practical qra models - ags (hk · 1 practical qra models for natural terrain hazards wing sun...

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Practical QRA Models Practical QRA Models for Natural Terrain Hazardsfor Natural Terrain Hazards

Wing SunWing SunGeotechnical Engineering OfficeGeotechnical Engineering Office

Risk Quantification

Risk Probability of Failure

Consequence of Failure

= ×Σ

How bad?

No. of fatalities per year

Acceptable risk level?

How likely?All slope hazards

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Risk AnalysisCost-benefitRisk Management

Elements of Risk Quantification

Hazard IdentificationFrequency Assessment

Consequence Assessment

Risk Probability of Failure

Consequence of Failure

= ×Σ

(15) Make conclusion and recommendation(15) Make conclusion and recommendation(14) Evaluate risk management strategy(14) Evaluate risk management strategy(13) Analyze risk(13) Analyze risk(12) Assess design events(12) Assess design events(11) Carry out consequence assessment(11) Carry out consequence assessment(10)(10) Identify debris runout paths and influence zonesIdentify debris runout paths and influence zones(9) Carry out frequency assessment(9) Carry out frequency assessment(8) Formulate hazard models(8) Formulate hazard models(7) Develop relevant regolith, engineering geological and geomor(7) Develop relevant regolith, engineering geological and geomorphological modelsphological models(6) Identify facilities and population at risk, and their degree(6) Identify facilities and population at risk, and their degree of proximity of proximity (5) Demarcate boundaries and types of catchment(5) Demarcate boundaries and types of catchment(4) Examine rainfall records and effects(4) Examine rainfall records and effects(3) Validate historical landslides(3) Validate historical landslides(2) Delineate study area(2) Delineate study area(1) Determine study objectives and approach(1) Determine study objectives and approach

(16) Document findings and communicate risk(16) Document findings and communicate risk

Practical QRA Models Practical QRA Models –– Key ModulesKey Modules

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Natural terrain Natural terrain landslide QRAlandslide QRA

on development at on development at Ling PeiLing Pei

ChekChekLapLapKokKok

airportairport

Lantau Lantau IslandIsland

TungTungChungChung

Ling PeiLing Pei

Ling Pei

Ling Pei

Small House

• New Territories Exempted Houses (Small Houses) for indigenous New Territories villagers

• 3-storey R.C. structures with ground floor occupied

• Increasing land demand for Small House development, esp. expansion of existing villages closer to steep hillside

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Natural Terrain Hazard Alert Zone

Limit of Alert Zone

Meet Alert Criteria Study is required

QRA carried out in 2004QRA carried out in 2004

UNACCEPTABLE

ALARP

INTE

NSE

SCR

UTI

NY

REG

ION

10- 3

10- 4

10- 5

10- 6

10- 7

10- 8

FF/yr/yr

Fatality Fatality ≥≥ NN1 10 100 1,000

Unacceptable

ALARP

Inte

nse

scru

tiny

Societal Risk Criteria Societal Risk Criteria (500 m)(500 m)

Personal IndividualPersonal IndividualRisk (IR) CriteriaRisk (IR) Criteria

Existing Facility:Existing Facility:

New Facility:New Facility:IR with 10IR with 10--55 per yrper yr

IR with 10IR with 10--44 per yrper yr

HKHK’’s s InterimInterim Risk Standards Risk Standards (GEO Report No. 75)(GEO Report No. 75)

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(2) Delineate study area(1) Determine study objectives and approach


Delineate Delineate Study AreaStudy Area

B= Main study area

A, C & D= Supplementary areas

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(7) Develop relevant regolith, engineering geological and geomorphological models(6) Identify facilities and population at risk, and their degree of proximity (5) Demarcate boundaries and types of catchment(4) Examine rainfall records and effects(3) Validate historical landslides(2) Delineate study area(1) Determine study objectives and approach


Historical Natural Terrain Landslide

(~ past 50 yrs)

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Validate Historical LandslidesValidate Historical Landslides

All genuine historical landslides

Landslideattributes landslides

(7) Develop relevant regolith, engineering geological and geomorphological models(6) Identify facilities and population at risk, and their degree of proximity (5) Demarcate boundaries and types of catchment(4) Examine rainfall records and effects(3) Validate historical landslides(2) Delineate study area(1) Determine study objectives and approach


