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ROAD DESIGN
STANDARD
PART 2.
PAVEMENT
CAM PW.03.102.99
2003
This document has been produced for the Kingdom of Cambodia as a joint Australia –
Cambodia project sponsored by the Australian Agency for International Development
(AusAID).
Valuable assistance and operational advice was provided by the staff of the Cambodian
Ministry of Public Works and Transport (MPWT) as follow:
I.
Steering Committee (Appendix H)
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
Mr. Tan Hay Sien,
Director of Infrastructure Department ............................................ Chairman
Dr. Yit Bunna,
Director of Public Works Research Centre ........................Deputy Chairman
Mr. Tauch Chan Kosal, Director of Heavy Equipment Centre ............................................... Member
Mr. Lim Sidenine,
Deputy Director of Bridge Construction Unit.................................... Member
Dr. Phung Katry,
Director of Waterway Department ................................................... Member
Mr. Prum Sakun,
Deputy Director of Cambodian Royal Railway ................................ Member
Representative from Sihanouk Ville Port (Mr. Ma Sun Huot)................................................... Member
Representative from Public Works Laboratory (Mr. Keo Leap)................................................ Member
Representative from Phnom Penh Institute of Technology (Mr. Chhouk Chhay Horng) ......... Member
Representative from Phnom Penh Public Works Department (Mr. Heng Nguon) ................... Member
Representative from Ministry of Water Resources and Meteorology....................................... Member
II.
Assistance Preparation Staff from Public Works Research Centre:
1.
2.
3.
4.
Mr. Nou Vaddhanak
Mr. Kong Sophal
Mr. Chan Somardy
Mr. Tep Virith
Technical research and specialist input was provided by the Australian consulting firms of
McMillan Britton & Kell Pty Limited and Willing & Partners Pty Ltd.
Reproduction of extracts from this publication may be made subject to due acknowledgment
of the source.
Although this publication is believed to be correct at the time of printing, neither the MPWT
nor AusAID accept responsibility for any consequences arising from the use of the information
contained in it. People using the information should apply, and rely upon, their own skill and
judgement to the particular issue which they are considering.
SECOND PRINTING
FINANCED BY THE ASIAN DEVELOPMENT BANK LOAN NO. 1659 CAM (SF)
ROAD DESIGN STANDARD
FOREWORD
The Cambodia Road Design Standard is intended to be used for the design of all
new roads in the Kingdom of Cambodia. The Cambodian Road Design Standard
consists of the following complementary documents which shall be considered
together:
-
CAM PW 03-101-99
Road Design Standard – Part 1 - Geometry;
-
CAM PW 03-102-99
Road Design Standard – Part 2 - Pavement;
-
CAM PW 03-103-99
Road Design Standard – Part 3 - Drainage;
For the purpose of regulating and interpreting the provisions of this Standard, the
AUTHORITY shall be the Cambodian Ministry of Public Works and Transport.
ROAD DESIGN PART 2 - PAVEMENT, CAM PW 03-102-99
FOREWORD
ROAD DESIGN STANDARD
TABLE OF CONTENTS
2.1
INTRODUCTION .................................................................................. 5
2.2
PAVEMENT DESIGN SYSTEM ........................................................... 6
2.2.1
General ................................................................................................ 6
2.2.2
Pavement Design System For New Pavements .............................. 6
2.2.2.1
Input Variables...................................................................................... 7
2.2.2.2
Selecting a Trial Pavement Cross -Section .......................................... 8
2.2.3
Design System For Pavement Overlays........................................... 8
2.2.3.1
General ................................................................................................. 8
2.2.3.2
Evaluating the Existing Pavement ........................................................ 9
2.2.3.3
Recognition of the Existing Pavement's Needs.................................. 10
2.2.3.4
Selection of Overlay Thickness .......................................................... 10
2.3
ENVIRONMENT ................................................................................. 12
2.3.1
General .............................................................................................. 12
2.3.2
Moisture Environment...................................................................... 12
2.3.3
Temperature Environment ............................................................... 14
2.4
SUBGRADE EVALUATION............................................................... 16
2.4.1
General .............................................................................................. 16
2.4.2
Measures Of Subgrade Support...................................................... 16
2.4.3
Factors To Be Considered In Estimating Subgrade Support....... 16
2.4.4
Methods Of Estimating Subgrade Support Values ....................... 18
2.4.5
Field Determination Of Subgrade CBR........................................... 18
2.4.5.1
In-situ CBR Test ................................................................................. 18
2.4.5.2
Cone Penetrometers........................................................................... 18
2.4.6
Laboratory Determination Of Subgrade CBR And
Elastic Parameters............................................................................ 19
2.4.6.1
Determination of Density for Laboratory Test..................................... 20
2.4.6.2
Determination of Design Moisture Content (DMC)............................. 20
2.4.7
Adoption Of Presumptive CBR Values........................................... 20
2.5
TRAFFIC INVESTIGATION ............................................................... 21
2.5.1
Estimating Flows .............................................................................. 21
2.5.1.1
Baseline traffic flows ........................................................................... 21
2.5.1.2
Traffic Forecasting .............................................................................. 22
2.5.2
Axle Loading ..................................................................................... 24
2.5.2.1
Axle load surveys................................................................................ 24
2.5.2.2
Axle Configurations and Equivalences ............................................... 24
2.5.2.3
Design Lanes...................................................................................... 25
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2.5.3
Design Period.................................................................................... 25
2.5.4
Traffic Growth ................................................................................... 26
2.5.5
Design Traffic For Flexible Pavement ............................................ 26
2.5.6
Design Traffic For Rigid Pavements............................................... 26
2.6
PAVEMENT MATERIALS.................................................................. 28
2.6.1
Granular Materials ............................................................................ 28
2.6.1.1
Introduction ......................................................................................... 28
2.6.2
Modified Materials ............................................................................ 28
2.6.3
Bitumen ............................................................................................. 29
2.6.3.1
Prime Coat.......................................................................................... 29
2.6.3.2
Tack Coat ........................................................................................... 29
2.6.3.3
Bituminous Surface treatment ............................................................ 29
2.6.3.3.1
Bituminous materials .......................................................................... 29
2.6.3.3.2
Aggregates ......................................................................................... 30
2.6.3.4
Asphaltic Concrete.............................................................................. 31
2.6.4
Concrete ............................................................................................ 32
2.6.4.1
Introduction ......................................................................................... 32
2.6.4.2
Sub-base Concrete............................................................................. 32
2.6.4.3
Base Concrete .................................................................................... 32
2.7
DESIGN OF NEW FLEXIBLE PAVEMENTS..................................... 34
2.8
DESIGN OF RIGID PAVEMENTS ..................................................... 43
2.8.1
General .............................................................................................. 43
2.8.2
Pavement Types ............................................................................... 43
2.8.2.1
Cement Concrete Pavements ............................................................ 43
2.8.2.2
Asphalt Surfaced Rigid Pavements .................................................... 44
2.8.3
Factors Used In Thickness Determination..................................... 44
2.8.3.1
Strength of Subgrade.......................................................................... 44
2.8.3.2
Concrete Strength............................................................................... 44
2.8.3.3
Design Traffic...................................................................................... 44
2.8.3.4
Provision of Sub-base......................................................................... 44
2.8.3.4.1
General ............................................................................................... 44
2.8.3.4.2
Bound Sub-base ................................................................................. 46
2.8.3.4.3
Lean Rolled Concrete Sub-base ........................................................ 46
2.8.3.4.4
Lean-Mix Concrete Sub-base............................................................. 46
2.8.3.4.5
Debonding of the Sub-base and Base................................................ 46
2.8.3.5
Concrete Shoulders ............................................................................ 47
2.8.3.6
Load Safety Factors............................................................................ 47
2.8.4
Base Thickness Design Procedure................................................. 47
2.8.4.1
General ............................................................................................... 47
2.8.4.2
Base Thickness Design Procedure .................................................... 47
2.8.4.3
Minimum Base Thickness................................................................... 61
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2.8.4.4
2.8.5
Provision of Dowels and Tie Bars....................................................... 61
Reinforcement Design Procedures................................................. 62
2.8.5.1
Special Requirements for Reinforcement In Jointed .............................
Unreinforced Pavements .................................................................... 62
2.8.5.2
Reinforcement In Jointed Reinforced Pavements .............................. 62
2.8.5.3
Reinforcement In Continuously Reinforced Pavements..................... 63
2.9
OVERLAY DESIGN............................................................................ 68
2.9.1
General .............................................................................................. 68
2.9.2
Basic Principles ................................................................................ 68
2.9.3
Pavement Testing ............................................................................. 68
2.9.3.1
Method of Deflection Testing.............................................................. 68
2.9.3.2
Selection of Test Sites ........................................................................ 68
2.9.3.3
Test Modes ......................................................................................... 69
2.9.3.4
Other Tests ......................................................................................... 70
2.9.3.5
Measurement of Pavement Temperature........................................... 70
2.9.4
Pavement Evaluation........................................................................ 70
2.9.4.1
Selection of Homogeneous Sections.................................................. 70
2.9.4.2
Characteristic Site Temperature......................................................... 71
2.9.4.3
Adjustment of the Characteristic Deflection and Characteristic ............
Curvature to Account for the Testing Temperature ............................ 71
2.9.4.4
Adjustment of Deflection Data to Account for Seasonal
Moisture Variations ............................................................................. 72
2.9.4.5
Design Traffic...................................................................................... 72
2.9.4.6
Performance Criteria (Design Deflection and Curvature)................... 73
2.9.4.7
Determination of Pavement Needs..................................................... 73
2.9.5
Selection Of Thickness .................................................................... 75
2.9.5.1
Granular Overlays............................................................................... 75
2.9.5.2
Asphalt Overlays................................................................................. 75
2.9.5.3
Characteristic Deflection (adjusted for temperature) Exceeds
the Design Deflection.......................................................................... 75
2.9.5.4
Characteristic Deflection (adjusted for temperature) Less Than
Design Deflection................................................................................ 78
2.9.5.5
Adjustment of Overlay Thickness to Allow for Locality Temperature . 78
2.9.5.6
Example of Asphalt Overlay Design ................................................... 79
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TABLE OF CONTENTS
ROAD DESIGN STANDARD
APPENDIX A
............................................................................................................ 81
APPENDIX B
............................................................................................................ 83
APPENDIX C
............................................................................................................ 84
APPENDIX D
............................................................................................................ 85
APPENDIX E
............................................................................................................ 89
APPENDIX F
............................................................................................................ 90
APPENDIX F
............................................................................................................ 91
APPENDIX F
............................................................................................................ 92
APPENDIX F
............................................................................................................ 93
APPENDIX G
............................................................................................................ 94
APPENDIX H
............................................................................................................ 96
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2.1
INTRODUCTION
This Standard contains procedures for the design of the following forms of road pavement
construction,
•
Flexible pavements consisting of unbound granular material.
•
Rigid pavements ( ie cement concrete pavements)
•
Overlays for flexible pavements.
The procedures in this Standard are intended for the design of pavements whose primary
distress mode is load associated. Where other modes of distress, such as environmental
distress, have a significant effect on environmental performance, their effect will have to be
separately assessed. It is assumed that pavements are constructed in compliance with
modern quality control standards.
Consideration of unsurfaced pavements has not been included in this Standard because
the performance of these pavements is heavily dependent on the performance of local
materials, local environmental conditions and maintenance policies.
Consideration of overlays for rigid pavements has also been omitted because experience
in this area has not been sufficiently extensive to allow formulation of a design procedure.
This Standard contains detailed discussion of subgrade evaluation, pavement materials
evaluation, analysis of traffic loading and structural design in addition to other factors
relevant to pavement design.
It is emphasised that this document should be used as a guide and not approached or
referred to as a limiting design specification. Some judgement will have to be exercised by
the designer in arriving at decisions as the parameters which are incorporated in particular
designs.
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2.1 INTRODUCTION
ROAD DESIGN STANDARD
2.2
PAVEMENT DESIGN SYSTEM
2.2.1
GENERAL
The aim of pavement design is to select the most economic pavement thickness and
composition that will provide a satisfactory level of service for the anticipated traffic.
To achieve this goal, the designer must have sufficient knowledge of the materials, the
traffic, the local environment and their interactions to be able to predict the performance of
any pavement composition. In addition he must know what level of performance, and what
pavement condition will be considered satisfactory in the circumstances for which he is
designing the pavement structure.
Figure 2.2.1 System for the Design of Pavements
Because of the many variables and interactions which influence the result, it is appropriate
to adopt a systematic approach to pavement design. Depending on the amount of data
which has to be provided, or conversely on the number of assumptions that have to be
made, a pavement design procedure may be complex at one extreme or very simple at the
other.
Design procedures contained in this Standard are based on two similar design systems
which are described in this Section.
One system is for the design of new pavements and the other is more specifically for the
design of overlays to rehabilitate existing flexible pavements. However, both are based on
the same underlying principles that are typical of those used to solve any engineering
design problem.
2.2.2
PAVEMENT DESIGN SYSTEM FOR NEW PAVEMENTS
The system for the design of pavements is shown in flow chart form in Figure 2.2.1.
Although in a practical design procedure some of the parts of the system may be omitted or
combined with others, it is convenient to use Figure 2.2.1 to demonstrate the relationships
between input variables, analytical methods and the decision processes which comprise
pavement design.
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2.2.2.1
Input Variables
(a)
Design Traffic
Axle numbers, load distribution, loading rate and tyre pressures can be significant in
determining pavement performance. Not only must the current traffic be taken into account,
but the change in volume and composition during the design period must also be
estimated. Detailed consideration of traffic is contained in Section 2.5.
(b) Subgrade and Pavement Materials
Ideally the designer's knowledge of the pavement and subgrade materials should include
the strength/stiffness parameters which can be used to quantify their load bearing
properties the variations in these parameters which result from changes in moisture and
temperature, increases in age, or cumulative distress during the design period the manner
in which they deteriorate and the significant reaction to load (stress or strain) which can be
used to quantify the rate of distress (refer to Table 2.2.1) the limiting value(s) of stresses
or strains at which a given degree of distress will occur, commonly known as the
performance criteria.
Table 2.2.1 Distress modes for flexible pavements
Distress Mode
Rutting
Likely Causes
Densification
Materials Affected
All but sound
cemented material
Cracking
Single high load, many repetitions of
normal loads, thermal cycling, shrinkage
Asphalt, cemented
material
Roughness
Variability of density, material properties
All
Some of the above apply to the analysis phase of the design system. For example,
parameters such as elastic stiffness are used in analytical models to determine load
induced stresses and strains.
The performance criteria on the other hand are used only to predict when distress will
occur.
Some analytical models have been developed in recent times that predict the development
of roughness from a knowledge of the variability of material properties and layer thickness,
among other things.
Some materials such as asphalt and cemented gravels are complex to the extent that their
performance criteria are a function of their stiffness. These relationships enable materials
design to be incorporated into the overall pavement design system, as for example the
design of a concrete mix is incorporated into the design of a concrete bridge beam.
A detailed consideration of subgrades and pavement materials is contained in Sections 2.4
and 2.6 respectively.
(c)
Environment
Variations in material properties due to changes in moisture and temperature may be
measured by testing. The values to be used in analysis will depend on the actual moisture
and temperature existing in service. Because of the complexity associated with this
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2.2 PAVEMENT DESIGN SYSTEM
ROAD DESIGN STANDARD
requirement it is usually necessary to characterise a particular site environment to some
extent. The significance of environmental effects depends on the materials that are
selected for the pavement, but it can also depend on the temporal distribution of traffic
loading.
A detailed consideration of environmental effects is contained in Section 2.3.
(d) Construction and Maintenance Considerations
Construction and, to a lesser extent, maintenance policies can influence the type of
pavement structure which is adopted. In addition, the properties of many materials are
dependent on construction influences, including the level of compaction, the method of
curing concrete or cemented materials, the type of equipment used for placing crushed
rock, and the extent of sub-surface drainage incorporated in the design.
2.2.2.2
Selecting a Trial Pavement Cross -Section
The design process consists of selection of a trial pavement cross-section and analysing its
performance when subjected to the input design parameters that are described in Section
2.2.1.
A trial pavement cross-section may often be selected by judgement or by using a simple
published design procedure. Many such procedures are empirical. Therefore, if one is
used, it is desirable that it has been derived from experience and observations that are
compatible with the design task at hand.
If such a simple design procedure is assumed to be sufficiently reliable for the designer's
needs, the design process is complete, since the following phases (analysis, distress
prediction and design modification) are all considered to be taken care of.
The example design charts in Section 2.7 of this Standard have been derived from the
design system, but in each case for a specific set of input parameters. These parameters
are listed on or adjacent to each chart.
2.2.3
DESIGN SYSTEM FOR PAVEMENT OVERLAYS
2.2.3.1
General
The System for the design of pavement overlays is shown in flow chart form in
Figure 2.2.2.
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Figure 2.2.2 System for the Design of Pavement Overlays
In principle there is little difference between the design of overlays and the design of new
pavements, since each involves consideration of traffic, material and environment, an
analysis, distress prediction and comparison of alternative designs. In practical terms the
major difference is that for overlay design to be successful the needs of the existing
pavement must be correctly diagnosed and then satisfied.
In broad terms the overlay design system comprises:
2.2.3.2
•
Evaluating the existing pavement condition.
•
Considering the traffic and environment to which it will be subjected in the design
period.
•
Determining if the pavement needs additional strength to provide satisfactory service
during the design period, and if possible the causes(s) of deficiencies.
•
Considering the materials which are available to overcome the pavement’s
deficiencies, their potential modes of failure , their load resisting capabilities and the
parameters which can be used to predict the rate at which distress will occur in the
overlaid pavement.
•
Determining the thickness of material that must be placed on the existing pavement to
provide satisfactory service in the design period.
Evaluating the Existing Pavement
This may be done by sampling and testing the existing pavement materials and the
subgrade, and assigning strength parameters so that the structure can be analysed to
determine its reaction to load.
Alternatively, a non-destructive method such as deflection testing can be used to obtain the
reaction to load directly. The method of analysing deflection testing can vary depending on
the amount and type of data that is collected during the deflection survey. As more
comprehensive data can be collected with recently developed equipment, such as the
Deflectograph, Falling Weight Deflectometer and Benkelman Beams adapted to measure
complete deflection bowls, better predictions can be made of the performance of the
existing pavement.
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The deflection testing and analysis method, which has been adopted in this Standard, is
described in detail in Section 2.9. Its aim is to predict the future traffic loading which the
pavement can support before permanent deformation reaches a tolerable limit, and also,
for pavements which have uncracked asphalt surfacing, the traffic loading which can be
supported before fatigue cracking occurs. These predictions take into account the
pavement's temperature and subgrade moisture at the time of testing, and the
environmental conditions which will apply during the pavement's service life.
2.2.3.3
Recognition of the Existing Pavement's Needs
With experience, the needs of an existing pavement can often be recognised by inspection
alone. Further information can be obtained by testing, the more detailed and
comprehensive the tests then the more reliable will be the identification of pavement
deficiencies and needs. Tests that directly measure a pavement's reaction to load, such as
deflection tests, should be used where possible. This is preferable to a mere comparison of
the pavement composition with that prescribed by empirical pavement design procedures
since the latter tend to apply only to pavements of "average" quality.
The measurements obtained by deflection testing, whether they be the maximum deflection
at each test site or additional parameters which describe the shape of the deflected
pavement surface, can be related to performance criteria. These performance criteria are
usually empirically based but may also be based on the theoretical data obtained from, for
example, a mathematical solution of elastic layered models. In practice there will be some
variability in deflection test results throughout a given length of pavement, reflecting the
variability in the many factors which contribute to pavement performance. By adopting a
statistical approach, characteristic deflection values can be assigned to the section of
pavement. This implies the acceptance of a probability that the performance of the ultimate
overlay design will be acceptable.
The most common performance criteria relate deflection under a standard load to the
number of repetitions, which can be tolerated before a critical pavement condition, is
reached. This is a very simplistic relationship, which assumes that the compound effect of
all forms of distress in a particular type of pavement can be predicted by the measurement
of only one reaction to load. More recently developed deflection testing and analysis
methods tend to isolate different distress modes, with the rate of distress in each case
being predicted by a different property of the deflected pavement shape with its own
limiting criterion. If the deflection measurements (or derived measures in the case of the
more sophisticated methods) exceed the limiting values given by the performance criteria,
then the existing pavement is assumed to be inadequate for the design traffic and some
treatment is required. This may include strengthening by the addition of a granular or
asphalt overlay or by reconstruction, but other measures such as additional drainage works
or resealing may also be effective.
2.2.3.4
Selection of Overlay Thickness
The thickness of overlay which is needed to strengthen the pavement depends on :
•
the material to be used
•
the increase in strength which is required to reduce the pavement's response to load
to tolerable limits as defined by the performance criteria
•
the amount of auxiliary work such as drainage improvement which is proposed in
conjunction with the overlay
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The required thickness can be determined from empirical relationships based on
observations of the effect of previous overlays. Mathematical predictions have also been
made using typical material stiffnesses. Even so the effect of any proposed drainage
improvements must be estimated, either by judgement based on experience or by analysis
assuming certain changes will be achieved in the pavement and the subgrade because of
the drainage works.
When more than one performance criterion has been used to evaluate the existing
pavement's needs and/or to select an overlay thickness, the controlling value will be the
minimum thickness which satisfies all of the criteria. If it is considered impractical to apply
the specified thickness (for example due to adjacent level controls), then a lesser amount
may have to be adopted. By comparing the estimated effect of the thinner overlay with the
limiting criteria, a prediction of the pavement's performance can be made. The value of the
overlay can then be compared with the anticipated benefits and a decision made regarding
its acceptability. For example, if the practical overlay may only last for one or two years it
may be more cost effective to reconstruct the pavement. The pavement evaluation and
overlay design methods which have been adopted in this Standard are described in detail
in Section 2.9.
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2.3
ENVIRONMENT
2.3.1
GENERAL
This Standard mainly describes procedures to enable pavements to be designed to
withstand load-associated distress. While environmentally induced distress is mentioned in
a number of passages, pavements where this is the major distress mode are not
specifically discussed.
