Lesson 5 Landslide 5.01 Prof. R. Nagarajan, CSRE , IIT Bombay GNR - - PowerPoint PPT Presentation

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

Lesson 5 Landslide

5.01

GNR 639

• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

• What is it?
• Causes
• What happens
• Where does it occur?
• Indicators?
• Monitoring
• Prevention
• Vulnerability
• Preparedness?

Landslide

5.02

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

The cohesion of materials on mountain slope is disturbed by exogenous or endogenous

• factors. Movement debris from these slope inflict damages.

Mass wasting is a natural process that continuously shapes the landscape that occurs without human involvement. Any movement of a mass of rock, soil or both down a slope by gravity, is called “landslide”. Depending on the thickness of the material removed from the in-situ surface, they are classified as

• superficial (0-3m) occur in areas that have slopes with high permeable soils on top of low

permeable bottom soils.

• shallow (3-10m), intermediate (10-30m), deep-seated (30-100m),
• very deep seated (100-300mm) the sliding surface is located below the maximum rooting

depth of trees (> 10meters). It involves deep regolith, weathered rock, and/or bedrock and includes large slope failure associated with translational, rotational, or complex movement.

• and extremely deep seated (>300m).

5.03

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

Common causes of landslides in soil are: 1) Falls of the parent material or residual soil from above, due to natural weathering processes; 2) Increased moisture content and consequent softening of the soil, or a rise in the water table. They are due to excessive tree clearance, poorly executed soak-away drainage or septic systems, or heavy rainfall; 3) Excavation without adequate support, increased surface load from fill placement, or inadequately designed shallow foundations; 4) Natural erosion at the toe of the slope due to scour by a river or the sea 5) Re-activation of an ancient landslide.

5.04

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

Causes include factors that increase the effects of down-slope forces and contribute to low or reduced strength.

Natural causes

• Increase in pore water pressure by saturation of slope material from either intense or prolonged rainfall

and seepage

• vibrations caused by earthquakes
• undercutting of cliffs and banks by waves or river erosion
• volcanic eruptions.

Human causes

• removal of vegetation
• interference or modification of natural drainage
• leaking pipes such as water and sewer reticulation
• modification of slopes by construction of roads, railways, buildings, etc
• verloading slopes
• mining and quarrying activities
• vibrations from heavy traffic, blasting, etc
• excavation or displacement of rocks.

5.05

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

Landslides are reported from landscapes are:

• commonly characterised by cliffs, steep slopes of colluvium deposits
• r gentle slopes of unstable geology
• slopes subjected to periods of prolonged or intense rainfall.
• locations which have previous evidence of landslide activity
• slopes made up of low strength, sensitive, collapsible weathered or

disjointed material with internal and external weaknesses.

5.06

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

Source courtesy: lampre-project.eu

5.07

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

Potential landslide sites

• Saturated ground or seeps in areas which are not typically wet
• new cracks and scarps or unusual bulges in the ground, roads or pavements
• movement of ancillary structures such as decks and patios in relation to a house
• Sticking doors and windows
• tilting or cracking of concrete floors and foundations
• broken water lines and other underground utilities
• leaning telephone poles, trees, retaining walls or fences
• ffset fence lines
• sunken or displaced road surfaces or kerbs
• a rapid increase in creek water levels, possibly accompanied by greater turbidity.

5.08

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

The observations prior to the reported landslide events 1)

• pen cracks, or steps, along contours;

2) ground water seepage, or springs; 3) bulging in the lower part of the slope; 4) hummocky ground; 5) trees leaning down slope, or with exposed roots; 6) debris/fallen rocks at the foot of a cliff; 7) tilted power poles, or fences 8) cracked or distorted structures. 5.09

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

• Rapid snow melting caused by sudden warming spells or by rain falling on snow can

add to hillside soil. Rain-on-snow events commonly reduce the water content of the snowpack and add sufficient water to soils to be significant in triggering landslides.

