LANDSLIDE HAZARD MANUAL

Document Sample
LANDSLIDE HAZARD MANUAL Powered By Docstoc
					                LANDSLIDE HAZARD MANUAL
                          Trainer‘s Handbook




                             Access to the basic
                               information and
                            education needed to
                            ensure a healthy and
                           safe life is a right of
                          every human being. It is
                           the duty of those who
                          possess them to actively
                              disseminate them.




                                                                   By: Patrik Meyer


Landslide Hazard Manual               1   www.engineering4theworld.org/LAP
ACKNOWLEDGEMENTS
The author wants to thank the Fulbright Commission for their financial and logistic support
during the work conducted in Chile. In addition, he wants to thank Professors Mauricio
Serracín, Ramón Verdugo, and Francisco Ferrando from the Universidad de Chile for their
unconditional support.



AUTHOR’S STATEMENT
The author of this manual believes that the value of any work is proportional to its capacity
to improve the living conditions of the less fortunate communities of this planet.
The purpose of this simplified manual is to provide an educational resource that should be a
simple but effective tool for the population of developing countries living under the landslide
threat.



REFERENCES
Most of the information and graphical material contained in this manual were gathered from
existing works. However, for the sake of keeping the manual as simple as possible the
references to these works were omitted in the text. Please contact the author
(patrik@engineering4theworld.org) to obtain a copy with full references.




Landslide Hazard Manual                       2   www.engineering4theworld.org/LAP
INDEX

1       BASICS ON LANDSLIDES..................................................................................................................... 4
    1.1     LANDSLIDE’S DRIVING FORCE.................................................................................................................. 4
    1.2       LANDSLIDE SPEED ................................................................................................................................ 5
    1.3       LANDSLIDE MATERIAL ......................................................................................................................... 6
2       LANDSLIDE TYPES .................................................................................................................................. 8
    2.1     SLIDING ................................................................................................................................................ 8
       2.1.1 Rotational Failure ......................................................................................................................... 8
       2.1.2 Translational Failure .................................................................................................................. 10
    2.2     ROCK FALL AND TOPPLING ................................................................................................................. 11
       2.2.1 Rock Fall ....................................................................................................................................... 11
       2.2.2 Rock Toppling............................................................................................................................... 12
    2.3     SPREADING ......................................................................................................................................... 12
    2.4     FAST DEBRIS FLOWS ......................................................................................................................... 12
    2.5     LAHARS (USGS) ................................................................................................................................ 14
3       HOW TO IDENTIFY LANDSLIDE HAZARDS ............................................................................... 15
    3.1          TERRAIN/MORPHOLOGIC FEATURES INDICATING RISK OF A LANDSLIDE .................................... 15
    3.2          ADDITIONAL LANDSLIDE RISK INDICATORS .................................................................................. 17
4       SLOPE DESTABILIZING FACTORS AND LANDSLIDE TRIGGERS .......................................... 19
    4.1     SLOPE DESTABILIZING FACTORS ..................................................................................................... 19
    4.2     TRIGGERING FACTORS ....................................................................................................................... 20
       4.2.1 Intense or Prolonged Rainfall .................................................................................................. 20
       4.2.2 Shocks or Vibrations ................................................................................................................. 22
       4.2.3 Human Intervention ................................................................................................................... 22
    4.3     COMBINATION OF SLOPE CHARACTERISTICS AND TRIGGERING FACTORS FOR LANDSLIDES...... 22
5       HOW TO MINIMIZE LANDSLIDE HAZARDS.............................................................................. 24
    5.1          PASSIVE INTERVENTION ................................................................................................................... 24
    5.2          ACTIVE PREVENTIVE INTERVENTION ............................................................................................... 24
6       DOS AND DON’TS ................................................................................................................................. 29
    6.1          PRIOR TO A POTENTIAL LANDSLIDE DUE TO INTENSE STORMS .................................................... 29
    6.2          WHAT TO DO DURING A LANDSLIDE ................................................................................................ 29
    6.3          WHAT TO DO AFTER A LANDSLIDE .................................................................................................. 29
    6.4          CONSTRUCTION DON’TS .................................................................................................................... 30
7       WORKSHOP TEACHING PROCEDURE .............................................................................................. 32
8       ADDITIONAL RESOURCES AND ANNEXES................................................................................. 33
1     Basics on Landslides