The environmental factors, which significantly affect pavement performance, are:
2.3.2
•
Moisture
•
Temperature
MOISTURE ENVIRONMENT
The moisture regime associated with a pavement has a major influence on the
performance of the pavement. The stiffness/strength of unbound materials and subgrades
is heavily dependent on the moisture content of the materials. Further guidance may be
obtained in NAASRA (1983).
The factors that must be assessed at the design stage include:
•
Rainfall/evaporation pattern
•
Permeability of wearing surface
•
Depth of water table
•
Relative permeability of pavement layers
•
Whether shoulders are sealed or not
•
Pavement type (boxed or full width)
Moisture changes in pavements usually result from one or more of the following sources:
(a) Seepage from higher ground to the road pavement
(b) Fluctuations in the water table.
(c) Infiltration of water through the surface of the road pavement and shoulders.
(d) Transfer of moisture as a result of moisture content or temperature differences in
either the liquid or vapour states, including transfer due to the moisture content at
construction differing from the equilibrium moisture content.
(e) The relative permeabilities of the pavement layers and subgrade. A significant
decrease in permeability with depth (permeability reversal) can lead to saturation of
the materials in the vicinity of the permeability reversal.
Of the above sources only (a), (b) and (c) can be controlled by the installation of properly
designed subgrade and pavement drains. Drains are only effective when subgrade
moisture is subject to hydrostatic head (ie positive pore pressures). It is common for fine
grained subgrade materials to have an equilibrium moisture content above optimum
moisture content yet, because they are unsaturated, they cannot be drained.
The above sources of moisture infiltration are illustrated in Figure 2.3.1.
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An alteration of the moisture content of the subgrade can result in two types of changes to
its condition; a change in the volume and/or a change in strength. The significance of these
changes will depend on their magnitude and the nature of the material in which the change
takes place. Particular problems associated with expansive clays are given in references at
the end of this Section.
The effect of changes in moisture content on the strength / stiffness of the subgrade is
taken into consideration by evaluating the strength parameters (eg CBR, modulus) at the
highest moisture content likely to occur during the design period. It is important that as
accurate an estimate as practicable be made for the design moisture content.
Figure 2.3.1 Movement of Moisture in Road Pavements
The sensitivity of the subgrade strength/stiffness to changes in moisture content should in
all cases be assessed. In general the following comments apply:
•
For sandy soils, small fluctuations in moisture content produce little change in volume
or strength/ stiffness.
•
For silty soils, small fluctuations in moisture content produce little change in volume
but may produce large changes in strength and/or stiffness.
•
For clay, small fluctuations in moisture may produce large variations in volume and if
the moisture content is near optimum moisture content large changes in
strength/stiffness may also occur.
Volume changes are minimised if the required density of the subgrade is obtained by
compaction at a moisture content representing the value, which occurs most frequently.
The moisture content that is used to compact the soil initially may also influence the extent
of volume change.
Estimation of both the design moisture content and the moisture content of minimum
volume change is usually based on the use of the Equilibrium Moisture Content (EMC)
concept where this is considered applicable.
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Equilibrium Moisture Content (EMC)
The term Equilibrium Moisture Content refers to the concept that, in some situations, the
moisture conditions under a sealed pavement reach a state of equilibrium with the moisture
regime of the local environment at sometime after construction. The principal variables
which control its state are:
•
Climate
•
Soil type
•
Depth to water table
•
Composition of the soil water
In treating soil water as a variable in the behaviour of unsaturated soil there are basically
only two ways of quantitatively expressing the soil water variable. These are:
•
In terms of the ratio of the soil water to another volumetric or gravimetric property of
the soil (eg gravimetric moisture content)
•
In terms of the energy state of the soil water, such as soil moisture suction. Soil
moisture suction is used here in the common context of negative pore pressures
(matrix potential). However, "suction" is sometimes used in the context of total
potential, when the osmotic (solute) potential of the soil is added to the matrix
potential.
For practical purposes, the condition at which soil strength is to be determined must finally
be expressed in terms of (gravimetric) moisture content. If soil moisture content has been
expressed in terms of soil suction, a conversion to moisture content is necessary to use
EMC. However, since the measurement and monitoring of soil suction in the field and the
determination of the relationship between soil suction and moisture content is difficult and
not in general use, such methods are not described here. Some references are NAASRA
(1974, 1983), OECD (1973). Richards (1969), Wallace (1974) and Waters and Kapitzke
(1974).
The conditions which leads to EMC are generally more stable towards the central portion of
the pavement. Up to about 1.5 metres from each edge, fluctuations in moisture conditions
can result from the relatively rapid changes in moisture content that can occur in the
shoulder. These changes can cause the critical moisture content (ie Design Moisture
Content) for the outer wheel path to be above the EMC estimated for the central portion of
the pavement.
In situations where changes in moisture content of the shoulders can be large, treatment of
these areas should be undertaken to minimise this difference. Where such treatment is not
applied or is not likely to be adequate, it will be necessary to adopt a design moisture
content (DMC) more than the EMC for the centre portion of the pavement. Procedures for
determining DMC are given in Section 2.4.
2.3.3
TEMPERATURE ENVIRONMENT
The temperature environment has a major influence on the performance of pavements
surfaced with asphalt wearing surfaces.
Asphalt becomes stiff and brittle at low temperatures while it is soft and visco-elastic at
higher temperatures. Permanent deformation in asphalt at high temperatures is not
considered as a failure mode in this Standard. The only failure mode considered for asphalt
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is flexural (fatigue) cracking. It is assumed that asphalt mixes are designed with sufficient
stability so that permanent deformation does not need to be considered at the design
stage.
The distribution of temperature both on a daily and seasonal basis has an important
bearing on pavement performance. If traffic loading occurs at night when temperatures are
low, a considerable reduction in the life of thin asphalt surfacing may occur. The interaction
of the traffic and temperature ranges must therefore be taken into account at the design
stage. A procedure for doing this is presented in Section 2.6.
Temperature may also affect the properties and performance of cemented layers and
concrete. Temperatures can have a significant effect on the rate of strength gain of these
materials and if high temperatures occur during construction, drying out will result,
impairing both the ultimate strength and fatigue characteristics of the materials.
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2.4
SUBGRADE EVALUATION
2.4.1
GENERAL
The support provided by the subgrade is the most important factor in determining
pavement design thickness, composition and performance. The subgrade strength is
dependent on the conditions at construction and during service. Soil type, density and
moisture content largely determine subgrade strength. The aim of subgrade evaluation is to
estimate a value of subgrade support to use in design.
2.4.2
MEASURES OF SUBGRADE SUPPORT
The measures of subgrade support used in this Standard are:
•
California Bearing Ratio (CBR)
•
Modulus of Subgrade Reaction (k)
The use of these measures for designing various pavement types is given in Table 2.4.1.
2.4.3
FACTORS TO BE CONSIDERED IN ESTIMATING SUBGRADE SUPPORT
The following factors must be considered in determining the design strength/stiffness of the
subgrade:
•
sequence of earthworks construction;
•
the compaction moisture content used and field density achieved;
•
moisture changes during service life;
•
subgrade variability.
The total pavement thickness may be governed by the presence of weak layers below the
design subgrade level.
Table 2.4.1 Use Of Subgrade Support Measures
Measure of Subgrade Support
Pavement Type
Use CBR
Flexible
OK
Rigid
OK
(a)
Use k
OK
Sequence of Earthworks Construction
In some cases it may be possible to select materials that will ultimately be located at the
subgrade level by involvement in pre-construction planning. Where there is uncertainty as
to which material will be available for use as a subgrade, a preliminary evaluation of
material may be necessary with confirmation at the time of construction
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(b) Compaction Moisture Content Used and Field Density Achieved
A guide to the effects of variations in relative density and compaction moisture contents on
subgrade is illustrated in Table 2.4.2 , Table 2.4.3 , and Table 2.4.4.
Table 2.4.2 Relative Values Of Subgrade Support For Clay (PI>30)
Density
1.05 MDD
1.00 MDD
0.95 MDD
UNSOAKED
Compaction Moisture
Content (relative to OMC)
0.9
1.0
1.05
4.0
3.5
3.0
3.5
3.0
2.5
2.5
2.0
2.0
Density
prior to 4
day soak
1.05 MDD
1.00 MDD
0.95 MDD
4 DAY SOAK
Compaction Moisture
Content (relative to OMC)
0.9
1.0
1.05
0.9
0.6
1.0
1.5
0.4
0.6
1.0
Table 2.4.3 Relative Values Of Subgrade Support For Clay (PI<30)
Density
1.05 MDD
1.00 MDD
0.95
MDD
UNSOAKED
Compaction Moisture
Content (relative to OMC)
0.9
1.0
1.05
2.0
1.8
1.2
1.0
1.2
1.0
1.0
Density
prior to 4
day soak
1.05 MDD
1.00 MDD
0.95 MDD
4 DAY SOAK
Compaction Moisture
Content (relative to OMC)
0.9
1.0
1.05
1.2
2.0
2.2
0.8
1.0
1.1
0.5
0.5
0.6
Table 2.4.4 Relative Values Of Subgrade Support For Silty Sand
Density
1.05 MDD
1.00 MDD
0.95 MDD
(c)
UNSOAKED
Compaction Moisture
Content
(relative to OMC)
0.9
1.0
1.05
2.0
1.8
1.2
1.0
1.2
1.0
1.0
Density
prior to 4
day soak
1.05 MDD
1.00 MDD
0.95 MDD
4 DAY SOAK
Compaction Moisture
Content
(relative to OMC)
0.9
1.0
1.05
1.2
2.0
2.2
0.8
1.0
1.1
0.5
0.5
0.6
Moisture Changes during Service Life
After construction, moisture conditions in subgrades will change subject to the influences
outlined in Section 2.3. Table 2.4.2 , Table 2.4.3 , and Table 2.4.4 contain a guide to the
magnitude of change in subgrade support, which can occur due to in-service moisture
variations. Moisture changes may occur on a seasonal, and perhaps also on a sporadic,
basis if the subgrade is subject to flooding. These variations, where possible, should be
taken into account.
(d) Subgrade Variability
Subgrades are inherently variable in nature and the design value for subgrade support
should be selected to reflect the degree of variability.
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2.4.4
METHODS OF ESTIMATING SUBGRADE SUPPORT VALUES
There are basically two modes of testing available for estimation of subgrade support
values; laboratory testing and field testing.
Field testing is only applicable where it is proposed that subgrade support values are to be
extrapolated from an existing pavement and the subgrade soil conditions are similar to
those of the proposed pavement.
Laboratory testing is applicable both where a suitable existing pavement for extrapolation
exists, or from first principles.
2.4.5
FIELD DETERMINATION OF SUBGRADE CBR
This procedure may be used to determine the design CBR where soils similar to those of
the subgrade of the road being designed, have existed under a sealed pavement for at
least two years and are at density and moisture conditions similar to those likely to occur in
service. Care must be taken to carry out tests when the subgrade is in a critical moisture
condition or, alternatively, seasonal adjustments may be made.
A number of field tests may be used to estimate subgrade CBR, eg. In-situ CBR test and
Cone Penetrometer.
The results of such tests should be analysed statistically and a design CBR chosen at a
percentile level appropriate to the particular case. The ten percentile level value (Mean
minus 1.3 times Standard Deviation) has been used commonly for design of highway
pavements.
2.4.5.1
In-situ CBR Test
The in-situ CBR test is given in AS 1289. This test is time consuming and expensive. The
number of tests required to establish the variability of the CBR for each type of material
may be so large as to make the use of the in-situ CBR test impracticable.
2.4.5.2
Cone Penetrometers
Cone penetrometer tests are described in AS 1289 and may be used for fine grained
subgrades.
CBR results can be determined from Figure 2.4.1 for the dynamic cone penetrometer and
from Figure 2.4.2 for the static cone penetrometer. The relationship given in Figure 2.4.2 is
a general relationship that suits most soil types. For further information relating to specific
soil types the following references may provide assistance: Schofield (1986), Mullholland
(1984) and Smith & Pratt(1983).
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Figure 2.4.1 Correlation of Dynamic Cone Penetration and CBR.
Figure 2.4.2 Correlation of Static Cone Penetration and CBR
When using the cone penetrometers extensively for subgrade investigation, a limited
number of in-situ CBR measurements should be carried out on the particular material being
tested to confirm that the adopted relationship is valid.
2.4.6
LABORATORY DETERMINATION OF SUBGRADE CBR AND ELASTIC PARAMETERS
This procedure may be used to determine design CBR where sufficient samples of the
subgrade material for the new pavement can be obtained for detailed laboratory
investigations and where a reasonable estimate can be made of likely subgrade density
and moisture conditions in service. The method is particularly useful when a close similarity
in density, moisture content and materials is not available between the proposed pavement
and any existing road.
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Laboratory tests may be undertaken on specimens compacted at the design moisture
content (DMC) and density, which correspond to those likely to occur in service or at a
particular compaction standard and moisture as a characterising test. Alternatively,
undisturbed samples can be obtained from the field by coring.
Methods for determining the design moisture content are given in Appendix D.
It may not always be practicable to prepare laboratory specimens at the selected density.
In such cases, at least four specimens should be prepared at the DMC and at densities as
close as possible to the characteristic value. The design value may be interpreted from
interpolation of the results for these specimens.
2.4.6.1
Determination of Density for Laboratory Test
The density selected for testing should correspond to that which will occur in service and
may be one of the following:
2.4.6.2
•
In-situ density of undisturbed or reworked subgrade as appropriate
•
Minimum standard of compaction achieved in construction (embankments)
•
Density after swelling has occurred (expansive soils)
Determination of Design Moisture Content (DMC)
There are several procedures for estimating the DMC. For practical application however, a
compromise must be reached between the level of precision to be obtained and the cost of
obtaining the necessary input data to determine the DMC. In all cases, however, the
designer should ensure, either on the basis of knowledge of moisture conditions likely to
occur in his locality, or by means of detailed field investigations that test moisture
conditions realistically represent service conditions.
Two methods for estimating the DMC are given in Appendix D.
2.4.7
ADOPTION OF PRESUMPTIVE CBR VALUES
This approach may be used when no other relevant information is available. It is
particularly useful for lightly trafficked roads where extensive investigations are not
warranted, and also at preliminary design stages for all roads. Typical presumptive values
of CBR are given in Table 2.4.5. However, such values should be determined on the basis
of local experience,
Table 2.4.5 Typical Presumptive Design CBR Values
Description of Subgrade
Material
USC
Classification
Highly Plastic Clay
CH
Silt
ML
Silty Clay
Sandy Clay
Sand
Typical CBR Values %
Well drained
Poorly drained
5
2.3
CL
SC
6.7
4.5
SW, SP
15 – 20
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2.5
TRAFFIC INVESTIGATION
2.5.1
ESTIMATING FLOWS
2.5.1.1
Baseline traffic flows
In order to determine the total traffic over the design life of the road the first step, is to
estimate baseline traffic flows. The estimate should be the (Annual) Average Daily Traffic
(ADT) currently using the route, classified into the vehicle categories of cars, light goods
vehicles, trucks (heavy goods vehicles) and buses. The ADT is defined as the total annual
traffic summed for both directions and divided by 365. It is usually obtained by recording
actual traffic flows over a shorter, period from which, the ADT is then estimated. For long
projects, large differences in traffic along the road may make it necessary to estimate the
flow at several locations. It should be noted that for structural design purposes the traffic
loading in one direction is required and for this reason care is always required when
interpreting ADT figures.
Traffic counts carried out over a short period as a basis for estimating the traffic flow can
produce estimates that are subject, to large errors because traffic flows can have large
daily, weekly, monthly and seasonal variations. The daily variability in traffic flow depends
on the volume of traffic. It increases as traffic levels fall, with high variability on roads
carrying less than 1000 vehicles per day. Traffic flows vary more from day-to-day than from
week-to-week over the year. Thus there are large errors associated with estimating
average daily traffic flows (and subsequently annual traffic flows) from traffic counts of only
a few days duration, or excluding the weekend. For the same reason there is a rapid
decrease in the likely error as the duration of the counting period increases up to one
week. For counts of longer duration improvements in accuracy are less pronounced. Traffic
flows also vary from month-month so that a weekly traffic count repeated at intervals during
the, year provides a better base for estimating the annual volume of traffic than a
continuous traffic count of the same duration. Traffic also varies considerably through a
24-hour period and this needs to be taken into account.
In order to reduce error, it is recommended that traffic counts to establish ADT at a specific
site conform to the following practice:
(i)
The counts are for seven consecutive days.
(ii)
The count on some of the days is for a full 24 hours, with preferably at least one 24
hour count on a weekday and one during a weekend. On the other days 16-hour
counts should be sufficient. These should be grossed up to 24 hour values in the
same proportion as the 16 hour/24 hour split on those days when full 24 hour counts
have been undertaken.
(iii) Counts are avoided at times when travel activity is abnormal for a short period due to
the payment of wages and salaries, public holidays etc. If abnormal traffic flows persist
for extended periods, for example during harvest times, additional counts need to be
made to ensure this traffic is properly included.
(iv) If possible the seven-day counts should be repeated several times throughout the
year.
(v) Country-wide traffic data should be collected on a systematic basis to enable seasonal
trends in traffic flows to be quantified. Unfortunately, many of the counts that are
available are unreliable, especially if they have been carried out manually. Therefore,
where seasonal adjustment factors are applied to traffic survey data in order to
improve the accuracy of baseline traffic figures, the quality of the statistics on which
they are based should be checked in the field.
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Classified traffic counts are normally obtained by counting manually. These counts can be
supplemented by automatic counters which use either a pneumatic tube laid across the
surface of the carriageway or a wire loop fixed to the carriageway surface or preferably,
buried just beneath it. Pneumatic tubes require regular maintenance and can be subject to
vandalism. Buried loops are preferred, but installing a loop beneath the road surface is
more difficult and more expensive than using a pneumatic tube.
In their basic form automatic counters do not distinguish between different types of vehicle
and so cannot provide a classified count. Modern detector systems are now available
which can perform classified vehicle counting, but such systems are expensive and not yet
considered to be sufficiently, robust for most developing country applications.
2.5.1.2
Traffic Forecasting
Even with a developed economy and stable economic conditions traffic forecasting is an
uncertain process. In a developing economy the problem becomes more difficult because
such economies are often very sensitive to the world prices of just one or two commodities.
In order to forecast traffic growth it is necessary to separate traffic into the following three
categories.
(a) Normal traffic. Traffic, which would pass along the existing road or track even if no
new pavement was provided.
(b) Diverted traffic. Traffic that changes from another route (or mode of transport) to the
project road because of the improved pavement but still travels between the same
origin and destination.
(c) Generated traffic. Additional traffic that occurs in response to the provision of new or
improved roads.
Normal traffic. The commonest method of forecasting normal traffic is to extrapolate time
series data on traffic levels and assume that growth will either remain constant in absolute
terms ie. a fixed number of vehicles per year (a linear extrapolation) or constant in relative
terms ie. a fixed percentage increase. Data on fuel sales can often be used as a guide to
country-wide growth in traffic levels, although improvements in fuel economy over time
should be taken into account. As a general rule it is only safe to extrapolate forward for as
many years as reliable traffic data exists from the past and for as many years as the same
general economic conditions are expected to continue.
As an alternative to time, growth can be related linearly to anticipated Gross Domestic
Product (GDP). This is normally preferable since it explicitly takes into account changes in
overall economic activity, but it has the disadvantage that a forecast of GDP is needed.
The use of additional variables, such as population or fuel price, brings with it the same
problem. If GDP forecasts are not available, then future traffic growth should be based on
time series data.
If it is thought that a particular component of the traffic will grow at a different rate to the
rest, it should be specifically identified and dealt with separately. For example a plan to
expand a local town or open a local factory during the design life of the road could lead to
different growth rates for different types of vehicles. Similarly there may be a plan to allow
larger freight vehicles on the road, in which case the growth rate for trucks may be
relatively low because each truck is heavier.
Whatever the forecasting procedure used, it is essential to consider the realism of
forecasting future levels. Even in the short term it is unlikely that developing countries will
sustain the high rates of growth experienced in the past and factors such as higher fuel
costs and vehicle import restrictions could also tend to depress future growth rates.
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Diverted traffic. Where there are parallel routes traffic will usually travel on the quickest or
cheapest route although this may not necessarily be the shortest. Thus surfacing an
existing road may divert traffic from a parallel and shorter route because higher speeds are
possible on the surfaced road. Origin and destination surveys should be carried out to
provide data on the traffic diversions likely to arise. Assignment of diverted traffic is
normally done by an all-or-nothing method in which it is assumed that all vehicles that
would save time or money by diverting would do so, and that vehicles that would lose time
or increase costs would not transfer. With such a method it is important that all perceived
costs are included. In some of the more developed countries there may be scope for
modelling different scenarios using standard assignment computer programs.
Diversion from other transport modes, such as rail or water, is not, easy to forecast.
Transport of bulk commodities will normally be by the cheapest mode, though this may not
be the quickest. However, quality of service, speed and convenience are valued by
intending consignors and for general goods diversion from other modes should not be
estimated solely on the basis of door to door transport charges. Similarly, the choice of
mode for passenger transport should not be judged purely on the basis of travel charges.
The importance attached to quality of service by users has been a major contributory factor
to the world-wide decline in rail transport over recent years.
Diverted traffic is normally forecast to grow at the same rate as "traffic' on the road from
which it is diverted.
Generated traffic. Generated traffic arises either because a journey becomes more
attractive by virtue of a factor time reduction or because of the increased development that
is brought about by the road investment. Generated traffic is difficult to forecast accurately
and can be easily overestimated. It is only likely to be significant in those cases where the
road investment brings about large reductions in transport costs. For example in the case
of a small improvement within an already developed highway system, generated traffic will
be small and can normally be ignored. However, in the case of a new road allowing access
to a hitherto undeveloped area, there could be large reductions in transport cost as a result
of changing mode. For example from animal based transport to motor vehicle transport. In
such a case generated traffic could be the main component of future traffic now.
The recommended approach to forecasting generated traffic is to use demand
relationships. The price elasticity of demand for transport is the responsiveness of traffic to
change in transport costs following a road investment. On inter urban roads a distinction is
normally drawn between passenger and freight traffic. On roads providing access to rural
areas a further distinction is usually made between agricultural and non-agricultural freight
traffic.
