion in Section 4.2.2.5).
For example, if a model is built in a wave basin with a wave-maker located offshore in deepwater conditions, then the wave set-up and the long waves will automatically be produced by
the bathymetry of the physical model. The design water level in the offshore part of the basin
should not include the set-up and long wave components. Alternatively, if a formula for the
design of a breakwater, or for the prediction of overtopping, requires the water depth at the
toe of the structure then all components of water level (including wave set-up and long wave)
should be included in the design water level.
1
2
There are at least three applications for which design water levels need to be (re)evaluated.
1
Assessment of existing flood defence structures (northern Europe). This corresponds to the
present situation, without considering sea level rise, where high return periods often
have to be estimated. For example, water defences in the Netherlands need to be
assessed to a level of 1 in 10 000 years (UK and Germany are lower). Figure 4.16 gives
more than 100 years of high water level measurements and the extrapolation of the
measurements to 10-4, giving a level of +5.0 m NAP (Dutch reference level).
3
4
5
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7
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Figure 4.16
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Measurements of high water levels during more than 100 years, including extrapolation
to return periods of more than 10 000 years, at the Hook of Holland, the Netherlands
(courtesy Rijkswaterstaat)
2
Design of future flood defences (northern Europe). Similar to the above except that the
expected sea level rise should be taken into account. This can be around 0.5 m per
century; the hydraulic boundary conditions will change as well (see Section 4.2.2.10).
3
Design of coastal structures such as breakwaters with return periods in the order of
50–100 years. Table 4.4 gives an example of design water levels at a specific location.
Some of the contributions depend on the water depth and an estimate of sea level rise is
considered on this example.
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Table 4.4
Example of contributions to design water level at a
specific location with a return period of 100 years
Item
Contribution to design water level (m)
h = 15 m*
h = 10 m
h=5m
Astronomical tide
1.3
1.3
1.3
Seasonal variation
0.10
0.10
0.10
Wind set-up/storm surge
0.20
0.25
0.30
Wave set-up
-0.03
0.03
0.10
Barometric pressure
0.20
0.20
0.20
–
–
–
Global sea level rise
0.25
0.25
0.25
Total
2.02
2.13
2.25
Seiches and long waves
Note
* h = water depth. The location has a mild sloping foreshore and is depth-limited.
Having determined the probability distribution of water levels, economic optimisation may
then be used to select the appropriate extreme design level and the corresponding risk.
Figure 4.17
Example of fitted exceedance curve for water
(storm surge) levels for a location on the
Dutch coast. NAP is a local reference level
Once exceedance curves for all water level components are determined, the next step is to
derive the combined (design) water level. The exceedance frequency is a function of the
exceedance frequencies of the components. In the worst case, when all components are fully
dependent, they occur simultaneously and the design level is simply obtained from the sum
of all components corresponding to a chosen frequency. Possible reductions in the severity of
the design level with respect to this worst case may arise from the degree of mutual
correlation between the water level components. Analysis of the underlying physical
processes may enable assessment of possible dependencies and may allow a joint probability
analysis of the water level effects (see Section 4.2.5) to be carried out to produce an
exceedance curve for the total water level.
Considering now the frequent problem of a design water level resulting from the
combination of tide and storm surges there are two approaches that can be used.
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(1) Separation of tides and storm surges
1
The tidal elevation is a purely deterministic motion that can be accurately predicted (see
Section 4.2.2.2), therefore a first approach is to separate in the measured high water levels
(HW), the tidal component and the storm surge component (defined as the difference
between measured sea level and predicted tidal level). The deterministic characteristic of the
astronomical tide means that the exceedance curve for the tidal level is known in principle
with very high precision. The exceedance curve for the storm surge is obtained by fitting
storm surge data to a standard statistical distribution (see Box 4.10 and Figure 4.17).
Equation 4.25 derived by Simon (1994) describes the probability that the high water level,
HWL (m), exceeds a given value Z*:
2
P ( Z *) = P ( HWL ≥ Z *) =
∫
Z max
Z min
p ( z ) S ( Z * − z ) dz
(4.25)
where z = tidal water level at high water, which lies between the (known) minimum and
maximum values Zmin and Zmax respectively; p(z) dz = probability that the tidal high water
level lies between z and z+dz; S(x) = probability distribution function of the storm surge
component, ie S(x) = P(Storm surge ≥ x).
3
4
As there are on average 705.8 high waters a year, the return period of the total water level,
TR(Z*) (years) at high water is described by Equation 4.26.
TR ( Z *) =
1
705.8 P ( Z *)
(4.26)
(2) Statistics on the measured total water level
Often very limited data is available on the separate component effects leading to extreme
water levels. In these cases a simple empirical approach that may be usefully adopted is the
method of analysis of annual extreme water levels. The required data is often readily
available from national sources, local ports and publications (eg Graff, 1981; Blackman,
1985). The method simply involves fitting the annual extreme water level data to an
appropriate long-term distribution (see Box 4.10; a Gumbel distribution is recommended for
water levels). The limitation is method sensitivity to outliers and the length of the records,
but the overall approach is justified by the fact that correlation between astronomical tide
and meteorological surge is very low in practice.
It is generally sufficient to work from the reliable published extreme water levels and to
convert them to the site of interest. Any uncertainty involved in calculating extreme water
levels in this way is usually small compared with uncertainties associated with prediction of
extreme wave conditions and to an assessment of their correlation with extreme water levels.
Examples of available extreme water level data and tables include:
!
United Kingdom. Many long-term sets of water level data around the UK have been
analysed (Graff, 1981; Coles and Tawn, 1990; POL, 1995) to predict extreme water levels
at about 50 specific locations. POL (1997) goes a stage further in inferring extreme water
levels at about 35 km intervals around the UK, taking account of the correlation between
tides and surges at individual A Class tide gauges and the spatial correlation between
nearby gauges, using a combination of statistical analysis and numerical tidal modelling.
!
France. In France, the Service Hydrographique et Océanographique de la Marine (SHOM)
has also published extreme water levels to consider for projects with return periods from
1 to 100 years along the Atlantic, Channel and North Sea coasts (Simon, 1994).
Sometimes very little data on water levels are available for the site of interest, whereas they
are available for neighbouring or comparable locations. Correlation techniques, interpolation
and extrapolation are useful ways to convert existing data from neighbouring locations to the
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site of interest (see Box 4.2). Although such methods may save time and cost, they should be
applied with care, especially around convex coastlines. Wind effects, strong currents and
differences in wave set-up will invalidate use of these methods. Correlation factors between
locations can be derived or verified from a limited number of simultaneous measurements,
both at the site for which the main data source exists and at the sites considered. Erroneous
design data may result from the use of such correlations to water level, which are beyond the
range of the verification.
Box 4.2
Simple approach to correlate extreme water levels
To derive a first estimate of a probability distribution of extreme water levels, for a site with only basic
astronomical tidal information, one approach is to correlate this site with one nearby for which both tidal
data and extreme water level predictions are available. Correlation is then achieved by assuming (Graff,
1981) that the ratio given in Equation 4.27 is the same for the two sites.
Extreme level-Mean High Water Spring (MHWS) level
Spring tidde range (MHWS- MLWS)
(4.27)
Where available and appropriate, a slightly more accurate estimate could be achieved by replacing spring
tidal range in the above ratio with the sum of the principal semi-diurnal tidal components, M2 + S2 (see
Section 4.2.2.2 for definitions).
4.2.3
Marine and estuarine currents
4.2.3.1
General
Although in a marine environment waves are usually the dominant loading (see Section 4.2.4),
currents should also be considered during the design of rock structures. This particularly
applies for estuaries where both marine and river dynamics are superimposed and combined
(see Section 4.2.3.2). For river environments currents are often the dominant loading; river
hydraulics are dealt with extensively in Section 4.3, and in particular in Section 4.3.2 for
river discharges and currents. This section focuses on marine and estuarine environments.
Depending on the environment (sea, river, estuary), currents have different origins, strength,
time scales and statistical characteristics. Along the coast and in estuaries most currents are
related to the tide, whereas in rivers the river discharge is the dominating factor. For marine
design conditions, however, wind- and wave-induced currents may also have to be considered.
Knowledge of currents may be required when considering structural design (stone stability),
construction and transport (required anchoring, possible speed of vessels). Indirectly,
currents may affect a structure through erosion of the sea bed.
Computation of flow conditions is based on the principle of conservation of mass and
momentum. Most problems can be solved by combining the conservation laws (or simplified
versions thereof) with a set of boundary conditions and experimentally determined parameters.
The basic equations and their simplifications can be found in the literature (Bonnefille,
1992). For practical marine and estuarine applications two situations can be distinguished:
!
a 2D horizontal area, that is the general case
!
a 3D case.
Simplified equations are presented in the following sections to predict the flow conditions.
4.2.3.2
Components of marine and estuarine currents
The response of rock and coarse sediments to currents is discussed in Section 5.2.3. Principal
sources and types of currents in marine and estuarine environments are (see the flow chart
in Figure 4.6):
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!
tidal currents
!
wind-induced currents
!
density currents
!
wave-induced currents (eg longshore currents)
!
ocean circulation currents (caused by the Coriolis effect induced by rotation of the Earth)
!
river discharge.
In most cases tidal currents are the most significant, and often the only ones considered in
the design process. Wind-induced currents may result from local differences in wind and/or
wave set-up (see Section 4.2.1 and Figures 4.11 and 4.12). Currents can be described over a
given time-scale by a time-averaged magnitude, direction and variability due to spatial and
turbulent effects. In addition, current velocities may vary in a vertical sense over the water
depth.
Except for density- and wind-induced currents, the vertical distribution of velocities can often
be described by a logarithmic function (see Section 4.3.2.4). Effects of wind, waves and
turbulence on the structure of current are also addressed in Section 4.3.2.4 and are not
repeated here.
Data on marine and estuarine current velocities can be obtained by direct measurement or by
use of numerical models (see Section 4.2.3.4), although in the latter case measurements to
provide boundary conditions (eg water levels) may still be needed. Alternatively, data on
currents for preliminary design purposes can also be obtained from the sources listed below.
Charts and tables for marine currents
In many countries coast or port authorities or the admiralty can provide tables and charts of
surface current velocities, observed in the vicinity of main shipping routes, ports, river mouths
and estuaries. These are useful, as long as it is recognised that surface velocities may, for
wind- and density-induced currents, differ significantly from the velocities closer to the bed.
Sources of data include the British and US admiralties, which hold data on surface currents
in many strategic marine areas all over the world. In France, the Service Hydrographique et
Océanographique de la Marine (SHOM) provides both measured tidal current velocities at
numerous places and charts of tidal currents produced from an advanced numerical model.
Marine and offshore activities have also often necessitated current (and other) measurements,
but such data may be in the private domain and difficult to obtain.
2
3
4
5
6
7
Correlation and transformation
When current data are available from one or more nearby locations, the currents for the site
of concern might be estimated from correlation, interpolation or extrapolation. However,
only for tidal- or wind-induced currents a more or less reliable correlation can be assumed
between neighbouring locations. The sites to be correlated should display good similarity
with regard to geography (alignment of coastline, exposure to wind and waves, location
relative to river mouths, bays, breakwaters) and bathymetry (depth contours). Correlation
factors for one or more other locations can be derived from a limited number of
simultaneous measurements both at the site and at the correlated sites.
8
9
Analytical models
Few types of current allow description with useful analytical expressions. Where such
derivations are possible, solutions are found for the governing equations of momentum and
continuity by making geometric simplifications and/or by neglecting terms in the equations.
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4 Physical site conditions and data collection
Even when such solutions are available, empirical input is often needed. Examples of
possibilities for analytical solution include:
4.2.3.3
!
the tidal current in the entrance of a harbour basin or estuary. If the geometry allows for
schematisation by a simple rectangular shape, the storage equation (based on continuity
only) can be used to relate the current velocity to the (known) water levels and width
and length of the basin (see Section 4.2.3.3 for examples of applications)
!
longshore and density currents may allow for an analytical approach, but rarely without
any empirical support (eg Bowen (1969) and Brocard and Harleman (1980)).
Estuarine flow conditions, including basin model and density currents
In river mouths and estuaries, river discharges determine the hydraulic conditions together
with the tide. In some cases, wind waves may also have some influence on the water motion.
In wide and in funnel-shaped estuaries the flow is two-dimensional, though a distinct pattern
of channels and tidal flats and banks still forms the main feature of the watercourse. Density
differences may also play a role. In this section attention focuses on a basin storage model
and on the interaction between tide and river runoff. The hydraulic interactions with closure
dams are discussed in Section 5.1.2.3.
Types of estuary and tidal inlet
From a practical point of view various types of estuary can be distinguished: short and long
estuaries, tidal rivers and tidal inlets.
!
Short estuary
The estuary length is small (less than 10–15 per cent) relative to the length of the tidal wave,
which ranges between 200 km and 1000 km, depending on the water depth and the period
of the tide (ie diurnal or semi-diurnal). The water surface in the estuary rises and falls as a
function of the tide at sea and the characteristics of the estuary, but remains practically
horizontal all the time. Analytical models of the hydrodynamics of an estuary have been
published (eg Friedrichs and Aubrey, 1994; Savenije, 1998).
!
Long estuary
The tidal wave propagates into the estuary and reflects against its inward boundary. Depending
on the estuary length, the tide can be amplified considerably as a result of reflection.
Freshwater inflows are usually of minor importance.
!
Tidal river
A long and relatively narrow watercourse, where the tide penetration is mainly governed by
the bed slope and the upstream river discharge. If the river mouth is funnel-shaped,
reflection can also be of importance.
!
Tidal inlet
In addition to these estuary types, tidal inlets can often also be of interest. Mehta and Joshi
(1986) developed a simple hydrodynamic model of such inlets for the case of a sinusoidal
tide. Their figures 2 to 5 may be used for practical applications.
The water motion in an estuary accords with physical laws (see Section 4.2.3.1) and is
governed by a set of boundary conditions:
342
!
the tide at the seaward boundary
!
the geometry of the estuary
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!
1
the upstream discharge.
In the case of tidal motion the physical laws reduce to the so-called long wave equations,
based on the assumption that vertical velocities and accelerations are negligible. Depending
on the type of estuary, the long wave equations may be further simplified.
2
Basin storage model for closure dams in estuaries
When a closure dam is constructed in an estuary the hydraulic resistance changes during the
construction phase, which affects the flow velocities and water levels in the estuary. The
discharge, water level and maximum flow velocity can be estimated using a basin storage
model, provided that the estuary length, Lb (m), is short relative to the length, L (m), of the
tidal wave (see Equation 4.28).
Lb / L < 0.05
3
(4.28)
4
5
Note: b is affected by horizontal closure while h0 is affected by vertical closure.
Figure 4.18
Definition sketch of basin model
Case 1 – sill. As long as there is no appreciable constriction at the estuary mouth, ie when b/hb
is sufficiently large (see definition sketch in Figure 4.18), the discharge Q (m³/s) through the
entrance attributable to the vertical tide inside the basin can be determined by using
Equation 4.29:
Q(t ) = B Lb
dh
dt
6
(4.29)
7
where Q(t) = tidal discharge (m³/s) and h = water level in the estuary or the basin (m).
In the case of a sinusoidal tide of amplitude h, Equation 4.29 becomes Equation 4.30:
Q(t ) =
2π
 2π t 
B Lb ˆh sin 