• The sudden lowering of the water level on a slope can trigger landslides in earth

dams, along coastlines and on the banks of lakes, reservoirs, canals and river.

• Increase in groundwater levels on hill slopes following periods of prolonged above-

normal precipitation can build up pore pressure and reduce effective strength of saturated slope materials and can trigger landslides.

• Landslides occur during or immediately after earthquakes as a result of two separate

but interconnected processes - seismic shaking and pore-water pressure generation. Seismically generated landslides tend to be more widespread and sudden.

• Cliff failures - Coastal cliffs and headlands exist are subjected to repeated cycles of

wetting and drying. They are also accompanied by the expansive effect of salt crystal growth in gaps in the rocks. 5.10

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

• Sand dune escarpment failures - Waves produced by large oceanic storms erode beaches

and cut escarpments into dunes. After an escarpment has eroded, assets located on the land are damaged by subsequent slumping of the dune.

• landslide dam, is a barrier lake across a river by debris flow, rock avalanche or volcano. A

common failure scenario is overflowing with subsequent dam breach and erosion by the

• verflow stream. Landslide dams are responsible for two types of flooding: back flooding

(upstream flooding) upon creation and downstream flooding upon failure. Compared with catastrophic down flooding, relative slow back flooding typically presents little life hazard, but property damage can be substantial. Preventive measure are 1) Stabilization of slope forming material; 2) Surface drainage control to prevent infiltration and pre pressure development; 3) Arrest of boulder movement – net, wall and Diversion of debris movement. Warning Devices such as trip wires, telephone alarm, sirens, evacuation plane etc are used. Warning devices of landslides would alert the effects of a materialized danger by slight modification. 5.11

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• Prof. R. Nagarajan, CSRE , IIT Bombay

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Type of movement Type of material Engineering soils Bed rock Predominantly coarse Predominantly fine Fall Rock fall Debris fall Earth fall Topple Rock topple Debris topple Earth topple Slide Rock slide Debris slide Earth slide Spread Rock spread Debris spread Earth spread Flow Rock flow Debris flow Earth flow

Velocity class

Description

Velocity (mm/sec) Typical velocity Probable destruction 7 Extremely Rapid > 5 X 103 > 5 m/sec Catastrophe of major violence, building destroyed by impact of displaced material 6 Very Rapid 5x103 to 5x101 5 m/sec to 3 m/min Some lives lost; velocity too great to permit all persons to escape 5 Rapid 5x101 to 5x10-1 3 m/min to 1.8 m/hr Escape evacuation possible; structu possession and equipments destroyed 4 Moderate 5x10-1 to 5x10-3 1.8 m/hr to 13 m/month Some temporary and insensitive structures can be temporarily maintained 3 Slow 5x10-3 to 5x10-5 13 m/month to 1.6 m/year Remedial construction can be undertaken during movement; insensitive structures can be maintained with frequent maintenan work if total movement is not large during a particular acceleration phase 2 Very slow 5x10-5 to 5x10-7 1.6 m/year to 16 mm/year Some permanent structures undamaged by movement 1 Extremely slow < 5x10-7 < 16 mm /year Imperceptible without instruments, construction possible with precautio

5.12

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

Source coutressy: usgs.gov

5.13

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

• Crown is not displaced material adjacent to highest parts of main scarp;
• Main scarp is the steep surface on undisturbed ground at upper edge of landslide

caused by movements of displaced material, away from undisturbed ground; it is visible part of the surface rupture;

• Top is the highest point of contact between displaced material and main scarp; Head is

upper parts of landslide along contact between displaced material and main scarp;

• Minor scarp is the steep surface on displaced material of landslide produced by

differential movements within displaced material;

• Main body is the part of displaced material of landslide that overlies surface of

rupture between main scarp and toe or surface of rupture;