Evidence from several evaluation studies carried out in developing countries shows price
elasticity of demand varies between 0.6 to 2.0, with an average of about 1.0. This means
that a one percent decrease in transport costs leads to a one percent increase in traffic.
Calculations should be based on door to door travel costs estimated as a result of origin
and destination surveys and not just on that part of the trip incurred on the road under
study.
The available evidence suggests that the elasticity of demand for passenger travel is
usually slightly greater than unity. In general the elasticity of demand for goods is much
lower and depends on the proportion for transport costs in the commodity price.
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2.5.2
AXLE LOADING
2.5.2.1
Axle load surveys
If no recent axle load data is available it is recommended that axle load surveys of heavy
vehicles are undertaken whenever a major road project is being designed. Ideally, several
surveys at periods that will reflect seasonal changes in the magnitude of axle loads are
recommended. Portable vehicle-wheel weighing devices are available which enable a
small team to weigh up to 910 vehicles per hour. Detailed guidance on carrying out axle
load surveys and analysing the results is given in TRRL Road Note 40 (Transport and
Road Research Laboratory (1978)).
It is recommended that an axle load survey be carried out by weighing a sample of vehicles
at the roadside. The sample should be chosen such that a maximum of about 60 vehicles
per hour is weighed. The weighing site should be level and, if possible, constructed in such
a way that vehicles are pulled clear of the road when being weighed. The portable
weighbridge should be mounted in a small pit with its surface level with the surrounding
area. This ensures that all of the wheels of the vehicle being weighed are level and
eliminates the errors which can be introduced by even a small twist of the vehicle. More
importantly, it also eliminates the large errors that can occur if all the wheels on one side of
multiple axle groups are not kept in the same horizontal plane. The load distribution
between axles in multiple axle groups is often uneven and therefore each axle must be
weighed separately. The duration of the survey should be based on the same
considerations as for traffic counting outlined in Section 2.5.1.1.
On certain roads it may be necessary to consider whether the axle load distribution of the
traffic travelling in one direction is the same as that of the traffic travelling in the opposite
direction. Significant differences between the two streams can occur on roads serving
docks quarries, cement works etc., where the vehicles travelling one way are heavily
loaded but are empty on the return journey. In such cases the results from the more heavily
trafficked lane should be used when converting commercial vehicle flows, to the equivalent
number of standard axles for pavement design. Similarly, special allowance must be made
for unusual axle load on roads which mainly serve one specific economic activity, since this
can result in a particular vehicle type being predominant in the traffic spectrum. This is
often the case. For example in timber extraction areas, mining areas and oil fields.
2.5.2.2
Axle Configurations and Equivalences
The damage due to different axle groups is dependent on the axle spacing, the number of
types per axle, the load on the group and the suspension. For design purposes, it is
generally appropriate to consider axle groups in terms of the following four types:
•
single axle with single wheels;
•
single wheels single axle with dual wheels;
•
tandem axles both with dual wheels;
•
tri-axles all with dual wheels.
Table 2.5.1 Axle Loads Which Cause Equal Damage
Axles
Configuration
Load (kN)
Single
Single
Single
Dual
53
80
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Tandem
Dual
135
Tri-axle
Dual
181
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The standard axle is defined as a single axle with dual wheels that carries a load of
8.2 tonnes. Loads on the axle configurations given above that cause the same amount of
damage as the standard axle are given in Table 2.5.1.
For axle group loads other than those in Table 2.5.1, the damage caused is expressed as
the number of standard axles which produce the same damage and is calculated as
follows:


Load on axle group
No. of standard axles for same damage = 

 Appropriate load from Table 2.5.1 
EXP
Where the exponent EXP may vary depending on the type of pavement. Commonly, a
value of 4 is adopted for the exponent in which case the number of standard axles for the
same damage is termed the number of equivalent standard axles (ESAs).
2.5.2.3
Design Lanes
Construction of now pavements and overlaying of existing pavements usually affects two or
more traffic lanes. It is usual practice to adopt the same pavement design for all lanes. The
design traffic should be that in the lane which carries the most commercial vehicular traffic
and it is designated the design lane.
2.5.3
DESIGN PERIOD
The design period is the length of time expressed in years before it is anticipated that
rehabilitation of the pavement will be necessary to restore shape, repair other forms of
distress, or to provide additional pavement strength.
Rehabilitation, which may consist of granular or asphalt overlay, major patching or
improvements or removal of selected areas of pavement materials, initiates a new design
period.
In this regard, resurfacing a pavement with a sprayed seal or a very thin asphalt overlay
does not in itself constitute rehabilitation in the pavement design sense.
Some typical design periods are outlined below:
•
New granular pavements
20 - 25 years
•
New rigid pavements
20 - 40 years
•
Asphalt overlays
10 - 15 years
•
Granular overlays
10 - 20 years
Various factors will influence the choice of design period. They include:
•
Maintenance strategies. Highly trafficked facilities will demand long periods of low
maintenance.
•
Funding considerations.
•
Other factors, such as inadequate geometry or traffic capacity, may limit the life of the
roadway and necessitate early reconstruction.
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2.5.4
TRAFFIC GROWTH
Based on road traffic survey information, it is reasonable, in most circumstances, to
assume that traffic volumes will increase geometrically either for the entire design period or
up to a stage where "road capacity" is reached. If “road capacity” is achieved traffic
volumes are assumed to remain constant for the remainder of the design period.
If there is an indication that "road capacity" is likely to be reached within the design period,
it is recommended that the designer establish that there is no planned upgrading of the
road geometry within the design period before he adopts "no growth" traffic volume for the
period of "full capacity". Adoption of "no-growth" traffic volumes for a period of "saturation"
will entail modification of the approach used below to aggregate daily traffic volumes for
total design traffic.
For geometric traffic growth throughout the design period, total traffic over the design
period is determined by multiplying the total traffic in the first year by the appropriate
Cumulative Growth Factor from Table 2.5.2.
Table 2.5.2 Cumulative Growth Factor
Design
Period
(Years)
5
10
15
20
25
30
35
40
2.5.5
Growth rate (% pa)
0
5
10
15
20
25
30
35
40
2
5.2
10.9
17.3
24.3
32
40.6
50.0
60.4
4
5.4
12.0
20.0
29.8
41.6
56.1
73.7
95.0
6
5.6
13.2
23.3
36.8
54.9
79.1
111.4
154.8
8
5.9
14.5
27.2
45.8
73.1
113.3
172.3
259.1
10
6.1
15.9
31.8
57.3
98.3
164.5
271
442.6
DESIGN TRAFFIC FOR FLEXIBLE PAVEMENT
The design parameter required is the number of ESAs. Annual average daily number of
ESAs, NE is calculated from Method 4 of Appendix C.
The design number of ESAs is then calculated as:
NE x 365 x GF
Where GF is the cumulative growth factor from Table 2.5.2.
This value is used as input to the design procedure outlined in Section 2.7 for flexible
pavements and Section 2.9 for overlays.
2.5.6
DESIGN TRAFFIC FOR RIGID PAVEMENTS
The design traffic is characterised by the cumulative number of commercial vehicle axle
groups expected in the design lane during the design period , together with the proportions
of each type of axle group and the distribution of load on each type of axle group.
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Loads on an axle group type are typically grouped into 10 kN intervals. Appendix F contain
examples of load distributions.
The design number of commercial vehicle axle groups over the design life of the pavement
is given by:
Cag = Cd x 365 x GF
Where:
Cag =
Cd =
GF =
design number of commercial vehicle axle groups.
initial number of commercial vehicle axle groups per day
the cumulative growth factor from Table 2.5.2.
The design procedure in Section 2.8 caters for each of the following axle types:
•
Single axles with single wheels;
•
Single axles with dual wheels;
•
Tandem axles with dual wheels; and
•
Tri-axles with dual wheels.
Other axle types are to be converted to one of the above as follows:
(i)
convert spread tandem axle loads to dual typed single axle loads on the basis that a
spread tandem axle is equivalent to two dual typed single axles, each of which has
half of the spread tandem axle load.
(ii)
Convert twin steer axles to single axles with single wheels on the basis that a twin
steer axle is equivalent to two single axles with single wheels each with half the load.
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2.5 TRAFFIC INVESTIGATION
ROAD DESIGN STANDARD
2.6
PAVEMENT MATERIALS
2.6.1
GRANULAR MATERIALS
2.6.1.1
Introduction
Granular material consists of gravel or crushed rock which have a grading that makes them
mechanically stable, workable and able to be compacted.
Modified granular materials consist of gravel or crushed rock to which small amounts of
stabilising agent have been added to improve their performance (eg by reducing plasticity)
without causing a significant increase in structure stiffness. Modified granular materials are
considered to behave as unbound granular materials.
Table 2.6.1 Physical Properties of Granular Pavement Material
Material
Sub base
Grading
Envelope
Liquid limit fraction passing
0.425 mm
Plasticity Index
Ratio fraction passing
0.075 mm sieve and
0.425 mm sieve
Abrasion
CBR 4 day soaked
No of cracked faces
Sodium sulphate soundness
loss
Sub base
Test
Method
Base
course
Shoulder
A-E
AASHTO
T27
A-C
A-D
< 35 %
< 10
T 89
T 90
< 25 %
<6%
< 35 %
>4 , <15
2/3
2/3
< 50 %
> 30 %
T 96
T 193
< 40 %
> 80 %
2
< 12 %
T 104
< 12 %
> 30 %
Table 2.6.2 Grading Requirements for Granular Pavement Material
Sieve
Designatio
n
50 mm
25 mm
10 mm
4.75 mm
2.00 mm
0.425 mm
0.075 mm
2.6.2
Grading
A
100
30 – 65
20 – 50
15 – 40
8 – 20
2–8
Grading
Grading
Grading
Grading
Grading
B
C
D
E
E
Percentage by weight passing square mesh sieves
100
100
100
75 – 95
100
100
100
100
40 – 75
50 – 85
49 – 77
30 – 60
35 – 70
50 – 90
20 – 45
25 – 50
40 – 70
40 – 100
55 – 100
15 – 30
15 – 35
20 – 50
30 – 70
40 – 100
5 - 15
5 - 15
5 – 20
6 - 20
8 - 25
MODIFIED MATERIALS
Bound pavement materials are those produced by additions of cement, lime or other
hydraulically binding agent to granular materials in sufficient quantities to produce a bound
layer with significant tensile strength.
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Table 2.6.3 Physical Properties of Bound Pavement Materials
Grades
Soil Cement Base
Desirable
Absolute
Well
Well
graded
graded
% retained on
4.75 mm sieve
%
Passing
0.075 sieve
Fraction
Passing
0.425 mm PI
LL
2.6.3
BITUMEN
2.6.3.1
Prime Coat
Soil Cement Sub - base
Desirable
Absolute
Well
Well graded
graded
Lime Soil
> 30 %
<6%
< 25 %
<15 %
< 40 %
< 10 %
< 30 %
< 40 %
< 40 %
< 20 %
< 40 %
6 % - 20 %
< 40 %
The prime coat shall be a medium or slow curing cutback liquid asphalt conforming to the
requirements of AASHTO M82 or slow setting emulsified asphalt conforming to the
requirements of AASHTO M82. Application temperatures shall be as follows:
Type and Grade
MC – 30
MC – 70
SC – 70
CSS – 1
2.6.3.2
Application Temperature
30 – 90 ºC
50 – 100 ºC
50 – 100 ºC
25 – 50 ºC
Tack Coat
The tack coat shall be one of the following bituminous materials:
Designation
Type of material
Application
temperature
Residual bitumen
application rates
RC – 70
Rapid curing liquid
asphalt
Rapid curing liquid
asphalt
Rapid setting
50 ºC – 100 ºC
0.1 – 0.3 l/m2
80 ºC – 100 ºC
0.1 – 0.3 l/m2
20 ºC – 70 ºC
0.1 – 0.3 l/m2
RC – 250
CRS – 2
2.6.3.3
Bituminous Surface treatment
2.6.3.3.1
Bituminous materials
Bituminous materials used in surface treatments shall be one of the types and grades listed
in the following table and approved by the Engineer.
Designation
60 – 70
80 – 100
RC – 250
RC – 800
RC – 3000
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Type of Material
Bitumen
Bitumen
Cutback Bitumen, Rapid Curing
Cutback Bitumen, Rapid Curing
Cutback Bitumen, Rapid Curing
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2.6 PAVEMENT MATERIALS
ROAD DESIGN STANDARD
RC – 2
CRS – 2
CRS – 3
Emulsified Bitumen
Cationic Emulsified Bitumen
Cationic Emulsified Bitumen
The materials shown above shall be in compliance with AASHTO designations M20 – 70,
M41 – 75, M140 – 82 and M208 – 81, as applicable. Bitumen shall only be cut back on site
if so instructed and approved by the Engineer.
2.6.3.3.2
Aggregates
Aggregates for bituminous surface treatments shall consist of clean, dry, hard durable
crushed stone or crushed gravel free from dust, clay, dirt and other deleterious matter.
Aggregates shall meet the quality requirements of AASHTO M80 except as altered herein.
All aggregates shall be mechanically screened to remove dust and small particles. Where
bitumen or cutback bitumen is used, aggregates shall be pre-coated. Where emulsified
asphalt is used, only washed aggregates will be allowed.
When subjected to the coating and stripping test, AASHTO test method T182, the
aggregates shall have a coated area of not less than 95 %. Aggregates which do not meet
this requirement may be used for bituminous surface treatments provided an approved
chemical additive or wetting agent is used to create a water resistant film.
When crushed gravel is used to produce sealing aggregate , not to less than 75 % by
weight of the particles shall have at least two fractured faces. The minimum size of stone to
be crushed to produce sealing aggregate shall be least four times the maximum size of the
sealing aggregate.
The aggregate shall have a percentage wear not exceeding 35 when tested for abrasion
resistance by AASHTO Method T96 and, when subjected to five cycles of the sodium
sulphate test for soundness ( AASHTO test Method T104 ) shall have a weight loss not
greater than 12 %. The flakiness index by British Standard 812, shall not exceed 33 %.
Aggregate sizes and gradings to be used in various applications of surface treatment shall
be determined using Table 2.6.4 , Table 2.6.5, and Table 2.6.7.
Table 2.6.4 Categories of Road Surface Hardness
Surface
Category
Very Hard
Penetration at
30 ºC (mm)
0–2
Hard
2–5
Normal
5–8
Soft
8 – 12
Definition
Surface such as concrete or chemically stabilised
roadbases into which negligible penetration of
chippings will occur under heavy traffic.
Granular roadbases into which chippings will
penetrate only slightly under heavy traffic.
Bituminous roadbase or basecourses into which
chipping will penetrate moderately under medium
and heavy traffic.
Bitumen rich asphalts into which chipping will
penetrate considerably under medium and heavy
traffic.
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ROAD DESIGN STANDARD
Table 2.6.5 Traffic Category For Surface Dressing
Category
Approximate Number of Vehicles with Unladen Weight
Greater Than 1.5 tonnes (per day)
Over 2000
1000 – 2000
200 – 100
20 – 200
Less than 20
1
2
3
4
5
Table 2.6.6 Recommended Maximum Chipping Size (mm)
Surface
Category
Very Hard
Hard
Normal
Soft
1
10
14
20
2
10
14
14
20
Traffic Category
3
6
10
14
14
4
6
6
10
14
5
6
6
6
10
Table 2.6.7 Grading Requirements For Surface Chip
Nominal
Size of
Material
25.0 mm
19.0 mm
12.5 mm
9.5 mm
2.6.3.4
25.0
mm
90-100
100
Percent by weight passing AASHTO sieve Size
19.0
12.5
9.5 mm
4.75m
2.36m
mm
mm
0.45
0-10
0-5
0-2
90.100
0.30
0-8
0-2
100
90.100
0-40
0-8
0-2
100
90-100
0-30
0-8
1.18
mm
0-0.05
0-0.05
0-0.05
0-2
Asphaltic Concrete
(a)
Coarse Mineral Aggregate
Coarse aggregate ( retained on the 4.75 mm sieve ) shall be crushed stone, or crushed
gravel, and unless otherwise stipulated, shall conform to the quality requirements of
AASHTO M 80.
When crushed gravel is used, it shall also meet the pertinent requirement of Section 2.2.1
of AASHTO M147-6S and not less than 75 % by weight of the particles retained on the
4.75 mm sieve shall have at least two fractured faces and 90 % one or more fractured
faces.
The abrasion loss (AASHTO T96) shall not exceed 40 %. Any aggregates liable to polish
shall not be used for the coarse aggregate fraction. The coarse aggregate shall be of such
gradation that when combined with other required aggregate fractions in proper proportion
the resultant mixture will meet the gradation required for the composition of the mixture.
(b) Fine Mineral Aggregate
Fine aggregate (passing the 4.75 mm sieve) shall consist of natural sand, stone
screenings, or a combination thereof, and shall conform to the quality requirements of
AASHTO M299 ASTM D10730. Fine aggregate shall be of such gradation that when
combined with other required aggregate fractions in proper proportions, the resultant
mixture will meet the gradation required for composition of the mixture. The sand
equivalence, tested in accordance with AASHTO T176, shall be greater than 50.
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2.6 PAVEMENT MATERIALS
ROAD DESIGN STANDARD
(c)
Mineral Filler
Filler material for asphaltic concrete shall conform to the requirements in AASHTO M17.
When the Strength Index as determined according to the Ontario Vacuum Immersion
Marshall Test or the US Army Corps of Engineers – Asphalt Institute Immersion Marshall
Test is than 75 % either 1 to 2 % of hydrated lime or 2 to 4 % of Portland cement by weight
may be added to the mix.
(d) Asphalt Materials
Asphalt cement shall conform to the requirements given in AASHTO M20-70.
Asphalt cement shall be designated by its penetration value ( eg AC 60-70). Cut back
asphalts shall be of the rapid curing type or the medium curing type and shall conform to
AASHTO designations M81-75 and M82-75 respectively. Cut back asphalt shall be
described by its kinematic velocity value at 60 ºC.( eg RC 250, MC 70)
2.6.4
CONCRETE
2.6.4.1
Introduction
Concrete (cement concrete) refers to a homogeneous mixture of hydraulic cement, fine
and coarse aggregate, water and chemical admixtures.
The cementitious portion of concrete may be of Portland cement or blended cement.
Blended cements consist of Portland cement mixed with additives such as ground
granulated blast furnace slag (slag) and/or pulverised fuel-ash (fly-ash).
Chemical admixtures may be used for set retardation, water reduction and air entrainment.
Concrete can be used as a sub-base in either flexible or rigid pavements and as a base in
rigid pavements.
2.6.4.2
Sub-base Concrete
Lean-mix concrete which is used for sub-base construction may contain a fly-ash blended
cement and is required to attain a characteristic 28 day compressive strength of 5 MPa
(with fly-ash) and 7 MPa (without fly-ash). The strength of concrete made using fly-ash
blended cement increases at a slower rate up to 28 days.
The construction of both rigid and flexible bases over poor subgrades is facilitated by the
adoption of a concrete sub-base. For example, weak subgrades may preclude the use of
rollers.
Where sub-base concrete is used in the design of a flexible pavement, for structural design
purposes the characteristics which must be known and evaluated are modulus, Poisson’s
ratio and performance under repeated loading.
2.6.4.3
Base Concrete
A rigid pavement is defined as a pavement having a base of cement concrete.
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2.6 PAVEMENT MATERIALS
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ROAD DESIGN STANDARD
The 28 day concrete flexural strength is a key design parameter in predicting pavement
performance.
The 28 day design flexural strength of concrete suitable for road pavement construction is
typically 3.0 to 5.0 MPa. Steel-fibre reinforced concrete should have a 28 day flexural
strength in the range 5.0 to 5.5 MPa.
Since at the time of undertaking the thickness design the concrete will only have a nominal
target strength, the design strength should be expressed in terms of the characteristic
flexural strength to the nearest 0.25 MPa.
A 28 day design characteristic flexural strength of 4.25 MPa is considered to correspond to
a 28 day characteristic compressive strength of 32 MPa. The durability of the concrete
wearing surface requires a 28 day characteristic compressive strength of not less than
32 MPa (Refer to AS 3600 “Concrete Structures” for concrete wearing courses subject to
highway traffic).
A typical relationship for converting 28 day compressive strength to 28 day flexural strength
for concrete with crushed aggregate is:
f cf = 0.75 ( f c )
0.50
(2 - 1.)
Where:
fc
fcf
=
=
28 day concrete compressive strength (MPa).
28 day concrete flexural strength (MPa).
The indirect tensile or splitting (Brazilian) test, has also been used for the control of
concrete strength in pavement work. A typical relationship for converting splitting strength
into flexural strength is:
f cf = 1.37 f cs
(2 - 2.)
Where:
fcs
=
28 day concrete splitting or indirect tensile strength.
The actual strength relationships for a given concrete mix will be dependent on the
properties of its constituents, particularly the micro-texture and particle shape of the coarse
aggregate. For pavement thickness design purposes the above relationships are
sufficiently accurate for concretes made with crushed aggregates possessing smooth
micro-texture.
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2.6 PAVEMENT MATERIALS
ROAD DESIGN STANDARD
2.7
DESIGN OF NEW FLEXIBLE PAVEMENTS
New flexible pavements shall be designed in accordance with the following charts.
