10/12/2011
Contents
Engineers Ireland South‐east Region
Kilbride Theatre, Ormonde Hotel, Kilkenny
• Introduction to AGEC • Types of Geotechnical Risk (Typical)
• Reasons for Management of Geotechnical Risk ‐ General and Statutory
Management of Geotechnical Risk • Typical Examples of Geotechnical Risk • Management of Geotechnical Risk: Risk Register
Dr Paul Jennings
Applied Ground Engineering Consultants (AGEC) Ltd www.agec.ie
• Questions and Answers.
Thursday 1 December 2011
Introduction to AGEC
• AGEC is an independent Irish company formed in April 2001 to provide geotechnical consultancy services
• AGEC
AGEC provides specialist geotechnical engineering advice to provides specialist geotechnical engineering advice to
consultants, contractors, private clients and local authorities, particularly for infrastructure and renewable energy projects • Main areas of geotechnical expertise include:
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Geotechnical Due Diligence & Management of ground investigations Foundation design Design of retaining structures Earthworks design Stability assessment of soil & rock slopes Procurement and management Site supervision
Specialist technical advice
Contractual advice
Expert witness advice.
Typical Geotechnical Risks
• Slope Instability
• Settlement
• Subsidence (sub‐surface voids)
• Groundwater
• Chemically reactive ground
• Contamination
• Unforeseen ground conditions (extent, type)
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di i
(
)
• Inadequate geotechnical investigation
• Inappropriate design.
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Reasons for Management of Geotechnical Risk ‐ General Reasons for Management of Geotechnical Risk Health and safety, environment, quality, programme and cost
• Ground conditions are always uncertain
• Compliance with standards reduces ground risk but does not eliminate ground risk
• Ground related risk generally have a significant impact
‐
Highly variable nature of the ground
‐
Soil/rock mechanics engineering is good but accuracy can be poor
‐
Multiple hazards (shear failure, deformation, groundwater, chemically reactive, obstruction, etc)
‐
Unforeseen ground conditions in early stages of works (delays following works)
In
ncrease project cost and d
delay
‐
Total Increase in Construction
n Cost (%)
100
• Ground related risks affect and influence many parts of a project
80
60
Typical upper bound
40
20
0
0
1
2
3
4
5
6
7
8
9
10 11
Ground Investigation Cost/Tender Construction Cost (%)
12
Reduced cost on geotechnical studies
Source: UK Highways Agency projects (1994)
Reasons for Management of Geotechnical Risk –
Statutory Framework (PSDP)
Reasons for Management of Geotechnical Risk ‐
Statutory Framework (Designer)
• Under Safety, Health and Welfare Regulations (1) there is a requirement to appoint a Project Supervisor Design Process (PSDP)
• Duties of PSDP with respect to risk/hazard management:
D ti
f PSDP ith
t t i k/h
d
t
• Under Safety, Health and Welfare Regulations (1) the designer has defined duties
• Duties of designer with respect to risk/hazard management:
D i
fd i
ih
i k/h
d
– Identify hazards arising from the design/technical/organisational/planning/time related aspects of the project
– Where possible eliminate the hazards or reduce the risk
– Communicate necessary control measures, design assumptions, or remaining risks to the PSCS (so they can be dealt with in the S&H Plan)
– Prepare S&H plan for any project where there is a Particular Risk(2) (or construction takes >500 person days or 30 working days)
– Role extends beyond design stage in temporary works during construction
• Other duties of PSDP:
–
–
–
–
Organise co‐operation between designers
Prepare a safety file for the completed structure and give it to the client
Notify the Authority and client of non‐compliance with any written directions issued
Issue directions to designers or contractors or others
– Identify any hazards that your design may present during construction and subsequent maintenance
– Where possible eliminate the hazards or reduce the risk – Communicate necessary control measures, design assumptions or remaining risks to the PSDP so they can be dealt with in the S&H Plan
• Other duties of designer:
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–
–
–
Co‐operate with other designers and the PSDP or PSCS
Take account of any existing safety and health plan or safety file
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y
Comply with directions issued by the PSDP or PSCS
Where no PSDP has been appointed, inform the client that a PSDP must be appointed
(1) Safety, Health and Welfare at Work (Construction) Regulations 2006 (S.I. No. 504 of 2006)
(2) For example with respect to the ground: Schedule 1, Item 1(b) and (c) state particular risk due to (b) burial under earthfall where the risk is particularly aggravated by the nature of the work or processes used or by the environment at the place of work
(1) Safety, Health and Welfare at Work (Construction ) Regulations 2006 (S.I. No. 504 of 2006)
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Slope Instability ‐ Landslides
Slope Instability ‐ Landslides and Run‐out
Peat
Rock with thin soil cover Till (sandstone)
Till (metamorphic)
Slope Instability – Peat Failures
Slope Instability – Peat Failures
Ballincollig failure (2008)
Multiple tension cracks
200m
Partially detached peat raft
Main debris track
General slope inclination 4 degrees
Temporary road construction in peat Area of worked blanket peat
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Slope Instability – Peat Failures
Slope Instability – Predicting Peat Failure
R314 road
Glenglassera failure (1986)
Deposition area/debris track
General slope inclination 5 degrees
1550m
Large partially detached peat raft
Road layout
Main debris track
Headward extension into forestry
Tension cracks
Slope Instability
Wind turbine location
Hydrological/environmental buffer
Slope Instability – Anecdotal Information
Preliminary Stage
• Identify general geotechnical conditions (eg initial walkover survey)
Certain soil types more prone to instability (eg peat)
• Certain soil types more prone to instability (eg peat)
• Examine available landslide databases
• Areas of previous failures indicate possible future failure (eg. anecdotal information)
• Avoid steep ground (but peat will fail at 4 degrees!)
