Intensive Course on QRA – Barcelona 2008 FRAMEWORK FOR LANDSLIDE QUANTITATIVE RISK ASSESSMENT - an overview- Jordi Corominas Department of Geotechnical Engineering and Geosciences Civil Engineering School of Barcelona Technical University of Catalonia - UPC Enginyers de Camins, Canals i Ports
33
Embed
FRAMEWORK FOR LANDSLIDE QUANTITATIVE … Course on QRA – Barcelona 2008 FRAMEWORK FOR LANDSLIDE QUANTITATIVE RISK ASSESSMENT - an overview-Jordi Corominas Department of Geotechnical
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Inte
nsiv
eC
ours
e on
QR
A –
Bar
celo
na 2
008
FRAMEWORK FOR LANDSLIDE QUANTITATIVE RISK ASSESSMENT
- an overview-Jordi Corominas
Department of Geotechnical Engineering andGeosciences
Civil Engineering School of BarcelonaTechnical University of Catalonia - UPC
Enginyers de Camins, Canals i Ports
Inte
nsiv
eC
ours
e on
QR
A –
Bar
celo
na 2
008
Definitions and terminologyLandslide Risk Management frameworkComponents of the QRAQualitative vs. Quantitative assessmentPurpose of the assessment and scale of work
CONTENTS
Inte
nsiv
eC
ours
e on
QR
A –
Bar
celo
na 2
008
Landslide Susceptibility. The classification, volume (or area), and spatial distribution of landslides which exist or potentially may occur in an area.
DEFINITIONS AND TERMINOLOGY
Inte
nsiv
eC
ours
e on
QR
A –
Bar
celo
na 2
008 Hazard The description of landslide hazard should include the
location, volume (or area), classification and velocity of the potential landslides and any resultant detached material, and the likelihood of their occurrence within a given period of time.
DEFINITIONS AND TERMINOLOGY
Inte
nsiv
eC
ours
e on
QR
A –
Bar
celo
na 2
008
Risk – A measure of the probability and severity of an adverse effect to health, property or the environment. (a) For life loss, the annual probability that the person most at risk in the risk zone will lose his or her life taking account of the landslide hazard, and the temporal spatial probability and vulnerability of the person (b) For property loss, the annual probability of the consequence or the annualised loss taking account of the elements at risk, their temporal spatial probability and vulnerability
DEFINITIONS AND TERMINOLOGY
Rockfall at Upper Island Cove . Source:www.heritage.nf.ca/environment/car1.html
Inte
nsiv
eC
ours
e on
QR
A –
Bar
celo
na 2
008
DEFINITIONS AND TERMINOLOGY
Elements at Risk – The population, buildings and engineering works, economic activities, public services utilities, infrastructure and environmental features in the area potentially affected by the landslide hazard
Vulnerability – The degree of loss to a given element or set of elements within the area affected by the landslide hazard. It is expressed on a scale of 0 (no loss) to 1 (total loss).
Zoning: The division of land into homogeneous areas or domains and their ranking according to degrees of actual or potential landslide susceptibility, hazard or risk.
Inte
nsiv
eC
ours
e on
QR
A –
Bar
celo
na 2
008
THE RISK MANAGEMENT FRAMEWORK
Fell et al. 2005
Inte
nsiv
eC
ours
e on
QR
A –
Bar
celo
na 2
008
LANDSLIDE RISK ASSESSMENT AND ZONING
Location, volume and classification ofexisting landslides
Location, volume and classification ofpotential landslides
Areas with a potential to experiencelandsliding in the future (traveldistance – head retreat)
Elements at riskVulnerabillitySpatial and temporal probabilityPotential damage (scenarios)
Hazard assessmentLandslide hazard map
Risk assessmentLandslide risk map
Inte
nsiv
eC
ours
e on
QR
A –
Bar
celo
na 2
008
Qualitativeis the most common adopted approach by many agencies in
the worldGoal: (a) evaluate and rank relative risk; (b) identification of
hotspots and prioritisation of actions to be undertaken
QuantitativeQRA is more and more a requirement of the administrations
and professional societies. It allows
(a) the direct comparison of the risk levels between areas(b) the cost-benefit analysis(c) the consideration of risk tolerance and acceptability
LANDSLIDE RISK ASSESSMENT AND ZONING: QUALITATIVE VS. QUANTITATIVE
Inte
nsiv
eC
ours
e on
QR
A –
Bar
celo
na 2
008
QUALITATIVE VS. QUANTITATIVE. SUSCEPTIBILITY MAPPING DESCRIPTORS
Large Landslides on Natural Slopes
Small Landslides on Natural Slopes
Rock FallsSusceptibility Descriptors
(a) Quantitative susceptibility descriptors
Factor of safety values from stability models
Factor of safety values from stability models
Factor of safety values from stability models
Absolute
Scores of contributing factors obtained from data treatment techniques
Geomechanicalratings (SMR, RMS)
Relative
(b) Qualitative susceptibility descriptors
Overlapping of index maps with or without weighting
Overlapping of index maps with or without weighting
Index map or parameter map
Presence or absence of activity indicators
% of area covered by landslide deposits
Density of scars on a rock slope
Presence or absence of landslides and their degree of preservation