Landslides are rock, earth, or debris flows on slopes due to gravity. They can occur
on any terrain given the right conditions of soil, moisture, and angle of slope.
Integral to the natural process of the earth’s surface geology, landslides serve to
redistribute soil and sediments in a process that can be in abrupt collapses or in
slow mud flows, debris flows, earth failures, slope failures, etc (Figure 1-1).
Landslides can be triggered by rains, floods, earthquakes, and other natural causes
as well as human-made causes, such as grading, terrain cutting and filling, excessive
development, etc. Because the factors affecting landslides can be geophysical or
human-made, they can occur in developed or undeveloped areas, or any area where
the terrain was altered for roads, houses, utilities, and even for lawns in one’s
backyard (USGS, Planning Research).




                          Figure 1-1: Different types of landslides.

1.1 Landslide’s Driving Force
The principal driving force for any landslide is the gravitational force (Figure 1-2)
and the tendency to move of this mass will be proportional to the hill slope angle.
The resisting forces preventing the mass from sliding down the slope are inversely
proportional to the same hill slope angle and proportional to the friction angle of
the material. As seen in Figure 1-3 the stability of the material resting on a slope


Landslide Hazard Manual                       4        www.engineering4theworld.org/LAP
will be reduced with an increased slope angle. In addition, the resisting forces can
be significantly reduced in case of rain or earthquake vibrations.




Figure 1-2: Effect of gravitational forces on a mass.




Figure 1-3: How an increasing slope will cause the sliding of the material on it.

1.2 Landslide Speed
The speed at which the different types of landslides occur varies greatly. From
Figure 1-4 it can be observed that the failure speed of rock falls is much higher
than the one observed in slumps or soil creeping. The speed of the landslide will
make an even more or less avoidable and therefore, more or less risky.




Landslide Hazard Manual                      5          www.engineering4theworld.org/LAP
           Figure 1-4: Relative failure speed for different types of landslides.

1.3 Landslide Material
The type of landslide that will occur in a given location will often depend on the
composition and type of material that makes up the ground near the surface. Table
1 shows the relationship that links the types of movement with the types of
material.


          Table 1: Type of landslide depending on the composition of the ground
                          TYPES OF MATERIAL
    TYPES OF                                                 Soils
    MOVEMENT              Bedrock
                                         Coarse Grained Soil Fine Grained Soil
    Falls                Rock fall       Debris fall             Earth fall
    Topples              Rock topple     Debris topple           Earth topple
           Rotational
    Slides               Rock slide      Debris slide            Earth slide
           Translational
    Lateral spreads       Rock spread Debris spread              Earth spread
    Flows           Rock flow      Debris flow        Earth flow
    Complex: Combination of two or more types of movement


It is important to distinguish the different types of landslides to be able to
understand how to deal with each of them. In Figure 1-5 a number of similar
landslides are shown. However, the ways to identify and mitigate them are often
different.




Landslide Hazard Manual                     6         www.engineering4theworld.org/LAP
                          Figure 1-5: Similar but different landslides.




Landslide Hazard Manual                        7         www.engineering4theworld.org/LAP
2     Landslide Types

As mentioned in the previous chapter, slope movements are defined by the type of
material that the slope is made up and the type of movement that the slope
undergoes. In this handbook only the major types of landslides will be described.

2.1 Sliding
A slide is a downslope movement of a soil or rock mass occurring dominantly along
rupture surfaces undergoing intense shear strain. Movement does not initially occur
simultaneously over the whole of what eventually becomes the landslide.
In slidings the soil mass moves along one or more discrete planes and the movement
can either be rotational or translational (Figures 2-1 a and b). In the rotational
case the failure surface(s) is curved and in the translational failure it is
approximately flat.




     Figures 2-1: a) Rotational failure with multiple planes. b) Translational failure.

