Slope Stability Assessment
By Ir. Liew Shaw Shong
G&P Geotechnics Sdn Bhd
One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Contents
• Overview
• Chap. 1: Failure Mechanisms (Contributory & Triggering)
• Chap. 2: Uncertainties & Assumptions
• Chap. 3: Slope Mass Properties
• Chap. 4: Methodology & Analysis
• Chap. 5: Factor of Safety
• Chap. 6: Hazard & Risk Assessments
2
Failure Mechanisms
Contributory & Triggering factors
Analytical Approaches :
• Deterministic approach
• Probabilistic approach
Natural slopes & Engineered slopes
Hazard & Risk
Overview on Slope Stability Assessment
3One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Contents
• Overview
• Chap. 1: Failure Mechanisms (Contributory & Triggering)
• Chap. 2: Uncertainties & Assumptions
• Chap. 3: Slope Mass Properties
• Chap. 4: Methodology & Analysis
• Chap. 5: Factor of Safety
• Chap. 6: Hazard & Risk Assessments
4One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Chap 1 Failure Mechanisms
• Landslide: Any perceptible down slope movement of rock or soil
• Necessary Condition for Slope Instability
– Gravitational force (Disturbing Force)
• Sufficient Conditions for Slope Instability
– Reduction of Slope Strength (Resistance) – Water!
– Additional disturbing forces (surcharge, groundwater drawdown)
– Change of slope geometry (steepening)
• FOS ≥ 1 (Stable) or FOS < 1 (Unstable)
FOS =
5One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Types of Landslides
(Nelson 2004)
Types of Movement
Falls
Topples
Slides
Rotational
Translational
Lateral Spreads
Flows (Slow Creep .vs. High Mobility)
Complex (Combination above)
6One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Classification of Mass WastingT
ype
of M
ovem
ent
Flo
wS
lide
Fal
lClassification
Creep
Earth Flow
Mudflow
Avalanche
Rotational Slide
Rock Slide
Debris Fall
Rockfall
MaterialDebris
Debris
Saturated Debris
Debris or Rock
Debris
Bedrock
Debris
Bedrock
VelocityImperceptibly Slow
Slope and Material Dependent <5 km/hr
Very Fast 100 km/hr
Slow-mod. (short)
Fast
Fast
Fast
Natural Factors for Landslides
• Geological Structures
• Weak or sensitive materials • Weathered materials• Sheared, jointed, or fissured materials• Adversely oriented discontinuity (bedding, schistosity, fault, unconformity, contact, and so forth)
• Contrast in permeability and/or stiffness of materials (Perched water regime)
8One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Natural Factors for Landslides
• Morphological Features
• Tectonic or volcanic uplift• Glacial/erosion rebound• Fluvial, wave, or glacial erosion of slope toe or lateral margins
• Subterranean erosion (solution, piping) • Deposition loading slope or its crest • Vegetation removal (by fire, drought)• Thawing Freeze-and-thaw weathering• Shrink-and-swell weathering
9One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Summary of Landslide Factors
Triggering Mechanisms• Intense Rain-Fall
• Water-Level Change
• Ground Water Flow
• Human activity
• Rapid Snowmelt
• Volcanic Eruption (Mt. St. Helen, USA)
• Earthquake Shaking (921 Chi-Chi Earthquake, Taiwan)
10One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Mt. St. Helen (USA)
11One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Earthquake Induced Landslide
12One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Shape of Slip Surface
Structurally Controlled 3D Blocks
•Planar
•Rigid Wedge Block
•Toppling
2D Plane Strain Failure
•Circular Failure
•Wedge Failure
Channelised Flow
13One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Distressed area
Channelised Flow – Technically challenging
Buildings
Modeling Debris Runout Modeling Debris Runout & Mobility& Mobility
Hydrological & Hydrogeological Cycles
(Nelson 2004) 15One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Hydrological & Hydrogeological Cycles
(Nelson 2004)
Retention
Precipitation
Transp
iratio
n
Evaporation
Evaporation
Underground Seepage
Surface Runoff
Infiltration/Percolation
Saturated
Unsaturated
16One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Effect of Water on Soils
Phreatic Surface
Vadose Zone
Saturation Zone
Degree of Saturation
Porewater Pressure
-u 0 +u
0 100%
Physics in Vadose Zone
17One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
`Hygroscopic
Zone
Effect of Water on Soils
Physics in Capillary Action
18One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
u : -ve
Effect of Water on Soils
Dry sand grains will form a pile. The slope angle is determined by the angle of repose (i.e., the steepest angle at which a pile of unconsolidated grains remains stable - controlled by the frictional contact between the grains. It usually lies between about 30 and 37 degrees.