# of landslides per square kilometer
Presence of absence of potential instability factors (cracks, dipping joints)
Field geomorphological analysis
Fell et al, 2008
Inte
nsiv
eC
ours
e on
QR
A –
Bar
celo
na 2
008
Very lowVery lowVery lowNon-susceptible
LowLowVery lowLow
MediumMediumLowMedium
HighHighMediumHigh
MagnitudeHighMediumLow
Frequency
HAZARD MATRIX: MAGNITUDE - FREQUENCY RELATIONSHIP
Inte
nsiv
eC
ours
e on
QR
A –
Bar
celo
na 2
008
MAGNITUDE – FREQUENCY. SINGLE LANDSLIDES VERSUS LANDSLIDING EVENTS
Landslide magnitude. It isa measure of the landslidesize (i.e. volume, area)
The magnitude of a landsliding event can be expressed by the number(or density) of triggeredlandslides
Inte
nsiv
eC
ours
e on
QR
A –
Bar
celo
na 2
008
ASSESSMENT OF THE LANDSLIDE RISK
R = H x Σ (E x V) Varnes (1984)
R: Risk. Expected damage from the occurrence of a hazardous event of a given magnitude
H: Hazard (probability of occurrence of a damaging event –i.e. rockfall- in a given place and in a given time span)
E: Exposed elementV: Vulnerability
Inte
nsiv
eC
ours
e on
QR
A –
Bar
celo
na 2
008
Risk maps provide a global view of the expected annualdamage due to the potential landslide hazardBased on the information supplied by risk maps and cost-benefit analyses, either protective or reinforcement workscan be envisaged to minimize risk level whereas alertsystems can be set up in places to protect human livesRisk maps are documents that are not intended for directuse in urban planning and development because theyreflect the current situation of the potential damages but notthe spatial distribution of the hazardous zones.Non-urbanized areas are usually displayed as having lowrisk level regardless the level of the existing hazard which isnot appropriate
ASSESSMENT OF THE LANDSLIDE RISK
Inte
nsiv
eC
ours
e on
QR
A –
Bar
celo
na 2
008
ASSESSMENT OF THE LANDSLIDE RISK
What should be taken into account The elements at riskThe vulnerability of the elements at risk (different vulnerabilities)The expected damages for given scenarios :
- Triggering events of a given magnitude (i.e. rainfall, earthquake, etc)- Landslides with a given probability of occurrence- Cascading effects (i.e. valley damming) - Risk remaining after protection works have been completed- Risk transfer
Inte
nsiv
eC
ours
e on
QR
A –
Bar
celo
na 2
008
FUTURE SCENARIOS
(A) Landslide distribution similar to that of the last 50 yr; (B) Landslideincrease: linear trend; (C) Landslide increase: exponential trend (Remondo et al, 2005)
Inte
nsiv
eC
ours
e on
QR
A –
Bar
celo
na 2
008
DIFFERENT VULNERABILITIES TO LANDSLIDING
Uncertainty on the expected landslidemagnitude and frequency
Vulnerability depends on the landslidemechanisms
Damage depends on the location of the exposed element relative to the landslide
Inte
nsiv
eC
ours
e on
QR
A –
Bar
celo
na 2
008
Van Westen et al, 2005
DIFFERENT VULNERABILITIES TO LANDSLIDING
The resistance of a building may be high enough to resist the impact of a falling block but it may be insuficient toavoid the development of tensioncracks due to differential displacementsproduced by a translational slide
Inte
nsiv
eC
ours
e on
QR
A –
Bar
celo
na 2
008
ASSESSING VULNERABILITY TO LANDSLIDING
Dai et al, 2002
Inte
nsiv
eC
ours
e on
QR
A –
Bar
celo
na 2
008
QUANTITATIVE RISK ASSESSMENT
Risk to properties (i.e building)
R(P) = P(L) x P(T:L) x P(S:T) x P(T:P) x P(S:P) x V(D) X C
R(P): expected annual loss due to landsliding (€/yr)P(L): probability of occurrence of a landslide of a given
magnitudeP(T:L): probability of a landslide reaching the building levelP(S:T): probability of the building being on the landslide pathV(D): vulnerability of the building C: cost of the building
the analysis must consider all landslide magnitudes and all the potentially affected buildings
Small < 1:100,000 Landslide inventory and susceptibility to inform policy makers and the general public
>10,000 square
kilometres
Medium 1:100,000
to 1:25,000
Landslide inventory and susceptibility zoning for regional and local development;
or very large scale engineering projects. Preliminary level hazard mapping for local
areas
1000 – 10,000 square kilometres
Large 1:25,000
to 1:5,000
Landslide inventory, susceptibility and hazard zoning for local areas
Preliminary level risk zoning for local areas and the advanced stages of planning for large
engineering structures, roads and railways
10-1000 square kilometres
Detailed > 5,000
Intermediate and advanced level hazard and risk zoning for local and site specific areas and for
the design phase of large engineering structures, roads and railways
Several hectares to tens of square
kilometres
Inte
nsiv
eC
ours
e on
QR
A –
Bar
celo
na 2
008
ZONING LEVELS & ACTIVITIES: ASSESSING LANDSLIDE FREQUENCY
For seismically-induced landslides, analyse displacements using ‘Newmark’ type analyses and for liquefiable soils, the likelihood of liquefaction and flow sliding.