Chart 1
Granular Roadbase / Surface Dressing
Chart 2
Composite roadbase (Unbound & Cement) / Surface Dressing
Chart 3
Granular Roadbase / Semi-Structural Surface
Chart 4
Composite Road base / Semi-Structural Surface
Chart 5
Granular Roadbase / Structural Surface
Chart 6
Composite Roadbase / Structural Surface
Chart 7
Bituminous Roadbase / Semi-Structural Surface
Chart 8
Cement Roadbase / Surface Dressing
ROAD DESIGN PART 2 - PAVEMENT, CAM PW 03-102-99
2.7 DESIGN OF NEW FLEXIBLE PAVEMENTS
34-97
ROAD DESIGN STANDARD
CHART 1 G RANULAR RO ADBASE / SURFACE DRESSING
T1
S1
SD
150
175
300
S2
SD
T2
T3
SD
SD
150
200
225*
200
300
300
SD
SD
150
200
150
200
175
200
200
200
SD
SD
150
200
250
225
SD
SD
150
200
175
150
SD
SD
SD
150
100
150
100
SD
150
150
S3
SD
150
200
S4
SD
150
125
S5
T4
SD
T5
SD
T6
225
250*
300*
325*
300
300
300
SD
200
SD
200
SD
225
225*
275*
300*
200
200
200
SD
200
275*
SD
200
200
SD
SD
200
325*
SD
SD
225
350*
SD
200
225
250
275
SD
SD
175
200
225
250
100
125
150
175
SD
SD
SD
SD
SD
150
175
200
225
250
S6
T8
SD
200
200
T7
Note:
1 * U p to 100mm of sub-base may be substituted with selected fill prov ided the sub-base
is not reduced to less than the roadbase thickness or 200mm whichev er is the greater.
The substitution ratio of sub-base to selected fill is 25mm : 32mm
2 * A cement or lime-stabilised sub-base may also be used.
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ROAD DESIGN STANDARD
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2.7 DESIGN OF NEW FLEXIBLE PAVEMENTS
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ROAD DESIGN STANDARD
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ROAD DESIGN STANDARD
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2.7 DESIGN OF NEW FLEXIBLE PAVEMENTS
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2.7 DESIGN OF NEW FLEXIBLE PAVEMENTS
ROAD DESIGN STANDARD
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2.7 DESIGN OF NEW FLEXIBLE PAVEMENTS
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ROAD DESIGN STANDARD
41-97
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2.7 DESIGN OF NEW FLEXIBLE PAVEMENTS
ROAD DESIGN STANDARD
ROAD DESIGN PART 2 - PAVEMENT, CAM PW 03-102-99
2.7 DESIGN OF NEW FLEXIBLE PAVEMENTS
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ROAD DESIGN STANDARD
2.8
DESIGN OF RIGID PAVEMENTS
2.8.1
GENERAL
This section provides guidance on the thickness design of rigid pavements proposed for
roads carrying commercial traffic with a design traffic loading exceeding one million
commercial vehicle axle groups. The information herein may not be appropriate for
residential or industrial pavements.
The design method is based on assessments of:
(i)
the predicted traffic volume and composition over the design period;
(ii)
the strength of the subgrade in terms of its California Bearing Ratio (CBR %); and
(iii) the strength of the concrete to be used in the pavement.
With these assessments remaining constant the concrete base thickness will vary
according to the type of shoulder and joint/reinforcement details adopted. The selection of
the overall pavement configuration is a matter for decision by the designer based on its
suitability for a particular project and economics.
2.8.2
PAVEMENT TYPES
2.8.2.1
Cement Concrete Pavements
A cement concrete pavement is defined as a pavement having a base of Portland cement
concrete. The principal types are:
•
jointed plain (unreinforced) concrete pavements (PCP);
•
jointed reinforced concrete pavements (JRCP);
•
continuously reinforced concrete pavements (CRCP).
The amount, if any, of reinforcement required in a concrete pavement is governed by the
spacing of contraction joints. The three main pavement configurations are:
(a) Unreinforced concrete pavements that have undowelled or dowelled contraction joints
at 4 to 5 m spacings.
(b) Reinforced concrete pavements which have dowelled contraction joints at
approximately 8 to 15 m spacings.
(c) Continuously reinforced concrete pavements where sufficient steel reinforcement has
been added to control crack widths and no contraction joints are required.
Additional types of concrete pavements are:
•
steel-fibre reinforced and
•
prestressed concrete pavements.
Design procedures for prestressed concrete pavements are not included in this Standard.
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2.8 DESIGN OF RIGID PAVEMENTS
ROAD DESIGN STANDARD
2.8.2.2
Asphalt Surfaced Rigid Pavements
Each type of concrete pavement described above may be provided with an asphalt
surface, typically up to 50 mm thick. The design procedure does not allow any contribution
by the asphalt surface to the structural performance of the pavement.
2.8.3
FACTORS USED IN THICKNESS DETERMINATION
2.8.3.1
Strength of Subgrade
For rigid pavement thickness design, the strength of the subgrade may be assessed in
terms of CBR. Methods of assessing the design CBR of the subgrade are discussed in
Section 2.4.
2.8.3.2
Concrete Strength
The determination of concrete strength is discussed in Section 2.6.4.
The 28 day flexural strength (modulus of rupture) of the concrete is used as the design
strength.
2.8.3.3
Design Traffic
The methods of determining the design traffic loading for rigid pavement thickness design
are included in Section 2.5.6.
2.8.3.4
Provision of Sub-base
2.8.3.4.1
General
Recommended minimum sub-base requirements are given in Figure 2.8.1.
For traffic loadings covered by this Standard the following recommendations are made:
(i)
the minimum sub-base thickness should be 100 mm.
(ii)
sub-base materials should be at least of the quality of bound material as described in
Clause 2.8.3.4.2; except that
(iii) where jointed undowelled bases are being designed lean-mix concrete is
recommended.
Note:
It is not the intention of this Standard to preclude sub-base materials and thicknesses
different to those described in Items (i) to (iii) above or as given in Figure 2.8.1 (in
combination with an appropriate base thickness) where these have been found to give
good long-term performance under particular conditions or whose performance is
supported by relevant research. If the use of unbound sub-base materials is considered, for
thickness design purposes the subgrade CBR is adopted as the effective CBR.
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2.8 DESIGN OF RIGID PAVEMENTS
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ROAD DESIGN STANDARD
Figure 2.8.1 Minimum Sub base requirements for Rigid pavements
The effective subgrade CBR for bound and lean-mix concrete sub-bases is obtained from
Figure 2.8.2. For subgrades with a design subgrade CBR of less than 2%, it may not be
possible to achieve compaction with rollers and the following design parameters are
recommended:
•
the provision of a 150 mm thick sub-base of lean mix concrete; and
•
the use of a maximum value of 5 % for the effective subgrade CBR.
Note:
Other sub-base types which can be adequately constructed may be used providing special
investigations into the assessment of the effective design subgrade CBR are carried out.
Figure 2.8.2 Effective Increase in Subgrade Strength due to
Provision of Bound (Or Mass Concrete) Sub-Base Course
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2.8 DESIGN OF RIGID PAVEMENTS
ROAD DESIGN STANDARD
A bound or lean mix concrete sub-base is provided under a concrete pavement for one or
more of the following reasons:
(a) to provide a stable working platform on which to operate construction equipment;
(b) to provide uniform support under the pavement;
(c) to reduce deflection at joints thus maintaining effective load transfer across contraction
joints by aggregate interlock (especially if no other load transfer devices are provided);
(d) to assist in the control of shrinkage and swelling of high volume change subgrade
soils; and
(e) to resist erosion of the sub-base and limit "pumping" at joints and slab edges.
Note:
Pumping is defined as the ejection of fine particles in suspension (usually in wet weather)
along or through transverse or longitudinal joints or cracks. It is caused by downward slab
movement as heavy axle loads traverse joints, Pumping leads to the removal of sufficient
sub-base or subgrade material so that slab ends are left unsupported resulting in cracking
or faulting of the slab.
2.8.3.4.2
Bound Sub-base
For the purpose of rigid pavement design, a bound sub-base is defined as being composed
of either:
(i)
cement-stabilised granular material with not less than 5 % by mass cementitious
content to ensure satisfactory erosion resistance (verifiable by laboratory erodability
testing). The cementitious content may include lime/fly ash and/or ground granulated
blast furnace slag; or
(ii)
dense-graded asphalt; or
(iii) lean rolled concrete having a characteristic 28 day strength of not less than 5 MPa.
2.8.3.4.3
Lean Rolled Concrete Sub-base
Lean rolled concrete as defined in Clause 2.8.3.4.2 (iii) should be considered for design
purposes to be a bound sub-base.
2.8.3.4.4
Lean-Mix Concrete Sub-base
Lean-mix concrete (LMC) is to have a characteristic 28 day compressive strength of not
less than 5 MPa (with fly-ash) or 7 MPa (without fly-ash), and be designed to have low
shrinkage, typically less than 450 microstrain.
Note:
Lean-mix concrete sub-bases are constructed as mass concrete without transverse joints
and will therefore develop cracks. It is intended to achieve a pattern of relatively closely
spaced and narrow cracks which in conjunction with a debonding layer will not reflect into
the base. This is controlled by limiting both the upper strength and shrinkage of the
sub-base concrete. These limitations are inherent in Figure 2.8.2.
2.8.3.4.5
Debonding of the Sub-base and Base
It is assumed that the sub-base and base are designed to be unbonded. This is
accomplished by application of a bond-breaking layer to the surface of the sub-base.
ROAD DESIGN PART 2 - PAVEMENT, CAM PW 03-102-99
2.8 DESIGN OF RIGID PAVEMENTS
46-97
ROAD DESIGN STANDARD
2.8.3.5
Concrete Shoulders
Provision is made in the design procedure for the incorporation of concrete shoulders.
Concrete shoulders enhance the pavement performance and enable a lesser base
thickness to be adopted. For the purposes of this Standard, a concrete shoulder is defined
as:
(a) a keyed and tied (in accordance with Clause 2.8.4.6.2) shoulder with a minimum width
of 1.5 m from the edge of the trafficked lane; or
(b) a 600 mm integrally cast widening of the trafficked lane, this may include integral
channel or kerb/ channel.
2.8.3.6
Load Safety Factors
In the design procedure, the axle loads are multiplied by a load safety factor (LSF). These
load safety factors are used to incorporate varying levels of design reliability. The following
values are recommended:
•
For major freeways and other multi-lane projects carrying
LSF = 1.2
uninterrupted flows of high volumes of commercial vehicles, and where high levels of
serviceability are sought throughout the design period with minimum maintenance.
•
This value of 1.2 maybe reduced to 1.15 taking into account factors such as the use of
appropriate weigh-in-motion data and the availability of alternative traffic routes. An
example would be the case of a very busy urban freeway with no alternative routes
and where weigh-in-motion data is available for a period of at least two months for a
nearby site consistent with that being designed.
•
For freeways, highways and arterial road projects with moderate
LSF = 1.1
volumes of commercial vehicles.
•
LSF =
1.0
For roads carrying low volumes of commercial vehicles.
2.8.4
BASE THICKNESS DESIGN PROCEDURE
2.8.4.1
General
The procedure for the determination of the thickness of rigid pavements is based on
"Thickness Design for Concrete Highway and Street Pavements," Portland Cement
Association USA (EB209.01P). 1984.
The two distress modes considered in this procedure are:
(i)
flexural fatigue cracking of the pavement base;
(ii)
subgrade/sub-base erosion arising from repeated deflections at joints and planned
cracks.
Account is taken of the presence or absence of dowelled joints or concrete shoulders. For
design purposes continuously reinforced pavements are treated as dowelled jointed
pavements.
Information is required on both axle types and load distributions and the number of
repetitions of each axis type/load combination expected to use the pavement during its
design life.
2.8.4.2
Base Thickness Design Procedure
A trial base thickness is selected and the total fatigue and erosion damage are calculated
for the entire traffic volume and composition during the design period. If either fatigue or
47-97
ROAD DESIGN PART 2 - PAVEMENT, CAM PW 03-102-99
2.8 DESIGN OF RIGID PAVEMENTS
ROAD DESIGN STANDARD
erosion damage exceeds 100 percent, the trial thickness is increased and the design
process is repeated. The design thickness is the least trial thickness which has a total
fatigue less than or equal to 100 percent and a total erosion damage less than or equal to
100 per cent.
The steps in the thickness design are illustrated in Figure 2.8.3 and are detailed in Table
2.8.1.
A pro–forma to assist with design calculations is provided in Appendix F.
ROAD DESIGN PART 2 - PAVEMENT, CAM PW 03-102-99
2.8 DESIGN OF RIGID PAVEMENTS
48-97
ROAD DESIGN STANDARD
Figure 2.8.3 Rigid Pavement Design System
49-97
ROAD DESIGN PART 2 - PAVEMENT, CAM PW 03-102-99
2.8 DESIGN OF RIGID PAVEMENTS
ROAD DESIGN STANDARD
Table 2.8.1 Design Procedure for Base Thickness
Step
1
2
3
Activity
Select a rigid pavement type, either jointed undowelled, jointed
dowelled or continuously reinforced concrete base.
Decide whether concrete shoulders are to be provided.
5
Using the design subgrade CBR and the predicted number of
commercial vehicle axle groups over the design period determine the
Figure 2.8.1.
sub-base thickness and type from
Using the design subgrade CBR and the selected sub base
determine the Effective Subgrade CBR from Figure 2.8.2.
Select the 28-day flexural strength of the concrete base (f’cf).
6
Select the appropriate load safety factor.
7
Select a trial base thickness (appropriate trial base thicknesses may
be governed by such factors as formwork depth or estimated from
experience or by using the example design charts provided herein).
For the Single Steer (SS) axle group, determine the equivalent stress
and the erosion factor from Table 2.8.2 or Table2.8.3 as appropriate.
Determine the stress ratio factor by dividing the equivalent stress by
the flexural strength.
For each load range for this axle group type, determine the load per
tyre on the axle group and multiply by the safety factor to Determine
the design load per tyre. If the design load per tyre exceeds 65 kN,
assume a value of 65 kN (the upper limit in Figure 2.8.4 to Figure
2.8.6)
Using the stress ratio factor and the design load, determine from
Figure 8.4 the allowable number of repetitions to fatigue starting with
the highest load per tyre of this axle group type.
Calculate the ratio of the expected fatigue repetitions to the allowable
repetitions. Multiply by 100 to determine the percentage
Fatigue.
Using the erosion factor, determine from
Figure 2.8.5 or Figure 2.8.6 (as appropriate) the allowable number of
repetitions for erosion.
Calculate the ratio of the expected erosion repetitions to the allowable
repetitions. Multiply by 100 to determine the percentage erosion
damage.
Repeat steps 11 to 14 each load per tyre on this axle group until the
allowable load repetitions as read from Figure 2.8.4 and
Figure 2.8.5 or Figure 2.8.6 exceed 107 and 108 respectively, at which
point further load repetitions are not deemed to contribute to
pavement distress.
Sum the percentage fatigue for all relevant loads of this axle group
type; similarly , sum the percentage erosion for all relevant loads of
this axle group type.
Repeat steps 8 to 16 for each axle group type.
Sum the total fatigue and total erosion damage for all axle group
types.
Steps 7 to 18 inclusive are repeated until the least thickness which
has a total fatigue less than of equal to 100 percent and also a total
erosion damage less than or equal to 100 percent is determined. This
is the base concrete pavement design thickness.
4
8
9
10
11
12
13
14
15
16
17
18
19
Reference
Section
2.8.2.1
Section
2.8.3.5
Section
2.8.3.4
Section
2.8.3.4
Section
2.8.3.2
Section
2.8.3.6
Appendix F
Note: Selection of the final base thickness may be governed by construction factors such
as survey levels, etc.
ROAD DESIGN PART 2 - PAVEMENT, CAM PW 03-102-99
2.8 DESIGN OF RIGID PAVEMENTS
50-97
ROAD DESIGN STANDARD
Figure 2.8.4 Fatigue Analysis with and without Concrete Shoulder –
Allowable load repetitions based on stress ratio.
51-97
ROAD DESIGN PART 2 - PAVEMENT, CAM PW 03-102-99
2.8 DESIGN OF RIGID PAVEMENTS
ROAD DESIGN STANDARD
Figure 2.8.5 Erosion Analysis without Concrete Shoulder –
Allowable Load repetitions based on Erosion factor.
ROAD DESIGN PART 2 - PAVEMENT, CAM PW 03-102-99
2.8 DESIGN OF RIGID PAVEMENTS
52-97
ROAD DESIGN STANDARD
Figure 2.8.6 Erosion Analysis with Concrete Shoulder –
Allowable Load Repetitions based on Erosion Factor
53-97
ROAD DESIGN PART 2 - PAVEMENT, CAM PW 03-102-99
2.8 DESIGN OF RIGID PAVEMENTS
ROAD DESIGN STANDARD
Figure 2.8.7 Recommended maximum tiebar spacing for concrete pavements assuming 12 mm
diameter tie bars, grade 400Y steel and subgrade friction factor of 1.5.