2.1.1     Rotational Failure
Rotational slides move along a surface of rupture that is curved and concave. If the
surface of rupture is circular the displaced mass may move along the surface with
little internal deformation. Rotational slides occur most frequently in homogeneous
materials. In Figure 2-2 a rotational failure is shown with the descriptive
characteristics of such a failure.




Landslide Hazard Manual                      8        www.engineering4theworld.org/LAP
               Figure 2-2: Rotational failure with defining characteristics.



The sketch in Figure 2-3 shows how a rotational failure of a slope that initially was
stable would occur due to the additional load due to the new construction on the
top of the slope.




        Figure 2-3: Sketch of a rotational slope failure due to additional loading.




Landslide Hazard Manual                     9         www.engineering4theworld.org/LAP
Figure 2-4: Rotational failure     Figure 2-5: Rain-induced slump failure

2.1.2     Translational Failure
Translational failures occur when the failure surface is approximately flat or
slightly undulated and the soil mass moves parallel to the surface of the terrain
(Figure 2-6). Translational slides generally are relatively shallower than rotational
slides. As translational sliding progresses, the displaced mass may break up and may
start flowing, becoming a debris flow rather than a slide.




Figure 2-6: Cross-section of a translational slope failure.




Landslide Hazard Manual                      10       www.engineering4theworld.org/LAP
2.2 Rock Fall and Toppling
Rock falls occur when blocks detached from steep slopes or walls descend freely at
high speed. The two different types of falls considered here are actual rock falls
where the rock units have no contact with the ground for a significant portion of
their displacement, and rock toppling, where the rock base remains constantly in
contact with the ground.

2.2.1      Rock Fall
Rock falls start with the detachment of rock from a steep slope along a surface on
which little or no shear displacement takes place. The material then descends
mainly through the air by falling, bouncing, or rolling. Movement is very rapid to
extremely rapid (David M. Cruden). Rock falls are very common and in most cases
they are easily identifiable as seen in Figure 2-7 and Figure 2-8.




Figure 2-7: Sketch of a typical rock fall site.




                             Figure 2-8: Typical rock fall site




Landslide Hazard Manual                      11       www.engineering4theworld.org/LAP
2.2.2     Rock Toppling
Rock toppling occurs when one or more rock units rotate about their base and
collapse (Figure 2-7).




                             Figure 2-9: Rock toppling process.

2.3 Spreading
The term spread describes sudden movements on water-bearing seams of sand or
silt overlain by homogeneous clays or loaded by fills. Lateral spreading occurs when
the soil mass spreads laterally and this spreading comes with tensional cracks in
the soil mass as seen in Figure 2-10.




                          Figure 2-10: Sketch of lateral spreading.

2.4 Fast Debris Flows
Debris flows start on steep slopes—slopes steep enough to make walking difficult.
Once started, however, debris flows can even travel over gently sloping ground.
The most hazardous areas are canyon bottoms, stream channels, areas near the
outlets of canyons, and slopes excavated for buildings and roads.
Debris flows (also referred to as mudslides, mudflows, or debris avalanches)
generally occur during intense rainfall on water saturated soil. They usually start on
steep hillsides as soil slumps or slides that liquefy and accelerate to speeds as
great as 35 miles (56 km) per hour. Multiple debris flows that start high in canyons



Landslide Hazard Manual                      12       www.engineering4theworld.org/LAP
commonly funnel into channels. There, they merge, gain volume, and travel long
distances from their source.
Debris flows commonly begin in swales (depressions at the top of small gullies) on
steep slopes (Figure 2-11), making areas downslope from swales particularly
hazardous. The case of Mt. Huascaran in Peru, 1970 ( Figure 2-13), which caused
over 20,000 casualties, is a dramatic example of the destruction power of such
events.
Road-cuts and other altered or excavated areas of slopes are particularly
susceptible to debris flows. Debris flows and other landslides onto roadways are
common during rainstorms, and often occur during milder rainfall conditions than
those needed for debris flows on natural slopes ( Figure 2-13).
Areas where surface runoff is channeled, such as along roadways and below
culverts, are common sites of debris flows and other landslides.