T
 T 
(4.30)
where, apart from the definitions shown in Figure 4.18, ˆh = amplitude of tide in the estuary
(m), t =time after the beginning of the tide (s), T = tidal period (s).
8
Cross-sectional mean velocity U (m/s) at the estuary mouth can be evaluated by Equation 4.31:
U=
Q
b h0
(4.31)
where h0 = water depth in the gap (m) that varies with the tidal time as h and b = width of
the estuary mouth (m).
Case 2 – vertical closure. When the closure dam forms an appreciable vertical constriction,
the tidal discharge through the mouth starts to decrease and the mean flow velocity in the
closure gap, U0 , depends on the water levels, h and H, inside and outside the basin
respectively. When the flow is into the basin, U0 can as a first estimate be determined by
using Equation 4.32:
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10
4 Physical site conditions and data collection
U 0 = 2 g ( H ( hb )
(4.32)
where H = sea-side water level above the dam crest (m) and hb = water level in the basin
above the dam crest (m).
Further discussion of discharge and velocity through the gap is given in Section 5.1.2.3
where discharge coefficients are introduced to improve precision. A simple model to calculate
the response water level of the basin, h, given the tide at the seaward side as the boundary
condition, H(t), is based upon Equation 4.33, which results from the combination of
Equations 4.29, 4.31 and 4.32:
B Lb
dh
= h0 b 2 g ( H ( hb ) + Qriver
dt
(4.33)
where Qriver = river discharge into the basin (m³/s), if relevant, h0 = water depth on the crest of
the closure dam (m) (see Section 5.1.2.3) and H, hb and b are defined according to Figure 4.18.
Combined closure. Assuming a sinusoidal tide at sea and Qriver = 0 m/s, the maximum flow
velocity in the closure gap during the tide, Ug or U0 (m/s), can be determined with the design
graph given in Figure 4.19. Note that Figure 4.19 plots Ug /√ ˆh, which is not a nondimensional quantity where Ug is in m/s and ˆh is in m. In this graph Y serves as an input
parameter, the value of which should be calculated with Equation 4.34:
B Lb
T
Y = 0.001 M 2
T b ˆh
(4.34)
where T = tidal period (s) and TM2 = period of semi-diurnal tide (= 44 700 s).
Figure 4.19
Design graph for maximum velocity;
note that hb should read h0 , the water
depth (on the sill) in the closure gap
This method is not valid for small closure gaps. If the gap is not wider than about 20 per cent
of the original width, it is recommended to use more sophisticated mathematical models.
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Interaction of tide and river runoff
For the discharge generated by a combination of a local horizontal tide Qtide(x) and river
runoff Qriver , the resulting horizontal tide or discharge Q(x), in a cross-section at a distance x
inland from the entrance of the estuary, can be determined by Equation 4.35.
) 2π t 
Q( x) = Qriver − Qtide ( x)cos +

 T 
(4.35)
2
Qtide(x) is the local amplitude of the pure horizontal tide, the value of which varies along the
estuary. The following cases can be distinguished (see Figure 4.20):
!
Qtide(x) >> Qriver entrance of the estuary
!
Qtide(x) > Qriver
section with bidirectional flow
!
Qtide(x) < Qriver
section with unidirectional flow
!
Qtide(x) = 0
river section.
3
Generally, the river discharge Qriver varies in time (see Sections 4.3.1 and 4.3.3). When Qriver
increases, Q during ebb increases and Q during flood decreases. In addition, the respective
duration of the ebb flow increases and that of the flood flow decreases. When the river
discharge is smaller, the tidal penetration length is greater and the tidal amplitude at a
certain location is larger.
4
5
6
Figure 4.20
Combined tide and river discharge
Density currents
Density-induced flow components may occur because of variations in the fluid density caused by
salinity (and/or temperature). The salinity of seawater is about 30 parts per thousand and varies
slightly (by some 5 ppt) from place to place. For the calculation of density-induced flow velocities
reference is made to the available mathematical models (see Sections 4.2.3.4 and 4.3.5.2).
Figure 4.21 shows examples of the velocity profile in an estuary with a river discharge for a
highly stratified and a well-mixed estuary. The highly stratified situation is characterised by a
salt wedge-type lower layer originating from the sea (with weak tidal velocities and hence
weak vertical mixing) and a freshwater upper layer originating from the river discharge. In
the well-mixed situation the fluid density is constant over the depth, but varies in
longitudinal direction from the seawater to the freshwater value. Whether an estuary is well
mixed or highly stratified can be evaluated with two stratification parameters, namely the
volume ratio number V (see Equation 4.36), the ratio of runoff volume and tidal prism and
the estuary number E (see Equation 4.37):
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V = QriverT / V f
(4.36)
E = Fr 2 / /
(4.37)
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7
8
9
10
4 Physical site conditions and data collection
where:
Qriver
=
river discharge (m!/s)
T
=
duration of tidal cycle (s)
Vf
=
volume of seawater entering the estuary at the entrance during flood (m!)
Fr
=
Froude number at the mouth = U max / gh (-)
Umax
=
maximum velocity in the entrance during a tidal cycle (m/s)
/
=
reduction factor (-).
Criteria for stratification are presented in Table 4.5.
Figure 4.21
Density variations and velocity profiles in a stratified and a mixed estuary
Table 4.5
Stratification criteria for estuaries
Stratification rate
Volume ratio number V
Estuary number E
Highly stratified
V > 1.0
E < 0.005
Partially stratified
0.1 < V < 1.0
0.005 < E < 0.2
V < 0.1
E > 0.2
Well-mixed
4.2.3.4
Numerical modelling of marine and estuarine currents
Modelling of water levels and currents is discussed in details in Section 4.3.5. Nowadays
numerical models are most often used to obtain current conditions in marine and estuarine
environments, and physical modelling is rarely used for this purpose.
When tides are the dominant phenomenon, 2DH models are used on the basis of depthintegrated long wave equations (also called Saint-Venant equations). Models of this type
include ADCIRC, DELFT-3D, MIKE-21 and TELEMAC-2D. An example of simulation is
presented in Figure 4.22. Such models are based on structured or unstructured
computational grids and use finite difference, finite volume or finite element methods to
solve the mass and momentum equations of the flow. The modelling of tidal flats is usually
included in such models, as well as the effect of wind stress at the free surface and
atmospheric pressure gradient. These models can be coupled with wave models to compute
wave set-up and wave-induced currents in the breaking zone.
For estuaries, when density and/or salinity effects are sensitive, 3D models are often
employed to provide a proper description of the hydrodynamics. These models solve the
Navier-Stokes equation with a free surface on a three-dimensional mesh (some examples are
DELFT-3D, MIKE-3 and TELEMAC-3D).
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In both cases, proper boundary conditions need to be imposed (water level and/or velocity
profile or discharge) as well as forcing conditions over the domain if applicable (wind field,
atmospheric pressure). The modelling of bottom roughness is often sensitive in such
computations and requires some attention during the construction and the calibration of the
model. To validate the model before using it for applications, it is also important to compare
the numerical results to measurements for a variety of conditions.
1
2
3
4
5
Figure 4.22
4.2.4
Example of tidal current field computed with a 2DH flow model (Morbihan Bay, France)
(courtesy Cetmef)
6
Wind-sea and swell
The principal loadings exerted by waves upon marine structures can be subdivided into wave
impact loads (short-duration pressures), drag loads (pressure plus shear) and inertia loads. In
the design process these loadings should be schematised and described as functions of wave
parameters. In this section, some important definitions, theoretical results and practical
relationships related to waves are given to determine the design conditions for a structure
exposed to wave attack.
NOTE: This section does not attempt to provide a complete text on waves. Additional
information can be found in reference textbooks (eg Dean and Dalrymple (1991, 2004),
Goda (2000), Tucker and Pitt (2001) etc).
4.2.4.1
8
General definitions related to waves, sea-states and wave climate
This section deals with gravity waves propagating at the surface of a water body (oceans, seas,
lakes, rivers etc) and generated by the action of the wind at the free surface. This covers
waves with typical periods ranging from 2 s to 30 s. One usually distinguishes between windsea and swell wave conditions:
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!
wind-sea – these waves are observed in the area where they are generated and occur as a
result of wind action. Wind-seas are characterised by short periods (2 s to 10 s typically)
and provide an irregular aspect of the sea surface
!
swell – these waves were generated away from the zone where they are observed and
there is no significant effect attributable to the local wind. Swell usually exhibits a more
regular pattern than wind-seas, with longer periods (10 s to 30 s).
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4 Physical site conditions and data collection
Temporal scales related to waves
Wave conditions can be analysed and considered at different temporal scales.
!
One individual wave
A typical time-scale is in the order of one wave period, say 10 s. There are various ways of
separating individual waves in a wave record (time series of sea surface elevation typically
sampled at a frequency of 2 Hz over a duration of 20 min to 1 hour). Figure 4.23
schematically shows the shapes of one such isolated wave both in space (left panel) and in
time (right panel). Note that the temporal and spatial profiles of the wave are symmetrical
with respect to the vertical axis as the x axis was chosen in the direction of wave propagation.
The wave height, H, is defined as the difference between the maximum and minimum
elevations of the sea-surface (peak to trough wave height) over the duration of the wave. This
duration is called the period, T, in the time domain and the wavelength, L, in the spatial
domain. Designing a structure with respect to one individual wave (a so-called maximum
wave) is not common practice for rubble mound breakwaters. This design approach is more
frequently employed for the design of vertical breakwaters and offshore structures in deep
water, such as oil or gas platforms and foundations for offshore wind turbines.
Figure 4.23
!
Definition sketch for individual wave parameters
A sea-state
This corresponds to a period of time over which the successive individual waves, although
different from each other, can be regarded as being the results of the same random process,
so that they have the same average properties in a statistical sense. For this reason, the
environmental conditions (such as wind speed, wind direction and water level) are assumed
to be constant over the duration of a sea-state (typical time-scale in the order of 3 hours, say
300–500 waves). Characteristic wave heights and periods of a sea-state can be obtained by a
statistical (or wave-by-wave) approach (see Section 4.2.4.4) or by a spectral approach (see
Section 4.2.4.5). The design of marine rock structures is mainly based on such characteristic
values of sea-states (eg significant wave height Hs , mean period Tm), representative of
extreme conditions (see below).
!
A storm event
A storm event can be described by several sea-states, eg the increasing phase, the maximum
phase and the decreasing phase. At locations under tidal influence the typical sea-state is very
often only 2–3 hours, but without tidal effects it may last 6 hours or longer depending on the
evolution in time of wind conditions (typical time-scale in the order of 12 hours to one day).
In the design process of marine rock structures it is important to take proper account of the
actual duration of storm events (in particular due to the effect of tides) for the site of interest,
when determining the sequence of sea-states (number, characteristics and duration of
successive sea-state conditions) to be tested on a physical model for instance.
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!
1
A short-term (or daily) wave climate
This is obtained by examining the characteristics of sea-states over a period of between one
and two years from a statistical approach (typical time-scale in the order of one year). It gives
the distribution of wave heights, periods, directions etc and the correlation between two of
these parameters (see Section 4.2.4.8). The short-term wave climate also uses a wave rose,
comparable to the wind rose. In addition, seasonal effects can be examined and quantified by
restricting the analysis of wave measurements to, for example, the winter season. The shortterm wave climate gives insight into operability for floating equipment and crest levels for
temporary haul roads. It usually provides valuable information on the incoming directions of
waves, to be combined with given wave heights and periods for defining design conditions.
!
4.2.4.2
3
A long-term (or extreme) wave climate
These terms describe the distribution and probability of occurrence of extreme sea-states
(storm). The distribution function of extremes is different to that used for the short-term
wave climate. It has to be based on a dataset of sufficient durations (typically 5–10 years)
containing a sufficient number of storms, so that extreme wave heights of very low
probability of occurrence can be estimated by statistical extrapolation (see Section 4.2.4.9).
The extreme wave climate is used for both the functional (hydraulic response) and structural
(stability) design of the structure. The typical return periods of wave events for design
conditions range from 25 to 100 years or higher, depending on the design life and
performance requirements of the structure (see Section 2.3).
4
Representation of regular/random and long-crested/short-crested waves
5
Waves at the sea surface always show irregular, more or less chaotic, patterns. The sea
surface motion results from a combination of waves having different heights, periods and
directions. The irregularity of wave heights and period gives raise to the terms of irregular
or random waves. The irregularity in propagation directions may be observed by considering
the length of wave crests on a picture of the ocean surface: when the waves have
approximately the same direction their crests are clearly identifiable, long and almost parallel
(so-called long-crested waves), whereas a spreading of wave energy over a range of directions
manifests itself by rather short and non-parallel crests (so-called short-crested waves).
Although all sea-states are irregular and short-crested in the general case, the representation
of regular long-crested waves is discussed first, followed by the irregular representation.
6
7
Description and definitions for individual waves or regular waves
The simplest approach to represent a series of waves corresponds to regular and long-crested
waves. In this basic representation, waves repeat indefinitely, each wave being identical to the
others, with the same height H. They are monochromatic and periodic both in time (with
period, T (s), and in space (with wavelength, L (m)) and unidirectional (with propagation
direction, + (°)). Alternatively, one can use the frequency f = 1/T (Hz or 1/s) or the angular
frequency, φ = 2) f = 2) /T (rad/s), to describe the temporal periodicity, and the wave
number, k = 2) /L (rad/m), to describe the spatial periodicity.
The parameters describing spatial periodicity (k or L) are related to the parameters describing
temporal periodicity (T, f or φ), together with the water depth, h, by the so-called dispersion
relation, which for the case of linear (small amplitude) wave theory is given by Equation 4.38.
φ 2 = g k tanh ( k h )
8
9
(4.38)
When the water depth, h, and wave period, T (or the angular frequency, φ), are known, the
determination of the wave number, k (or the wavelength L = 2) /k), requires the resolution
of the implicit Equation 4.38. Iterative numerical schemes may be employed to solve this
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4 Physical site conditions and data collection
equation accurately whenever necessary, but explicit approximations, such as given in
Box 4.3, can also be used.
The propagation velocity of wave crests (phase speed) is c = L/T = φ /k (m/s) and the
propagation velocity of energy (group velocity) is given by cg = ∂φ/∂k (m/s). In linear wave
theory, based on Equation 4.38, the expressions for phase and group velocity are given by
Equations 4.39 and 4.40 respectively.
c=
g
tanh ( k h ) =
φ
g
tanh ( k h )
k
(4.39)
2k h 
1)