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41.686Total

00.00910.00-0.102000

00.00910.00-0.101995

00.1143>0.15-0.201994

21.1146>0.30-0.351993

10.2094>0.20-0.251992

10.0422>0.10-0.151999

00.00910.00-0.101990

00.00910.00-0.101989

00.00910.00-0.101988

00.0422>0.10-0.151987

00.0422>0.10-0.151998

00.0422>0.10-0.151997

00.00910.00-0.101996

00.00910.00-0.101991

00.00910.00-0.101986

00.00910.00-0.101985

Number of LandslidesZone24-hour

Rainfall

Actual Number of Landslides

Normalised Annual Maximum Rolling 24-hour Rainfall

Year

Normalized Max. 24-hr Rainfall0%0% 10%10% 20%20% 30%30% 40%40%

10001000

100100

1010

11

0.10.1

0.010.01Eve

nt- b

a sed

La n

d slid

e D

ens i

ty ( n

o./k

m2)

Rainfall-landslidecorrelation

Ling Pei (1985 Ling Pei (1985 –– 2000)2000)

(15) Make conclusion and recommendation(14) Evaluate risk management strategy(13) Analyze risk(12) Assess design events(11) Carry out consequence assessment(10) Carry out frequency assessment(9) Identify possible debris runout paths and influence zones(8) Formulate hazard models(7) Develop relevant regolith, engineering geological and geomorphological models(6) Identify facilities and population at risk, and their degree of proximity (5) Demarcate boundaries and types of catchment(4) Examine rainfall records and effects(3) Validate historical landslides(2) Delineate study area(1) Determine study objectives and approach

(16) Document findings


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Debris slide

Debris avalanche Channelised debris flow

Mechanisms of landslide debris movementMechanisms of landslide debris movement

Types of CatchmentTypes of Catchment ––Predicting types of debris movement that may occurPredicting types of debris movement that may occur

Planar hillside Planar hillside (S)(S) •• Debris may slide down Debris may slide down the hillside as an intact the hillside as an intact slab and result in an slab and result in an open slope debris slideopen slope debris slide

•• If disintegration occurs If disintegration occurs during debris movement, during debris movement, the landslide becomes the landslide becomes an open slope debris an open slope debris avalancheavalanche

Nam Long Shan Road

1994 Shum Wan Road landslide1994 Shum Wan Road landslide

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Incised drainage channel Incised drainage channel (C)(C)

•• A A channelisedchannelised debris flow debris flow would occur if the debris would occur if the debris enters into an incised enters into an incised drainage line or depression drainage line or depression that constraints the debris that constraints the debris flow pathflow path

•• Entrainment of loose Entrainment of loose material, if present, may material, if present, may occur and escalate the occur and escalate the debris flow volume and debris flow volume and mobilitymobility

2000 Tsing Shan Debris Flow2000 Tsing Shan Debris Flow

More subtle drainage line or topographic depression More subtle drainage line or topographic depression (T)(T)

•• The mechanism becomes a mixed debris The mechanism becomes a mixed debris avalancheavalanche--andand--flow, which is intermediate flow, which is intermediate between an open slope landslide and a between an open slope landslide and a channelisedchannelised debris flowdebris flow

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Catchments demarcation and classification

Map drainage lines on site

(7) Develop relevant regolith, engineering geological and geomorphological models(6) Identify facilities and population at risk, and their degree of proximity(5) Demarcate boundaries and types of catchment(4) Examine rainfall records and effects(3) Validate historical landslides(2) Delineate study area(1) Determine study objectives and approach


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Screening Criteria

Matching of Catchments & Houses

(15) Make conclusion and recommendation(14) Evaluate risk management strategy(13) Analyze risk(12) Assess design events(11) Carry out consequence assessment(10) Carry out frequency assessment(9) Identify possible debris runout paths and influence zones(8) Formulate hazard models(7) Develop relevant regolith, engineering geological and geomorphological models(6) Identify facilities and population at risk, and their degree of proximity (5) Demarcate boundaries and types of catchment(4) Examine rainfall records and effects(3) Validate historical landslides(2) Delineate study area(1) Determine study objectives and approach

(16) Document findings


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Colluvium

Terrain and RegolithClassification

Geological map

Colluvium

Weathered rockShallow failureShallow failure

Large failureLarge failure

ColluviumColluvium : shallow : shallow Weathered rock :Weathered rock :‘‘RetreatRetreat’’