• Avoid run‐out tracks of landslide debris (several kilometres!)
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g
Detailed Design Stage
• Detailed walk‐over survey
• Detailed ground investigation
• Detailed analysis and stability assessment
• Appropriate design, mitigation, zonation
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Settlement and Subsidence ‐ Karst
Settlement and Subsidence – Karst Example
E i ti
Existing ground surface
d f
Soil arch eventually collapses causing subsidence at surface
Drop out sinkholes form as a cavity migrates up from rockhead with time as material is carried from the soil into the limestone rock by movement of groundwater
Soil
Rockhead
Void in limestone rock
Settlement and Subsidence – Karst Example
Limestone
Settlement and Subsidence – Mine Collapse Example
Plan of aqueduct
SUBSURFACE LASER SCANNING LTD.
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Settlement and Subsidence
Chemically Reactive Ground
Preliminary Stage
• Examine available databases (GSI karst, EPA soils maps, mining records, anecdotal information)
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/
g/
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( g
• Identify general karst/mining/soft ground conditions (eg walkover survey)
• Certain soil/rock types more prone to settlement/subsidence
• Areas of previous subsidence indicate possible future problems
• Avoid areas of high potential settlement/subsidence (may not be practical)
• Associated risks – flooding, radon
Detailed Design Stage
•
•
•
•
Chemically reactive ground can be either:
• Brown field sites (eg industrial sites, landfills)
• Green field sites (eg naturally occurring)
Green field sites (eg naturally occurring)
Common potential issues:
• Acidity (pH value)
• Chlorides
• Sulphates and sulphides
• Industrial/domestic contamination
Industrial/domestic contamination
Detailed walk‐over survey
Detailed ground investigation, geophysics, sub‐surface surveying
Detailed analysis and assessment of settlement/subsidence
Appropriate foundation design, mitigation and zonation
Chemically Reactive Ground
Chemically Reactive Ground
Sulfides
• Well known sulfide is Iron Sulfide (FeS2) or “pyrite”
• Pyrite has received much press in recent years because the mineral has been found in the sub‐floor fill of damaged houses in North County Dublin
• Most limestone and calcareous mudstone rocks in Dublin and neighbouring counties contain pyrite
• Oxidisation of pyrite can have the following negative consequences
• Groundwater can be polluted with sulfuric acid
G
d
b
ll d i h lf i
id
• Sulfuric acid can attack concrete and steel
• Concrete may be subject to sulfate attack
• Growth of expansive crystals (gypsums) heave
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Chemically Reactive Ground
Chemically Reactive Ground
Chemically Reactive Ground
Inadequate Geotechnical Investigation Preliminary Stage
• Examine available databases (GSI, EPA soils maps, historical records)
• Identify general areas of reactive ground conditions (eg initial walkover survey)
• Certain soil/rock types prone to producing reactive ground conditions • Anecdotal information
• Areas of previous problems indicate possible future problems
• Avoid areas of high potential (may not be practical)
Large ‐scale peat slide
Detailed Design Stage
Detailed Design Stage
• Detailed walk‐over survey and mapping of exposures
• Detailed ground investigation including petrographic analysis
• Appropriate foundation design, specification and mitigation
Original: 731 GI locations (mostly probes) in 345ha site = 2 per ha
Final: 5808 GI locations in 345ha site = 17 per ha
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Inappropriate Design ‐ Pit Collapse
Inadequate Geotechnical Investigation • Employee killed when trial pit collapsed
• Lone working in unsupported pit
• Aim of geotechnical investigation: “to establish the soil, rock and groundwater conditions, to determine the properties of the soil and rock, and to gather additional relevant knowledge about the site.”