+1 +
2 + sinh ( 2 k h ) 
(4.40)
cg = n c with n =
Note that the factor n has two asymptotic values: (1) when the relative water depth, kh (-), is
small, n tends towards 1; (2) when kh is large n tends towards ½ ; in this case the wave energy
propagates at a speed that is half of that of individual waves. For these asymptotic cases,
particular expressions of k, L, c and cg may be derived analytically and are listed in Table 4.6,
together with the non-dimensional criteria for using these approximations. For values in
deep water (large value of kh), the subscript “0” or “o” was used conventionally (eg Lo for the
deep-water wavelength). Here the latter, “o” (of offshore), is used. From Table 4.6 it should
be noted, for example, that in shallow-water conditions, c and cg do not depend any more on
the wave period, T, and that all waves have the same velocity (non-dispersive waves), which,
in this case, equals the velocity of energy.
Box 4.3
Explicit approximations of the linear dispersion relation for water waves
There are numerous approximations of the dispersion relation given by Equation 4.38. Equation 4.41 gives
the rational one proposed by Hunt (1979) at order 9, which is very accurate (always less than 0.01 per
cent of relative error in kh):
( k h ) 2 = ( ko h ) 2 +
9
1+
ko h
∑ a (k h)
n
o
n
(4.41)
n =1
where ko = 2)/Lo = φ2/g = deep-water wave number (rad/m) and the values of an are as follows:
a1 = 0.66667
a6 = 0.00654
a2 = 0.35550
a7 = 0.00171
a3 = 0.16084
a8 = 0.00039
a4 = 0.06320
a9 = 0.00011.
a5 = 0.02174
Hunt (1979) also provides a similar formula at order 6, with a relative error in kh always less than 0.2 per
cent.
Alternatively, the simpler explicit formulation by Fenton and McKee (1990) (see Equation 4.42) can be
used. Although it is less accurate than the former (1.5 per cent of maximum relative error), it is easier to
use on a calculator.
3/ 2 

)
φ2 
h  (

k=
coth
φ
+



+
g 
g  ( 
( 


2/3
or equivalent:
{
}
3/ 4
L = Lo tanh ( ko h ) 

(
2/3
(4.42)
Other explicit expressions have been proposed by Eckart (1952), Wu and Thornton (1986), Guo (2002).
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Table 4.6
1
Asymptotic values of the dispersion relation and related quantities
Approximations with criteria
Shallow-water or long wave
approximation ( small kh )
Deep-water or short wave
approximation ( large kh )
h/L < 1/25 or T g / h > 25
h/L > 1/2 or T g / h < 4
Dispersion relation
φ 2 = gh k 2
φ 2 = gko
Wave number k (rad/m)
k = ω / gh
ko = φ 2 /g
Wavelength L (m)
L = T gh
Lo = gT 2 /(2 π)
Phase speed c (m/s)
c = gh
co = gT/(2 π)
Group velocity cg (m/s)
cg = c = gh
cgo = ½ co = gT/(4 π)
Variable
2
3
Description and definitions for irregular waves or sea-states
For a sea-state, composed of waves having different characteristics but belonging to the same
random process (ie constant environmental conditions), two approaches are used to describe
the wave field.
1
2
4.2.4.3
Long-crested random waves are still unidirectional, but include a range of wave heights
and periods. The irregular or random wave train is composed of successive waves having
different heights and periods. Two approaches are used to describe random waves and
are set out below: the statistical (or wave-by-wave) approach, which consists of
determining the statistical distributions of wave heights, periods, directions etc (see
Section 4.2.4.4), and the spectral approach, which is based on the determination and use
of the spectrum of wave energy (see Section 4.2.4.5). In both cases, representative
parameters can be calculated to characterise the sea-state (eg the significant wave height
Hs and the mean wave period Tm).
Short-crested random waves additionally include a range of directions, defined in terms
of the standard deviation of wave energy propagation direction or some other standard
spreading function. A more complete description of the sea-state is given by the
directional spectrum (S(f, + )), which gives the distribution of wave energy as a function of
frequency and direction (see Section 4.2.4.5). Short-crested waves provide the best
representation of true ocean waves, and this representation of wave conditions has now
become the standard way of dealing with wave actions in the engineering practice. The
direction of wave incidence and the angular spreading of wave energy have been shown
to have some effects on wave-structure interaction processes, such as stability of rubble
mound breakwaters, run-up and overtopping (Galland, 1995; Donnars and Benoit, 1997).
5
6
7
Characterisation of wave conditions and wave kinematics
8
Characterisation of wave conditions by non-dimensional numbers
In order to characterise wave conditions, to investigate which processes are dominant during
wave propagation and transformation, and/or to estimate wave loading on structures, several
non-dimensional numbers are used. They can be computed for regular waves or random
waves by using representative wave parameters. The most useful parameters are set out below.
!
The relative water depth: kh or h/L and the non-dimensional period T g / h
They are used to determine the manner in which seabed bathymetry affects waves. For
example, the parameters were used in the previous section (see Table 4.6) to derive
approximations of phase speed and group velocity in low and large relative water depths
respectively.
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4
9
10
351
4 Physical site conditions and data collection
!
The wave steepness s = H/L and the relative wave height H/h
They are measures of non-linearity of the wave (see Figure 4.23). They are used in particular
to quantify the importance of non-linear effects and they appear in the formation of criteria
for predicting wave breaking. A specific use of the wave steepness is made if the wave height
is taken at the toe of the structure and the wavelength in deep water. In fact this is a fictitious
wave steepness so = H/Lo and is often used in design formulae for structures. The main goal
in this case is not to describe the wave steepness itself, but to include the effect of the wave
period on structure response through Lo = gT2/(2)), which is only valid offshore.
!
The Ursell number U (-)
This is a combination of the former numbers and is presented in Equation 4.43. It is used to
characterise the degree of non-linearity of the waves.
U=
!
H L2
h3
)H
=+ 
 h 
)h
+L
 