Small to medium scale failureSmall to medium scale failure

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(9) Carry out frequency assessment(8) Formulate hazard models(8) Formulate hazard models(7) Develop relevant regolith, engineering geological and geomor(7) Develop relevant regolith, engineering geological and geomorphological modelsphological models(6) Identify facilities and population at risk, and their degree(6) Identify facilities and population at risk, and their degree of proximity of proximity (5) Demarcate boundaries and types of catchment(5) Demarcate boundaries and types of catchment(4) Examine rainfall records and effects(4) Examine rainfall records and effects(3) Validate historical landslides(3) Validate historical landslides(2) Delineate study area(2) Delineate study area(1) Determine study objectives and approach(1) Determine study objectives and approach


Hazard ModelHazard Model

TypeType(by (by catchment )catchment )

CC == channelized channelized debris flowdebris flow

TT == Mixed debris Mixed debris flow/avalanche flow/avalanche along topographic along topographic depressiondepression

SS == Open slope debris Open slope debris slide/avalancheslide/avalanche

ScaleScale

H1 H1 = 50 m= 50 m33 notional notional (20 to 200 m(20 to 200 m33))H2 H2 = 500 m= 500 m33 notional notional (200 to 2,000 m(200 to 2,000 m33))H3H3 == 5,000 m5,000 m33 notional notional (2,000 to 20,000 m(2,000 to 20,000 m33))H4H4 == 20,000+ m20,000+ m33 notional notional (> 20,000 m(> 20,000 m33))

CC

TT

SS

a,ba,ba,ba,b

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(9) Carry out frequency assessment(8) Formulate hazard models(7) Develop relevant regolith, engineering geological and geomor(7) Develop relevant regolith, engineering geological and geomorphological modelsphological models(6) Identify facilities and population at risk, and their degree(6) Identify facilities and population at risk, and their degree of proximity of proximity (5) Demarcate boundaries and types of catchment(5) Demarcate boundaries and types of catchment(4) Examine rainfall records and effects(4) Examine rainfall records and effects(3) Validate historical landslides(3) Validate historical landslides(2) Delineate study area(2) Delineate study area(1) Determine study objectives and approach(1) Determine study objectives and approach


Typical Landslide Frequency AssessmentTypical Landslide Frequency Assessment

• Assess the baseline landslide frequency for the different terrain units and landslide types

• Construct magnitude-frequency curves, accounting for landslide type and volume (and recognition in API)

• Spatially distribute and adjust area-based frequency to account for susceptibility and expert panel judgment

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Susceptibility Analysis Susceptibility Analysis ––where landslides may more likely occurwhere landslides may more likely occur

HistoricalHistoricallandslideslandslides

LandslideLandslidepotentialpotential

(by correlation)(by correlation)

LandslideLandslidecorrelationcorrelation

factorsfactors

SlopeSlopeGradientGradient

SolidSolidGeologyGeology

Landslide density distribution by susceptibility analysisLandslide density distribution by susceptibility analysis

00ff

5f5f10f10f20f20f20f20f10f10f

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Landslide Distribution in Area B

6

5

1

0

0

0

1

00

1

2

3

4

5

6

7

8

< 60 60 - 200 200 - 600 600 - 2000

Volume of Landslide

No.

of L

ands

lide

Area B (CDF)

Area B (OHF)

Total Landslide Distribution in All Areas

41

28

51

4

8

2

10

5

10

15

20

25

30

35

40

45

50

< 60 60 - 200 200 - 600 600 - 2000

Volume of Landslide

No.

of L

ands

lide

Total Area (CDF)

Total Area (OHF)

Frequency-Magnitude Distribution

Terrain TypeTerrain Type

--2%2%H2bH2b(600 (600 –– 2,000)2,000)

5%5%12%12%H2aH2a(200 (200 –– 600)600)

47%47%43%43%H1bH1b(60 (60 –– 200)200)

94% 94% **86% 86% **H1aH1a(20 (20 –– 60)60)

BBAAVol. (Vol. (mm33))

* 4000* 4000’’ aerial photo aerial photo recognition factor 50%recognition factor 50%