ROAD DESIGN PART 2 - PAVEMENT, CAM PW 03-102-99
2.8 DESIGN OF RIGID PAVEMENTS
54-97
ROAD DESIGN STANDARD
Table 2.8.2 Equivalent Stresses And Erosion Factors
For Pavements With No Concrete Shoulders
Slab
Effective
Thickness CBR of
(mm)
Subgrade
Equivalent
Stresses
SS
SD
TAD
TRD
SS
Erosion Factors
Undowelled
Dowelled or CRC
SD TAD
TRD
SS
SD
TAD TRD
150
150
150
150
150
150
150
150
5
10
15
20
25
35
50
75
1.70
1.62
1.59
1.56
1.54
1.49
1.43
1.38
2.72
2.56
2.48
2.43
2.37
2.26
2.15
2.02
2.25
2.09
2.01
1.97
1.92
1.82
1.73
1.64
1.68
1.58
1.53
1.51
1.48
1.43
1.40
1.36
2.80
2.79
2.78
2.77
2.77
2.76
2.74
2.72
3.40
3.39
3.38
3.37
3.37
3.36
3.34
3.32
3.50
3.46
3.44
3.43
3.42
3.39
3.36
3.33
3.55
3.50
3.47
3.46
3.44
3.40
3.37
3.32
2.60
2.59
2.59
2.59
2.59
2.58
2.57
2.56
3.21
3.20
3.20
3.19
3.19
3.18
3.17
3.16
3.30
3.28
3.27
3.26
3.25
3.23
3.21
3.19
3.37
3.32
3.30
3.29
3.28
3.25
3.22
3.19
160
160
160
160
160
160
160
160
5
10
15
20
25
35
50
75
1.54
1.47
1.44
1.41
1.39
1.34
1.30
1.24
2.49
2.34
2.26
2.22
2.17
2.07
1.96
1.85
2.08
1.92
1.84
1.80
1.76
1.67
1.58
1.49
1.55
1.44
1.39
1.37
1.34
1.29
1.25
1.23
2.72
2.71
2.70
2.69
2.69
2.68
2.66
2.64
3.32
3.31
3.30
3.29
3.29
3.28
3.26
3.24
3.43
3.39
3.37
3.36
3.35
3.32
3.28
3.26
3.47
3.43
3.41
3.40
3.38
3.34
3.30
3.25
2.52
2.51
2.51
2.50
2.50
2.49
2.49
2.48
3.12
3.11
3.11
3.10
3.10
3.09
3.09
3.08
3.22
3.20
3.19
3.18
3.17
3.15
3.13
3.12
3.30
3.26
3.24
3.23
3.21
3.18
3.15
3.12
170
170
170
170
170
170
170
170
180
180
180
18 0
180
180
180
180
5
10
15
20
25
35
50
75
5
10
15
20
25
35
50
75
1.41
1.34
1.31
1.29
1.27
1.23
1.19
1.14
1.29
1.23
1.20
1.18
1.16
1.12
1.09
1.03
2.27
2.14
2.07
2.03
1.99
1.90
1.81
1.70
2.10
1.98
1.92
1.88
1.84
1.76
1.67
1.57
1.93
1.78
1.71
1.67
1.63
1.54
1.46
1.37
1.81
1.66
1.59
1.55
1.51
1.43
1.35
1.26
1.44
1.33
1.28
1.26
1.23
1.18
1.14
1.10
1.35
1.24
1.19
1.17
1.14
1.09
1.05
1.01
2.64
2.62
2.62
2.61
2.61
2.60
2.58
2.57
2.57
2.55
2.55
2.54
2.54
2.53
2.51
2.49
3.24
3.22
3.22
3.21
3.21
3.20
3.18
3.17
3.17
3.15
3.15
3.14
3.14
3.13
3.11
3.10
3.37
3.33
3.31
3.30
3.28
3.25
3.22
3.19
3.33
3.28
3.25
3.24
3.23
3.20
3.17
3.13
3.43
3.38
3.35
3.34
3.32
3.28
3.24
3.19
3.37
3.32
3.29
3.28
3.26
3.22
3.19
3.14
2.44
2.43
2.43
2.42
2.42
2.41
2.40
2.40
2.36
2.35
2.35
2.35
2.35
2.34
2.33
2.32
3.04
3.03
3.03
3.02
3.02
3.01
3.01
3.00
2.97
2.96
2.96
2.95
2.95
2.94
2.93
2.92
3.15
3.13
3.12
3.11
3.10
3.08
3.06
3.04
3.09
3.07
3.05
3.04
3.03
3.01
2.99
2.97
3.24
3.20
3.18
3.17
3.15
3.12
3.08
3.05
3.20
3.15
3.12
3.11
3.09
3.06
3.02
2.99
190
190
190
190
190
190
190
190
5
10
15
20
25
35
50
75
1.19
1.13
1.10
1.09
1.07
1.03
1.00
0.96
1.95
1.84
1.78
1.75
1.71
1.63
1.55
1.46
1.69
1.55
1.49
1.45
1.41
1.33
1.26
1.17
1.27
1.16
1.11
1.09
1.06
1.01
0.97
0.91
2.50
2.48
2.48
2.47
2.47
2.46
2.44
2.43
3.11
3.09
3.08
3.07
3.07
3.06
3.04
3.03
3.28
3.23
3.20
3.19
3.17
3.14
3.10
3.07
3.32
3.27
3.24
3.23
3.21
3.17
3.14
3.09
2.29
2.28
2.28
2.27
2.27
2.26
2.26
2.25
2.90
2.89
2.88
2.88
2.88
2.87
2.86
2.85
3.03
3.00
2.98
2.98
2.97
2.95
2.93
2.91
3.15
3.10
3.07
3.06
3.04
3.00
2.97
2.93
200
200
200
200
200
200
200
200
210
210
210
210
210
210
210
210
5
10
15
20
25
35
50
75
5
10
15
20
25
35
50
75
1.10
1.05
1.02
1.01
0.99
0.96
0.92
0.89
1.02
0.97
0.94
0.93
0.92
0.89
0.86
0.82
1.81
1.70
1.65
1.62
1.59
1.52
1.44
1.36
1.69
1.59
1.54
1.51
1.48
1.41
1.35
1.27
1.60
1.46
1.40
1.36
1.33
1.25
1.18
1.10
1.50
1.38
1.32
1.28
1.25
1.18
1.11
1.03
1.20
1.10
1.05
1.02
0.99
0.94
0.89
0.84
1.14
1.04
0.99
0.96
0.93
0.88
0.83
0.78
2.44
2.42
2.42
2.41
2.40
2.39
2.38
2.36
2.38
2.36
2.36
2.35
2.34
2.33
2.32
2.30
3.04
3.02
3.02
3.01
3.01
3.00
2.98
2.96
2.99
2.97
2.96
2.95
2.95
2.94
2.92
2.90
3.23
3.18
3.15
3.14
3.12
3.09
3.06
3.00
3.18
3.13
3.10
3.09
3.07
3.04
3.01
2.95
3.27
3.22
3.19
3.18
3.16
3.12
3.09
3.04
3.23
3.18
3.15
3.13
3.11
3.07
3.04
2.98
2.23
2.22
2.22
2.21
2.21
2.20
2.19
2.18
2.17
2.16
2.15
2.14
2.14
2.13
2.13
2.12
2.83
2.82
2.82
2.81
2.81
2.80
2.79
2.78
2.77
2.76
2.75
2.75
2.75
2.74
2.73
2.72
2.97
2.95
2.93
2.92
2.91
2.89
2.87
2.85
2.92
2.89
2.87
2.87
2.86
2.84
2.81
2.79
3.10
3.05
3.02
3.01
2.99
2.95
2.92
2.88
3.06
3.01
2.98
2.96
2:94
2.90
2.88
2.83
Note: SS - single axle, single -tyres; SD - single axle, dual tyres; TAD - tandem axle, dual tyres; TRD - triple axle, dual tyres
55-97
ROAD DESIGN PART 2 - PAVEMENT, CAM PW 03-102-99
2.8 DESIGN OF RIGID PAVEMENTS
ROAD DESIGN STANDARD
Table 2.8.2 (Cont.) Equivalent Stresses And Erosion Factors
For Pavements With No Concrete Shoulders
Slab
Effective
Thickness CBR of
(mm)
Subgrade
Equivalent
Stresses
SS
SD
TAD
TRD
SS
Erosion Factors
Undowelled
Dowelled or CRC
SD TAD
TRD
SS
SD
TAD TRD
220
220
220
220
220
220
220
220
5
10
15
20
25
35
50
75
0.94
0.90
0.88
0.87
0.85
0.82
0.79
0.76
1.58
1.49
1.44
1A2
1.39
1.33
1.27
1.19
1.42
1.30
1.25
1.22
1.18
1.11
1.04
0.97
1.08
0.98
0.93
0.91
0.88
0.83
0.79
0.73
2.33
2.31
2.30
2.29
2.29
2.28
2.26
2.24
2.93
2.91
2.90
2.89
2.89
2.88
2.86
2.85
3.14
3.09
3.06
3.05
3.03
2.99
2.96
2.92
3.19
3.13
3.10
3.09
3.07
3.03
3.00
2.95
2.11
2.10
2.09
2.08
2.08
2.07
2.07
2.06
2.71
2.70
2.69
2.69
2.69
2.68
2.67
2.66
2.87
2.84
2.82
2.81
2.80
2.78
2.76
2.72
3.02
2.96
2.93
2.92
2.90
2.86
2.83
2.78
230
230
230
230
230
230
230
230
240
240
240
240
240
240
240
240
5
10
15
20
25
35
50
75
5
10
15
20
25
35
50
75
0.88
0.84
0.82
0.81
0.80
0.77
0.74
0.71
0.82
0.79
0.77
0.76
0.75
0.72
0.69
0.67
1A9
1.24
1.36
1.34
1.31
1.25
1.19
1.12
1.40
1.32
1.28
1.26
1.23
1.17
1.12
1.05
1.35
1.24
1.19
1.16
1.12
1.05
0.99
0.91
1.29
1.18
1.13
1.10
1.06
0.99
0.94
0.86
1.03
0.94
0.89
0.87
0.84
0.78
0.74
0.70
0.98
0.89
0.85
0.83
0.80
0.74
0.70
0.66
2.28
2.26
2.25
2.24
2.23
2.21
2.20
2.19
2.23
2.21
2.20
2.19
2.18
2.17
2.15
2.13
2.88
2.86
2.85
2.84
2.83
2.81
2.80
2.79
2.83
2.81
2.80
2.79
2.78
2.76
2.75
2.74
3.10
3.05
3.02
3.00
2.98
2.94
2.91
2.86
3.08
3.01
2.98
2.96
2.94
2.90
2.86
2.83
3.14
3.09
3.06
3.05
3.03
2.99
2.95
2.91
3.11
3.05
3.02
3.01
2.99
2.95
2.91
2.86
2.05
2.04
2.03
2.03
2.03
2.02
2.01
2.00
1.99
1.98
1.98
1.97
1.97
1.96
1.95
1.94
2.65
2.64
2.64
2.63
2.63
2.62
2.61
2.60
2.60
2.59
2.58
2.57
2.57
2.56
2.55
2.54
2.82
2.79
2.77
2.76
2.75
2.73
2.70
2.68
2.78
2.74
2.72
2.72
2.71
2.69
2.66
2.63
2.98
2.92
2.89
2.88
2.86
2.82
2.78
2.74
2.94
2.88
2.85
2.84
2.82
2.78
2.74
2.69
250
250
250
250
250
250
250
250
5
10
15
20
25
35
50
75
0.77
0.74
0.72
0.71
0.70
0.68
0.65
0.63
1.33
1.25
1.21
1.18
1.16
1.11
1.06
0.99
1.23
1.12
1.07
1.04
1.01
0.95
0.89
0.82
0.94
0.86
0.81
0.79
0.76
0.71
0.67
0.61
2.18
2.16
2.15
2.14
2.13
2.12
2.10
2.08
2.78
2.76
2.75
2.74
2.73
2.71
2.70
2.69
3.02
2.97
2.94
2.93
2.91
2.87
2.83
2.79
3.07
3.01
2.98
2.97
2.95
2.91
2.88
2.83
1.94
1.93
1.93
1.92
1.92
1.91
1.90
1.89
2.54
2.53
2.53
2.52
2.52
2.51
2.50
2.49
2.73
2.70
2.68
2.67
2.66
2.64
2.61
2.59
2.90
2.65
2.82
2.80
2.78
2.74
2.70
2.65
260
260
280
260
260
260
260
260
5
10
15
20
25
35
50
75
0.73
0.70
0.68
0.67
0.66
0.64
0.61
0.59
1.26
1.18
1.15
1.12
1.10
1.05
1.00
0.95
1.18
1.08
1.03
1.00
0.97
0.91
0.85
0.78
0.90
0.82
0.78
0.75
0.73
0.68
0.64
0.58
2.13
2.11
2.10
2.09
2.08
2.07
2.05
2.03
2.73
2.71
2.70
2.69
2.69
2.68
2.65
2.64
2.99
2.93
2.90
2.89
2.87
2.83
2.80
2.75
3.03
2.98
2.95
2.93
2.91
2.87
2.84
2.78
1.89
1.88
1.88
1.87
1.87
1.86
1.85
1.84
2.49
2.48
2.48
2.47
2.47
2.46
2.45
2.44
2.69
2.66
2.64
2.63
2.62
2.59
2.56
2.54
2.87
2.81
2.78
2.76
2.74
2.70
2.67
2.61
270
270
270
270
270
270
270
270
5
10
15
20
25
35
50
75
0.66
0.66
0.64
0.63
0.62
0.60
0.58
0.56
1.19
1.12
1.09
1.06
1.04
0.99
0.95
0.89
1.13
1.03
0.98
0.96
0.93
0.87
0.81
0.74
0.87
0.79
0.75
0.72
0.70
0.65
0.61
0.57
2.09
2.07
2.06
2.05
2.04
2.02
2.00
1.99
2.69
2.67
2.66
2.65
2.64
2.63
2.61
2.59
2.95
2.90
2.87
2.85
2.83
2.79
2.76
2.70
3.00
2.94
2.91
2.90
2.88
2.84
2.80
2.75
1.84
1.83
1.83
1.82
1.82
1.81
1.80
1.79
2.44
2.43
2.43
2.42
2.42
2.41
2.40
2.39
2.65
2.62
2.60
2.59
2.58
2.55
2.52
2.50
2.83
2.78
2.75
2.73
2.71
2.67
2.63
2.58
280
280
280
280
280
280
280
280
5
10
15
20
25
35
50
75
0.65
0.62
0.60
0.60
0.59
0.57
0.55
0.53
1.13
1.06
1.03
1.01
0.99
0.94
0.90
0.86
1.08
0.99
0.94
0.92
0.89
0.83
0.78
0.71
0.83
0.75
0.72
0.69
0.67
0.62
0.59
0.53
2.05
2.03
2.01
2.00
1.99
1.97
1.96
1.94
2.65
2.63
2.62
2.61
2.60
2.58
2.56
2.55
2.92
2.86
2.83
2.82
2.80
2.76
2.72
2.68
2.97
2.91
2.88
2.87
2.85
2.81
2.77
2.72
1.60
1.79
1.78
1.77
1.77
1.76
1.75
1.74
2.40
2.39
2.38
2.37
2.37
2.36
2.35
2.34
2.62
2.58
2.58
2.55
2.54
2.51
2.48
2.46
2.80
2.74
2.71
2.70
2.68
2.64
2.60
2.55
Note: SS - single axle, single tyres; SD - single axle, dual tyres; TAD - tandem axle, dual tyres; TRD - triple axle, dual tyres
ROAD DESIGN PART 2 - PAVEMENT, CAM PW 03-102-99
2.8 DESIGN OF RIGID PAVEMENTS
56-97
ROAD DESIGN STANDARD
Table 2.8.2 (Cont) Equivalent Stresses And Erosion Factors
For Pavements With No Concrete Shoulders
Slab
Effective
Thickness CBR of
(mm)
Subgrade
Equivalent
Stresses
SS
SD
TAD
TRD
SS
Erosion Factors
Undowelled
Dowelled or CRC
SD TAD
TRD
SS
SD
TAD TRD
290
290
290
290
290
290
290
290
5
10
15
20
25
35
50
75
0.61
0.59
0.58
0.57
0.56
0.54
0.52
0.50
1.08
1.01
0.98
0.96
0.94
0.90
0.86
0.81
1.04
0.95
0.90
0.88
0.85
0.80
0.75
0.68
0.80
0.73
0.70
0.67
0.65
0.60
0.56
0.52
2.01
1.99
1.97
1.96
1.95
1.93
1.92
1.90
2.61
2.59
2.58
2.57
2.56
2.54
2.52
2.50
2.89
2.83
2.80
2.79
2.77
2.73
2.69
2.64
2.93
2.88
2.85
2.83
2.81
2.77
2.74
2.68
1.75
1.74
1.74
1.73
1.73
1.72
1.71
1.70
2.35
2.34
2.34
2.33
2.33
2.32
2.31
2.30
2.58
2.54
2.52
2.51
2.50
2.47
2.44
2.42
2.77
2.71
2.68
2.67
2.65
2.61
2.56
2.51
300
300
300
300
300
300
300
300
5
10
15
20
25
35
50
75
0.58
0.56
0.55
0.54
0.53
0.51
0.49
0.47
1.03
0.97
0.94
0.92
0.90
0.86
0.82
0.78
1.00
0.91
0.87
0.85
0.82
0.77
0.72
0.65
0.77
0.70
0.67
0.65
0.63
0.58
0.54
0.50
1.97
1.95
1.93
1.92
1.91
1.89
1.88
1.86
2.57
2.55
2.54
2.53
2.52
2.50
2.48
2.46
2.86
2.80
2.77
2.76
2.74
2.70
2.66
2.61
2.90
2.85
2.82
2.80
2.78
2.74
2.70
2.65
1.71
1.70
1.69
1.68
1.68
1.67
1.66
1.65
2.31
2.30
2.30
2.29
2.29
2.28
2.26
2.26
2.55
2.51
2.49
2.48
2.46
2.43
2.41
2.37
2.74
2.68
2.65
2.64
2.62
2.58
2.53
2.48
310
310
310
310
310
310
310
310
5
10
15
20
25
35
50
75
0.55
0.53
0.52
0.51
0.50
0.49
0.47
0.45
0.98
0.92
0.89
0.88
0.86
0.82
0.78
0.74
0.97
0.89
0.84
0.82
0.79
0.74
0.69
0.63
0.74
0.68
0.65
0.63
0.60
0.55
0.51
0.48
1.94
1.91
1.89
1.89
1.88
1.86
1.84
1.82
2.54
2.51
2.49
2.49
2.48
2.46
2.44
2.42
2.83
2.77
2.74
2.73
2.71
2.67
2.63
2.58
2.88
2.82
2.79
2.77
2.75
2.71
2.67
2.62
1.67
1.66
1.65
1.64
1.64
1.63
1.62
1.61
2.27
2.26
2.25
2.24
2.24
2.23
2.22
2.21
2.51
2.47
2.45
2.44
2.43
2.40
2.37
2.34
2.71
2.65
2.62
2.61
2.59
2.55
2.50
2.45
320
320
320
320
320
320
320
320
5
10
15
20
25
35
50
75
0.53
0.51
0.50
0.49
0.48
0.46
0.44
0.43
0.94
0.88
0.85
0.84
0.82
0.78
0.75
0.71
0.93
0.85
0.81
0.79
0.76
0.71
0.67
0.61
0.71
0.65
0.62
0.60
0.58
0.54
0.51
0.45
1.90
1.87
1.85
1.85
1.84
1.82
1.80
1.78
2.50
2.48
2.46
2.45
2.44
2.42
2.40
2.38
2.80
2.74
2.71
2.70
2.68
2.64
2.60
2.55
2.85
2.79
2.76
2.74
2.72
2.68
2.64
2.59
1.63
1.62
1.61
1.60
1.60
1.59
1.58
1.57
2.23
2.22
2.21
2.20
2.20
2.19
2.18
2.17
2.48
2.44
2.42
2.41
2.40
2.37
2.33
2.31
2.89
2.63
2.60
2.58
2.56
2.52
2.47
2.42
330
330
330
330
330
330
330
330
5
10
15
20
25
35
50
75
0.50
0.48
0.47
0.46
0.46
0.45
0.42
0.41
0.90
0.85
0.82
0.80
0.78
0.74
0.71
0.68
0.90
0.82
0.79
0.76
0.74
0.69
0.64
0.59
0.69
0.63
0.60
0.58
0.56
0.52
0.48
0.45
1.87
1.84
1.82
1.81
1.80
1.78
1.76
1.74
2.47
2.44
2.42
2.42
2.41
2.39
2.36
2.35
2.78
2.72
2.69
2.67
2.65
2.61
2.57
2.52
2.82
2.76
2.73
2.72
2.70
2.66
2.62
2.57
1.59
1.58
1.57
1.56
1.56
1.55
1.54
1.53
2.19
2.18
2.17
2.16
2.16
2.15
2.14
2.13
2.45
2.41
2.39
2.38
2.36
2.33
2.30
2.28
2.66
2.60
2.57
2.55
2.53
2.49
2.45
2.40
340
340
340
340
340
340
340
340
5
10
15
20
25
35
50
75
0.48
0.46
0.45
0.44
0.44
0.43
0.40
0.39
0.86
0.80
0.78
0.77
0.75
0.72
0.68
0.65
0.87
0.79
0.76
0.73
0.71
0.66
0.62
0.56
0.65
0.61
0.58
0.57
0.55
0.51
0.47
0.43
1.84
1.81
1.79
1.78
1.77
1.75
1.73
1.71
2.44
2.41
2.39
2.38
2.37
2.35
2.33
2.31
2.75
2.69
2.66
2.64
2.62
2.58
2.54
2.49
2.79
2.74
2.71
2.69
2.67
2.63
2.59
2.54
1.55
1.54
1.53
1.52
1.52
1.51
1.50
1.49
2.15
2.14
2.14
2.13
2.12
2.11
2.10
2.09
2.42
2.38
2.36
2.35
2.33
2.30
2.27
2.24
2.63
2.57
2.54
2.52
2.50
2.46
2.42
2.37
350
350
350
350
350
350
350
350
5
10
15
20
25
35
50
75
0.46
0.44
0.43
0.42
0.42
0.41
0.39
0.37
0.83
0.78
0.75
0.74
0.72
0.69
0.65
0.62
0.85
0.77
0.74
0.71
0.69
0.64
0.60
0.54
0.63
0.59
0.56
0.55
0.53
0.49
0.46
0.42
1.80
1.77
1.75
1.75
1.74
1.72
1.69
1.67
2.41
2.38
2.36
2.35
2.34
2.32
2.29
2.28
2.72
2.67
2.64
2.62
2.60
2.56
2.52
2.47
2.77
2.71
2.68
2.66
2.64
2.60
2.56
2.51
1.51
1.50
1.50
1.49
1.49
1.48
1.46
1.46
2.11
2.10
2.10
2.09
2.09
2.08
2.07
2.06
2.39
2.35
2.33
2.32
2.30
2.27
2.24
2.21
2.61
2.55
2.52
2.50
2.48
2.44
2.39
2.34
Note: SS - single axle, single tyres; SD - single axle, dual tyres; TAD - tandem axle, dual tyres; TRO - triple axle, dual tyres
57-97
ROAD DESIGN PART 2 - PAVEMENT, CAM PW 03-102-99
2.8 DESIGN OF RIGID PAVEMENTS
ROAD DESIGN STANDARD
Table2.8.3 Equivalent Stresses And Erosion Factors
For Pavements With Concrete Shoulders
Slab
Effective
Thickness CBR of
(mm)
Subgrade
Equivalent
Stresses
SS
SD
TAD
TRD
SS
Erosion Factors
Undowelled
Dowelled or CRC
SD TAD
TRD
SS
SD
TAD TRD
150
150
150
150
150
150
150
150
5
10
15
20
25
35
50
75
1.42
1.36
1.33
1.32
1.30
1.27
1.23
1.20
2.16
2.04
1.98
1.94
1.90
1.82
1.74
1.65
1.81
1.70
1.65
1.62
1.59
1.53
1.49
1.43
1.45
1.39
1.36
1.35
1.33
1.30
1.27
1.26
2.34
2.32
2.32
2.31
2.30
2.29
2.27
2.25
2.94
2.92
2.92
2.91
2.90
2.89
2.87
2.85
2.99
2.94
2.91
2.90
2.88
2.85
2.82
2.79
3.00
2.94
2.91
2.90
2.88
2.84
2.81
2.77
2.14
2.13
2.12
2.11
2.10
2.08
2.06
2.04
2.74
2.72
2.72
2.71
2.70
2.69
2.67
2.65
2.78
2.73
2.70
2.69
2.67
2.64
2.60
2.57
2.81
2.75
2.72
2.70
2.67
2.63
2.59
2.56
160
160
160
160
160
160
160
160
5
10
15
20
25
35
50
75
1.29
1.24
1.21
1.20
1.18
1.15
1.12
1.10
1.98
1.87
1.82
1.79
1.75
1.67
1.60
1.52
1.67
1.56
1.51
1.49
1.46
1.41
1.36
1.30
1.33
1.26
1.23
1.21
1.20
1.17
1.15
1.13
2.26
2.24
2.24
2.23
2.23
2.22
2.20
2.18
2.87
2.85
2.84
2.83
2.83
2.82
2.80
2.78
2.93
2.88
2.85
2.84
2.82
2.79
2.75
2.72
2.95
2.89
2.86
2.84
2.82
2.78
2.75
2.69
2.06
2.04
2.04
2.03
2.02
2.00
1.98
1.97
2.66
2.64
2.64
2.63
2.62
2.61
2.59
2.57
2.72
2.67
2.64
2.62
2.60
2.56
2.53
2.50
2.77
2.69
2.66
2.64
2.62
2.57
2.53
2.49
170
170
170
170
170
170
170
170
5
10
15
20
25
35
50
75
1.17
1.13
1.11
1.10
1.08
1.05
1.03
1.02
1.83
1.73
1.68
1.65
1.62
1.55
1.49
1.41
1.55
1.45
1.40
1.38
1.35
1.30
1.25
1.19
1.22
1.16
1.13
1.12
1.10
1.07
1.04
1.03
2.19
2.17
2.17
2.16
2.16
2.15
2.13
2.11
2.80
2.78
2.77
2.76
2.76
2.75
2.73
2.71
2.88
2.83
2.80
2.79
2.77
2.73
2.70
2.66
2.90
2.84
2.81
2.79
2.77
2.73
2.70
2.64
1.99
1.97
1.96
1.95
1.95
1.94
1.91
1.89
2.59
2.57
2.57
2.56