2
(4.43)
The surf similarity parameter ξ , also known as the Iribarren number, Ir (see Equation 4.44)
This is used for the characterisation of many phenomena related to waves in shallow water,
such as wave breaking, run-up and overtopping. It reflects the ratio of bed slope and
fictitious wave steepness, so.
ξ=
tan /
tan /
=
=
so
H / Lo
tan /
( 2π H ) ( g T 2 )
(4.44)
When the deep-water wave length, Ho, is used instead of H, this number is denoted ξo or Iro .
This parameter is often used for beaches, and often for design of structures too. It gives the
type of wave breaking and wave load on the structure. Actually, waves can break first on the
depth-limited foreshore before reaching the structure and then break once again on to the
structure. On the foreshore the breaker type is generally spilling, sometimes plunging. On
the structure itself it is never spilling, but plunging (gentle structure slope), surging or
collapsing (see Section 4.2.4.7 for the definition of breaker types).
When using these parameters for random waves, it should be stressed and indicated (as a
subscript of these parameters, for example) which characteristic wave height and period are
being used in their evaluation (eg subscript “p” if the peak period Tp is used, and “m” if the
mean period Tm is used).
For further discussion on the use and the notation of ξ, please also refer to Section 5.1.1.1.
Overview of methods for computing wave kinematics
Many wave theories are available to derive other wave parameters and kinematics (velocities,
accelerations, pressure etc) from the above-mentioned basic parameters (eg H and T, plus
possibly a flow speed). The majority of design methods are based on Stokes linear wave
theory (ie small amplitude wave theory) derived for a flat bottom (ie constant water depth). A
major advantage of linear theory in design procedures is that the principle of superposition
can be applied to wave-related data, obtained from a composite wave field. Using linear wave
theory, practical engineering approximations can be derived for regular waves propagating
in deep and shallow water respectively (see Table 4.6). Expressions for orbital velocities ux , uy ,
uz and pressure p are presented below as Equations 4.45 to 4.48 for the case of a regular
wave with a height H, period T (angular frequency φ = 2)/T) and direction + with respect to
352
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4.2 Hydraulic boundary conditions and data collection – marine and coastal waters
the x axis. Other expressions for accelerations, particle displacements, etc can be found in
reference textbooks such as Dean and Dalrymple (1991).
u x ( x, y , z , t ) =
u y ( x, y , z , t ) =
(
)
(
(
)
(
(
)
! !
H cosh k ( h + z )
φ
cos+ cos k ⋅ x − φ t
2
sinh ( k h )
! !
H cosh k ( h + z )
φ
sin + cos k ⋅ x − φ t
2
sinh ( k h )
! !
H sinh k ( h + z )
u z ( x, y , z , t ) = φ
sin k ⋅ x − φ t
2
sinh ( k h )
p ( x, y , z , t ) = − ∈ g z + ∈ g
(
(
)
)
(4.45)
)
(4.46)
)
1
2
(4.47)
! !
H cosh k ( h + z )
φ
cos k ⋅ x − φ t
2
cosh ( k h )
(
)
(4.48)
Linear wave theory becomes less applicable when the wave shape deviates from purely
sinusoidal and when wave steepness (s = H/L) increases. Non-linear analytical wave theories
that may be used in these situations include Stokes’ higher order wave theories, cnoidal wave
theory, solitary wave theory and Dean’s Stream Function theory. The description of these
theories is beyond the scope of this manual but can be found in Sobey et al (1987), Fenton
(1990) and Fenton (1999), for example. An overview of the applicability of wave theories is
given in Figure 4.24. Note that Tapp stands for the period for which the applicable model of
wave theory is searched (ie Tm or Tp).
Numerical stream function methods (based on a Fourier decomposition of the stream function
of the flow) are superior to all analytical theories (eg Stokes or cnoidal theories), whatever the
water depth. Thus the recommendation for practical applications is to use this stream function
approach (see Dean, 1965; Rienecker and Fenton, 1981; Fenton, 1988). Also note that some
semi-empirical wave theories have been proposed for the case of a sloping bottom, namely the
covocoidal theory of Swart and Crowley (1988) and the method of Isobe and Horikawa (1982).
3
4
5
6
7
8
Figure 4.24
Range of applicability of wave
theories (from American
Petroleum Institute, 1993)
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NOTE: The numbers in Figure 4.24 (3, 5... etc) stand for the order of the stream function.
9
Orbital velocities near the sea bed are required for design of rockfill used in offshore
protection of pipelines under (combined current and) wave attack (see Section 5.2.2.5).
Kirkgöz (1986) has shown that linear wave theory gives reasonable agreement with observed
near-bed orbital velocities under the wave crest even at the transformation point of plunging
breakers. In fact, this is true for the wave crest phase, but laboratory experiments show that
10
353
4 Physical site conditions and data collection
the linear theory significantly overestimates (by up to 40 per cent) the velocity under the
wave trough in the breaking zone (eg Benoit et al, 2003).
Soulsby (1987) has provided design curves based on linear wave theory (see Figure 4.25) that
enable calculation of near-bed orbital velocities for both monochromatic (regular) and
random waves, where the maximum horizontal orbital bed velocity uo was obtained from
Equation 4.45 applied at the bottom (namely at z = -h) (see Equation 4.49).
uo =
Figure 4.25
1
H
φ
2 sinh ( k h )
(4.49)
Near-bed orbital velocity for monochromatic waves and a
spectrum of waves (from Soulsby, 1987)
4.2.4.4
Statistical properties and distribution of waves in a sea-state
Wave statistics play the major role in determination of design loads and risk assessment and thus
in the overall design of rock structures in coastal and shoreline engineering. Some explanation
of basic statistical wave properties and representative wave parameters is therefore necessary.
Wave-by-wave analysis and representative wave parameters
As indicated in Section 4.2.4.2, wind-generated waves are irregular (non-periodic) and a
typical record of sea-surface elevation is depicted in Figure 4.26. This figure also illustrates
the definition of the zero-crossing method to separate individual waves: each time the wave
signal crosses the mean water level a new wave is counted. The individual wave period Tj of
the wave j is the time between two successive zero-crossings and the corresponding lowest
trough to highest crest height defines the height, Hj , of that individual wave. Two variants of
the method exist: zero up-crossing and zero down-crossing (IAHR/PIANC, 1986). The latter
is recommended, as the waves that are isolated by this approach have more physical
meaning. The individual waves are thus composed of the trough and the following crest, as
depicted on Figures 4.23 and 4.26.
Figure 4.26
354
Typical record of irregular sea and principle of the zero down-crossing method
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4.2 Hydraulic boundary conditions and data collection – marine and coastal waters
The standard recording period is 20 minutes to one hour (every three hours or every hour),
but it can also be continuous. The important point is that a sea-state is a stationary process
for a certain time only and so the analysis of a continuous record should be restricted to a
duration over which the conditions can be assumed to be statistically stationary. On the
other hand, to be statistically correct there should be a minimum number of waves in the
record, typically at least 200 or 300 waves but preferably 500 waves.
From the records, the series of N waves (Hj , Tj) (j = 1, … , N) are sorted by decreasing wave
height and a number of characteristic wave heights and periods may then be determined
(IAHR/PIANC, 1986), the most often used being defined in Table 4.7.
In particular, note that two definitions are used for computing some representative wave
heights of a sea-state of given duration:
HP% is the wave height that is exceeded by P per cent of the wave heights in the seastate. In particular, H2% is used in the design process of a breakwater (especially for
predicting run-up and overtopping)
!
H1/Q corresponds to the average height of the 1/Q largest wave heights in the sea-state.
The most important wave heights of this type for design-related aspects are the
significant wave height H1/3 = Hs (average of the highest 1/3 wave heights in the seastate), H1/10 , H1/100 and H1/250 .
To obtain reliable estimates of larger wave heights (ie low values of P for HP% and high values
of Q for H1/Q), the time-series of measured surface elevation should contain a sufficiently
large number of waves. For example, the stable estimate of H1/250 requires a very long
record; for a sea-state comprising 500 waves, which is already quite a large number, H1/250
will be determined as the average of only the two largest wave heights of that record. The
same comment applies for the maximum wave height that has a large variability from one
occurrence to another for given sea-state conditions. That is why the use of more stable wave
heights (although larger than the mean wave height) such as H1/3 or H1/10 is preferred to
characterise sea-state conditions.
4
5
6
Characteristic wave heights and periods of a sea-state from a wave-by-wave analysis
Characteristic wave parameter
Definition
Mean wave height Hm
Hm =
Root-mean-square wave height Hrms
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2
3
!
Table 4.7
1
1
N
H rms =
N
∑H
j
7
j =1
1
N
N
∑H
2
j
j =1
Significant wave height Hs = H1/3
Average of the highest 1/3 of wave heights in the record
Wave height H1/10
Average of the highest 1/10 of wave heights in the record
Wave height H1/100
Average of the highest 1/100 of wave heights in the record
Wave height H1/250
Average of the highest 1/250 of wave heights in the record
Wave height H2%
Wave height exceeded by 2% of wave heights in the record
Maximum wave height Hmax
Highest wave height in the record
Mean wave period Tm
Tm =
Significant wave period Ts = T1/3 (sometimes
also referred to as TH1/3 )
Average of the periods associated with the largest 1/3 of
wave heights in the record (ie average of periods of the
waves selected to compute H1/3)
Period of maximum wave height THmax
Period of the largest wave height in the record
Maximum wave period Tmax
Largest wave period in the record
1
N
9
N
∑T
8
j
j =1
10
355
4 Physical site conditions and data collection
Distribution of individual wave heights in a sea-state
During each sea-state a (short-term) distribution of wave heights applies. Once the
distribution function of wave heights is known, all the characteristic wave heights listed in
Table 4.7 can be computed. Some basic and important results for wave distributions are
summarised below: first for the deep-water case, and then for the shallow-water case. The
latter is more important for the design of coastal structures, but also more difficult to model
and parameterise.
!
Distribution of deep-water wave heights
In deep water the water surface elevation usually follows a Gaussian process and thus the
individual wave heights closely follow the Rayleigh distribution. Note that the Rayleigh
distribution is a particular case of the Weibull distribution, with a fixed shape parameter of 2
(see Box 4.10). This distribution is fully defined by a single parameter, which may be either
the mean wave height Hm or the root mean square (rms) wave height Hrms , or alternatively
the variance of the free-surface elevation m0 . Equation 4.50 gives the equivalent forms of the
cumulative distribution function.
2
)
) π ) H 2 
) H2 
 = 1 − exp + − )+ H  
P ( H ) = P( H < H ) = 1 − exp + −
 = 1 − exp + − +

+ 8m0 
+ 4  Hm  
+  H rms  






(4.50)
Equation 4.51 gives the corresponding probability density function.
p( H ) =
2
) π ) H 2  2 H
)
) H2  π H
H
+− +
=
+ − )+ H  
exp + −
exp
exp
=

2
+ 8m0  2 H m2
+ 4  H m   H rms
+  H rms  
4m0






(4.51)
The variance m0 can be computed from the free-surface elevation signal Δ(t) (see Equation
4.52) or from the wave spectrum E(f) (it corresponds to the area between spectrum and the
x-axis, see Section 4.2.4.5).
m0 = Δrms 2 =
1
T
T
∫ (Δ (t ) −Δ ) dt
2
(4.52)
0
Figure 4.27 shows (on linear-log scale) the Rayleigh distribution.
Figure 4.27
356
Example of a shallow-water observed distribution of wave heights compared with
the Rayleigh distribution
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4.2 Hydraulic boundary conditions and data collection – marine and coastal waters
A shortcoming of the Rayleigh distribution is that it is not bounded by an upper maximum
value. Thus the maximum wave height can neither be defined nor computed in a
deterministic way from this distribution. However, the representative wave heights HP%
and H1/Q can be computed analytically (see Equations 4.53 and 4.54) from the Rayleigh
distribution (eg Massel, 1996; Goda, 2000).
(
H P%
= − ln P
100
H rms
H1/ Q
= Q erfc
H rms
)
(4.53)
+<
( ln Q ) + ln Q , with: erfc( x) = ∫x exp(−t 2 ) dt
3
4
Characteristic wave height ratios for a sea-state with a Rayleigh distribution of wave
heights
Wave height ratios
Characteristic height H
H/√m0
H/Hm
H/Hrms
H/Hs
1
0.399
0.353
0.250
Mean wave height Hm
2.507
1
0.886
0.626
Root-mean-square wave height Hrms
2.828
1.128
1
0.706
Significant wave height Hs = H1/3
4.004
1.597
1.416
1
Wave height H1/10
5.090
2.031
1.800
1.273
Wave height H1/100
6.673
2.662
2.359
1.668
Wave height H2%
5.594
2.232
1.978
1.397
Standard deviation of free surface σΔ = √m0
!
2
(4.54)
The most important and useful results are listed in Table 4.8. An important issue is the
estimation of the maximum value of the wave height for the case of sea-states of finite
duration. This maximum wave height cannot be determined in a deterministic manner. One
can, however, derive a probability density function for the (statistical) ratio Hmax/Hs (eg
Massel, 1996; Goda, 2000). Two important representative values, namely the mode and the
mean values, can be expressed analytically (see Equations 4.55 and 4.56) and computed (see
Table 4.9 for some typical results).
Table 4.8
1
5
6
7
Mode of the distribution
The most probable value of the ratio Hmax/Hs for a record consisting of N waves is given by
Equation 4.55.
 H max 
=