(Nelson 2004)
Dry sand
Angle of repose
Grain-to-grain frictional contact
19One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Effect of Water on Soils
Slightly wet soil materials exhibit a very high angle of repose because surface tension between the water and the grains tends to hold the grains in place.
Wet sand
Angle of repose
Surface tension thin film
20One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Effect of Water on Soils
When the material becomes saturated, the strength may reduce significantly and it may tend to flow… water (between the grains) eliminates grain to grain frictional contact.
Angle of repose
Fully saturated sand
Water surrounds the grain and prevent grain-to-grain contact
21One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Effect of Water on Soils
Toe erosion undermining the slope mass
22One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Tunneling/Piping Phenomena in the Vadose Zone (Jones, 1981)
Effect of Water on Soils
23One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Effect of Water on Soils
24One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Effective Stress and Strength
Before Rainfall After Rainfall
σe = σT – P σe = σT – (P+∆P) σT : Total Stress
P : Fluid pressure of groundwater (or soil water)
∆P : Positive pore pressure increment (suction reduction or
positive hydrostatic pressure)
σe : Effective stress (stress supported by the soil skeleton)
Note: fluid pressure is negative (less than atmospheric) if unsaturated and becomes positive when saturated
P+∆P
σT
P
σT
Slope Stability
Steps to perform Slope Stability Analysis
• understand the development & shape of slopes• understand the external effects (likes seismic loading, surcharge, saturation) on slope and embankments
• determine the short-term & long-term stability conditions & mode of operational conditions
• understand failure mechanisms & choose right stability analytical model
• evaluate the possibility of failure of natural or engineering slopes
26One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Contents
• Overview
• Chap. 1: Failure Mechanisms (Contributory & Triggering)
• Chap. 2: Uncertainties & Assumptions
• Chap. 3: Slope Mass Properties
• Chap. 4: Methodology & Analysis
• Chap. 5: Factor of Safety
• Chap. 6: Hazard & Risk Assessments
27One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Chap 2 Uncertainties & Assumptions
• Idealisation & Simplification of Geological/Hydro-geological/Geotechnical models
– Subsurface conditions (Inadequate investigation)
– Relict structures
– Groundwater regime (Rapid Drawdown/Artesian/Perched Water Table)
– Geomorphological conditions
• Accuracy of analytical model
– Postulation of possible Failure Mechanisms
– Upper bound solution
– Equilibrium of Slide forces & moment
28One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Model Idealisation & Simplification
FOS = 1.07
Bedrock
Residual Soils
29One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Road Cutting
Model Idealisation & Simplification
FOS = 1.42
Bedrock
Residual Soils
30One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Road Cutting
Rock Mass Structures
31One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Groundwater Regime
32One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Chap 2 Uncertainties & Assumptions
• Idealisation & Simplification of Geological/Hydro-geological/Geotechnical models
– Subsurface conditions (Inadequate investigation)
– Relict structures
– Groundwater regime (Rapid Drawdown/Artesian/Perched Water Table)
– Geomorphological conditions
• Accuracy of analytical model
– Postulation of possible Failure Mechanisms
– Upper bound solution
– Equilibrium of Inter-slide Forces & Moment
33One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Cutting Earthworks
Soil Nails That Have Been Installed
Finite Element Analyses
Dev. of Plastic Points In FEM (After Cutting of 12 Upper Berms)
34One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Limit Equilibrium Stability Analyses
Global Stability FOS=1.01
Full Installation of Soil Nail (Except Berm 1)
35One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Chap 2 Uncertainties & Assumptions