                   Figure 2-11: Two views of debris flow environments.




Figure 2-12: Mt. Huascaran landslide.   Figure 2-13: Debris flow can carry large stones.




Landslide Hazard Manual                    13       www.engineering4theworld.org/LAP
2.5 Lahars (USGS)
Lahars are mudflows or debris flows composed mostly of volcanic materials on the
flanks of a volcano are called lahars. These flows of mud, rock, and water can rush
down valleys and stream channels at speeds of 20 to 40 miles per hour (32 to 64
km per hour) and can travel more than 50 miles (80 km). Some lahars contain so
much rock debris (60 to 90 percent by weight) that they look like fast-moving
rivers of wet concrete. Close to their source, these flows are powerful enough to
rip up and carry trees, houses, and huge boulders miles downstream. Farther
downstream they entomb everything in their path in mud.
Historically, lahars have been one of the deadliest volcano hazards. They can occur
both during an eruption and when a volcano is quiet. The water that creates lahars
can come from melting snow and ice (especially water from a glacier melted by a
pyroclastic flow or surge), intense rainfall, or the breakout of a summit crater lake.
Large lahars are a potential hazard to many communities downstream from glacier-
clad volcanoes.




                   Figure 2-14: Active volcano with lahar in the front.




Landslide Hazard Manual                    14        www.engineering4theworld.org/LAP
3     How to Identify Landslide Hazards

The prediction or identification a landslide is essential to minimize or control the
hazard. Usually this is done using costly procedures as surveying, monitoring, or soil
testing, which are not affordable or feasible in rural regions with no resources.
Therefore, simpler, but still effective methods have to be used to assess the
stability of a slope or decide if a given location is safe for construction. Figure 3-1
shows an overview of some of the morphologic and structural landslide indicators.
Two sources of useful information will be presented here: terrain morphology and
landslide risk indicators.




Figure 3-1: Morphologic and structural landslide indicators.

3.1 Terrain/Morphologic Features Indicating Risk of a Landslide
       Steep slopes: construction on or at the base of steep slopes has to be done
       carefully. As can be seen in Figure 3-2 the driving ground failure forces
       increase with increasing slope angle. To build on slopes with slope angles
       larger than 25 degrees one has to make sure that the ground is reasonable
       stable. This can be done by investigating the neighboring houses and terrain
       to see if the area has any landslide history. The inherent stability of a slope



Landslide Hazard Manual                     15       www.engineering4theworld.org/LAP
       will depend on three factors: the soil composition, the slope angle, and the
       slope height. Slopes higher than 40 meters and with angles over 30 degrees
       should be avoided if possible.




Figure 3-2: An increasing slope angle A also results in an increase of the driving force D.


       Old landslides/rock fall sites: construction on or near old landslides should
       be avoided for two reasons. First, the old landslide can be reactivated, for
       example, by heavy rainfall or an earthquake. Second, because another
       landslide could occur in the same location as the previous one and slide down
       over the old landslide.




                Figure 3-3: Sketch and picture of rock fall environment.



       New cracks or unusual bulges in the ground or street pavements. Cracks
       in the ground (Figure 2-4) are indicators that the ground is moving, either
       moving slowly (creep) or initiating a landslide. No construction should be done
       on or near such terrain without undertaking significant remedial actions
       (which are often not feasible).


Landslide Hazard Manual                     16        www.engineering4theworld.org/LAP
Figure 3-4: Cracks in the ground are indicators that the ground is creeping.