(
 H s  mode
!
ln N
2
(4.55)
Mean value of the distribution
8
The mean value of the ratio Hmax/Hs for a record consisting of N waves (see Equation 4.56).
The mean value is greater than the mode, because of the skewed shape of the distribution:
) ln N

 H max 
ο
=+
+


(
+
2
2 2 ln N 
 H s  mean 
(4.56)
9
where ο = Euler constant ≈ 0.5772.
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4 Physical site conditions and data collection
Table 4.9
Mode and mean values of the wave height distribution in a sea-state composed of N
waves following a Rayleigh distribution of wave heights
Wave height distribution
property
Number of waves, N, for the mode and mean values
100
200
500
1000
2000
5000
10 000
(Hmax/Hs)mode
1.52
1.63
1.76
1.86
1.95
2.06
2.15
(Hmax/Hs)mean
1.61
1.72
1.84
1.94
2.02
2.13
2.21
!
Distribution of shallow-water wave heights
In shallow water, the wave height distribution is affected by non-linear effects and by wave
breaking: it differs significantly from the Rayleigh distribution. The highest waves break first
and, if many of the highest waves break, a lot of waves with more or less the same height are
present. In Figure 4.28 an example is also shown of a shallow-water wave height distribution.
Several attempts have been made recently to propose distribution models for wave heights in
the shoaling and breaking zone. They are based on the use of a Beta-Rayleigh distribution
(Hughes and Borgman, 1987), a Weibull distribution (Glukhovskiy, 1966), a composite
Weibull distribution (CWD) (Battjes and Groenendijk, 2000) or a modified distribution
(Mendez et al, 2004). Among them, the CWD of Battjes and Groenendijk (2000) has been
successfully tested on a large quantity of data (small-scale and large-scale experiments) and
may be used for engineering applications (see Figure 4.28 and Box 4.4).
Figure 4.28
Comparison of measured (solid triangles) and calculated by the Composite Weibull
Dsitribution (CWD) model (drawn line) wave height distributions on slope 1:100,
m0 = 0.0011 m² and h = 0.27 m (from Battjes and Groenendijk, 2000)
Joint distribution of individual wave heights and periods
Theoretical models of the joint distribution function of wave heights and periods f (H, T) for
individual waves within a sea-state have been given by Longuet-Higgins (1975, 1983) and
Cavanié et al (1976). Comparisons of these theories to experimental data can be found in, eg,
Goda (1978). The scatter of the period, T , depends on the shape and width of the spectrum.
Coefficients used in the above-mentioned models should be computed from the frequency
spectrum (such as the spectral width parameter, ν², in Table 4.11).
This joint distribution is of little interest for the design of structures, however, so results are
not reported here, but can be found in the references cited above. For design purposes, it is
more relevant to consider the joint distribution of the significant wave height and a
characteristic period (eg Tm or Tp) (see Section 4.2.4.8).
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4.2 Hydraulic boundary conditions and data collection – marine and coastal waters
Box 4.4
1
The composite Weibull distribution (CWD) of wave heights in shallow water
Battjes and Groenendijk (2000) proposed use of a combination of two Weibull distributions (see Equation
4.57) to describe the cumulative distribution of wave heights in shallow water and the breaking zone:
(
(
)
1 − exp − H / H 2 for H < H
(
1)
tr

(4.57)
P(H ) = P ( H < H ) = 
3.6
1 − exp − ( H / H 2 )
for H ≥ H tr

where Htr = transitional wave height (m), defined by Equation 4.58 and H1, H2 = scale parameters (m).
)
The use of two distributions is more suitable for describing wave breaking correctly. The largest waves
break first, while there is no change for the smallest waves. This gives a non-homogeneous dataset of
waves: broken waves and non-broken waves. The CWD distribution reproduces this physical effect: a
Rayleigh distribution for the lowest part of the distribution (as in deep water) and a Weibull for the upper
part. The transitional wave height is computed with Equation 4.58, in which the bed slope, tan/ , and the
local water depth, h, are the parameters.
H tr = ( 0.35 + 5.8 tan / ) h
(4.58)
2
3
The method also requires the knowledge of the root mean square (rms) wave height, but generally this
wave height is not available, and the variance, m0, or the spectral significant wave height, Hm0 , is known
(from the application of a spectral wave propagation model for instance) (see Section 4.2.4.5). So an
additional relationship (see Equation 4.59) has been proposed to start from the spectral wave height, Hm0.
H rms = 0.6725 + 0.2025 ( H m0 / h )  H m0
(4.59)
One has then to compute the non-dimensional transitional wave height Htr /Hrms , which is used as input
to Table 2 of Battjes and Groenendijk (2000) to find the (non-dimensional) characteristic heights:
H1/3/Hrms , H1/10/Hrms , H2%/Hrms , H1%/Hrms and H0.1%/Hrms . Some particular values have been extracted
from this table and are included in Table 4.10, only for the ratios H1/10/Hrms and H2%/Hrms (see Table 2
of Battjes and Groenendijk (2000) for other values of the transitional wave height and other wave heights).
Table 4.10
Characteristic
height
Values of H1/10/Hrms and H2%/Hrms for some values of Htr /Hrms
4
5
Non-dimensional transitional wave Htr /Hrms
0.05
0.50
1.00
1.20
1.35
1.50
1.75
2.00
2.50
3.00
H1/10/Hrms
1.466
1.467
1.518
1.573
1.626
1.683
1.759
1.786
1.799
1.800
H2%/Hrms
1.548
1.549
1.603
1.662
1.717
1.778
1.884
1.985
1.978
1.978
The final step is the computation of the dimensional wave heights from the ratios read in the table and
the value of Hrms . Equation 4.60 is an example: this one is for the computation of H2% .
H 2% = ( H 2% / H rms )Table H rms
6
(4.60)
Figure 4.28 shows a result of the CWD distribution compared to laboratory measurements.
7
8
9
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4 Physical site conditions and data collection
Wave group statistics
As already mentioned, a sea-state is composed of a series of waves that are quite different
from one another: irregular or random characteristics of the sea-state, but a closer inspection
often reveals that the wave heights are not randomly distributed. Very often there are short
series of several (say 5–10) higher waves, and then a series of lower waves, and again a series
of higher waves. This is called wave grouping. Several parameters have been proposed by
various authors to measure the groupiness of waves in sea-states (eg Goda, 1970a; Kimura,
1981; Funke and Mansard, 1981; van Vledder, 1993).
Laboratory experiments have shown that wave grouping may have an effect on some aspects
of wave structure interactions. It has some limited but noticeable effects on the stability of a
rubble mound breakwater (damage increase with groupiness of waves), and a stronger
influence on some other aspects, like run-up and overtopping, mainly due to the presence of
bound long waves associated with wave groups (Galland and Manoha, 1991; Van Gent, 2001).
4.2.4.5
Spectral description of waves and wave spectra
Spectral analysis and representative wave parameters
In general an observed wave field can be broken down into a number of individual
sinusoidal wave components, each with its own height H, frequency f and direction +. The
distribution of wave energy as a function of wave frequency is commonly presented by the
one-dimensional wave energy density spectrum, denoted as EΔΔ(f). The directional spread
can be included by using a two-dimensional or directional spectrum, with f and + as
independent variables: SΔΔ(f, +).
The estimation of the wave energy density spectrum from a record of sea-surface elevation
fluctuations is obtained by Fourier transform techniques. A detailed description of these
mathematical treatments can be found in, eg, Goda (2000) or Tucker and Pitt (2001). The
key points of the analysis are:
!
an appropriate selection of the sampling rate and of the length of the records that
determine the accuracy of the analysis: 2–4 Hz is recommended, with a duration of at
least 20 min, and preferably 30–60 min
!
an appropriate selection of the spectral bandwidth or the degrees of freedom to be used
in the spectral analysis
!
an appropriate selection of the limits fmin and fmax for the computation of the spectral
moments. It is recommended to choose fmin equal or lower than half of the peak
frequency (0.5 fp) or 0.033 Hz when a large band of peak frequencies is anticipated in
order to separate long-period components from the short waves. fmax should be less than
the Nyquist frequency (equal to half the sampling rate) but greater than 5fp or 1–2 Hz so
as to catch the high-frequency tail of the spectrum properly.
From a given spectrum EΔΔ(f), several representative wave parameters (eg the spectral
significant wave height, peak and mean periods) may be computed, as defined in Table 4.11
(IAHR/PIANC, 1986).
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Table 4.11
1
Characteristic wave parameters from a spectral analysis
Characteristic wave parameter
Definition
Variance m0
m0 =
Moments of order n of the spectrum mn
mn =
Spectral significant wave height Hm0
H m 0 = 4 m0
Mean energy wave height HE
H E = 8 m0
∫
f max
E ( f )df
f min
∫
f max
f min
2
f n E ( f )df
3
Method 1 (so called Delft method)
Peak frequency fp and peak period Tp = 1/fp
The peak frequency is the frequency of the maximum
value (peak) of the spectrum.
For a discrete spectrum, it may be the discrete
frequency at which the spectrum peaks, but this
choice is not very appropriate since the discrete
peak frequency is not continuous.
Two more convenient methods for computing fp are
given (see Young (1995) for a detailed discussion of
the relevance of these various peak periods).
f pDm =
∫
f2
f1
f E ( f ) df
∫
f2
f1
E ( f ) df
where f1 and f2 are two frequency thresholds around
the discrete peak frequency at which the spectrum
values are m% of the maximum discrete peak value.
Usually, m = 80 per cent (or sometimes 60 per cent)
is used.
Method 2 (so called Read method)
∫
f pRm =
f max
f min
f E n ( f ) df
∫
f max
f min
E n ( f ) df
where the exponent n is usually taken as 4 or 5.
5
Mean wave period Tm01 = T01
T01 = 1/f01 = m0/m1
Mean wave period Tm02 = T02
T02 = 1/f02 =
Mean energy period TE = Tm-1,0 = T-10
TE = Tm-1,0 = T-10 = 1/f-10 = m-1/m0
Spectral width parameter ν2
ν2 =
m0 m 2
m12
ε 2 = 1−
Spectral width parameter ε2
m0 / m 2
−1
6
m 22
m0 m4
<
E ( f ) exp ( i 2 π f T ) df
∫
κ=
Spectral width parameter κ
(Van Vledder and Battjes, 1992)
02
0
7
m0
Note that there are various estimates of the mean wave period, among which the mean energy
period TE or Tm-1,0 (or T-10 in short) has recently been applied for the design of structures. It
is simply the averaged period weighted by the energy spectrum (see Equation 4.61).
+< E ( f )
+<
df
T ⋅ E ( f )df
m−1
f
0
(4.61)
Tm −1,0 = T−10 = TE =
= +<
= 0 +<
m0
E ( f )df
E ( f )df
∫
∫
0
∫
∫
8
0
It was observed that if bimodal waves are present, or in case of very flat spectra without peak
as a result of heavy wave breaking, the mean energy period Tm-1,0 is a better parameter, as Tp
is not easy to establish in those cases. This parameter gives a little more weight to the longer
periods and is closer to the peak period than the mean period T02, for instance.
The relationship between Tp and Tm-1,0 can be obtained by numerical evaluation of Equation
4.62 if the analytical expression of the variance spectrum E(f) is known. Dingemans (1987)
computed the ratio Tm-1,0/Tp for various spectral expressions including the PiersonMoskowitz (PM) and the JONSWAP spectra (given by Equations 4.63 and 4.67 respectively).
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361
9
10
4 Physical site conditions and data collection
Some of the results obtained by Dingemans for various values of the peak enhancement
factor ο in the JONSWAP spectrum are given in Table 4.12.
Table 4.12
Ratio of the peak period Tp over the mean energy period Tm-1,0 for a JONSWAP spectrum
as a function of the peak-enhancement factor ο , based on Dingemans (1987)
Peak enhancement factor, ο, in JONSWAP spectrum
Tp/Tm-1,0
1 (PM)
2
3
3.3
5
7
10
15
20
1.167
1.132
1.112
1.107
1.088
1.074
1.061
1.048
1.040
For single-peaked spectra with a clear peak, based on a few hundred measured spectra in
wave flumes for various research projects, it was found that the ratio of Tp and Tm-1,0 , as
given in Equation 4.62, is a good approximation.
T p = 1.1 Tm −1,0
(4.62)
In the absence of other information this relationship (see Equation 4.62) can be used as a
rule of thumb if design formulae require the mean energy period Tm-1,0 where only the peak
period, Tp is known. However, for very shallow foreshores and/or for double-peaked spectra
the correct Tm-1,0 should be determined, based on physical model research or the
appropriate numerical modelling.
Energy density spectra of sea-states
!
Spectra of deep-water waves
Examples of a spectrum are given in Figure 4.29 that are frequently used to describe random
wave fields. Governing parameters are also shown. A variety of semi-empirical wave spectra
have been presented, each having its specific range of applicability.
Two of the most widely used are the spectrum described by Pierson and Moskowitz (1964)
and the JONSWAP spectrum (Hasselmann et al, 1973), shown on Figure 4.29. These spectra
are formulated using a power function with respect to the frequency f (or angular frequency
φ = 2)f) containing several scaling parameters and constants. They can be obtained by
specifying either the wind speed, Uw , at a given elevation above the mean sea level (MSL)
and the fetch length, F, or alternatively the spectral significant wave height, Hm0, and peak
frequency, fp.
Both these spectra were originally derived by assuming a tail proportional to f -5 for the highfrequency range of the spectrum. Recent theoretical work and subsequent reanalyses of data
(eg Toba, 1973; Donelan et al, 1985; Battjes et al, 1987; Alves et al, 2003) have however
concluded that a tail proportional to f -4 is more appropriate to describe the equilibrium
spectra in the high-frequency range. The original and modified versions of these spectra are
briefly presented hereafter. It is recommended to use the updated versions for wave spectra
in deep water (namely the f -4 high-frequency tail).
The Pierson-Moskowitz (PM) spectrum: the PM spectrum represents a fully developed sea in
deep water. In its original form, see Equation 4.63, it has a high-frequency tail proportional
to f -5 and was derived as a function of a single parameter, the wind speed, U19.5 , at an
elevation of 19.5 m above MSL:
original
EPM
( f ) =/
−4