• Slope Geometry & Loading conditions
- Assessment of probable loading scenarios
- Future possible changes of site conditions
• Mass Properties
– Stress conditions (Stress path/Change of principal stress direction)
– Reliability of mass properties of slope
– Strength anisotropy
– Mobilized strength, peak/residual strength
36One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Variation of Site Conditions
37One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Raising Water
Inundation
Recess of Water (Drawdown condition)
Phreatic Water Table & Steady State Seepage
38One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Chap 2 Uncertainties & Assumptions
• Slope Geometry & Loading conditions
- Assessment of probable loading scenarios
- Future possible changes of site conditions
• Mass Properties
– Stress conditions (Stress path/Change of principal stress direction)
– Reliability of mass properties of slope
– Strength anisotropy
– Mobilized strength, peak/critical/residual strengths
39One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Contents
• Overview
• Chap. 1: Failure Mechanisms (Contributory & Triggering)
• Chap. 2: Uncertainties & Assumptions
• Chap. 3: Slope Mass Properties
• Chap. 4: Methodology & Analysis
• Chap. 5: Factor of Safety
• Chap. 6: Hazard & Risk Assessments
40One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Chap 3 Slope Mass Properties
Sources of Deriving of Strength Parameters
• Laboratory tests (Tri-axial strength tests, shear box test)
• Field tests (Vane shear tests, piezocones)
• Observation of Rock Mass Structure & Joint Surface Condition (Homogenous & Isotropic)
• Back-analysed operational mobilised strength parameters
Failure Criteria
• Mohr-Coulomb criterion (homogeneous soil strength)
– τ = c’ + σ’n tanφ’ (Saturated soils)– τ = C’ + σ’n tanφ’ (Unsaturated soils)
• Generalised Hoek-Brown criterion (rock mass strength, 2002)
– σ’1 = σ’3 + σci (mbσ’3/σci+ s)a
where mb, s & a are function of GSI & D (disturbance factor)
41One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Geological Strength Index
• Estimate Jointed Rock Mass Peak Strength & Deformation Parameters
• Block size/Discontinuity Spacing < 25% of Dimension of Excavation (otherwise governed by rock structure)
• GSI depends on
• Rock Structure (Interlocking condition)
• Block Surface (Roughness condition)
42One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
APPLICATION
43One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
DISCONTINUITY TESTS
One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Unconfined Confined
DISCONTINUITY TEST
One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
σ3 σ1
ROCK SLOPE
One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
ROCK MASS SHEAR STRENGTH
47One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
ROCK SLOPE STABILITY ANALYSIS
Limit Equilibrium Analysis
48One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
ROCK SLOPE AND DISCONTINUITY
Depend on discontinuities surface friction 49One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
SLIP SURFACE SHAPES
50One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
FAILURE ENVELOPE
The Mohr-Coulomb criterion expressed the relationship between the shear stress and normal stress at failure along a shear surface.
( ) ( ) βσσσσσ 2cos2
1
2
13131 −++=n
'tan' φστ nc +=
51One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
PROBLEMS WITH MOHR-COULOMBMohr-Coulomb criterion is applicable for discontinuities and discontinuous rock masses,
hence remains one of the most commonly applied failure criterion. But several key
limitations apply to rock slope stability analyses.
Non linear failure
envelopesScale effect
52One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
m and s are derived from
empirical charts that are
related to rock mass quality
DESIGN PARAMETERS
53One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
STABILITY ANALYSIS DESIGN PROCESS
54One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Contents
• Overview
• Chap. 1: Failure Mechanisms (Contributory & Triggering)
• Chap. 2: Uncertainties & Assumptions
• Chap. 3: Slope Mass Properties
• Chap. 4: Methodology & Analysis
• Chap. 5: Factor of Safety