• Prosecution of Employer under 2007 Corporate Manslaughter Act (UK) p y
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g
( )
• Spacing and depth of ground investigation:
S i
d d th f
di
ti ti
Source
IS EN 1997‐2: 1997 (Eurocode 7, Part 2, Annex B3)
BS5930: 1999, Code of Practice for Site Investigations, clause 12.6 Spacing
Highways Agency (1997), clause 2.30
Quotation/Reference
“ for high‐rise and industrial structures, a grid pattern with points at 15 m to 40 m distance”
“for linear structures (roads, railways, channels, pipelines, dikes, tunnels, retaining walls), a spacing of 20 m to 200 m”
“Although no hard and fast rules can be laid down, a relatively close spacing between points of exploration e.g. 10m to 30m is often appropriate for structures.”
“No hard and fast rules can be given for the depth and spacing of exploratory holes. This will depend on the specific circumstances of each site and the amount and quality of existing information. Some guidance is given in BS 5930. The selection criteria for the depth and spacing of exploratory holes should always be to ensure that sufficient information is obtained to enable the proposed works to be adequately designed.”
• Type of geotechnical investigation‐
see for example IS EN 1997‐2: 1997 (Eurocode 7, Part 2)
Management of Risk: Geotechnical Risk Register (GRR) Example of Geotechnical Risk Register
No.
Hazard
Cause
Potential Impact
Category
• GRR comprises a list of geotechnical hazards and risk control measures attached to various elements of the proposed route at any project stage (eg route selection/pre planning planning
any project stage (eg route selection/pre‐planning, planning, design, construction and operation)
• A subjective qualitative scale is used to define risk
• Hazards are rated in terms of how likely they are to occur (the Probability) and to what degree they would affect the project (the Impact)
• The degree of risk is determined by combining the probability and impact assessments:
impact assessments:
Risk = Probability × Impact R = P × I
Clayton, CRI (2001). Managing Geotechnical Risk – Improving Productivity in UK Building and Construction. Prepared under the DETR Partners in Technology programme for the Institution of Civil Engineers. Thomas Telford, London.
1
Liquefaction of
1. High/rising tidal
base of excavation waters causing
liquefaction (quick
conditions) of sand in
Sand / subsoil
mixing with water excavation base
and forming liquid 2. Inadequate site
investigation
material.
information
3 IInadequate
3.
d
t design
d i
and understanding of
ground conditions
4. Improper
construction
2
Escape of
potential
contaminated
water from works
into surface water
channels
Possible
contaminants
from leakages,
spills or
fines/suspended
solids
Specific
Risk Rating
Risk Control Measure (RCM)
P
I
R
Design Control
1. Health & Safety
2. Programme
3. Cost
1. Risk of death or
injury by drowning
2. Damage to plant
3. Loss and
cessation of works
2
3
6
1. Review of previous excavations in the
locality and in similar ground
2. Detailed site investigation to include trial
trenches to expose soils
3. Boreholes and trial pits to be taken
below base of excavation
4. Specify method statement from the
Contractor for working in tidal sands and
check
h k th
thatt he
h iis ffully
ll cognisant
i
t with
ith ground
d
conditions
5. Check of implications of over-excavation
6. Check requirement to have ballast stone
available to place in base of excavation
1. Extended periods of
wet weather and
under-design of
temporary pumping
2. Over-pumping of
excavation into
surface water channel.
3. Potential
contamination from
run-off from works
4. Potential
contamination from
backfill material
1. Environmental
1. Risk of
contamination of
surface water
3
4
12
1. Walk-over survey to identify areas
where greater risk of water entering works
and becoming contaminated
2. Detailed site investigation to include trial
trenches to expose soils and monitoring of
groundwater along route
3. Spillages from plant - addressed in
environmental impact statement
4. Consider limiting the extent of
works/excavation opened in sensitive
areas
5. Specify method statement from
contractor that clearly demonstrates their
awareness of this issue
6. Identify any sensitive receivers along
route
1. Carry out extensive site investigation.
2. Walk-over survey of route to identify
areas of variable ground (e.g. shallow rock,
till, peat/organic clay)
3. Selection of conservative design
parameters to allow for variable conditions
on site
4. Require detailed construction method
statement that clearly demonstrates
understanding of the ground conditions and
risks involved
5. Monitoring and observation method
proposed as part of construction controls
1. Carry out extensive site investigation
2. Walkover survey of route to identify
areas of variable ground (e.g. shallow rock,
till, peat/organic clay)
3. Detailed method statement to be
prepared with respect to excavation
3
Unexpected hard
obstructions in
excavations, e.g.