 
)
−5
 −1.25 + f  (
f
exp

+ fp  (
( 2) )4
 (


g2
(4.63)
where / = 0.0081, the empirically determined equilibrium range level, known as the Phillips
constant (-); fp =
362
PM
gν 19
.5
U 19.5
(l/s) and ν 19PM.5 = 0.14, the non-dimensional equilibrium peak frequency.
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4.2 Hydraulic boundary conditions and data collection – marine and coastal waters
Alternatively, this spectral form can be expressed as a function of given spectral significant
wave height, Hm0 , and peak frequency, fp , the corresponding formulation (see Equation 4.64)
sometimes also referred to as the Bretschneider (B) spectrum.
B
EPM
(f)=
−4 

5 2 4 −5
5) f  (

H m0 f p f exp  − +
 4+ fp  (
16
 (


(4.64)
Similarly, Goda (2000) reformulated this expression (see Equation 4.65) as a function of the
significant wave height H1/3 and significant period T1/3 .
−4
Goda
EPM
( f ) = 0.257 H12/ 3 T1−/ 43 f −5 exp  −1.03 (T1/ 3 f ) 

(
g2
( 2) )4 f p
f
−4
2
(4.65)
As stated above, all recent works favour a f -4 power law for the high-frequency range of the
spectrum and the use of the 10 m wind speed, U10 , as input wind velocity. Thus the
recommended form of the modified Pierson-Moskowitz spectrum for fully developed seas is
presented as Equation 4.66, after Donelan et al (1985) and Alves et al (2003).
updated
EPM
( f ) =/
1
−4 
 )
f  (


+
exp −
 + fp  (
 (
 
(4.66)
3
4
gν PM
PM
where / = 0.00615, the modified equilibrium range level (-); fp = 10 (1/s) and ν10 = 0.123,
U 10
the non-dimensional equilibrium peak frequency (-).
The JONSWAP (JOint North Sea WAve Project)” spectrum. The JONSWAP spectrum (J)
(Hasselmann et al, 1973) represents fetch-limited sea-states, ie growing sea. Its original
formulation (see Equation 4.67) includes an additional term compared to the original PM
spectrum (see Equation 4.63) and also depends on the fetch length, F. It has a sharper peak
than the PM spectrum. This original JONSWAP form has an f -5 high-frequency tail:
E Joriginal ( f ) =
−4

 
)
−5
− 5 + f  ( ο δ
f
exp
 4+ fp  (
( 2) )4
 (


/ g2
(4.67)
5
6
where:
 gF >
/ = 0.076 2 <
U <
 10 =
−0.22
(
(-)
f p = 3.5
)
2
)
+ f / f p − 1  (-)
δ = exp + −

2σ 2

+


g  gF ><
2 <
U 10  U 10
=
−0.33
(1/s)
7
σ = 0.07 if f ≤ fp and 0.09 if f > fp (-)
ο = peak enhancement factor that varies between 1 (in this case giving the original PM
spectrum) and 7, with an average value of 3.3 (-).
As for the PM spectrum, Goda (1988) proposed an alternative approximate expression (see
Equation 4.68) for the case where the significant wave height H1/3 and the significant period
T1/3 are specified:
−4 

5) f  ( δ

E JGoda ( f ) = β J H12/ 3 f p4 f −5 exp  − +
ο
 4+ fp  (
 (


where:
βJ =
Tp =
CIRIA C683
0.0624
0.230 + 0.0336ο − 0.185(1.9 + ο )−1
8
(4.68)
9
(1.094 − 0.01915 ln ο ) (-)
T1 / 3
1
(s).
=
f p 1 − 0.132(ο + 0.2 )−0.559
10
363
4 Physical site conditions and data collection
As stated above, a spectral form of the JONSWAP spectrum with a f -4 power law for the highfrequency range is preferable. Modified forms have among others been proposed by Donelan
et al (1985) and Aono and Goto (1995), which are summarised in Box 4.5.
Box 4.5
Modified JONSWAP spectra compatible with a f-4 high-frequency tail
Modified JONSWAP spectrum as proposed by
Donelan et al (1985) with input variables U10
and F or m0 and Tp
Modified JONSWAP spectrum as proposed by
Aono and Goto (1994) with input variables H1/3
and T1/3
Expression of frequency spectrum:
Expression of frequency spectrum:
E(f) = / (2))-4 g2 fp-1 f-4 exp[ – (f/fp)-4 ] οδ
E(f) = / (2))-3 g u* f -4 exp[ - (f/fp)-4 ] οδ
with the following relationships:
with the following relationships:
/ = 0.006 (U10 /cp)0.55
for 0.83 < U10 /cp < 5
u* = (H1/3)2 / (g B2 (T1/3)3)
B = 0.067
ο = 1.7
for 0.83 < U10 /cp < 1
fp = 1 / (1.136 T1/3)
fp* = fp u* / g
ο = 1.7 + 6 log (U10 /cp)
for 1 < U10 /cp < 5
ο = 6 (fp*)0.15
/ = 0.17 ο -1/3
σ = 0.08 + 0.32 (U10 /cp) -3 for 1 < U10 /cp < 5
σ1 = 0.144 for f < fp
σ2 = 0.07 (fp*)-0.16 for f > fp
δ = exp[- (f/fp – 1)2 / (2σ 2) ]
δ = exp[- (f/fp -1)2 / (2σ 2) ]
where cp = phase speed corresponding to the
peak frequency (cp = g / (2) fp) in deep water);
U10/cp = 0.83 corresponding to the point of full
development; both fp and cp are a function of the
wind-speed U10 and the fetch length F, through:
This spectrum conforms to the 3/2 power law of
Toba (1973, 1997), H* = B T*3/2, with a slight
modification of the B coefficient: 0.067 instead of
the original value of 0.062 (Toba, 1973).
fp U10/ g = 1.845 (g F/U102)-0.23 .
Young (1992) derived relationships to calculate
the spectrum directly from the variance m0 and
the peak period Tp through:
/ = 200 g-1.571 (m0)0.786 (Tp)-3.143
ο = 6.489 + 6 log[(2.649⋅107 g-2.857 (m0)1.429
(Tp)-5.714)]
σ = 0.08 + 6.94⋅10-26 g8.571 (m0)-4.287 (Tp)17.142
Figure 4.29
364
Pierson-Moskowitz and JONSWAP spectra
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4.2 Hydraulic boundary conditions and data collection – marine and coastal waters
!
1
Spectra of shallow-water waves
To cover both fetch-limited sea and shallow-water effects, the TMA (for Texel-Marsen-Arsloe
experiments) spectrum were developed (Hughes, 1984; Bouws et al, 1985). This spectrum
consists of factors originating from the Pierson-Moskowitz and from the JONSWAP spectra.
Additionally, a factor φ(φh) has been introduced to describe the effect of the water depth.
Equation 4.69 gives the description of the TMA spectrum, which can be used for spectral
shape in shallow-water conditions:
(4.69)
ETMA ( f ) = E J ( f ) φ (φh )
where:
φh = 2) f h / g
2
.
3
The additional factor φ(φh) describes the influence of the water depth, h. It can be
approximated within 4 per cent by Equation 4.70.
1 2
for φh > 1
 φh
φ (φh ) =  2
1 − 1  2 − φ  2 for φ > 1
h
h
 2 
(4.70)
4
The question of the equilibrium form of spectra in the surf zone was recently addressed by
McKee Smith and Vincent (2003), who showed that the surf-zone spectra evolve to contain
two equilibrium ranges when expressed as a function of the wave-number k. The higherfrequency range is similar to that proposed by Toba (1973, 1997) in deeper water with the
form k-5/2 and is valid for kh > 1. The second range, between the peak wave-number kp and
k = 1/h shows a form k-4/3, similar to the one proposed by Zakharov (1999).
5
Directional wave spectra
The directional wave spectrum S(f,+) describes the dependence of wave energy or free-surface
variance both on frequency, f, and direction of wave propagation, +. Equation 4.71, which is
often used in this form, describes the conventional decomposition of the directional spectrum:
S ( f ,+ ) = E ( f ) D ( f ,+ )
6
(4.71)
where E(f) = classical frequency spectrum, as used in the previous part of this section, and
D(f,+) = the directional spreading function (DSF).
7
Equation 4.72 gives the relationship between the classical frequency spectrum and the
directional spectrum.
E( f ) =
2)
∫ S ( f ,+ )d+
(4.72)
0
8
The DSF D(f,+) satisfying two important properties is given by Equations 4.73 and 4.74.
D(f,+) ≥ 0 for + ∈ [0 , 2)]
2)
∫ D( f ,+ )d+ = 1
0
(4.73)
(4.74)
The former condition or property (see Equation 4.73) expresses that the DSF is a nonnegative function, whereas the latter is a direct consequence of Equation 4.71. The DSF thus
models the directional spreading of the wave energy at each frequency f. The problem of
directional analysis thus consists in determining the directional spectrum, S(f,+), or
equivalently the variance spectrum E(f) and the DSF D(f,+) at each frequency. To that end, at
least three signals of wave properties have to be measured simultaneously. This can be
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9
10
4 Physical site conditions and data collection
achieved by using floating directional buoys (recording either the heave, pitch and roll
signals or three displacements), or an array of wave gauges etc. This is a difficult problem,
however, as the continuous function D(f,+) has to be estimated from a very limited number of
measured data. A review of measuring techniques and directional analysis methods to obtain
D(f,+) is presented in Benoit et al (1997b).
For practical purposes analytical expressions of the DSF have been derived for uni-modal
sea-states (one dominant wave direction). Examples of such DSF models are the ones from
Mitsuyasu et al (1975) and Donelan et al (1985), given in Box 4.6. Additional information on
directional parameters can be found in Goda (1997) and in reference textbooks (eg Massel,
1996; Goda, 2000).
Box 4.6
Two analytical models for directional spreading functions (DSF)
cos2s(+/2) model of Mitsuyasu et al (1975)
sech2(β+ ) model of Donelan et al (1985)
Expression of DSF:
Expression of DSF:
D(f,+) = ½ β [1/cosh [(β (+ - +m))]]²
D(f,+) = ∆ cos2s[(+ – +m)/2]
where +m(f) = mean wave direction and
∆(s) = constant so that Equation 4.74 is satisfied.
where +m(f) is the mean wave direction.
The parameter β controls the angular spreading of
wave energy. It is frequency-dependent and reads:
The exponent s controls the angular spreading
of wave energy (higher values of s correspond to
narrower and sharper DSF). It is frequencydependent and reads:
β = 2.61 (f/fp)1.3
for 0.56 < f/fp < 0.95
β = 2.28 (f/fp)-1.3
for 0.95 < f/fp < 1.6
s/sp = (f/fp)5
β = 1.24
for 1.6 < f/fp
for f < fp
s/sp = (f/fp)-2.5 for f > fp
sp = smax , value of the exponent at the peak
frequency where it is maximum. This means that
the angular spreading of wave energy is narrowest
at the peak frequency. Mitsuyasu et al (1975)
established that sp varies in the range of 5 to 20
for wind-generated waves and its value is a
function of the non-dimensional peak frequency as:
sp = 11.5 (2) fpU10/g)-2.5
With these expressions the angular spreading of
wave energy is minimum at a frequency about
5 per cent less than the peak frequency.
Banner (1990) modified the last expression of β,
which is frequency-independent, and found a
better agreement with measured directional
spectra by using:
β = -0.4 + 0.8393 exp[-0.567 ln(f/fp)2]
for 1.6 < f/fp
Goda (1997) proposed to simply use the following
constant values:
sp = 10
for wind waves
sp = 25
for swell with short decay distance
sp = 75
for swell with long decay distance
Relationships between statistical and spectral parameters
!
Deep-water waves
Assuming that the water surface elevation follows a stationary Gaussian process, and hence
that the wave heights are Rayleigh-distributed, Equations 4.75 and 4.76 give the relationship
between statistical and spectral parameters.
Significant wave heights:
H1/3 = Hm0
(4.75)
Mean wave periods:
Tm = T02
(4.76)
Most sea-state parameters can be expressed in terms of the spectral moments as included in
Table 4.11. See also Table 4.8 for some practical conversion factors for height parameters of
Rayleigh-distributed waves.
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Note that the factor “4” in the relationship H s = 4 m0 is a theoretical value based on the
assumption that the Rayleigh distribution applies. Practically, analysis of real records display
values down to 3.6 and a value of 3.8 is recommended by Goda (2000) for deep-water waves.
This corresponds to H1/3 = 0.95 Hm0.
NOTE: Some misunderstanding may arise from the literature where the notation Hs is often
used to designate either H1/3 or Hm0 (without precisely stating which of these wave heights is
considered) and the Hrms notation is often used to designate HE .
Concerning wave periods, it is not possible to derive universal relationships between, eg,
the mean period Tm and the peak period Tp , as the ratio depends on the spectral shape.
Wave data analysis and numerical simulations by Goda (1988, 2000) have revealed a range
for various conversion factors:
!
Tm /Tp = 0.71 to 0.82 for a PM spectrum
!
Tm /Tp = 0.79 to 0.87 for a JONSWAP spectrum.
Generally, T1/3/Tp = 0.90 to 0.96 and T1/3/Tm = 1.13 to 1.33 were found to apply. From the
analysis of simulated wave data Goda (1988, 2000) concluded that T1/3 is a more reliable
characterisation than Tm for wind-generated waves.
The mean energy period, Tm-1,0 , has recently been observed to be a better and more stable
characteristic period for stability design formulae (see Section 4.2.4.5). Equation 4.63 gives a
practical relationship to estimate Tm-1,0 from Tp .
Dingemans (1987) computed and tabulated numerical values of the ratios of various mean
periods (Tm-1,0 , T01 , T02) over the peak period Tp for PM and JONSWAP spectra,
considering both f-4 and f-5 high-frequency tails, as well as different values of the peakenhancement factor, ο (-).
!
It should be emphasised that Equation 4.75 applies for deep-water conditions, but that it is
not suitable for shallow-water conditions. For shoaling and pre-breaking wave conditions, the
ratio H1/3/Hm0 becomes higher than 1, and may reach values up to 1.3 or even 1.5
(Thompson and Vincent, 1985; Hamm, 2001). In particular, Thompson and Vincent (1985)
proposed Equation 4.77 for the envelope of the above ratio for pre-breaking waves:




4
5
7
(4.77)
8
Generation of waves in the ocean and on inland waters
9
Mechanisms of wave generation and evolution in the ocean
The main process of interest in the course of wave generation is the action of the wind that
provides energy to the wave field. The generation of waves by wind is a complex process of
interactions between the atmosphere and the ocean surface. However, empirical relationships
have been derived to describe the growth of wave height under the action of constant and
homogeneous wind, as well as the evolution of the wave period. They are important in
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−0.43642 
For shallow-water applications, the use of a shallow-water distribution model for wave heights,
such as the CWD of Battjes and Groenendijk (2000) presented in Box 4.4 allows the ratio of H1/3
over Hm0 to be computed. But it should be kept in mind that this model invokes an empirical
relationship between Hm0 and Hrms , and so the results are affected by this parameterisation.
4.2.4.6
2
6
Shallow-water waves
)
) h 
) H1/ 3 
+

= exp + 0.02289 +
++

+ gT p2 
 H m0 max
+



1
367
10
4 Physical site conditions and data collection
engineering practice as they allow easy estimation of wave characteristics from the wind
characteristics or climatology. Some of these relationships are given in this section. They can
only be used when a stationary sea-state can be assumed. During storm conditions, however,
this does not apply, as the wave field is developing under influence of the wind shear upon
the water. A wave field under influence of wind (wind-sea) is different from a wave field that
is not exposed to wind (ie swell). In general, swell can be related to distant storms and is
characterised by a narrower spectrum of relatively lower frequencies (higher periods)
compared to wind-sea conditions.
Few processes need to be taken into account when waves are in deep water. When designing
for waves in shallow water, more influences have to accounted for (see Section 4.2.4.7). In
deep water, in addition to wave generation by wind, three other principal processes need to
be considered.
!
Deep-water wave breaking or white-capping. Waves in deep water may break when a
certain limiting wave steepness (s = H/L) is exceeded (see Section 4.2.4.3). For regular
waves in deep water the wave height is limited by steepness according to the breaking
criterion of Miche (1944) to about 1/7 of the wavelength. In practice, only individual
waves in a random sea approach this value and calculated steepnesses using significant
wave height Hs and peak wave period Tp rarely exceed sop = 0.05. For steepness
computed with the mean wave period, this is som = 0.07. This factor is, of course,
considered implicitly in the empirical wave growth formulae.
!
Energy transfer between frequencies. Non-linear energy transfers between wind waves
make the wave spectrum evolve: the peak tends to become sharper and the peak
frequency decreases as the waves interact during propagation. In deep water, these
interactions occur between quadruplets of waves and are resonant interactions.
Combined with frequency dispersion, they lead to the formation of swell conditions
(long-period and almost regular waves). Such non-linear interactions can be predicted
only by the use of advanced third-generation spectral wave models, although swell can of
course be measured directly.
!
Wave reflection and diffraction by islands or rocks (see Section 4.2.4.7).
Empirical methods for estimating wave conditions from wind characteristics
Like individual waves under the influence of wind, the wave spectrum also displays an
evolution with time and/or with distance in the wind direction. Consequently, representative
parameters of the sea-states (such as Hm0, Tm, Tp etc) also evolve with time and/or distance.
Wind-induced wave growth has traditionally been described by using empirical formulae,
some of them being presented in this section.
The approach to determine sea growth by analysis and numerical modelling of the wave
spectrum has been developed, but empirical methods still play an important role.
Meteorological and hydraulic institutes have expended considerable effort on numerical
wave forecasting. With these numerical models the instantaneous wave parameters are
derived from the energy content of the wave field, which is computed as being distributed
within the directional wave spectrum. The necessary input for these models is wind fields,
obtained from synoptic weather charts. The models account for the above-mentioned
processes, namely energy gain derived from transfer from wind energy, energy loss caused by
dissipation (breaking, bottom friction), wave-wave interactions and energy transfer among
individual wave components of the frequency spectrum (see Section 4.2.4.10).
Empirical wave growth formulae are based upon the relations between characteristic wave
parameters in the standard wind field. This wind field is given by an average wind speed
(Uw , U10 ; see Section 4.2.1); the fetch, F (the wind-exposed distance to the coast, measured
in the upwind direction), and the duration, t , of the wind field. An additional characteristic
parameter is the water depth, h, which is usually assumed constant over the area of interest.
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A fully developed sea has, for a given Uw , reached its maximum (equilibrium) wave height
and period. In a fetch-limited or growing sea at least one of the parameters (F, t or h) poses a
limiting condition to the actual sea as long as they have not reached a certain minimum value
beyond which the limiting condition vanishes. Using g/Uw2 as scale factor for H, F and h, and
g/Uw as scale factor for t and T, the empirical wave growth formulae are usually written in a
non-dimensional form as H* = f(h*, F*, t*) and T* = f(h*, t*).
!
Open ocean conditions (deep water)
Various empirical relationships have been proposed by various authors for more than 50
years. Some of them have been plotted in non-dimensional form in Figure 4.30 for the nondimensional significant wave height gHs /U102 as a function of non-dimensional fetch gF/U102 .
1
2
3
4
5
Figure 4.30
Comparison of some wave prediction formulae for deep-water conditions
6
It is clear from this figure that these formulae are not equivalent and produce different
estimates of wave height. Based on various comparisons with experimental data, the
following sets of equations are recommended.
1.
Formulae from Sverdrup-Munk-Bretschneider (SMB), as presented in SPM (CERC, 1977).
These formulae were originally introduced by Sverdrup and Munk (1947) and further
revised by Bretschneider (1954, 1970). They appear in the third edition of the Shore protection
manual [SPM] (CERC, 1977). They allow estimation of the significant wave height Hs (m) (see
Equation 4.78) and significant wave period Ts (s) (see Equation 4.79) generated by a constant
and homogeneous wind. Information required is the velocity at 10 m above MSL, U10 (m/s),
blowing over a fetch of length F (m), for fully developed conditions, ie if the duration of wind
action is greater then tmin (hours), tmin can be calculated by Equation 4.80.
0.42 
)
) gF 

+
= 0.283 tanh + 0.0125 + 2 
2

+U 
U10

+
10




(4.78)
0.25 
)
) gF 

+
+

= 7.54 tanh + 0.077

+U2 
U10

+
10




(4.79)
gH s
gTs
g tmin
U10
where
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(
8
9
(4.80)
)
1/ 2


= 0.00183 exp  0.0161 x 2 − 0.3692 x + 2.2024
+ 0.8798 x (


) gF 
x = ln + 2 
+U 
 10 
7
.
10
369
4 Physical site conditions and data collection
Prediction curves for significant wave height and significant wave period based on these
formulae are given in SPM (CERC, 1977) (vol I, pp 3-36 and 3-37). Note that the fourth
edition of SPM (CERC, 1984) contains different wave prediction formulae and curves, based
on an intermediate calculation of wind stress and modified to conform to the JONSWAP
formulae. The reliability for all situations of the SPM (CERC, 1984) formulae has recently
been questioned, particularly for extreme events and/or short fetch conditions. They are now
considered to be less reliable than the SMB formulae and should therefore not be used for
practical applications.
2.
Formulae from Wilson (1965), revisited by Goda (2003).
Wilson (1965) produced an alternative set of formulae to estimate the significant wave height
Hs = H1/3 (m) (see Equation 4.81), the significant wave period Ts = T1/3 (s) (see Equation
4.82) and the minimum duration tmin (hours) (see Equation 4.83), with the same notation and
convention for units as above.
−2 
) )
1/ 2
) g F   
+ +
= 0.3 +1 − 1 + 0.004 + 2 
2
+
+ U   
U10
++ +
 10   