• Foot is portion of landslide that has moved beyond toe of surface of rupture and
• verlies original ground surface;
• Tip is point on toe and farthest from top of the landslide;
• Toe is the lower curved margin of displaced material of a landslide, most distant

from main scarp;

5.14

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

• Surface of rupture is the surface that forms the lower boundary of displaced

material below original ground surface; mechanical idealization of surface of rupture is called slip surface;

• Toe of surface of rupture is the intersection between lower part of the surface of

rupture of a landslide and original ground surface;

• Surface of separation is the part of original ground surface overlain by foot of

landslide; Displaced material from its original position on slope by movement in landslide forms both depleted mass and accumulation;

• Zone of depletion is an area of landslide within which displaced material lies

below original ground surface; Zone of accumulation is an area of landslide which displaced material lies above original ground surface;

• Depletion is the volume bounded by main scarp, depleted mass and original

ground surface; Depleted mass is the volume of displaced material that overlies surface of rupture but underlies original ground surface;

• Accumulation is volume of displaced material that lies above original ground

surface;

5.15

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

5.16

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

Source courtesy: projects.noc.ac.in

5.17

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• Prof. R. Nagarajan, CSRE , IIT Bombay

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Variables in run out studies

• Maxi. Run out distance- Lr

Flowage Index Lf Specific run out Spec r Relative run out Rel.r Mean depth to terminal depth D.r.t Run out volume V cubic r Area f run out A r Mean angle of surface rupture β sor Maimum angle of runout depth β r Mean angle of terminal slope β t Mean depth of scar Ds Length of scar Ls Area of scar As Initial volume V Liquid limit Wl Water content Ws Clay content C Approximate Mobility Index AMI Reciprocal of AMI 1./AMI Critical thickness of run out Tcr

5.18

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

Class Description 1 Slopes which show no evidence of previous landslide activity and which by stress analysis , analogy with other slopes or by analysis of stability factors are considered highly unlikely to develop landslides in the foreseeable future. 2 Slopes which show no evidence of previous landslide activity but which are considered likely to develop landslides in the

• future. Landslide potential indicated by stress analysis,

analogy with other slopes or by analysis of stability factors;several subclasses may be defined. 3 Slopes with evidence of previous landslide activity but which have not undergone movement in the previous 100 years. 4 Slopes infrequently subject to new or renewed landslide

• activity. Triggering of landslides results from events with

recurrence interval greater than five years. 5 Slopes frequently subject to new or renewed landslide

• activity. Triggering of landslides results from events with

recurrence intervals of upto five years. 6 Slopes with active landslides. Material is continually moving, and landslide forms are fresh and well defined. Movement may be continuous or seasonal.

Intensity Damage None, Building is intact 1 Negligible: Hairline cracks in walls or structural members, no distortion of structure or detachment of external architectural details. 2 Light: Building continue to be habitable; rapair not urgent. Settlement of foundations , distortion of structure and inclination of walls are not sufficient to compromise overall stability. 3 Moderate: walls out of perpendicular by 1-2 degrees, or substantial cracking has

• ccurred to structural members; or foundations have settled during differential

subsidence of at least 15 cm; building requires evacuation and rapid attention to ensure its continued life. 4 Serious: walls out of perpendicular by several degrees; open cracks in walls; fracture of structural members; fragmentation of masonry; differential settlement of at least 25 cm compromises foundation; floors may be inclined by 1-2 degrees, or ruined by soil heave; internal partition walls will need to be replaced; door and window frames too distorted to use; occupants must be evacuated and major repairs carried out. 5 Very serious: walls out of plumb by 5-6 degrees; structure grossly distorted and differential settlement will have seriously cracked floors and walls or caused major rotation or slewing of the building(wooden buildings may have detached completely from their foundations)partition walls and brick infill will have at least partly

• collapsed. roof may have partially collapsed; outhouses, poches and patios may have

been damaged more seriously than the principal structure itself. Occupants will need to be rehoused on a long-term basis, and rehabilitation of the building will probably not be feasible. 6 Partial collapse: Requires immediate evacuation of the occupants and cordoning off the site to prevent accidents with falling masonry. 7 Total collapse: Requires clearance of the site.