Assess geotechnical parameters of the soils. Model slope factors of safety from geotechnical parameters and rainfall frequency or piezometric data.
Advanced
For seismically induced landsliding, relate sliding to seismic loading including the peak ground acceleration and magnitude of the earthquake using empirical methods.
Analysis of rainfall including the effects of antecedent rainfall. Search for critical rainfall and its return period
Prepare series of landslides using proxy data such as silent witnesses (e.g. damage to trees), dendrochronology and dating techniques
Assess the historic frequency from incident databases: develop and use frequency volume curves.
Intermediate
Identify and count the number of landslides from aerial photographs taken at known time intervals and from field work
relative freshness of the morphological features of the scars and landside depositstaking into account the presence of active geomorphic events
Basic
Activities
Inte
nsiv
eC
ours
e on
QR
A –
Bar
celo
na 2
008
Basic level
Geomorphological approach
ZONING LEVELS & ACTIVITIES: ASSESSING LANDSLIDE FREQUENCY
Inte
nsiv
eC
ours
e on
QR
A –
Bar
celo
na 2
008
ZONING LEVELS & ACTIVITIES: ASSESSING LANDSLIDE FREQUENCY
Basic level
Geomorphological approach
i.e.: Density of scars, # open cracks
Inte
nsiv
eC
ours
e on
QR
A –
Bar
celo
na 2
008
ZONING LEVELS & ACTIVITIES: ASSESSING LANDSLIDE FREQUENCY
For seismically-induced landslides, analyse displacements using ‘Newmark’ type analyses and for liquefiable soils, the likelihood of liquefaction and flow sliding.
Assess geotechnical parameters of the soils. Model slope factors of safety from geotechnical parameters and rainfall frequency or piezometric data
Advanced
For seismically induced landsliding, relate sliding to seismic loading including the peak ground acceleration and magnitude of the earthquake using empirical methods.
Analysis of rainfall including the effects of antecedent rainfall. Search for critical rainfall and its return period
Prepare series of landslides using proxy data such as silent witnesses (e.g. damage to trees), dendrochronology and dating techniques
Assess the historic frequency from incident databases: develop and use frequency volume curves.
Intermediate
Identify and count the number of landslides from aerial photographs taken at known time intervals and from the field work
relative freshness of the morphological features of the scars and landside deposits taking into account the presence of active geomorphic events
Basic
Activities
Inte
nsiv
eC
ours
e on
QR
A –
Bar
celo
na 2
008
ZONING LEVELS & ACTIVITIES: ASSESSING LANDSLIDE FREQUENCY
Intermediate level
Landslide incident records
Hungr et al. 1998
Inte
nsiv
eC
ours
e on
QR
A –
Bar
celo
na 2
008
ZONING LEVELS & ACTIVITIES: ASSESSING LANDSLIDE FREQUENCY
For seismically-induced landslides, analyse displacements using ‘Newmark’ type analyses and for liquefiable soils, the likelihood of liquefaction and flow sliding.
Assess geotechnical parameters of the soils. Model slope factors of safety from geotechnical parameters and rainfall frequency or piezometric data
Advanced
For seismically induced landsliding, relate sliding to seismic loading including the peak ground acceleration and magnitude of the earthquake using empirical methods.
Analysis of rainfall including the effects of antecedent rainfall. Search for critical rainfall and its return period
Prepare series of landslides using proxy data such as silent witnesses (e.g. damage to trees), dendrochronology and dating techniques
Assess the historic frequency from incident databases: develop and use frequency volume curves.
Intermediate
Identify and count the number of landslides from aerial photographs taken at known time intervals and from the field work
relative freshness of the morphological features of the scars and landside deposits taking into account the presence of active geomorphic events
Basic
Activities
Inte
nsiv
eC
ours
e on
QR
A –
Bar
celo
na 2
008
ZONING LEVELS & ACTIVITIES: ASSESSING LANDSLIDE FREQUENCY
Advanced levelProbabilistic models
Salciarini et al. 2007
Inte
nsiv
eC
ours
e on
QR
A –
Bar
celo
na 2
008
REFERENCES
Fell, R.; Corominas, J. ; Cascini, L.; Leroi, E. and Savage, W.Z. (2008, in press)“International Guidelines for Landslide Susceptibility, Hazard and Risk Zoning”. Engineering Geology