−5 
) )
1/ 3
) gF   
+
g Ts
= 8.61+1 − +1 + 0.008 + 2   
+
+ U   
U10
++ +
 10   



g Hs
) gF 
U10 tmin
= 0.01194 + 2 
+U 
F
 10 
−0.27
g tmin
or
U10
(4.81)
(4.82)
) gF 
= 0.01194 + 2 
+U 
 10 
0.73
(4.83)
Prediction curves for significant wave height and significant wave period are given in
Figure 4.31.
3.
Formulae from Kahma and Calkoen (1992).
Kahma and Calkoen (1992) have performed a detailed analysis of wind wave growth by
taking into account the stability of the air-sea interface. They showed that unstable conditions
lead to an increase of wave height and period and proposed two sets of formulae: one for
stable conditions and one for unstable conditions, as well as a composite formula for the
entire dataset. The composite formula is in quite close agreement with the SMB and Wilson
formula (see Figure 4.30). The formula for unstable conditions can be used to obtain
conservative estimates of wave parameters. The three sets of formulae have the same form
shown by Equations 4.84 and 4.85 with values of coefficients listed in Table 4.13.
) gF 
= A+ 2 
2
+

U10
 U10 
g Hs
) gF 
= C+ 2 
+U 
U10
 10 
g Ts
Table 4.13
B
D
(4.85)
Coefficients in the wave prediction curves of Kahma and Calkoen (1992)
A
B
C
D
Stable stratification
3.86⋅⋅10-3
0.38
0.5236
0.24
Unstable stratification
2.94⋅⋅10-3
0.47
0.4425
0.28
Composite dataset
2.88⋅⋅10-3
0.45
0.4587
0.27
Coefficients in Equations 4.84 and 4.85
370
(4.84)
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4.2 Hydraulic boundary conditions and data collection – marine and coastal waters
1
2
3
4
5
6
Figure 4.31
Prediction curves for significant wave period (upper panel) and significant
wave height (lower panel) in deep-water conditions (from Wilson (1965),
formulae revisited by Goda (2003)
7
Reservoirs and lakes
The prediction methods presented above cannot be directly applied to inland waters,
reservoir and lakes, as the majority of all wave measurements from which these methods
were derived have been carried out in open sea conditions. However, wave prediction is a
particularly important consideration where reservoirs are concerned, as construction of the
appropriate wave protection should be completed in advance of the filling of the reservoir and
hence measurements of wave climate are excluded from the design process. Measurements
obtained on UK reservoirs (Owen, 1988) showed that none of the open ocean methods give
particularly good agreement for all conditions.
Three methods are considered here for dealing with such inland water cases: Saville method,
the Donelan method and the Young and Verhagen method . It is suggested that these should
be adopted for small and medium lakes and reservoirs. For very large fetches, open sea
methods are probably the best to apply.
8
9
10
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371
4 Physical site conditions and data collection
(a) Saville method (or SMB method with effective fetch)
This method uses the SMB wave prediction formulae and curves for open waters (see
Equations 4.78 and 4.79), and adapts them to reservoirs using the concept of effective fetch
(Saville et al, 1962). The definition of the effective fetch is illustrated in Figure 4.32. A
noticeable feature is that the effective fetch is independent of wind speed. The effective fetch
from Saville should not be used with any other wave prediction formulae than SMB:
significant underestimates of wave height will result otherwise.
F=
Figure 4.32
∑ x cos/ = 39252 = 3415 m
∑ cos/ 11.4954
i
Example calculation of effective fetch length by Saville’s method
(b) Donelan method
The Donelan method is presented in a series of papers (Donelan, 1980; Bishop and Donelan,
1989; Bishop et al, 1992; Donelan et al, 1992). It is based on the idea that the fetch length
should be measured along the wave direction rather than the wind direction and that the
wind speed used for wave prediction should therefore be the component along the wave
direction. The method does not assume coincident wind direction, φw , and wave direction, +.
If the gradient of fetch about wind direction is large, one can expect that the wave direction
is biased towards longer fetches. For long and narrow water bodies the wave direction is
probably along the water body axis for a wide range of wind directions (rather than the wind
direction). Differences up to 50° for |φw - + | have been observed on Lake Ontario.
For fetches of general shape, the predominant wave direction was assumed to produce the
maximum value of wave period (for a given wind speed). For a point with known fetch
distribution F+ (F+ is the fetch along the direction + ), the relation between the wave direction,
+ , and the wind direction, φw , can be obtained by maximising the product cos(φw - + ) F+0.426.
For any irregular shoreline, and a given wind direction, the value of + satisfying this condition
can only be determined by trial and error (Bishop and Donelan, 1989; Massel, 1996). As + is
independent of wind speed only one set of calculations is needed for a particular water body.
Once + has been determined, the significant wave height, peak period and minimum wind
duration are derived from Equations 4.86–4.88 (modified from the JONSWAP formulae).
)

+

g Hs
g F+
= 0.00366 +
2
2
+ U10 cos (+ − φw ) 
U10 cos (+ − φw )


(
372
)
(
)
0.38
(4.86)
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4.2 Hydraulic boundary conditions and data collection – marine and coastal waters
)

g Tp
+

g F+
= 0.542 +
2
U10 cos (+ − φw )
+ U10 cos (+ − φw ) 


(
1
0.23
(4.87)
)
)

+

g tmin
g F+
= 30.1+
2
U10 cos (+ − φw )
+ U10 cos (+ − φw ) 


(
0.77
(4.88)
)
2
The value of the directional fetch, F+ , is limited by the criterion expressed by Equation 4.89
to avoid over-development of wave energy.
)

+

g tmin
g F+
= 30.1+
2
U10 cos (+ − φw )
+ U10 cos (+ − φw ) 


(
0.77
(4.89)
)
3
At this value of non-dimensional directional fetch, F+ , fully development of waves is reached,
resulting in Equations 4.90 and 4.91.
gH s
(U cos (+ − φ ))
= 0.285
(4.90)
gT p
U10 cos (+ − φw )
= 7.56
(4.91)
5
Young and Verhagen method
Young and Verhagen (1996) analysed a large set of wave measurements performed on Lake
George (Australia). From this comprehensive dataset they were able to propose wave
prediction formulae including both the effect of fetch F and water depth h (see Equations
4.92 and 4.93). The formulae are based on the form of the formulae of SPM (1984) for wave
generation in finite water depth:
)
) B1  
= 0.241+ tanh A1 tanh +

2
U10
 tanh A1  

gH s
where:
) gh 
A1 = 0.493+ 2 
+U 
 10 
and
)
) B2  
= 7.519 + tanh A2 tanh +

2
U10
 tanh A2  

1.01
) gh 
A2 = 0.331+ 2 
+U 
 10 
and
(4.92)
) gF 
B1 = 0.00313+ 2 
+U 
 10 
0.57
7
.
0.37
(4.93)
) gF 
B2 = 0.0005215+ 2 
+U 
 10 
8
0.73
.
This latter method offers the advantage of taking account of the actual water depth, which is
important for reservoirs. Indeed, the mean water level in a reservoir may change
significantly over a year leading to significant variations of fetch length and water depth.
Both these parameters are present is the above formulae.
Later Young (1997) observed that these formulae fail to correctly model the wave height for
short fetches, which was attributed to the fact that the formulae revert to JONSWAP
formulae (Hasselmann et al, 1973) for such cases. For a better treatment of this case, he
proposed an equation that has to be integrated numerically to obtain a wave growth curve.
CIRIA C683
6
0.87
0.75
gT p
where:
4
w
10
(c)
2
373
9
10
4 Physical site conditions and data collection
Hurricane waves
Hurricane wave conditions can be predicted by the parametric wave model of Young (1988).
The model captures the physics of tropical cyclone waves via the JONSWAP formulation of
wave spectrum. The model is forced by the surface wind beneath the moving storm and
prescribes maximum wave height and period, which is the severe swell wave generated by
the storm. The US Army Corps of Engineers has adopted this formulation and a monogram
in the Coastal engineering manual [CEM] (USACE, 2003).
Comments on the applicability of wave prediction formulae
The simple prediction formulae listed above may be used on real cases provided that the
water depth does not vary significantly over the area and that the wind field is homogenous
(both in speed and direction). The following should be noted on their general applicability:
4.2.4.7
1
The above formulae may not be suitable for the particular situation where fetches are
very limited (shorter than 1 km), but where the wind is extremely strong (in the order of
100 km/h or more). This is the situation encountered in the estimation of the wave
height in a harbour basin or a reservoir in violent storm conditions. This corresponds to
non-dimensional fetches gF/U102 close to 1 or less. In such situations the wave heights
grow to 1 m within a few hundred metres of fetch. Most of the wave prediction formulae
are not calibrated in this situation. Van der Meer et al (2003) addressed this item and
compared a number of formulae, with the final conclusion that the Wilson (1955)
formulae are suitable in this situation (Equations 4.81 and 4.83).
2
Only simple methods are given here for the derivation of wave conditions. Nowadays in
many situations numerical wave models are used. Most of these models are thirdgeneration spectral wave models (such as WAM, SWAN, TOMAWAC, WAVEWATCH
models for example). Of course numerical modelling requires more human and
computational effort to obtain wave predictions, but it is much more reliable than the
simple methods described above. Such numerical models should be employed when the
bathymetric configuration is irregular and/or when the wind condition is not
homogeneous over the water domain or changing with time. Such wave models are
briefly described in Section 4.2.4.10.
Transformation of waves in the nearshore and coastal zones
For coastal structures, the effects of water-depth reduction and coastal forms on the incoming
waves should be accounted for. These factors transform the incoming waves by refraction,
shoaling, diffraction and eventually wave breaking. Wave breaking results in significant
dissipation of energy and is often the major factor limiting the design wave height and
consequently the loading on the structure. All these phenomena are a function of water
depth, so a proper description of bathymetry is required (see Section 4.1). This section
presents graphs and formulae for the designer to make a first assessment of the influence of
these phenomena. However, to complete a full, spatial description of wave parameters,
appropriate numerical models of wave propagation should be used (see Section 4.2.4.10).
Refraction
Refraction is the change in the wave propagation velocity, and consequently also in the
direction of wave propagation, when waves propagate in varying water depth. In decreasing
water depth the direction of wave incidence, β (°), relative to the structure inclines towards
the direction normal to the depth contours. This usually implies that the wave crests tend to
become more parallel to the coastline when approaching more shallow water (see Figure 4.33).
The corresponding change in wave height (relative to the deep-water wave height, Ho),
caused by redistribution of energy along the wave crests, is usually expressed in the
refraction coefficient KR .
374
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4.2 Hydraulic boundary conditions and data collection – marine and coastal waters
1
2
(a)
3
4
Figure 4.33
(b)
Examples of wave refraction
5
Applying linear wave theory to a regular wave with wave number k and direction βo in deep
water the local wave direction β at a water depth h is found from Equation 4.94.
β = arcsin ( sin β o tanh ( k h ) )
(4.94)
6
The corresponding refraction coefficient, KR, is computed from Equation 4.95.
1/ 2
K R = ( cos β o cos β )
(4.95)
For irregular seas, a representative effective value should be obtained by applying an
averaging procedure to a range of relevant frequencies f, or corresponding wave numbers k,
and offshore directions βo. Thereby weight factors should be determined to account for the
relative contributions (∆E)ij from intervals (∆f, ∆β) to the total energy content m0 of the
directional spectrum S(f, β).
7
Neglecting shoaling effects, this leads to Equations 4.96 and 4.97.
1
m0
( ∆E )ij =
KR =
∫ ∫ S ( f , β ) df dβ
8
∆f ∆β
∑ ∑ ( ∆E ) ( K )
i
(4.96)
j
ij
2
R ij
(4.97)
For practical reasons, intervals ∆f and ∆β of varying widths are usually chosen, centred on a
number of representative values for f and β respectively (eg requiring equal energy
contributions for each interval). Applying an extended form of this procedure, Goda (2000)
has given diagrams (see Figure 4.34) for KR in a directional wave field on a coast with
straight, parallel depth contours.
9
10
CIRIA C683
375
4 Physical site conditions and data collection
Figure 4.34
Refraction coefficient, KR, for an
irregular directional wave field
on a coast with straight, parallel
depth contours (Goda, 2000)
Shoaling
Shoaling is a change in wave height when waves propagate in varying water depths. The
shoaling effect is normally expressed in terms of the shoaling coefficient, KS, which is defined
as the local wave height H relative to Ho. Using linear wave theory KS can, for a given wave
period T, be written as a function of water depth h (see Equation 4.98).

)
2kh  
K S =  tanh(kh) +1 +
(

 sinh(2kh)  (
−1 2
(4.98)
Under the usual limitations related to the linear wave theory, the above equation gives
appropriate estimates fo