5.19

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

Factors and Causes of landslides and slope instability (Cooke & Doornkamp 1974) Factors that contribute to increased shear stress:

• Removal of lateral support by erosion of the lower part of the slope, by artificial cuts etc.
• surcharge; loading of the slope crest with an external load
• internal increase in the weight of the slope material (as by water saturation)
• ground vibrations and the earthquake mechanism of landslide generation
• undermining of the slope
• lateral pressure in cracks (for example ,by water freezing)
• tectonics of regional tilting

Factors that contribute to reduced shear strength

• properties of clay, such as shrinking and swelling
• gross structure of rock(faults, joints, bedding etc)
• pore pressure effects
• freeze-thaw effects
• drying and desiccation
• loss of capillary tension
• Breakdown of soil structure (weathering reduces effective cohesion c')
• Deterioration of inter-granular cement (reduction of cohesive strength)

Parameters of Landsliding

• Total vertical fall
• slide mass
• Velocity of movement
• Horizontal distance of movement
• Average slope over which the slide moves
• Cohesion of sliding mass
• Topography and geometry of bed surface
• pore pressures within the sliding mass
• shear strength and shear stresses
• Type of failure plane under the sliding mass and its shape
• Mechanism of sliding

5.20

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

5.21

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• Prof. R. Nagarajan, CSRE , IIT Bombay

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Source courtesy: bgs.ac.uk Source courtesy: southamption.ac.uk

5.22

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

Lake formed by landslide debris

5.23

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• Prof. R. Nagarajan, CSRE , IIT Bombay

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Source courtesy: conservationengineers.org

5.24

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• Prof. R. Nagarajan, CSRE , IIT Bombay

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Source courtesy:easyfreshslides.com

5.25

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• Prof. R. Nagarajan, CSRE , IIT Bombay

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Source courtesy:alber.ac.uk

5.26

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

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• Prof. R. Nagarajan, CSRE , IIT Bombay

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Instrumentation monitoring

• Rain gauges – rainfall intensity
• Piezometer – water pressure
• Ecogram – sound of movement
• Video camera – surface movement
• Extensometer – position alteration
• Bench mark – base line observation for measurements

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• Prof. R. Nagarajan, CSRE , IIT Bombay

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Source courtesy: old.settlements.com

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• Prof. R. Nagarajan, CSRE , IIT Bombay

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Source courtesy:livescience.com

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• Prof. R. Nagarajan, CSRE , IIT Bombay

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Vulnerability, exposure and risk assessment of landslides

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• Prof. R. Nagarajan, CSRE , IIT Bombay

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5.34

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

Vulnerability to landsliding depend on

• 1. Run out distance; 2. the volume and velocity of sliding; 3. elements at risk (buildings and other

structures), their nature and their proximity to the slide; 4. the elements at risk (persons), their proximity to the slide, the nature of the building/road that they are in, and where they are in the building, on the road. 5.35

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• Prof. R. Nagarajan, CSRE , IIT Bombay

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Landslide Vulnerability & Notion of Risk

Type of Risk Definition Acceptable Society desires to achieve Tolerable Society wants to live with so as to secure certain net benefits Individual Imposed on a particular individual due to landslide hazard Societal Imposed to society as a whole Voluntary Voluntarily faced to gain benefits Involuntary Imposed by a controlling body, not the free choice of people Specific Evaluated for a specific element at risk Total Sum of specific risks 5.36

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GNR 639 : Natural Disaster And Management

Vulnerability Assessment

• A set of prevailing or consequential conditions, which adversely affect the community’s ability

to prevent, mitigation, prepare for or responds to hazard events.

