climate impact forecasting for slopes
TRANSCRIPT
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Climate Impact Forecasting for Slopes
Stuart Hardy
Slope Remediation - Current Practice
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Contents of Talk
• What Do We Do?
• Why Do We Do It?
• How Do We Do It?
• The Future For Slope Stability Assessment
• Questions We Would Like To Raise
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Contents of Talk
• What Do We Do?
• Why Do We Do It?
• How Do We Do It?
• The Future For Slope Stability Analysis
• Questions We Would Like To Raise
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What Do We Do?
• We work for all the major earthwork infrastructure owners
– British Waterways
– Network Rail
– London Underground Limited
– Highways Agency
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Contents of Talk
• What Do We Do?
• Why Do We Do It?
• How Do We Do It?
• The Future For Slope Stability Assessment
• Questions We Would Like To Raise
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Why Do We Do It?
• Interruption of services
• Emergency works
• High costs
• Loss of revenue
• Loss of customers
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Contents of Talk
• What Do We Do?
• Why Do We Do It?
• How Do We Do It?
• The Future For Slope Stability Assessment
• Questions We Would Like To Raise
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How Do We Do It?
1. Inspection of earthworks & risk assessment
2. Detailed investigation and design of stabilisation measures
3. Applied research projects
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1. Earthwork Inspections
• Each operator has developed their own system
– Network Rail (RT/CE/S/065)
– LUL (E 3735)
– HA (HD 41/03)
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2. Detailed Analysis
• Limit Equilibrium Techniques to Assess Stability
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2. Detailed Design
• Contiguous Bored Pile Wall
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2. Detailed Design
• Soil Nailing
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2. Detailed Design
• Gabion Walls/Reinforced Earth
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2. Detailed Design
• None of the inspection standards fully address the
influence of vegetation on slope stability or
vulnerability to seasonal rainfall effects
• None of the commonly used design methods can
take account of the effect of vegetation or seasonal
rainfall effects
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3. Research Projects
• LUL Research Stage II – Assessment of Cuttings and
Embankments (LUL)
• Queensbury Instrumented Embankment (LUL)
• Seasonal Preparedness (NR)
• The Effect of Vegetation on Slope Stability (RSSB)
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Contents of Talk
• What Do We Do?
• Why Do We Do It?
• How Do We Do It?
• The Future For Slope Stability Assessment
• Questions We Would Like To Raise
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The Future For Slope Stability Assessment
• Extended Use of SMD for risk assessment
SMD
Rainfall
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The Future For Slope Stability Assessment
• Use of more advanced analysis tools
– Finite Element/Difference
• Hydrological (CHASM, VADOSE)
• Geotechnical (Plaxis, FLAC)
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CHASM – Modelling rainfall effects on slope pore pressures
• CHASM can be used to model the effect of any combinations of rainfall events on the stability of a slope
Reduction in Suctions with Time
0
0.5
1
1.5
2
2.5
3
3.5
-10 -8 -6 -4 -2 0 2 4
pore pressure (m)
dep
th b
elo
w s
lop
e s
urf
ace (
m)
10 days
15 days
20 days
25 days
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CHASM – Modelling rainfall effects on slope pore pressures
Reduction in FoS from Initial Value
70%
80%
90%
100%
110%
0 5 10 15 20 25 30
time (days)
Fo
S a
s %
of
ba
se
lin
e
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Progressive Failure
• FLAC can be used to model the effect of vegetation
on progressive failure
Winter –Embankment Swells
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Progressive Failure
Track Heaves
Winter –Embankment Swells
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Progressive Failure
Plastic Strains Develop at toe
Φpeak
Φresidual
Winter –Embankment Swells
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Progressive Failure
Zero Pore pressure line Low Pore Water Pressures
Summer –Embankment Shrinks
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Progressive Failure
Track Settles
Summer –Embankment Shrinks
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Progressive Failure
Plastic Strains Not Recovered
Φpeak
Φresidual
Summer –Embankment Shrinks
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Progressive Failure
Continued Cycling
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Progressive Failure
Continued Cycling
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Progressive Failure
Failure!
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Questions We Would Like to Raise
• Can we gain a better understanding of the interaction of
climate and vegetation with slope behaviour?
• Can this be engineered to positively benefit a slope?
• Can Soil Moisture Deficit be modified to take account of slope
orientation and slope angle when making the risk assessment
for a certain slope?
• Will this greater understanding allow us to move away from
hard structural solutions like bored piles/soil nails?
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www.mottmac.com
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Life expired embankments
• On going deformation
• Speed restrictions
• Expensive maintenance
• Unpredictable costs
• Dissatisfied customers
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1. Earthwork Inspections
• Inspection procedures take into account
– Slope geometry (angle and height)
– Observations of water (seepage, ponding)
– Evidence of instability (bulges, tension cracks or crooked trees)
• Condition rating
– Serviceable, marginal or poor for LUL and NR procedure
– Class 1, 2, or 3 for HA
• Crude Risk Assessment
– Inspection regime
– Remediation of slope
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2. Detailed Analysis
• LUL Design Standards
– For a London Clay Embankment
– Foundation Material: φ’ = 21°, c ‘ = 2kPa γ = 19 kN/m3
– Embankment Material: φ’ = 21°, c ‘ = 1kPa γ = 19 kN/m3
– Four options available for pore pressure conditions
– For slope covered with mature trees, the pore pressure is
hydrostatic below zero pressure line which is assumed 2m below
surface
– Track loading of 30kPa applied from sleeper end to sleeper end