2.55
2.53
2.51
2.49
2.66
2.61
2.58
2.57
2.55
2.51
2.47
2.43
2.72
2.64
2.61
2.59
2.57
2.53
2.48
2.43
180
180
180
180
180
180
180
180
5
10
15
20
25
35
50
75
1.07
1.03
1.01
1.01
1.00
0.98
0.95
0.94
1.70
1.60
1.55
1.53
1.50
1.44
1.38
1.31
1.44
1.35
1.30
1.28
1.25
1.20
1.16
1.10
1.13
1.07
1.04
1.03
1.01
0.98
0.96
0.94
2.13
2.11
2.10
2.09
2.09
2.08
2.06
2.04
2.73
2.71
2.71
2.70
2.69
2.68
2.66
2.64
2.83
2.78
2.75
2.73
2.71
2.67
2.64
2.61
2.86
2.79
2.76
2.74
2.72
2.68
2.64
2.60
1.92
1.90
1.89
1.88
1.88
1.87
1.84
1.82
2.52
2.50
2.50
2.49
2.48
2.46
2.44
2.42
2.61
2.56
2.53
2.51
2.49
2.45
2.42
2.36
2.68
2.60
2.57
2.54
2.52
2.47
2.42
2.37
190
190
190
190
190
190
190
190
5
10
15
20
25
35
50
75
0.99
0.96
0.94
0.93
0.92
0.90
0.88
0.87
1.58
1.49
1.44
1.42
1.40
1.35
1.29
1.22
1.35
1.26
1.21
1.19
1.17
1.12
1.08
1.02
1.05
0.99
0.97
0.96
0.94
0.91
0.88
0.86
2.07
2.05
2.04
2.03
2.03
2.02
2.00
1.98
2.67
2.65
2.64
2.63
2.63
2.62
2.60
2.58
2.78
2.72
2.70
2.69
2.67
2.63
2.60
2.55
2.82
2.75
2.72
2.70
2.68
2.64
2.60
2.55
1.86
1.84
1.83
1.82
1.81
1.79
1.77
1.76
2.46
2.44
2.43
2.42
2.41
2.40
2.38
2.36
2.57
2.51
2.48
2.46
2.44
2.40
2.36
2.32
2.64
2.56
2.53
2.50
2.48
2.43
2.38
2.31
200
200
200
200
200
200
200
200
5
10
15
20
25
35
50
75
0.91
0.89
0.87
0.86
0.85
0.83
0.82
0.81
1.47
1.39
1.35
1.33
1.30
1.25
1.20
1.14
1.27
1.18
1.15
1.12
1.10
1.05
1.01
0.95
0.99
0.93
0.90
0.89
0.87
0.84
0.82
0.80
2.01
1.99
1.98
1.97
1.97
1.96
1.94
1.92
2.61
2.59
2.59
2.58
2.57
2.56
2.54
2.52
2.74
2.69
2.66
2.64
2.62
2.58
2.54
2.51
2.78
2.71
2.68
2.66
2.64
2.60
2.55
2.50
1.80
1.78
1.77
1.76
1.75
1.73
1.71
1.69
2.40
2.38
2.37
2.36
2.35
2.33
2.31
2.30
2.52
2.46
2.43
2.42
2.40
2.36
2.32
2.27
2.60
2.52
2.49
2.46
2.44
2.39
2.33
2.28
210
210
210
210
210
210
210
210
5
10
15
20
25
35
50
75
0.85
0.82
0.80
0.80
0.79
0.77
0.76
0.75
1.38
1.30
1.27
1.24
1.22
1.17
1.13
1.07
1.20
1.11
1.08
1.05
1.03
0.98
0.94
0.90
0.93
0.87
0.84
0.83
0.81
0.78
0.76
0.74
1.96
1.94
1.93
1.92
1.91
1.90
1.88
1.86
2.56
2.54
2.53
2.52
2.51
2.49
2.48
2.47
2.70
2.65
2.62
2.60
2.58
2.54
2.51
2.45
2.75
2.67
2.64
2.62
2.60
2.56
2.51
2.46
1.74
1.72
1.71
1.70
1.69
1.67
1.65
1.64
2.34
2.32
2.31
2.30
2.29
2.28
2.26
2.24
2.48
2.42
2.39
2.37
2.35
2.31
2.27
2.22
2.57
2.49
2.45
2.43
2.40
2.34
2.29
2.22
Note: SS - single axle, single tyres; SD - single axle, dual tyres; TAD - tandem axle, dual tyres; TRO - triple axle, dual tyres
ROAD DESIGN PART 2 - PAVEMENT, CAM PW 03-102-99
2.8 DESIGN OF RIGID PAVEMENTS
58-97
ROAD DESIGN STANDARD
Table2.8.3 (Cont.) Equivalent Stresses And Erosion Factors
For Pavements With Concrete Shoulders
Slab
Effective
Thickness CBR of
(mm)
Subgrade
Equivalent
Stresses
SS
SD
TAD
TRD
SS
Erosion Factors
Undowelled
Dowelled or CRC
SD TAD
TRD
SS
SD
TAD TRD
220
220
220
220
220
220
220
220
5
10
15
20
25
35
50
75
0.79
0.77
0.76
0.75
0.74
0.72
0.71
0.70
1.30
1.22
1.19
1.17
1.15
1.11
1.06
1.01
1.13
1.05
1.02
0.99
0.97
0.92
0.88
0.85
0.87
0.81
0.79
0.78
0.76
0.73
0.71
0.69
1.91
1.89
1.88
1.87
1.86
1.85
1.83
1.81
2.51
2.49
2.48
2.47
2.46
2.45
2.43
2.41
2.67
2.61
2.58
2.56
2.54
2.50
2.47
2.41
2.72
2.64
2.61
2.58
2.56
2.52
2.48
2.41
1.68
1.66
1.66
1.65
1.64
1.62
1.60
1.58
2.29
2.27
2.26
2.25
2.24
2.22
2.20
2.18
2.44
2.38
2.35
2.33
2.31
2.27
2.23
2.18
2.54
2.46
2.42
2.39
2.37
2.32
2.26
2.19
230
230
230
230
230
230
230
230
5
10
15
20
25
35
50
75
0.74
0.72
0.71
0.70
0.69
0.68
0.67
0.66
1.22
1.15
1.12
1.10
1.08
1.04
1.00
0.96
1.08
1.00
0.97
0.94
0.92
0.87
0.83
0.80
0.82
0.77
0.75
0.74
0.72
0.69
0.67
0.65
1.86
1.84
1.83
1.82
1.81
1.80
1.78
1.76
2.46
2.44
2.43
2.42
2.41
2.40
2.38
2.36
2.63
2.57
2.54
2.52
2.50
2.46
2.43
2.37
2.69
2.61
2.58
2.55
2.53
2.48
2.44
2.37
1.63
1.61
1.60
1.59
1.58
1.56
1.54
1.53
2.23
2.21
2.21
2.20
2.19
2.17
2.15
2.13
2.40
2.34
2.31
2.29
2.27
2.23
2.19
2.12
2.50
2.42
2.39
2.36
2.34
2.28
2.22
2.16
240
240
240
240
240
240
240
240
5
10
15
20
25
35
50
75
0.69
0.67
0.66
0.65
0.65
0.64
0.63
0.62
1.16
1.09
1.06
1.04
1.02
0.98
0.95
0.89
1.02
0.95
0.92
0.89
0.87
0.83
0.79
0.76
0.78
0.72
0.70
0.69
0.68
0.66
0.63
0.61
1.81
1.79
1.78
1.77
1.76
1.75
1.73
1.71
2.41
2.39
2.38
2.37
2.36
2.35
2.33
2.31
2.60
2.54
2.51
2.49
2.47
2.43
2.39
2.34
2.66
2.58
2.55
2.52
2.50
2.45
2.41
2.34
1.58
1.56
1.55
1.54
1.53
1.51
1.49
1.48
2.18
2.17
2.15
2.14
2.13
2.11
2.10
2.08
2.36
2.30
2.27
2.25
2.23
2.19
2.15
2.10
2.47
2.39
2.36
2.33
2.31
2.25
2.19
2.13
250
250
250
250
250
250
250
250
5
10
15
20
25
35
50
75
0.65
0.63
0.62
0.61
0.61
0.60
0.59
0.58
1.09
1.03
1.00
0.99
0.97
0.93
0.90
0.86
0.98
0.90
0.87
0.85
0.83
0.79
0.75
0.72
0.73
0.69
0.67
0.66
0.64
0.61
0.59
0.57
1.77
1.74
1.73
1.72
1.72
1.71
1.68
1.66
2.37
2.35
2.34
2.33
2.32
2.30
2.28
2.27
2.56
2.50
2.47
2.45
2.43
2.39
2.36
2.30
2.63
2.55
2.52
2.49
2.47
2.42
2.38
2.31
1.54
1.52
1.50
1.49
1.48
1.46
1.44
1.43
2.14
2.12
2.11
2.10
2.09
2.07
2.05
2.03
2.32
2.26
2.23
2.22
2.20
2.16
2.11
2.06
2.45
2.37
2.33
2.30
2.28
2.22
2.16
2.10
260
260
260
260
260
260
260
260
5
10
15
20
25
35
50
75
0.61
0.60
0.59
0.58
0.57
0.56
0.56
0.55
1.04
0.98
0.95
0.94
0.92
0.88
0.85
0.81
0.93
0.86
0.83
0.81
0.79
0.75
0.71
0.68
0.71
0.66
0.63
0.62
0.61
0.59
0.56
0.54
1.72
1.70
1.69
1.68
1.67
1.66
1.64
1.62
2.33
2.30
2.28
2.28
2.27
2.26
2.24
2.22
2.53
2.47
2.44
2.42
2.40
2.36
2.32
2.27
2.61
2.53
2.49
2.46
2.44
2.39
2.35
2.28
1.49
1.47
1.46
1.45
1.44
1.42
1.40
1.38
2.09
2.07
2.06
2.05
2.04
2.02
2.00
1.98
2.29
2.23
2.20
2.18
2.16
2.12
2.08
2.01
2.42
2.34
2.30
2.28
2.25
2.19
2.13
2.06
270
270
270
270
270
270
270
270
5
10
15
20
25
35
50
75
0.57
0.55
0.55
0.54
0.54
0.53
0.53
0.52
0.99
0.93
0.90
0.89
0.87
0.84
0.80
0.77
0.89
0.83
0.80
0.78
0.76
0.72
0.68
0.65
0.66
0.62
0.60
0.59
0.58
0.56
0.53
0.52
1.68
1.66
1.65
1.64
1.63
1.61
1.59
1.58
2.28
2.26
2.25
2.24
2.23
2.22
2.20
2.18
2.50
2.44
2.41
2.39
2.37
2.33
2.29
2.24
2.58
2.50
2.47
2.44
2.42
2.37
2.32
2.25
1.45
1.43
1.41
1.40
1.39
1.37
1.35
1.34
2.05
2.03
2.02
2.01
2.00
1.98
1.96
1.94
2.25
2.20
2.17
2.15
2.13
2.09
2.04
1.99
2.39
2.31
2.27
2.25
2.22
2.16
2.11
2.03
280
280
280
280
280
280
280
280
5
10
15
20
25
35
50
75
0.54
0.52
0.52
0.51
0.51
0.50
0.50
0.49
0.94
0.89
0.86
0.85
0.83
0.80
0.76
0.74
0.86
0.79
0.76
0.74
0.73
0.69
0.66
0.62
0.63
0.60
0.58
0.57
0.56
0.54
0.51
0.49
1.64
1.62
1.61
1.60
1.59
1.57
1.55
1.54
2.25
2.22
2.20
2.20
2.19
2.18
2.16
2.14
2.48
2.41
2.38
2.36
2.34
2.30
2.26
2.21
2.56
2.48
2.44
2.42
2.39
2.34
2.29
2.22
1.40
1.38
1.37
1.36
1.35
1.33
1.31
1.29
2.01
1.99
1.97
1.96
1.95
1.93
1.91
1.89
2.22
2.16
2.13
2.12
2.10
2.06
2.01
1.96
2.37
2.29
2.25
2.22
2.20
2.14
2.08
2.00
Note: SS - single axle, single tyres; SD - single axle, dual tyres; TAD - tandem axle, dual tyres; TRD - triple axle. dual tyre
59-97
ROAD DESIGN PART 2 - PAVEMENT, CAM PW 03-102-99
2.8 DESIGN OF RIGID PAVEMENTS
ROAD DESIGN STANDARD
Table2.8.3 (Cont) Equivalent Stresses And Erosion Factors
For Pavements With Concrete Shoulders
Slab
Effective
Thickness CBR of
(mm)
Subgrade
Equivalent
Stresses
SS
SD
TAD
TRD
SS
Erosion Factors
Undowelled
Dowelled or CRC
SD TAD
TRD
SS
SD
TAD TRD
290
290
290
290
290
290
290
290
5
10
15
20
25
35
50
75
0.51
0.50
0.50
0.49
0.49
0.48
0.47
0.47
0.90
0.85
0.82
0.81
0.79
0.76
0.73
0.70
0.82
0.76
0.73
0.72
0.70
0.66
0.63
0.60
0.60
0.57
0.55
0.54
0.53
0.51
0.49
0.47
1.61
1.58
1.56
1.56
1.55
1.53
1.51
1.50
2.21
2.18
2.16
2.16
2.15
2.14
2.12
2.10
2.45
2.39
2.36
2.34
2.32
2.28
2.23
2.18
2.54
2.46
2.42
2.39
2.37
2.32
2.27
2.19
1.36
1.34
1.33
1.32
1.31
1.29
1.27
1.25
1.97
1.94
1.92
1.92
1.91
1.89
1.87
1.85
2.19
2.13
2.10
2.08
2.06
2.02
1.98
1.93
2.34
2.26
2.22
2.20
2.17
2.11
2.05
1.98
300
300
300
300
300
300
300
300
5
10
15
20
25
35
50
75
0.49
0.48
0.47
0.46
0.46
0.46
0.45
0.45
0.86
0.81
0.78
0.77
0.76
0.73
0.70
0.67
0.79
0.73
0.70
0.69
0.67
0.64
0.60
0.57
0.58
0.55
0.53
0.52
0.51
0.49
0.46
0.45
1.57
1.55
1.53
1.52
1.51
1.49
1.48
1.46
2.17
2.15
2.14
2.13
2.12
2.10
2.08
2.06
2.42
2.36
2.33
2.31
2.29
2.25
2.20
2.15
2.52
2.44
2.40
2.37
2.35
2.30
2.24
2.17
1.32
1.30
1.29
1.28
1.27
1.25
1.23
1.21
1.93
1.91
1.89
1.88
1.87
1.85
1.83
1.81
2.16
2.10
2.07
2.05
2.03
1.99
1.95
1.90
2.32
2.24
2.20
2.18
2.15
2.09
2.03
1.95
310
310
310
310
310
310
310
310
5
10
15
20
25
35
50
75
0.46
0.45
0.45
0.44
0.44
0.43
0.43
0.42
0.81
0.77
0.75
0.74
0.72
0.69
0.67
0.63
0.76
0.70
0.68
0.66
0.64
0.61
0.58
0.54
0.55
0.52
0.50
0.50
0.49
0.47
0.44
0.43
1.54
1.51
1.49
1.49
1.48
1.46
1.44
1.42
2.14
2.11
2.09
2.09
2.08
2.06
2.04
2.02
2.40
2.33
2.30
2.28
2.26
2.22
2.18
2.13
2.50
2.42
2.38
2.35
2.33
2.28
2.22
2.15
1.29
1.27
1.25
1.24
1.23
1.21
1.19
1.17
1.89
1.87
1.86
1.85
1.84
1.82
1.79
1.77
2.13
2.07
2.04
2.03
2.01
1.97
1.92
1.87
2.30
2.22
2.18
2.15
2.13
2.07
2.01
1.93
320
320
320
320
320
320
320
320
5
10
15
20
25
35
50
75
0.44
0.43
0.43
0.42
0.42
0.41
0.41
0.41
0.78
0.74
0.72
0.71
0.69
0.66
0.64
0.62
0.74
0.68
0.65
0.64
0.62
0.59
0.55
0.53
0.53
0.50
0.48
0.48
0.47
0.45
0.43
0.41
1.50
1.48
1.46
1.45
1.44
1.42
1.41
1.39
2.11
2.08
2.06
2.06
2.05
2.03
2.01
1.99
2.37
2.31
2.28
2.26
2.24
2.20
2.15
2.10
2.48
2.40
2.36
2.33
2.31
2.26
2.20
2.12
1.25
1.23
1.22
1.21
1.20
1.18
1.15
1.13
1.85
1.83
1.82
1.81
1.80
1.78
1.76
1.74
2.10
2.05
2.02
2.00
1.98
1.94
1.89
1.84
2.27
2.19
2.15
2.13
2.10
2.04
1.98
1.91
330
330
330
330
330
330
330
330
5
10
15
20
25
35
50
75
0.42
0.41
0.41
0.40
0.40
0.39
0.39
0.39
0.74
0.71
0.69
0.68
0.67
0.64
0.61
0.59
0.71
0.65
0.63
0.62
0.60
0.57
0.53
0.51
0.51
0.48
0.46
0.46
0.45
0.43
0.41
0.39
1.47
1.44
1.42
1.42
1.41
1.39
1.37
1.35
2.07
2.05
2.03
2.02
2.01
1.99
1.97
1.95
2.35
2.29
2.26
2.24
2.21
2.17
2.13
2.06
2.46
2.38
2.34
2.31
2.29
2.24
2.18
2.10
1.22
1.19
1.17
1.17
1.16
1.14
1.12
1.10
1.82
1.79
1.77
1.77
1.76
1.74
1.72
1.70
2.07
2.02
1.99
1.97
1.95
1.91
1.87
1.80
2.25
2.17
2.13
2.11
2.08
2.02
1.96
1.88
340
340
340
340
340
340
340
340
5
10
15
20
25
35
50
75
0.40
0.39
0.39
0.38
0.38
0.37
0.37
0.37
0.71
0.68
0.66
0.65
0.64
0.62
0.59
0.57
0.69
0.64
0.61
0.60
0.58
0.55
0.52
0.49
0.49
0.47
0.45
0.44
0.43
0.41
0.39
0.38
1.44
1.41
1.39
1.39
1.38
1.36
1.34
1.32
2.04
2.02
2.00
1.99
1.98
1.96
1.94
1.92
2.33
2.26
2.23
2.21
2.19
2.15
2.10
2.05
2.44
2.36
2.32
2.29
2.27
2.22
2.16
2.08
1.18
1.16
1.15
1.14
1.13
1.11
1.08
1.06
1.78
1.76
1.75
1.74
1.73
1.71
1.69
1.67
2.05
1.99
1.96
1.94
1.92
1.88
1.84
1.79
2.23
2.15
2.11
2.09
2.06
2.00
1.94
1.86
350
350
350
350
350
350
350
350
5
10
15
20
25
35
50
75
0.38
0.37
0.37
0.36
0.36
0.36
0.36
0.35
0.69
0.65
0.63
0.62
0.61
0.59
0.57
0.55
0.67
0.62
0.59
0.58
0.56
0.53
0.50
0.47
0.47
0.45
0.44
0.43
0.42
0.40
0.38
0.36
1.41
1.38
1.36
1.36
1.35
1.33
1.31
1.29
2.01
1.98
1.96
1.96
1.95
1.93
1.91
1.89
2.31
2.24
2.21
2.19
2.17
2.13
2.08
2.03
2.43
2.35
2.30
2.28
2.25
2.19
2.14
2.06
1.15
1.13
1.11
1.10
1.09
1.07
1.05
1.03
1.75
1.73
1.71
1.70
1.69
1.67
1.65
1.63
2.02
1.97
1.94
1.92
1.90
1.86
1.81
1.76
2.21
2.13
2.09
2.07
2.04
1.98
1.92
1.84
Note: SS - single axle, single tyres; SD - single axle, dual tyres; TAD - tandem axle, dual tyres; TRD - triple axle. dual tyres
ROAD DESIGN PART 2 - PAVEMENT, CAM PW 03-102-99
2.8 DESIGN OF RIGID PAVEMENTS
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ROAD DESIGN STANDARD
2.8.4.3
Minimum Base Thickness
Irrespective of the base thickness determined in accordance with procedure, the minimum
allowable thickness of concrete base to be trafficked by commercial vehicles shoulder be:
(i)
150 mm; except for
(ii)
steel – fibre reinforced concrete where the minimum thickness of base should be not
less than 125 mm.
These minimum thickness of concrete base also apply to asphalt surfaced rigid pavements.
2.8.4.4
Provision of Dowels and Tie Bars
The thickness design procedure provides for the option of dowelled or undowelled
contraction joints, as well as the option of adopting concrete shoulders (defined in Section
2.8.3.5 ).
2.8.4.4.1
Dowels
Dowel bars are to be plain steel bars of Grade 250R and 450 mm long. Dowels should be
straight with one and free from burrs. Appropriate dowel diameters are given in
Table 2.8.4.
Dowels at a spacing 300 mm should be installed at transverse contraction joints where
applicable. Dowels must be securely held parallel to each other, to the road centreline and
to the centreline of surface of the finished pavement. More than half of the smooth end of
the dowels should be coated with a debonding agent to ensure lack of bond to the concrete
on that side of the joint.
Table 2.8.4 Appropriate Dowel Diameters
Slab Thickness mm
*Dowel Diameter mm
20
125 < h ≤ 140
24
140 < h ≤ 160
28
160 < h ≤ 190
33
190 < h ≤ 220
36
220 < h ≤ 250
* AS 2338 preferred dimensions of wrought metal products
2.8.4.4.2
Tie Bars
Tie bars prevent separation of the pavement at longitudinal joints, allowing warping or
curling to occur without excessive restraint.
Tie bars are to be 12 mm diameter Grade 400 Y deformed steel bars, one metre long,
placed centrally in the joint at spacing determined from Figure 2.8.7. A coefficient of
friction of 1.5 ( between base and sub-base ) is assumed in Figure 2.8.7. Table 2.8.5 gives
indicative values of the coefficient of friction for different bond-breaking systems. For the
coefficient of friction of 1.0 an increase of 30 % in the spacing given in Figure 2.8.7 is
required and a coefficient of 2.0 requires a 30 % reduction in the spacing derived from
Figure 2.8.7.
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ROAD DESIGN STANDARD
Table 2.8.5 Values of Coefficient of Friction
Coefficient of Friction
1.0
1.5
2.0
2.8.5
Bond-breaking system
A bituminous sprayed seal applied to the sub base surface
A thin coat of wax debonding agent applied to the sub base
surface
A chlorinated rubber curing compound applied to the sub
base surface or use of an asphalt sub base
REINFORCEMENT DESIGN PROCEDURES
The purpose of reinforcing steel in rigid pavements is not to prevent cracking of the
concrete, but to hold tightly closed any cracks that do occur in such manner that the load
carrying capacity of the slab is preserved.
In jointed pavements the amount of steel is governed by the spacing of contraction joints.
In the case of continuously reinforced pavements, sufficient steel is provided to eliminate
the need for contraction joints.
2.8.5.1
Special Requirements for Reinforcement In Jointed Unreinforced Pavements
In jointed unreinforced pavements, reinforcement (usually in the form of welded wire fabric)
is sometimes necessary to control cracking. Concrete slabs which are reinforced are those
in which it is anticipated that cracks could occur due to stress concentrations which cannot
be avoided by re-arrangement of the slab pattern. Typical applications are:
(i)
odd-shaped slabs
(ii)
mismatched joints; and
(iii) slabs containing pits or structures.