boulders, rock
outcrops
1. Ground conditions
differing from those
indicated from site
investigation
2. Inadequate site
investigation
information
1. Programme
2. Cost
1. Delays to works
2. Increased noise
levels due to
additional rock
breaking
requirements
4
2
8
4
Open excavations
and holes filled
with disturbed
peat
1. Excavation works
2. Displacements and
slides
3. Improper
construction methods
1. Health & Safety
2. Environmental
3. Programme
4. Cost
1. Risk of death or
injury from falling
into excavation
2. Damage to plant
3
5
15
Construction / Operations
Control
Risk Rating
after RCM
Contingency Measures
P
I
R
1. Site supervision staff to inspect
excavation daily
2. No/limited access into excavation
3. Areas of unexpectedly deep and weak
ground to be reported and await further
instruction
4. Works sequenced to tides and
weathered conditions
5 S
5.
Supervision
i i tto ensure construction
t ti
carried out as detailed in the method
statement
6. Limited exposure of excavation base
to avoid potential for base (liquefaction)
failure
1. Supervision staff to be fully briefed on
the ground conditions, design
requirements and construction
methodology
2. Supervising staff aware of weather
forecasts
3. Appropriate pumping facilities to be
put in place during the construction
phase and silt traps/bunds constructed
4. Temporary bunds and drains to be
installed as appropriate
5. Supervision to ensure construction
carried out as detailed in the method
statement
6. Measures to prevent
contamination/clean up contamination
before work continues
1
3
3
1. Stop works
2. Ballast stone to be placed in base of excavation
3. Ensure localised area made stable
1
4
4
1. Stop work
2. Environmental Manager to be notified immediately.
3. Establish if contamination includes oil / diesel
4. Identify source of contamination and solve problem
immediately as per EMP.
5. Oil contaminated water to be treated prior to discharge
(use oil interceptors if appropriate)
6. Excess water to be diverted into drainage channels
with filtration / sedimentation as required
7. Use simple and effective filtration measures to remove
particle load e.g. straw bales/terram in drainage channels
8. Sedimentation tanks to be used (and cascaded if
necessary)
9. Use adjacent areas within temporary working area as
natural filter in agreement with NPWS e.g. for high levels
of suspended peat
10. Reserve / additional pumping facilities to be available
1. Construction personnel briefed on
expected ground conditions
2. Reporting by site staff on change in
ground conditions from that predicted
3. Advance notice of change in predicted
ground condition to be fed to designers
4. Supervision to ensure construction
carried out as detailed in the method
statement
1
2
2
1. Stop works
2. Area to be assessed
3. Use rock breakers/non-explosive pre-splitting of rock
using expansive grouts or similar
1. Appropriate sequencing of works
2. Supervision of works by suitably
qualified person
3. Tool box talks to be carried out prior
to works
4. Ensure no excavations left open or
unprotected
5. Backfill to be with a suitable material
6. Supervision to ensure construction
carried out as detailed in the method
statement
2
3
6
1. Stop work
2. Backfill open excavations with stone
3. Over excavate disturbed peat localised area and
backfill with stone
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Content of Geotechnical Risk Register (GRR) Hazard
Cause
Potential Impact
Category
Specific
Risk Rating
P
I
Risk Control Measure (RCM)
R
Hazards
Hazard & Cause
Design Control
Risk Rating following RCM
Construction / Operations Control
P
I
Contingency Measures
Cause
Potential Impact
Category
Risk Control Measures (RCM)
g
• Design Control
• Construction / Operation Control
Risk Rating following RCM
P × I = R
Hazard
R
Risk Rating
P × I = R
Potential Impact
Example List of Geotechnical Hazards
1.
1
2.
3.
4.
5.
6.
7.
7
8.
9.
10.