• Chap. 6: Hazard & Risk Assessments
55One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Chap 4 Methodology & Analysis
Analytical Models
• Limit Equilibrium Method
– Kinematic stability of rigid body (Markland Analys)
– Slide methods
– Predefined slip surface for FOS computation
– Either force equilibrium or moment equilibrium or both
• Finite Element/Difference Method
– Deformation
– Failure mechanisms
– Strain & stress compatible
Analysis Types
• Drained analysis (Effective stress)
• Undrained analyses (Total stress)
56One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Chap 4 Methodology & AnalysisLimit Equilibrium
Method
Static Equilibrium Inclination & Relationship of Inter-slice Forces
Force Moment
Ordinary/Swedish – 1936 - � Ignore H & V
Janbu (Simplified) – 1954 � - Ignore V, Consider H
Janbu (Generalised) � - Consider both V & H (Line of Thrust & Moment Equilibrium of Slides)
Bishop (Simplified) – 1955 - ���� Ignore V, Consider H
Morgestern-Price - 1965 ���� ���� Consider both V & H (Variable)
Spencer – 1967 ���� ���� Consider both V & H (Constant)
Lowe-Karafiath � - Consider both V & H
Corps of Engineers � - Consider both V & H
Sarma – 1973 � � V = C + H tan φ57One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Chap 4 Methodology & Analysis
Equilibrium
∑F=0
∑M=0
VH
58One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Generalised Limit Equilibrium Frameworks (GLE)
– Fredlund (1977 & 1981)
V=H λ f(x)
H : Interslice normal force
V : Interslice shear force
INFINITE SLOPE FAILURE
resista
nceβ
Sliding surface
h
b
Vertical
slice
W
59One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Chap 4 Methodology & Analysis
FORCE EQUILIBRIUM
– THE SLICE
W
W P
W N
cl + W Ntan φφφφ'
WN = Wsinβ
l = length of sliding
surface
'tan' φσ ncs +=
Terzaghi Equation as based of
Mohr-Coulomb Failure Envelope
60One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Chap 4 Methodology & Analysis
Chap 4 Methodology & Analysis
61One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Chap 4 Methodology & Analysis
Conditions :
• Groundwater Regime (Rapid Drawdown/Artesian/Perched Water Table)
• Submerged slope
• Tension cracks
• Surface loadings/surcharge
• Global/local stability
62One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Contents
• Overview
• Chap. 1: Failure Mechanisms (Contributory & Triggering)
• Chap. 2: Uncertainties & Assumptions
• Chap. 3: Slope Mass Properties
• Chap. 4: Methodology & Analysis
• Chap. 5: Factor of Safety
• Chap. 6: Hazard & Risk Assessments
63One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Chap 5 Factor of Safety
• Definition of FOS:
– Resistance/Disturbance (Fr/Fd, Mr/Md, H/Hc, τavai./ τmob.)
– Strength Reduction Factor
• Determination of FOS:
– Condition of Application (Long/short terms)
– Reliability of soil parameters & analytical model
– Consequences
64One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Chap 5 Factor of SafetyReferences FOS Requirements
BS6031 1.3~1.4 for first time slide
1.2 for slide with pre-existing slip surface
JKR Road Works 1.2 for unreinforced slope & embankment on soft ground
1.5 for reinforced slope
Hong Kong Geoguide
1.0~1.4 for new slopes depending on risk categories
1.0~1.2 for existing slope depending on risk categories
NAVFAC DM7.1 1.5 for permanent loading condition
1.15 to 1.2 for transient load
Britain National Coal Board 1970
1.5/1.35 (peak/residual strength used) for risky slope
1.25/1.15 (peak/residual strength used) for non-risky slope
Canada, Mines Branch 1972
1.5/1.3 (peak/residual strength used) for risky slope
1.3/1.2 (peak/residual strength used) for non-risky slope
65One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Table 2. Partial factor recommended in EN1997-1 Annex A - Updated in 2007Design Approach 1 Design Approach 2
Design Approach 3
Combination 1 Combination 2 Combination 2 - piles & anchors Combination 1 Slopes
A1 M1 R1 A2 M2 R2 A2 M1 or M2 R4 A1 M1 R2 A1 M=R2 A1 A2 M2 R3
ActionsPermanent
Unfav 1.35 1.00 1.00 1.35 1.35 1.35 1.00
Fav 1.00 1.00 1.00 1.00 1.00 1.00 1.00
Variable Unfav 1.50 1.30 1.30 1.50 1.50 1.50 1.30
Soil
tan φφφφ' 1.00 1.25 1.00 1.25 1.00
Struct
Actions
Geotech
Actions
1.25