2.8.5.2
Reinforcement In Jointed Reinforced Pavements
The required area of reinforcing steel in jointed reinforced pavements is given by the
equation:
As =
Where
AS =
fs =
g
h
L
M
µ
=
=
=
=
=
µLM gh
2 fs
(2 - 3.)
the required area of steel (mm2/m width of slab).
the allowable tensile stress of the reinforcing steel (MPa).
Usually 0.6 times the yield strength.
the acceleration due to gravity (m/s2 )
thickness of the slab (m).
the distance between untied joints and/or free edges of the slab (m).
the mass per unit volume of the slab (kg/m3)
the coefficient of friction between the concrete base slab and the sub-base;
this varies from 1.0 to 2.0 depending on the type of debonding layer applied to
the sub-base (see Clause 2.8.4.4.2).
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ROAD DESIGN STANDARD
The areas of longitudinal steel provided by rectangular and square mashes are detailed in
Table 2.8.6. Experience has shown that the use of slab lengths of over 15 metres could
reduce joint performance, costs and riding quality. Slabs in excess of 15 metres in length
are not recommended.
Table 2.8.6 Dimensions and Mass of Plant Hard – Drawn Steel Wire Fabric
Cross wires
Longitudinal wires
Ref
No.
Size
mm
Pitch
mm
Rectangular meshes
F1218 12.5
100
F1118 11.2
100
F1018 10
100
F918
9
100
F818
8
100
F718 7.1
100
F928
9
200
F828
8
200
Square meshes
F81
8
F102
10
F92
9
F82
8
F72
7.1
F62
6.3
F52
5
F42
4
100
200
200
200
200
200
200
200
Size
mm
Pitch
mm
Area of crosssection
Long. Cross
mm2/mmm2/m
Mass per unit area
kg/ m2
8
8
8
8
8
8
8
8
200
200
200
200
200
200
250
250
1 227
985
785
636
503
396
318
251
251
251
251
251
251
251
201
201
11.606
9.707
8.138
6.967
5.919
5.081
4.076
3.552
8
10
9
8
7.1
6.3
5
4
100
200
200
200
200
200
200
200
503
393
318
251
198
156
98
63
503
393
318
251
198
156
98
63
7.892
6.165
4.994
3.946
3.108
2.447
1.542
0.987
The use of steel fibre reinforced concrete is appropriate where increased flexural strength
is required to control cracking in odd-shaped slabs and where increased abrasion
resistance is required for durability. This type of pavement is often used for toll plazas,
roundabouts and bus-stops. Steel fibres are between 15 mm and 50 mm in length with
either enlarged ends which act as anchorages and/or crimping to improve bond. Typically,
15 mm to 50 mm fibres are added to the concrete at a rate of approximately 75 to 45 kg/m
3 respectively (referred to as the fibre "loading"). Steel fibre reinforced concrete may be
used for thin bonded overlays for which fibre "loadings" would be about 33 % higher.
Steel fibre reinforced concrete should have a 28 day flexural strength of not less than
5.5 MPa.
2.8.5.3
Reinforcement In Continuously Reinforced Pavements
2.8.5.3.1
Longitudinal Reinforcement
The action of the steel reinforcement is initially to provide restraint to shrinkage of the
concrete and finally to tie the planned cracks together.
With the pavement ends anchored, the steel initially remains unstressed while tension
builds up in the concrete. When cracking occurs, local tension results in the steel and limits
the opening of the crack.
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ROAD DESIGN STANDARD
This tension is balanced by compression elsewhere in the steel, until further cracking
develops. The final distribution of stresses are tensile in the concrete and compressive in
the steel between cracks, and tensile in the steel at the cracks. Due to the stresses in the
steel changing so rapidly, adequate bond strength between steel and concrete is essential.
The proportion of the cross sectional area of the pavement which is to be longitudinal
reinforcing steel in continuously reinforced concrete pavements is given by the equation:
 ft' 
 f  d b (eS + eT )
b
p= 
2W
where:
p
=
f’t/fb =
db
es
=
=
eT
=
W
=
(2 - 4.)
the required proportion of the area which is to be longitudinal reinforcing steel.
This is the ratio of the cross sectional area of the reinforcing steel to the gross
area of the cross section of the slab.
the ratio of the direct tensile strength of the immature concrete to the average
bond strength between the concrete and steel. The value of this ratio may be
assumed to be 1.0 for plain bars or 0.5 for deformed bars complying with
AS 1302.
diameter of longitudinal reinforcing bar (mm).
the estimated shrinkage strain. The shrinkage strain may be considered to be
in the range 200 to 300 microstrain for a concrete with a laboratory shrinkage
not exceeding 450 microstrain at 28 days when tested in accordance with
AS 1012 Part 13 (after three weeks air drying).
the estimated maximum thermal strain from the peak hydration temperature to
the lowest likely seasonal temperature. A value of 300 microstrain may be
assumed, except when the average diurnal temperature at the time of placing
concrete is 10 ºC or less, when a value of 200 microstrain may be assumed.
the maximum allowable crack width (mm). A value of 0.3 mm should be used
in normal conditions, with 0.2 mm for severe exposure situations.
Equation (2 - 4.) indicates that the proportion of steel is inversely proportional to the bond
strength. In order to provide adequate bond capacity, the longitudinal reinforcing steel
should be detailed as follows:
(i)
Deformed bars should be used.
(ii)
The diameter of the bars should not exceed 20 mm.
(iii) The centre-to-centre spacing of the bars should not be greater than 225 mm.
For deformed bars, Equation (2 - 4.) may be simplified as:
p=
0.25 d b (eS + eT )
W
(2 - 5.)
To ensure against yielding of the steel, the actual steel reinforcement ratio should exceed
the critical value given by the following equation:
p crit =
where:
Pcrit =
f ct (1.3 − 0.2 µ )
f sy − m f ct
(2 - 6.)
the minimum proportion of longitudinal reinforcement to match the design
concrete strength.
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2.8 DESIGN OF RIGID PAVEMENTS
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ROAD DESIGN STANDARD
fct
=
µ
=
fsy =
M
=
The concrete tensile strength (MPa). A value not exceeding 60 % of the 28
day concrete flexural strength (fet) may be assumed.
the coefficient of friction between the concrete base slab and the sub-base;
this varies from 1.0 to 2.0 depending on the type of debonding layer applied to
the sub-base (Clause 8.4.4.2).
the characteristic (95 %) yield strength (0.2 % proof stress) of the longitudinal
reinforcing steel. A value of 430 MPa may be assumed for deformed bars
conforming to AS 1302.
the ratio of the elastic moduli of steel to concrete, Es / Ec. A value of 7.5 may
be assumed.
Equation (2 - 6.) indicates that the critical proportion of longitudinal reinforcing steel
increases more rapidly than the tensile strength of the concrete. The minimum percentage
of longitudinal steel to be provided is 0.6 per cent.
In the design of continuously reinforced pavements, it is important that an optimum amount
of longitudinal steel of suitable type is provided so that crack spacing and crack width can
be controlled.
If the spacing of the cracks is too wide, the cracks themselves will become wide with a
consequent loss in aggregate interlock load-transfer and accelerated corrosion of the steel.
If the spacing between cracks is too small, disintegration of the slab may commence. The
function of the longitudinal steel is to keep the cracks in the concrete tightly closed, thereby
ensuring load transfer across the cracks and also preventing the ingress of water and grit
into the cracks.
The theoretical spacing of cracks in continuously reinforced pavements may be estimated
by the following equation:
f ct2
Lcr =
m p 2 u f b [(eS + eT ) Ec − f ct ]
where:
Lcr =
fct =
m
p
u
=
=
=
fb
=
eS =
eT =
Ec =
(2 - 7.)
the theoretical spacing between cracks
the tensile strength of the concrete (MPa). the ratio of the elastic moduli of
steel to concrete Es / Ec. A value of 7.5 may be assumed.
the area of longitudinal steel per unit area of concrete (ie., steel ratio)
the area of longitudinal steel per unit area of concrete (ie steel ratio)
the perimeter of bar per unit area of steel which may be simplified to 2/radius
of the bar (m-u)
the bond stress (MPa); for mature concrete, and when deformed bars are
used this maybe assumed as 2fct
the estimated shrinkage strain. The shrinkage strain may be considered to be
in the range 200 to 300 microstrain for a concrete with a laboratory shrinkage
not exceeding 450 microstrain at 28 days when tested in accordance with
AS 1012 Part 13 (after three weeks air drying).
the estimated maximum thermal strain from the peak hydration temperature to
the lowest likely seasonal temperature. A value of 300 microstrain may be
assumed, except when the average diurnal temperature at the time of placing
concrete is 100 ºC or less, when a value of 200 microstrain may be assumed.
the modulus of elasticity of concrete (MPa).
This equation indicates that the spacing of cracks is inversely proportional to p, u and fb;
consequently to ensure fine cracks and optimum crack spacings, the percentage
reinforcement and perimeter to area relationship of the bars should be high. A closer
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2.8 DESIGN OF RIGID PAVEMENTS
ROAD DESIGN STANDARD
spacing of cracks is also obtained when the bond stresses are high, therefore the use of
deformed bars is preferred.
Experience with continuously reinforced pavements indicates that the optimum crack
spacing is between 1.0 and 2.0 metres.
Size and spacing of reinforcement may be determined by reference to Figure 2.8.8.
2.8.5.3.2
Transverse Reinforcement
The required area of transverse reinforcing steel (As) in continuously reinforced pavements
is calculated using Equation (2 - 3.).
Note: The following detailing is recommended:
(i)
Deformed bars not less than 12 mm in diameter.
(ii)
A maximum centre-to-centre bar spacing of 750 mm.
ROAD DESIGN PART 2 - PAVEMENT, CAM PW 03-102-99
2.8 DESIGN OF RIGID PAVEMENTS
66-97
ROAD DESIGN STANDARD
Figure 2.8.8 Reinforced Design Chart for Continuously reinforced concrete pavements using
Grade 400 Y steel in accordance with AS 1302-1991
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2.8 DESIGN OF RIGID PAVEMENTS
ROAD DESIGN STANDARD
2.9
OVERLAY DESIGN
2.9.1
GENERAL
The purpose of overlay design is to determine the appropriate thickness of either an
asphalt or granular layer which, when placed on an existing pavement, will overcome the
strength deficiencies of the pavement and retain its own structural integrity throughout the
design period. The adopted system for overlay design is described in Section 2.2.3. One of
the most important aspects of the overlay design system is the identification of the
pavement's deficiencies and needs. The procedures which follow depend on deflection
testing to do this although other tests may be used to supplement the deflection data.
2.9.2
BASIC PRINCIPLES
Experience has shown that the pavement deflection caused by a standard axle load is an
indication of the rate at which permanent pavement deformation will occur under traffic. As
the functional adequacy of the pavement is dependent, in part, on this permanent
deformation, a relationship between the cumulative number of standard axle loads and
measured surface deflection can be developed. Using this relationship a design deflection
can be determined for any particular traffic loading. If actual deflections are kept below this
design deflection, permanent deformation should be kept to an acceptable level.
Where asphalt surfacing exists or is proposed, the level of deflection alone does not give a
reliable indication of the likelihood of fatigue cracking. It has been found that a better
prediction of fatigue performance is obtained from the curvature of the deflected pavement
surface.
The curvature of the deflection bowl is defined by a curvature function which is described in
Section 2.9.3.3.
For any particular design traffic loading there is a tolerable level of curvature function. If the
actual curvatures are kept below this value then an acceptable fatigue life for asphalt will
result. Maximum deflection is used to control fatigue cracking in cemented materials as no
appropriate curvature function has yet been developed for this purpose.
2.9.3
PAVEMENT TESTING
2.9.3.1
Method of Deflection Testing
Two methods of deflection measurement are commonly used. Two common methods used
to measure deflection include the Benkelman Beam and the Lacroix Deflectograph.
Although the principles applied to obtain deflection readings are the same for each device,
the ancillary equipment, such as the vehicles used to apply the test load in each case, may
differ slightly. The relative effect of each device theoretically varies to some extent
depending on the composition of the pavement being tested. The following analysis and
design procedures are applicable to either Benkelman Beam or Deflectograph data.
2.9.3.2
Selection of Test Sites
When deflection testing is being undertaken by the Deflectograph, it is necessary to select
only the transverse location of wheel path positions, because the longitudinal spacing of
test sites is automatically controlled. Wheel path positions should be selected keeping in
mind any proposed changes to the road alignment.
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2.9 OVERLAY DESIGN
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ROAD DESIGN STANDARD
For Benkelman Beam testing, the spacing of individual test sites in a given section of road
is arranged so that the pavement designer can review the general pattern of the deflections
of the whole section of road and define subsections of consistent deflection pattern. An
adequate number of results for each sub-section, at least 10 and preferably upwards of 30,
must be obtained for the purposes of statistical analysis. Normally the spacing used lies
between 5 m and 200 m with 50 m being a common value. Similar comments; apply to the
selection of test sites in wheel path positions.
2.9.3.3
Test Modes
The Deflectograph and Benkelman Beam are capable of obtaining measurements for
several forms of pavement reaction to load. Different procedures or test modes are used
depending on the information required. The two pavement reactions used for analysis in
this Standard are:
(a) Maximum Deflection
For the Deflectograph this is the maximum reading recorded for each test site. For the
Benkelman Beam the "maximum deflection" may be taken as the total deflection minus the
residual deflection.
(b) Deflection Bowl
The deflection bowl is the shape of the pavement surface caused by a load applied to it. It
is not usually measured directly but is estimated using the principle of superposition from a
series of deflection readings taken at a specific point on the pavement as the load
approaches or recedes from that point. For example the deflection in a deflection bowl at a
point 200 mm from the point of maximum deflection, is assumed to be equal to the
deflection of a specific test site when the moving test load is 200 mm away. The shape of
the deflection bowl is therefore obtained by plotting recorded deflection against the
distance to load for a series of positions of the load.
While this is more easily obtained with the Deflectograph it can also be measured without
much difficulty by making relatively inexpensive modifications to a Benkelman Beam.
The Curvature Function CF of a deflection bowl is given by:
CF
where
Do
=
D200 =
=
Do - D200
maximum deflection for a test site
the deflection measured at the site when the test load is 200 mm from the
point at which the maximum deflection was produced (in the direction of
travel)
Figure 2.9.1 shows in schematic form the dimension represented by the curvature
function.
Figure 2.9.1 Curvature Function
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2.9 OVERLAY DESIGN
ROAD DESIGN STANDARD
2.9.3.4
Other Tests
Sometimes it is desirable to supplement deflection tests with other data to identify the
pavement's needs with more confidence, especially for large jobs. Section 2.9.4 contains
some guidance regarding the interpretation of deflection test data.
This information can also be used to select an appropriate supplementary testing program
where necessary.
2.9.3.5
Measurement of Pavement Temperature
Variations in temperature result in significant changes in the stiffness of asphalt and
therefore in the strength of pavements containing asphalt layers. The temperature of
asphalt surfacing must, therefore, be recorded at a depth of 30 mm during deflection
testing so that appropriate adjustments can be made during the analysis and design
phases. If weather conditions vary during the deflection survey, then several
measurements of temperature must be taken and different adjustments made for
corresponding sections of the test length.
2.9.4
PAVEMENT EVALUATION
2.9.4.1
Selection of Homogeneous Sections
In practice the strength of a pavement varies from site to site and it may be necessary to
divide the test section into subsections having relatively uniform deflection and/or curvature
patterns. In selecting homogeneous subsections consideration should be given to the
following:
•
Subgrade type and likely variations
•
Drainage
•
Seepage
•
Topography
•
Construction and maintenance history
•
Pavement composition (particularly overall depth and the thickness of any asphalt or
cemented layer)
The preferred method of obtaining some of this information is by site inspection during
which surface defects should also be recorded to assist in the interpretation of deflection
test results.
Single "characteristic" values of deflection and curvature are then assigned to these
subsections for evaluation purposes. Homogeneous subsections may be considered to be
those whose deflection and curvature values have a coefficient of variation (ie standard
deviation divided by mean) of 0.25 or less.
The characteristic deflection, CD, of a section or subsection of pavement is a value
calculated from the test deflections and equal to the average deflection µ plus a factor f
times the standard deviation, S.
Thus
CD = µ + f S
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2.9 OVERLAY DESIGN
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ROAD DESIGN STANDARD
where f is selected by the designer to provide a suitable characteristic design deflection.
This should correspond to the degree of reliability required in the rehabilitation treatment.
Recommended values of f, given in Table 2.9.1 will generally be appropriate. However, it
must be appreciated that because of the widely different conditions which can apply to
particular roads in the one category, adoption of another value may be necessary.
The Characteristic Curvature of a length of pavement is equal to the mean of the test
curvature functions.
Table 2.9.1 Recommended Values For “ f “
Road Functional Class
F
1 and 6
2.00
2, 7, 8 and 9
1.65
3, 4 and 5
1.30
For definition of classes see Appendix A.
2.9.4.2
% of all deflection which will be
covered by the characteristic
deflection
97.5
95
90
Characteristic Site Temperature
Because the strength of asphalt varies with temperature, the performance of a pavement
which contains asphalt will reflect the temperature regime at the locality in question.
A site may be characterised by a weighted mean annual pavement temperature (WMAPT)
for the purpose of analysing deflections and designing asphalt overlays.
Usually deflection testing will be carried out when the pavement is at a temperature other
than the WMAPT. In these cases an adjustment must be applied to convert the measured
deflections to values representative of the pavement response at the WMAPT.
2.9.4.3
Adjustment of the Characteristic Deflection and Characteristic Curvature to Account
for the Testing Temperature
The method for adjusting measured deflections to allow for temperature is as follows.
Step 1
fT =
Determine the temperature factor fT where
Measured temperature at time of testing
Assumed WMAPT for the site
Step 2
From Figure 2.9.2 determine the Deflection Adjustment Factor considering the
existing asphalt thickness. No temperature adjustment is required if the pavement does not
contain asphalt.
Step 3
Divide the characteristic deflection by the Deflection Adjustment Factor.
The Characteristic Curvature function is adjusted for temperature using a similar method to
that described for deflection adjustment.
The temperature adjusted curvature function is calculated by dividing the measured value
by the Curvature Adjustment Factor from Figure 2.9.2.
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Figure 2.9.2 Temperature Correction for deflection and curvatures.
2.9.4.4
Adjustment of Deflection Data to Account for Seasonal Moisture Variations
In some localities a slight increase in deflection during or soon after wet seasons is
common due to higher moisture contents under the pavement at these times. However the
seasonal effect of moisture is not a straightforward rainfall / deflection relationship.
Account must be taken of changes in moisture regime which includes surface infiltration,
permeability of the pavement layers and subgrade, evaporation and drainage conditions at
the site. The evaporation and drainage factors limit the quantity of water available to
infiltrate the subgrade while the permeability controls the rate of infiltration and
consequently the time lag between the incidence of rain and Its effect on deflection.
There are insufficient data available to enable a general relationship to be developed for
the effect of seasonal moisture variations on deflections. It is suggested that site specific
data be obtained where possible and used to account for this phenomenon.
2.9.4.5
Design Traffic
The design traffic to be used for the evaluation of existing pavements and for overlay
design should be based on a design period which may be defined as the time from when
rehabilitation and/or testing occurs until further treatment is necessary. The method to be
used for calculating the design traffic is the same as that described in Section 2.5.
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2.9.4.6
Performance Criteria (Design Deflection and Curvature)
The adopted relationship between design deflection and traffic loading is contained in
Figure 2.9.3. Curve 1 controls the rate of permanent deformation in the pavement and
subgrade and may be used for all pavements regardless of surfacing type, as the fatigue
performance of asphalt surfacing is controlled by means of the curvature criteria. Curve 2 is
intended to be used to inhibit cracking in pavements with cemented bases in lieu of a
separate curvature function as none has been developed to date. The design deflection
criteria may be applied to any locality regardless of the temperature regime. Curves 1 and
2 are considered to define deflection levels associated with satisfactory pavement
performance for the relevant traffic loading.
Figure 2.9.3 Design Deflection Levels by Design Traffic (ESA)
The adopted relationship between curvature and traffic loading is contained in Figure 2.9.4.
It should be noted that it is applicable to dense graded asphalt mixes. There is insufficient
field data available to provide fatigue performance criteria for other mix types such as open
graded asphalt.
2.9.4.7
Determination of Pavement Needs
In many instances the needs of an existing pavement can be readily identified by an
experienced observer. Deflection testing and the analyses described previously
supplement these observations. Experience gained in the assessment of pavement
conditions by means of deflection testing, particularly when test sites are closely spaced,
has enabled certain general guidelines to be established. Some of these are listed below to
assist the designer.
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Figure 2.9.4 Design Curvature Function Design Traffic (ESA)
(a) very high deflections (more than 1.5 mm) indicate weak subgrade conditions, and low
deflections a strong subgrade.
(b) high values of curvature function indicate a weak or very thin pavement, or a
pavement with cracked surfacing, and low curvature functions a strong pavement.
(c) substantially different deflections and curvature functions between left and right test
wheel paths may indicate the presence of a former pavement widening or verge water
ingress.
(d) a high deflection peak near a pavement edge may be caused by poor local drainage
such as a blocked subsurface drain.
(e) a series of high deflection peaks across all test wheel paths sometimes indicates a
poorly back filled culvert or service trench or a poorly drained junction between two
pavement types.
(f)
a generally low but extremely variable deflection pattern may indicate an old failing
pavement which may be cracked or poorly patched.
(g) a relatively widely spread peak of high deflections across all test wheel paths may
indicate a poorly drained cut-fill area.
(h) residual deflections - generally the Benkelman Beam records a positive residual
deflection of up to 0.15 mm. This is thought to be of little concern. A substantial
positive residual implies a weak pavement, probably poor compaction. A negative
residual deflection may indicate that shoving is taking place in the pavement and the
situation requires further investigation, but is also common in pavements with
cemented layers where the beam supports are within the deflection bowl.