• These long-term factors, weaknesses of constraints affect a household, community’s or society’s

ability (or inability) to absorb losses after disasters and to recover from the damage.

• Estimating the weakness of elements at risk and analyzing the cause and root of cause which

place these elements at risk.. Because of that in a given situation some people are in trouble while others are relatively protected.

• Hazard is the trigger event, which sets off an earthquake, volcanic eruption, landslide or civil
• conflict. Unsafe Condition is where people and property are exposed to risk of disaster.

community vulnerable to a particular hazard either due to physical environment or unstable economy and low – income levels. 5.37

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• Prof. R. Nagarajan, CSRE , IIT Bombay

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Vulnerability needs to be modelled in a 3-D array based on :

1.Magnitude(M(x)) (x) is the vector of parameters for defining the magnitude of the landslide such as: volume(x1) velocity(x2) depth(x3) Run out(x4) Areal extent(x5) 2.Elements at risk (E (x)) (x) is the vector of elements at risk such as: Physical(building, road, lifelines, etc.) Societal(lives lost, injuries,etc.) Economical(Monetary) Environmental 3.Scale (S) (Specific/local vs.Global / regional)

5.38

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

(source courtesy: NHRA 2010)

5.39

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• Prof. R. Nagarajan, CSRE , IIT Bombay

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GIS-based conceptual integrated system 5.40

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5.41

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

Distributed landslide risk assessment

• It provides a risk map that depicts the level of risk in terms of fatality or economic loss at different locations
• f a given region quantitatively or qualitatively.

Site-specific risk assessment

• Examine possible triggering factors, such as earthquakes or/and rainstorms;
• Identify possible failure modes;
• Estimate probability of failure for each failure mode;
• Evaluate runout behavior of landslide debris for each failure mode;
• Assess the risk for each failure mode; and Sum the risk for all possible failure modes

Landslide risk management

• Planning control - reducing expected elements at risk
• Engineering solution strategy - reduce either the probability of landsliding or spatial impact;
• Acceptance strategy - acceptable or unavoidable;
• Monitoring and warning system strategy - reduce expected elements at risk by evacuation

Risk scenarios 5.42

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Risk management - Landslide

• Risk analysis

Hazard analysis Exposure analysis Vulnerability analysis Socio-economic assessment

• Risk assessment

Evaluation of resilience, coping and adaptive capacity Tolerable / acceptable risks

• Risk communication

Warning systems Maori related risk research Public participation Planning & policy

• Post disaster activities - Emergency management

5.43

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

Capacity Assessment

• Strengths and resources that presents in individuals, and enable them to cope up with,

withstand, prepare for, prevent, mitigation, or quickly recover from a disaster.

• Categorized into - physical/materials, social/organizational and attitudinal / motivational
• factors. Determine how people cope in times of crisis to reduce the damaging effects of

hazards.

• Understanding of people’s previous experience and the coping strategies that they have

developed, or to reduce disaster risk and the controller who has access and control over these resources.

• Capacity Assessment Matrix Hazard Capacities - (Physical and Tools) Capacities ( Financial,

Social, Services) 5.44

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5.45

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

Treatment Slope conditions Remedies Cable anchors Dipping rock beds Prevent / treat early stages of failure Wire meshes Steep rock slopes Contain rock falls Concrete impact wall Moderate slope Contain sliding or rolling blocks Shotcrete Soil or jointed rock Prevent movement Rock filled buttress Strong soils or soft rock Prevent / treat during early stages Gabion wall Strong soils or soft rock Prevent during early stages Crib wall Moderately strong soil Prevention Reinforced earth wall Soil / weathered rock Prevention Concrete gravity wall Soil / rock Prevention Anchored concrete curtain Soil / weathered rock Prevent or treat early to intermediate stage Bored or root wall Soil / weathered rock Prevent or treat early stage

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

Source courtesy:pwri.go.jp

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Source courtesy: sabo-int.org

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• Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management