Effective cohesion1.00 1.25 1.00 1.25 1.00 1.25
Undrained strength 1.00 1.40 1.00 1.40 1.00 1.40
Unconfined stregnth 1.00 1.40 1.00 1.40 1.00 1.40
Weight density 1.00 1.00 1.00 1.00 1.00 1.00
Spread
footings
Bearing 1.00 1.00 1.40 1.00
Sliding 1.00 1.00 1.10 1.00
Driven piles
Base 1.00 1.30 1.10 1.00
Shaft (compression) 1.00 1.30 1.10 1.00
Total / combined 1.00 1.30 1.10 1.00
Shaft in tension 1.25 1.60 1.15 1.10
Bored piles
Base 1.25 1.60 1.10 1.00
Shaft (compression) 1.00 1.30 1.10 1.00
Total / combined 1.15 1.50 1.10 1.00
Shaft in tension 1,25 1.60 1.15 1.10
AnchorsTemporary 1.10 1.10 1.10 1.00
Permanent 1.10 1.10 1.10 1.00
Retaining
walls
Bearing capacity 1.00 1.00 1.40 1.00
Sliding resistance 1.00 1.00 1.10 1.00
Earth resistance 1.00 1.00 1.40 1.00
Slope Earth resistance 1.00 1.00 1.10 1.00
Chap 5 Factor of Safety
66One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Contents
• Overview
• Chap. 1: Failure Mechanisms (Contributory & Triggering)
• Chap. 2: Uncertainties & Assumptions
• Chap. 3: Slope Mass Properties
• Chap. 4: Methodology & Analysis
• Chap. 5: Factor of Safety
• Chap. 6: Hazard & Risk Assessments
67One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Chap 6 Hazard & Risk Assessments
Risk Mitigation over :
� Natural Terrain Slopes
� Engineered Slopes
• Unreinforced Slopes• Reinforced Slopes
68One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
� Experience from man-made slopes not necessary applicable to natural terrain
� Low frequency high magnitude event� Visual Impact
∴ New technical approach:� React-to-known hazard� Mitigation works� Risk Assessment� New analytical tools, e.g. debris mobility
evaluation, landslide susceptibility map, etc.
Natural terrain landslide risk (Hong Kong Experience)
69One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Many landslides
in a heavy rainstorm
Many landslidesMany landslides
in a heavy rainstormin a heavy rainstorm
Small failure can be serious for HighrisesSmall failure can be Small failure can be serious for Highrisesserious for Highrises
Increasing risk
due to developing closer
to natural hillside
Increasing risk Increasing risk
due to developing closerdue to developing closer
to natural hillsideto natural hillside
Low-frequency
large-magnitude event
LowLow--frequencyfrequency
largelarge--magnitude eventmagnitude event
70One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Natural Terrain Landslides Natural Terrain Landslides Natural Terrain Landslides
Natural Terrain FailureNatural Terrain Failure
Propensity ~ 1 / 2km2 /yr
Fatality (PLL) ≤≤≤≤ 5 / yr
Propensity ~ 1 / 2kmPropensity ~ 1 / 2km2 2 /yr/yr
Fatality (PLL) Fatality (PLL) ≤≤≤≤≤≤≤≤ 5 / yr5 / yr
ManMan--made Slope Failuremade Slope Failure
Potential Loss of LifePotential Loss of LifePotential Loss of Life
Propensity ~ 1 / km2 /yr
Fatality (PLL) ≤≤≤≤ 10 / yr
Propensity ~ 1 / kmPropensity ~ 1 / km2 2 /yr/yr
Fatality (PLL) Fatality (PLL) ≤≤≤≤≤≤≤≤ 10 / yr10 / yr
60% Steep 60% Steep
Natural HillsideNatural Hillside
71One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
UNACCEPTABLE
ALARP
INTE
NS
E
SC
RU
TIN
Y
RE
GIO
N
10- 3
10- 4
10- 5
10- 6
10- 7
10- 8
F/yr
Fatality ≥ N
1 10 100 1,000
UnacceptableUnacceptableUnacceptableUnacceptable
ALARPALARPALARPALARP
Intense
Intense
Intense
Intense
Scrutiny
Scrutiny
Scrutiny
Scrutiny
Region
Region
Region
Region
Personal Individual Risk (IR) Criteria
Existing Facility:
New Facility:
IR with 10-5 per yr
IR with 10-4 per yr
Interim Risk Standards Interim Risk Standards Interim Risk Standards Interim Risk Standards
(GEO Report No. 75)(GEO Report No. 75)(GEO Report No. 75)(GEO Report No. 75)
Technical Challenge – Natural terrain landslide risk
Societal Risk Criteria : FSocietal Risk Criteria : F--N CurveN Curve
72One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010
Broadly Broadly Broadly Broadly AcceptableAcceptableAcceptableAcceptable
Risk Reduction Trend (Hong Kong Experience)
GEOestablished
1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000
Postulated risk trend
Landsliprisk
Checknew works
Upgradeold slopes
Rehousesquatters
Publiceducation
74One-Day Short Course on Slope Engineering, Promenade Hotel at Kota Kinabalu on 30 June 2010