Landslide frequency analysisH1a: 20 m3 to 60 m3 H1b: 60 m3 to 200 m3

H2b: 600 m3 to 2,000 m3H2a: 200 m3 to 600 m3

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(11) Carry out consequence assessment(10) Identify debris runout paths and influence zones(9) Carry out frequency assessment(9) Carry out frequency assessment(8) Formulate hazard models(8) Formulate hazard models(7) Develop relevant regolith, engineering geological and geomor(7) Develop relevant regolith, engineering geological and geomorphological modelsphological models(6) Identify facilities and population at risk, and their degree(6) Identify facilities and population at risk, and their degree of proximity of proximity (5) Demarcate boundaries and types of catchment(5) Demarcate boundaries and types of catchment(4) Examine rainfall records and effects(4) Examine rainfall records and effects(3) Validate historical landslides(3) Validate historical landslides(2) Delineate study area(2) Delineate study area(1) Determine study objectives and approach(1) Determine study objectives and approach


Typical Landslide Consequence AssessmentTypical Landslide Consequence Assessment

• Assess debris runout paths (debris may not always travel down the steepest path)

• Assess debris mobility, using empirical debris runout data and debris dynamic modelling (2- or 3-D mobility models)

• Consider effects of landslide volume and mechanisms, debris runout mechanisms, entrainment/deposition, etc.

• Assess vulnerability factors for different hazards• Assess temporal and spatial distribution of population

at risk• Consider possibility of building collapse and other

knock-on effects

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DEM Catchment-facility matching

Probabilistic matching tableGIS-based runout path

Facility at risk Boundary segments

Terrain typeTerrain units

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(11) Carry out consequence assessment(10) Identify debris runout paths and influence zones(9) Carry out frequency assessment(9) Carry out frequency assessment(8) Formulate hazard models(8) Formulate hazard models(7) Develop relevant regolith, engineering geological and geomor(7) Develop relevant regolith, engineering geological and geomorphological modelsphological models(6) Identify facilities and population at risk, and their degree(6) Identify facilities and population at risk, and their degree of proximity of proximity (5) Demarcate boundaries and types of catchment(5) Demarcate boundaries and types of catchment(4) Examine rainfall records and effects(4) Examine rainfall records and effects(3) Validate historical landslides(3) Validate historical landslides(2) Delineate study area(2) Delineate study area(1) Determine study objectives and approach(1) Determine study objectives and approach


Consequence AssessmentConsequence Assessment

•• Consequence =Consequence =ΣΣ (no. of people in a facility) (no. of people in a facility) ×× (Vulnerability Factor)(Vulnerability Factor)

Average number of people expected to be present in the facility at any time (i.e. accounting for temporal probability of presence). For the construction of the F-N curve, need to consider the temporal presence of different number of people in probabilistic terms (e.g. via an Event Tree). Population survey may be required.

Corresponds to spatial relationship between the people and landslide, with consideration of mechanism and scale of landslide, debris mobility, any structural protection, chance of escape, etc.

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0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 20 40 60 80 100 120 140 160Distance that Distal End of Debris Travels beyond

the Location of the Small House (m)

Deg

ree of

Dam

age to

Gro

und

Floo

r of S

mall H

ouse

0.00030.00490.05630.18720.40420.52830.64400.74430.78730.82490.85700.88350.9044SH2b(600 –2000)

0.00000.00000.00030.02650.14510.25150.38130.51510.57790.63540.68640.73000.7656SH2a

(200 – 600)

0.00000.00000.00000.00000.00730.03240.08600.17140.22170.27300.32240.36790.4071SH1b

(60 - 200)

0.00000.00000.00000.00000.00000.00000.00040.00740.01720.03240.05230.07500.0977SH1a

(20 – 60)

1301201008060504030252015105

Proximity Zone (Plan Distance in m of Facility from Source of Landslide)Landslide Volume

(m3)

20 20 –– 60 m60 m3 3

60 60 –– 200 m200 m3 3

200 200 –– 600 m600 m3 3 600 600 –– 2,000 m2,000 m3 3

•• Empirical correlation (travel angle and distance)Empirical correlation (travel angle and distance)

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5,000304

1,0001,000

2025

3

1,0005,000

1520

2

500500

811

1

ξ(m/s2)

φ(deg)

Gp

Probabilistic DistributionProbabilistic Distributionfor Long Runout Casesfor Long Runout Cases

Small

~50%

~30%

~20%

Prob.