A well defined area of low deflections measured by the Deflectograph in a section
containing otherwise moderate to high deflections may indicate unstable pavement
material.
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2.9.5
SELECTION OF THICKNESS
2.9.5.1
Granular Overlays
Granular overlays are usually placed on existing granular pavements. If the existing
pavement has a bituminous surfacing then it is usually desirable to break the seal to
ensure that water is not trapped in the overlay. The selection of overlay thickness is based
on the characteristic deflection of the existing pavement and the reduction required to
reach the design deflection. Based on available field data it may be assumed that a 6
percent reduction in deflection will result for each 25 mm of granular overlay thickness. The
required overlay thickness may be obtained directly by using Figure 2.9.5.
Figure 2.9.5 Effect of Granular overlay on Deflection
These relationships apply to cases where no other major improvements are made at the
time of placing the overlay such as if extensive drainage works were carried out.
2.9.5.2
Asphalt Overlays
If it is proposed to provide additional pavement strength or improved riding quality by
means of an asphalt overlay, the following procedure should be used to select the
appropriate overlay thickness. In the case of overlaying to improve riding quality, the
thickness of asphalt required may need to be thicker than determined by this procedure to
satisfy shape requirements. The procedure is summarised in Figure 2.9.6 in flow chart
form.
2.9.5.3
Characteristic Deflection (adjusted for temperature) Exceeds the Design Deflection
The overlay thickness required is the maximum of those needed to satisfy the deflection
criteria and also the fatigue criteria. Figure 2.9.7 is used to select the overlay thickness TD
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2.9 OVERLAY DESIGN
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needed to reduce the Characteristic Deflection to the Design Value. Note that
Characteristic Deflection must first be adjusted for temperature as described in Section
2.9.4.3 if the existing pavement has an asphalt surface.
Figure 2.9.6 Effect of Asphalt Overlay on deflection
Similarly F is used to select the overlay thickness TC needed to reduce the curvature to the
tolerable value. The appropriate overlay is then the maximum of TD and TC.
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Figure 2.9.7 Pavement Analysis and Asphalt Overlay Design
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2.9.5.4
Characteristic Deflection (adjusted for temperature) Less Than Design Deflection
If the existing pavement does not have an asphalt surface then no asphalt is required for
strengthening purposes.
If it is proposed to place an asphalt overlay for other reasons, such as for regulation of
surface levels, or if the existing pavement has an asphalt surface, then a check must be
made to ensure that the design curvature function is not exceeded.
The minimum overlay thickness required to reduce the characteristic curvature to the
tolerable value may be obtained from Figure 2.9.8.
Figure 2.9.8 Reduction in D0 - D200 due to Asphalt Overlay
2.9.5.5
Adjustment of Overlay Thickness to Allow for Locality Temperature
The overlay thicknesses given in Figure 2.9.7 and F apply to a locality where the WMAPT
is 25 ºC. Where higher WMAPT's apply, a given thickness of asphalt will be less effective
in reducing deflections because of its reduced stiffness, and for temperatures below 25 ºC
the reverse will hold. Therefore the overlay thickness TD, appropriate to a particular site
should be calculated by multiplying the value obtained from Figure 2.9.7 by a factor
obtained from Figure 2.9.9.
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Figure 2.9.2 Overlay Adjustment Factors
The required overlay thickness TC, obtained from Figure 2.9.8 need not be adjusted to
allow for temperature because although curvature reduction will be less at high
temperatures, the asphalt will have a greater fatigue life which provides a compensating
effect. The greater curvature reduction at low temperatures will also be compensated by a
relatively lower fatigue life.
2.9.5.6
Example of Asphalt Overlay Design
A section of pavement which contains 50 mm of asphalt situated in a locality where the
WMAPT is 30 ºC produced the following reaction to load when deflection testing was
carried out using the Deflectograph. The pavement temperature at the time of testing was
20 ºC.
Given that
• Calculated Characteristic Deflection = 1.20 mm
• Characteristic Curvature = 0.26 mm
• Design Traffic loading = 5 x 101 ESA
Then
• Design Deflection (from
Figure 2.9.3) = 0.95 mm
• Design Curvature (from
Figure 2.9.4) = 0.13 mm
• Temperature factor = Tmeasured / Tstandard = 20 / 30 = 0.67
• From Figure 2.9.2 the deflection adjustment factor =0.96
• Temperature adjusted characteristic deflection = 1.20 / 0.96 = 1.25 mm
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• Overlay thickness TD required to reduce the characteristic deflection to the design
deflection (when WMAPT is 25º C) from Figure 2.9.3 = 70 mm.
• Overlay Adjustment factor for WMAPT 30 ºC from Figure 2.9.9 = 1.13
• Overlay thickness To required to reduce the characteristic deflection to the design
deflection for WMAPT 30 ºC = 70 X 1.13 = 80 mm
CHECK FOR FATIGUE CRACKING
• From
Figure 2.9.2 the curvature adjustment factor = 0.96
• Temperature adjusted characteristic curvature = 0.26 / 0.96 = 0.27 m
• Overlay thickness TC required to reduce the characteristic curvature to the design
curvature from F = 100 mm
• No adjustment is made to TC to account for temperature.
• Required overlay thickness is the larger of TD and TC = 100 mm ie. the overlay
thickness required to satisfy both permanent deformation and asphalt fatigue criteria.
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APPENDIX A
DEFINITIONS OF TERMS
Annual Average Daily
Traffic (AADT)
The total yearly traffic volume divided by 365.
California Bearing Ration
(CBR)
The ration expressed as a percentage between a test load
and an arbitrarily defined standard load. This test load is
that required to cause a plunger of standard dimensions to
penetrate at a specified rate into a specifically prepared soil
specimen.
Commercial Vehicle
A vehicle having at least one axle with dual wheels and/or
having more than two axles.
Course
One or more layers of the same material within a pavement
structure.
Curvature Function
Of a deflection bowl is the difference in maximum deflection
at a test site and the deflection at a point 200 mm from the
point at which the maximum deflection was produced (in
the direction of travel).
Cemented Materials
Those produced by addition of cement, lime or other
hydraulically binding agent to granular materials in
sufficient quantities to produce a bound layer with
significant tensile strength.
Deflection
The vertical elastic (recoverable) deformation of a
pavement surface between the tyres of a standard axle.
A period considered appropriate to the function of the road.
It is used to determine the total traffic for which the
pavement is designed.
Design Period
Design Subgrade Level
(DSL)
The level of the prepared formation after completion of
stripping and excavation or filling and upon which the
pavement is to be constructed. (Design Subgrade Level =
Finished Surface Level-Nominated Pavement Thickness).
Layer
The portion of a pavement course placed and compacted
as an entity.
Modified Materials
Granular materials to which small amounts of stabilising
agent have been added to improve their performance (e.g.
by reducing plasticity) without causing a significant
increase in structural stiffness. Modified materials are
considered to behave as unbound materials.
Modulus of Subgrade
Reaction
The slope of the straight line drawn from the origin to a
given point on the stress deflection curve obtained from a
plate bearing test.
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ROAD DESIGN STANDARD
Pavement (Structure)
The portion of the road, excluding shoulders, placed above
the design subgrade level for the support of, and to form a
running surface for, vehicular traffic.
Permeability Reversal
Occurs at a pavement layer interface when the coefficient
of saturated permeability of the upper layer is at least 100
times greater than that of the layer below it.
Roughness
The roughness of the pavement surface in counts/km as
measured by a Roughness Meter.
Shoulder
The portion of the road contiguous and flush with the
pavement.
Stabilisation
The treatment of a road pavement material to improve it or
to correct a known deficiency and thus enhance its ability to
perform its function in the pavement.
Standard Axle
Single Axle with dual wheels loaded to a total mass of 8.2 t.
Traffic Lane
The portion of a carriageway allotted for use of a single
lane of vehicles.
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APPENDIX B
PAVEMENT LIFE MULTIPLIERS
To utilise Pavement Life Multipliers in a design procedure, it is necessary to know the
day/night traffic spectrum.
If PD = % of ESAs during day (7 am to 9 pm)
then (100- PD) = % of ESAs at night (9 pm to 7 am)
PLM =
100
PD
+
100 - PD
PLM D
PLM N
where PLM = Pavement Life Multiplier total traffic
To input the Pavement Life Multiplier into a design procedure, the normal traffic loading N
(in ESAs) is divided by the Pavement Life Multiplier to give a modified traffic loading NA.
This modified loading is then used for any part of the design procedure relating to the
asphalt layers. (eg to check tolerable deflections for pavements surfaced with asphalt).
NA = N/PLM
NA = Design Traffic Loading for asphalt (ESAs)
N = Standard Design Traffic Loading (ESAs)
The method of calculation of Pavement Life Multipliers is given in detail in Youdale (1984).
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ROAD DESIGN STANDARD
APPENDIX C
METHODS FOR CHARACTERISING INITIAL DAILY TRAFFIC
Calculate initial daily ESAs as follows:
Ne =
NA1J F E1J +
j
NA2J F E2J +
j
NA3J F E3J +
j
NA4J F E4J
j
Where NAij is the average daily number
of axles (in the first year) of type I, carrying a load of magnitude j and FEij is the number of
ESAs for each pass of the axle group I carrying load j with the summations being taken
over the appropriate load ranges. Values for FEij are contained in Table C1.
Table C1 – Number of ESA’s per Axle Group
Load on axle
group kN
20
3040
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
210
220
230
240
250
260
270
280
290
Single Axle
Single Tyre
0.02
0.10
0.32
0.79
1.6
3.0
5.2
Number of ESA’s
Single Axle
Dual Axle
Dual tyres
Dual Tyres
0
0
0.02
0
0.06
0.01
0.15
0.02
0.32
0.04
0.59
0.07
1.0
0.12
1.6
0.20
2.4
0.30
3.6
0.44
5.1
0.62
0.86
1.2
1.5
2.0
2.5
3.2
3.9
4.8
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APPENDIX C
Tri Axle
Dual Tyres
0
0
0
0.01
0.01
0.02
0.04
0.06
0.09
0.14
0.19
0.27
0.36
0.47
0.61
0.78
0.98
1.2
1.5
1.8
2.2
2.6
3.1
3.6
4.3
5.0
5.7
6.6
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APPENDIX D
DETERMINATION OF DESIGN MOISTURE CONTENT
D.1
Introduction
These procedures may be used to estimate design surged moisture conditions. Two
procedures are given and these are based on field studies which indicate that a reasonable
prediction of moisture conditions in a surged may be made by assessing the conditions of
existing similar subgrades in the vicinity and/or the moisture conditions in natural ground
below the zone of seasonal influence. A flow chart for the two methods is given in Figure
D1.
In many cases a detailed investigation to determine design moisture content is not
warranted and this applies for example where local policies, reflecting local experience,
define test conditions. As a particular example there are several circumstances where
saturated conditions may be anticipated (eg below ground water tables, areas of
inundation) and tests may be carried out under soaked conditions without further
evaluation.
D.2
Prediction Of DMC From Existing Roads
D.2.1
Considerations in Use of Method
This procedure may be used to predict DMC provided the following features are similar for
the road being designed and the existing roads.
a)
Soil Density
The effect of subgrade density on moisture content is difficult to establish and for this
reason, efforts should be made to measure the existing moisture content at sites where the
in-situ density corresponds closely with that proposed for the new pavement. Where
differences occur, particularly when the existing density is greater that the proposed
density, care should be exercised and an adjustment made on the following bases:
• Existing density less than proposed density: no adjustment.
• Existing density greater than proposed density:
FMC = FMCe + 12.5 (FD-PD)
where
PD
= Proposed subgrade density (t/m3)
FD
= Existing subgrade density (t/m3)
FMCe
= Existing subgrade gravimetric moisture content(%)
applies for PD and FD > 1.1 t/m3.
(b) Drainage Conditions
The following drainage conditions for the existing and proposed pavements should
correspond:
• Position of catch drains, table drains and subgrade pavement drains
• Shoulder crossfall and condition (eg vegetated, sealed)
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• Longitudinal grade
• Formation profile (boxed, full width)
• Cut or fill
When selecting sites for measuring moisture conditions, care should be taken to ensure
measurements are taken well away from any trees as they can greatly influence subgrade
moisture conditions. This is particularly true during the spring and summer growth seasons.
(c)
Position of the Water Table, Climate and Land
The depth of permanent ground water, climatic conditions and topography of the existing
and proposed pavements should be similar.
(d) Pavement Composition
Where the pavement is composed of a number of courses above the subgrade and the
coefficient of saturated permeability of the subgrade is estimated to be at least 100 times
less than that of the course above it (permeability reversal), consideration should be given
to assessing the subgrade on the basis of soaked conditions if rainfall conditions warrant.
For accurate prediction of DMC from tests on existing roads, consideration should be given
to the following:
i)
Time Since Completion of Seal
If the period of sealing is not less than two years, the effect of time on the subgrade
moisture content can usually be neglected. If the age of the seal is less than two years, this
method may not be reliable.
ii)
Soil Type
The field Moisture Content (FMC) of the subgrade in the proposed pavement may be
estimated from the existing subgrade using the following equations:
Proposed
Existing
Subgrade
Subgrade
Where:
OMC
=
Optimum Moisture Content for standard compactive effort,
PL
=
the Plastic Limit.
The equation expressed in Plastic limit is only applicable to fine grained soils, ie more than
80 % passing a 425 µm sieve.
The values of the FMC obtained from the above two equations should be averaged.
D.2.2
Details of Procedure
The procedure consists of the following steps.
(a) Select sections of the existing road with conditions which correspond to those which
will exist in the road being designed.
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(b) Within the sections chosen for investigation, select a number of sites for sampling.
The longitudinal location of the sites should be in a random pattern and appropriate to
the accuracy of the prediction required. The lateral location of sites will normally be in
the outer wheel paths. A check on the moisture condition of the inner wheel path
should be made to ensure that the design moisture content is based on the correct
value. If the cross section of the road differs markedly from that proposed to be used,
judgement will be required in the selection of the lateral position of sampling to ensure
correspondence of conditions.
(c) For each section, sample the subgrade at the sites selected and also the
corresponding proposed subgrade. Sampling of the existing road should be at a depth
of approximately 300 mm below subgrade. Measure the field moisture contents and
carry out classification tests.
(d) At each site on the existing road, determine the field moisture content (FMC).
(e) Derive the ratio FMC / OMC or, for a fine grained soil, FMC / PL.
(f)
Analyse these ratios statistically for all sites in the section and adopt the 90 th
percentile (mean + 1.3 standard deviations). Other percentile values may be adopted
if considered more appropriate.
(g) Multiply the 90 th percentile values of the above ratios respectively by the OMC (or
PL) of the proposed subgrade.
(h) The DMC may be obtained by adopting the values derived in (g) with corrections
applied for seasonal variations and edge effects. If data on seasonal variations is not
available, but a regular rainfall pattern exists, the indications are that the worst
moisture conditions in subgrades occur at, or shortly after, times when rainfall is high
and evaporation is low.
D.3
Prediction Of DMC By Site
D.3.1
Investigation
In cases where a satisfactory degree of correspondence between the pavement
characteristics of existing and proposed pavements cannot be established, the following
procedure can be adopted to estimate the DMC of the proposed subgrade:
(a) Delineate the terrain through which the road will pass into units of similar
physiographic features. This can be done from either aerial photographs, maps or field
inspection. If is assumed that terrain units of the same type will have the same
subgrade moisture conditions.
(b) Take samples at selected positions in units representative of each terrain type at a
level below the zone of seasonal variation (not less than two metres) where the water
table is below this zone and at a depth of 300mm above the water table if this occurs
at a depth of less than two metres. The number of units taken as representative of
each terrain type and the number of samples taken, will depend on the precision of the
estimate required. Representative samples of the subgrade material proposed should
also be obtained if the above samples are not appropriate.
(c) Determine the FMCs and carry out classification testing on all samples.
(d) Derive the ratio FMC/OMC and for a fine grained soil FMC/PL. (This is not necessary
if the subgrade will consist of the same material being sampled at depth).
(a) Analyse these ratios statistically (on FMC only if material identical to subgrade) for
each sample in the terrain unit and adopt the 90th percentile value (mean +1.3
standard deviation). Other percentiles may be used if considered more appropriate.
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ROAD DESIGN STANDARD
(f)
Multiply the 90th percentile values of the above ratios respectively by the OMC and
PL of the proposed subgrade.
(g) The DMC may be obtained by adopting the values derived in (f) (and (e) when the
subgrade is similar to moisture content samples) with corrections applied for edge
effects.
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APPENDIX E
THE EFFECT OF ASPHALT THICKNESS ON THE FATIGUE LIFE OF
ASPHALT SURFACED PAVEMENTS
Some of the example design charts which are contained in this Standard indicate that for a
given design traffic, asphalt stiffness, thickness of granular or cemented base or subbase,
and subgrade stiffness, two asphalt thicknesses provide the same theoretical fatigue
performance. The reason for this can be explained by examining the relationship between
asphalt thickness and horizontal strain at the bottom of the asphalt induced by a standard
load for a given composition of underlying material. A typical relationship is illustrated in
Figure E.1.
As asphalt thickness is increased horizontal strain increases from a negative value (ie
compression) at zero asphalt thickness to low positive values (tension). Asphalt layers
which are relatively thin and represent only a small proportion of the overall pavement
stiffness offer little resistance to the flexure of the underlying structure. In this range of
thickness the greater the depth of asphalt the greater the magnitude of tensile strain
induced at its underside.
With further increases in thickness the asphalt layer begins to exert an influence on the
total pavement structure. A peak strain level is reached usually in the range of 40-80 mm
for highway traffic loading. Further increases in asphalt thickness reduce the flexure of the
structure and the resulting strain in the asphalt.
Figure E1 Asphalt Strain vs Thickness
Therefore there are generally two asphalt thicknesses that give the same magnitude of
strain, one to the left of the maximum point on the curve and one to the right.
The discontinuity that occurs at the broken line shown on some of the charts represents the
pavement composition where the overall life of the pavement is determined equally by
asphalt fatigue and subgrade strain criteria.
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APPENDIX E
ROAD DESIGN STANDARD
APPENDIX F
EXAMPLES OF USE OF DESIGN PROCEDURES FOR RIGID
PAVEMENTS – SHEET 1
CALCULATION OF CONCRETE PAVEMENT THICKNESS
Project: _____________________________________________
Date: ____________
Source of Load Data ......................... ________________
Characteristic (28 day)
CRC/Dowelled joints ........................ yes _____ no _____
Flexural Strength f’ of ________ MPa
Concrete Shoulder............................. yes _____ no _____
Subgrade CBR ________ %
Design Period ............................................. _________ years
Sub-base Thickness & Type_______ mm
Design Traffic ................................... _________ CV axle groups
Effective CBR ________ %
Load Safety Factor LSF .................... _________
TRIAL BASE THICKNESS
________ mm
Fatigue Analysis
Axle
Load
(kN)
Design
Load/Tyre
(kN)
Expected
Repetitions
Allowable
Repetitions
Fatigue
(%)
Erosion Analysis
Allowable
Repetitions
Damage
(%)
SINGLE AXLES / SINGLE WHEELS (SS)
Equivalent Stress ______
Stress Ratio Factor ______ Erosion Factor ______
Single-steer axles
Twin-steer axles
SINGLE AXLES / DUAL WHEELS (SD)
Equivalent Stress ______
Stress Ratio Factor ______ Erosion Factor ______
Non-steer single axles
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APPENDIX F
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APPENDIX F
EXAMPLES OF USE OF DESIGN PROCEDURES FOR RIGID
PAVEMENTS – SHEET 2
Fatigue Analysis
Axle
Load
(kN)
Design
Load/Tyre
(kN)
Expected
Repetitions
Allowable
Repetitions
Fatigue
(%)
TANDEM AXLES / DUAL WHEELS (TAD)
Equivalent Stress ______
Stress Ratio Factor ______
Non-steer double axles
Erosion Analysis
Allowable
Repetitions
Damage
(%)
Erosion Factor ______
TRI - AXLES / DUAL WHEELS (TRD)
Equivalent Stress ______
Stress Ratio Factor ______
Erosion Factor ______
Non-steer triple axles
TOTAL Fatigue
%
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APPENDIX F
ROAD DESIGN STANDARD
APPENDIX F
EXAMPLES OF USE OF DESIGN PROCEDURES FOR RIGID
PAVEMENTS – SHEET 3
CALCULATION OF EXPECTED REPETITIONS
Project ____________________________________________ Date: _______
Load
(Axle kN)
Proportion
Of Loads X
(%/100)
Proportion
Of Axle
Group (%/100)*
X
Design Traffic
CV Axle Groups
=
Expected
Repetitions
SINGLE AXLES / SINGLE WHEELS
Single-steer axles
Twin-steer axles
SINGLE AXLES / DUAL WHEELS
Non-steer single axles
*
**
A constant for each axle type.
A constant for the design (CV = commercial vehicles).
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APPENDIX F
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APPENDIX F
EXAMPLES OF USE OF DESIGN PROCEDURES FOR RIGID
PAVEMENTS – SHEET 4
Load
(Axle
kN)
Proportion
Of Loads
X
(%/100)
Proportion
Of Axle
Group (%/100)*
X
Design Traffic
CV Axle Groups
=
Expected
Repetitions
TANDEM AXLES / DUAL WHEELS
Non-steer double axles
SINGLE AXLES / DUAL WHEELS (TRD)
Non-steer triple axles
93-97
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APPENDIX F
ROAD DESIGN STANDARD
APPENDIX G
Prakas No. 377, Dated 11th October, 2001
ROAD DESIGN PART 2 - PAVEMENT, CAM PW 03-102-99
APPENDIX G
94-97
ROAD DESIGN STANDARD
Prakas No. 377, Dated 11th October, 2001 (Cont.)
95-97
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APPENDIX G
ROAD DESIGN STANDARD
APPENDIX H
Decision No. 328, Dated 13th November, 1998
ROAD DESIGN PART 2 - PAVEMENT, CAM PW 03-102-99
APPENDIX H
96-97
ROAD DESIGN STANDARD
Decision No. 328, Dated 13th November, 1998 (Cont.)
End of Document
97-97
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APPENDIX H