Risk Rating
Specific
P
I
Risk Control Measure (RCM)
R
Design Control
Risk Rating following RCM
Construction / Operations Control
P
I
Contingency Measures
R
Slope Instability
Slope
Instability
Settlement
Subsidence (sub‐surface voids)
Groundwater
Chemically reactive ground
Contamination
Eroding/mobile ground conditions (coastal/marine)
Eroding/mobile ground conditions (coastal/marine)
Unforeseen ground conditions (extent, type)
Inadequate geotechnical investigation
Inappropriate design
Contingency Measures
*Any hazard can be sub‐divided in terms of a sub‐set or geographic location
Potential Impact
Cause
Potential Impact
Category
Specific
Risk Rating
P
I
Risk Control Measure (RCM)
R
Design Control
Category:
All hazards belong to one of the following categories:
•
•
•
•
•
Health & Safety
H
lth & S f t
Environmental
Programme
Cost
Quality Risk Rating following RCM
Construction / Operations Control
P
I
Contingency Measures
Hazard
Cause
R
Potential Impact
Category
Examples of specific hazards are as follows:
•
•
•
•
Risk of injury or death (Health & Safety)
Change of hydrology (Environmental)
Collapse of excavation (Programme)
Damage to plant (Cost)
Risk Rating
Specific
P
I
Risk Control Measure (RCM)
R
Design Control
Risk Rating following RCM
Construction / Operations Control
P
I
Contingency Measures
R
Probability ×
b bili
Impact = Risk ik
P × I = R Specific:
1
IMPACT (I)
Hazard
Risk Rating
2
3
4
5
PROBABILITY (P)
PROBABILITY (P)
1 2 3 4 5
1
Negligible
1 2 3 4 5
2
Possible
2 4 6 8 10
3
Likely
3 6 9 12 15
4
Probable
4 8 12 16 20
5
Very Likely
5 10 15 20 25
IMPACT (I)
1
Very Low
2
Low
Routine
3
Medium
Requires Attention
4
High
Unacceptable
Very High
5
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Risk Control Measures
Hazard
Cause
Potential Impact
Category
Risk Rating
Specific
P
I
Risk Control Measure (RCM)
R
Design Control
Construction / Operations Control
Risk Rating following RCM Risk Rating following RCM
P
I
Contingency Measures
Hazard
R
Cause
Potential Impact
Category
• If the risk is deemed excessive, then Risk Control Measures (RCM) are required to lessen the risk • These can be:
¾ Design controls:
eg. Detailed site investigation, locally re‐routing, micro‐siting
Specific
Risk Rating
P
I
Risk Control Measure (RCM)
R
Design Control
Construction / Operations Control
Risk Rating following RCM
P
I
Contingency Measures
R
• Following the applications of the Risk Control Measures, the degree of risk is again assessed
• Ideally, the Risking Rating should now be tolerable
¾ Construction or operation controls:
eg. Site supervision staff to inspect critical pylon locations
• Risk Control Measures mitigate the Probability and/or the Impact
Control & Reporting of GRR
Contingency Measures
Hazard
Cause
Potential Impact
Category
Specific
Risk Rating
P
I
Risk Control Measure (RCM)
R
Design Control
Construction / Operations Control
Risk Rating following RCM
P
I
Contingency Measures
•
R
• Contingency Measures are then considered, should the hazard occur, eg.
¾ Stop works
¾ Monitor situation
• The risk register is generally a live document: as new hazards, risk control measures or contingency measures present themselves, these should be added
these should be added
•
•
The GRR is a key method of communication of risk between the various parties at different stages of the project (eg route selection pre‐planning
selection, pre
planning, planning, design, construction and planning design construction and
operation)
Geotechnical risk management should be integrated into the overall project management process
Review and feedback allows continuous improvement of the risk management system
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Summary ‐ Management of Geotechnical Risk Worked Examples ‐ Peat Slide
Hazard
Cause
Potential Impact
Category
Risk Rating
Specific
P
I
Risk Control Measure (RCM)
R
Design Control
Construction / Operations Control
Risk Rating following RCM
P
I
Contingency Measures
R
• Ground conditions are always uncertain
• Realistically, not all ground risk can be avoided or eliminated
Potential Impact
Hazard
Peat Slide
1. Risk of death or injury by inundation
2. Environmental damage
3. Damage to persons, plant, property and livestock
4. Loss and cessation of works
5. Adjacent land affected due to peat/ground movement
Risk Rating
2 × 5 = 10
• Compliance with standards reduces ground risk but does not eliminate ground risk
• Ground related risk can generally have a significant impact
• Management of ground risk is essential for success:
Risk Control Measures (RCM)
• Design Controls (list)
• Construction / Operation Controls (list)
Risk Rating following RCM
1 × 5 = 5
Contingency Measures
‐ allow for sufficient budget ‐ use the right managements tools
‐ employ appropriate specialists
1. Stop works
2. Use sheetpiling to stop ground movements
3. Monitor movements following installation of sheetpiles until
movements have ceased
4. Reduce speed of works
5. Reduce excavation lengths prior to backfilling with stone
Questions & Answers
Thank You
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