Increasing mobilityIncreasing mobility

•• Dynamic Dynamic modellingmodelling (probabilistic runout parameters) (probabilistic runout parameters)

Historical Runout DataHistorical Runout Data

Long runout casesback-analyzed by DMM

Travel Distance (m)Tra

vel A

ngle

(deg

ree)

Cases backCases back--analyzed by DMManalyzed by DMM

No.

of L

ands

lides

~20%~30%

~50%

Gp 1 Gp 2 Gp 3 Gp 4

Frequency of Damage

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(15) Make conclusion and recommendation(14) Evaluate risk management strategy(13) Analyze risk(12) Assess design events

(11) Carry out consequence assessment(11) Carry out consequence assessment(10) Identify debris runout paths and influence zones(10) Identify debris runout paths and influence zones(9) Carry out frequency assessment(9) Carry out frequency assessment(8) Formulate hazard models(8) Formulate hazard models(7) Develop relevant regolith, engineering geological and geomor(7) Develop relevant regolith, engineering geological and geomorphological modelsphological models(6) Identify facilities and population at risk, and their degree(6) Identify facilities and population at risk, and their degree of proximity of proximity (5) Demarcate boundaries and types of catchment(5) Demarcate boundaries and types of catchment(4) Examine rainfall records and effects(4) Examine rainfall records and effects(3) Validate historical landslides(3) Validate historical landslides(2) Delineate study area(2) Delineate study area(1) Determine study objectives and approach(1) Determine study objectives and approach


< 10< 10--55

< 5 x 10< 5 x 10--66 < 10< 10--66

< 10< 10--77

Individual Risk (IR)Individual Risk (IR) and Frequency of Damage

2525°° AngularAngular

elevationelevation

Individual Risk (IR) < 10Individual Risk (IR) < 10--55 /year/yearAcceptableAcceptable

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Individual Risk (IR)Individual Risk (IR)

Individual Risk Individual Risk (IR) < 10(IR) < 10--55 /year/year

AcceptableAcceptable< 10< 10--55

< 5 x 10< 5 x 10--66

< 10< 10--66

< 5 x 10< 5 x 10--77

< 10< 10--77

Risk contribution Risk contribution from different terrain from different terrain

unitsunits

Societal RiskSocietal RiskSocietal risk of 76 planned Small Houses

= 1.8 x 10-4 PLL/year

• Risk level to an individual living in a Small House is acceptable

• High concentration of Small Houses near the hillside, and overall risk to the community not ‘unacceptable’ but should be evaluated by ALARP principle

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(15) Make conclusion and recommendation(14) Evaluate risk management strategy(13) Analyze risk(13) Analyze risk(12) Assess design events(12) Assess design events



ALARP Principle : Cost-benefit Analysis

Maximum Justifiable ExpenditureMaximum Justifiable Expenditure

= Risk x Design Life x Equivalent Value of Life= Risk x Design Life x Equivalent Value of Life

Cost of Small HousesCost of Small Houses

= 76 x (700 x 3 x HK$ 1,500)= 76 x (700 x 3 x HK$ 1,500)

= HK$ 250 Million = HK$ 250 Million

= 1.8 x 10= 1.8 x 10--44 x 120 x HK$ 33 Millionx 120 x HK$ 33 Million

= HK$ 0.7 Million= HK$ 0.7 Million (~ 0.3% of cost of small houses)(~ 0.3% of cost of small houses)

Based on:Based on:Value of life = $33MValue of life = $33MAversion factor = 1Aversion factor = 1

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Risk Mitigation Based on ALARP Principle

Max. Just. ExpenditureMax. Just. Expenditure= $ 0.7 Million= $ 0.7 Million

Not costNot cost--effectiveeffective

Possible SchemePossible Scheme

(1) Flexible barrier(1) Flexible barrierCost ~ $ 0.7 MCost ~ $ 0.7 M

(2) Raised platform (2) Raised platform Cost ~ $ 0.8 MCost ~ $ 0.8 M

HouseHouseRaisedRaisedplatformplatformCost exceeds $20 MCost exceeds $20 M

Large checkLarge check--damsdams

(15) Make conclusion and recommendation(15) Make conclusion and recommendation(14) Evaluate risk management strategy(14) Evaluate risk management strategy(13) Analyze risk(13) Analyze risk(12) Assess design events(12) Assess design events


(16) Document findings and communicate risk


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Ling Pei Natural Terrain Hazard StudyLing Pei Natural Terrain Hazard Study

ADR 4/2004ADR 4/2004

Thank YouThank You

practical qra models - ags (hk · 1 practical qra models for natural terrain hazards wing sun...

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