       Sunken or down-dropped road beds
       Springs, seeps, or saturated ground in areas that have not typically been wet
       Rapid increase in creek water levels, possibly accompanied by increased
       turbidity (soil content)
       Sudden decrease in creek water levels though rain is still falling or just
       recently stopped

3.2 Additional Landslide Risk Indicators

       Ancillary structures such as decks and patios tilting and (or) moving relative
       to the main house
       Tilting or cracking of concrete floors and foundations
       Soil moving away from foundations
       Broken water lines and other underground utilities
       Leaning telephone poles, trees, retaining walls, or fences
       Offset fence lines or retaining walls
       Springs, seeps, or saturated ground in areas that have not typically been wet
       New cracks or unusual bulges in the ground or street pavement
       Rapid increase in creek water levels, possibly accompanied by increased
       turbidity (soil content)
       Sticking doors and windows, and visible open spaces indicating jambs and
       frames out of plumb




Landslide Hazard Manual                    17        www.engineering4theworld.org/LAP
Figure 3-5: Bent trees = Creep                Figure 3-6: Tilted fences indicate creep.


       Sticking doors and windows, and visible open spaces indicating jambs and
       frames out of plumb
In most cases in the field there will be a combination of morphological and landslide
risk indicators to be considered.




Landslide Hazard Manual                  18        www.engineering4theworld.org/LAP
4     Slope Destabilizing Factors and Landslide Triggers
Some slopes are susceptible to landslides whereas others are more stable. Many
factors contribute to the instability of slopes, but the main controlling factors are
the nature of the underlying bedrock and soil, the configuration of the slope, the
geometry of the slope, and ground-water conditions.

4.1 Slope Destabilizing Factors
       Undercutting of a slope by stream erosion, wave action, glaciers, or human
       activity such as road building




Figure 4-1: Roadcuts can destabilize a slope Figure 4-2:Cut-fill has to be done carefully

       Deforestation and vegetation loss (Figure 4-3) may reduce up to 90% the
       stability of some slopes. Poorly planned forest clearing may increase rates of
       surface water run-off or ground-water infiltration. Inefficient irrigation or
       sewage effluent disposal practices may result in increased ground-water
       pressures, which in turn can reduce the stability of rock and sediment.




Landslide Hazard Manual                    19        www.engineering4theworld.org/LAP
Figure 4-3: Deforestation of a slope could result in an increased landslide hazard.

        Loading on upper slopes result in an additional load to be carried by the
        slope, which could result in its failure (Figure 4-4).




         Figure 4-4: Sketch of a rotational slope failure due to additional loading.


        Lack of sufficient drainage due to a number of civil works will result in high
        water content in the soil and destabilizing it.



4.2 Triggering Factors
Three distinct physical events occur during a landslide: the initial slope failure, the
subsequent transport, and the final deposition of the slide materials. Landslides
can be triggered by gradual processes such as weathering, or by external
mechanisms including:

4.2.1      Intense or Prolonged Rainfall
Intense or prolonged rainfall rapid snowmelt or sharp fluctuations in ground-water
levels can all trigger a landslide (Figure 4-5). In case of clayey soils, prolonged


Landslide Hazard Manual                      20        www.engineering4theworld.org/LAP
rainfall will be the main triggering factor. This is because clayey soils often need
days of rainfall to cause their saturation. Intense rainfall over a short period of
time will, however, not be sufficient to cause its saturation and trigger a landslide.
In the case of residual and granular soils, this is not the case. These soils’
structure allows for relatively rapid drainage and prolonged (not intense) rainfall
cannot saturate them. It is intense rainfall that will cause their saturation and the
consequent reduction of frictional forces in the material (due to the increase in
pore pressure), resulting in a potential landslide. For these types of soils the
landslides will either occur during the downpour or shortly thereafter. Hourly
rainfall of more than 40mm is enough to trigger a landslide. With hourly rainfall
over 70mm the landslide hazard becomes severe.




                    Figure 4-5: Rotational landslide triggered by rain.

The two principal reasons why landslides are triggered by these conditions are a
rise of pore pressure and an increase of the slope weight. During intense or
prolonged rainfall soils tend to saturate (Figure 4-6) resulting in an increase of the
pore pressure. Any increase in pore pressure will result in an equal diminution of
the effective stress in the soil, which in turn results in a reduction in the frictional
forces.




Landslide Hazard Manual                     21        www.engineering4theworld.org/LAP
          Figure 4-6: Effect of prolonged or intense rainfall on granular soils.

4.2.2     Shocks or Vibrations
Shocks or vibrations caused by earthquakes (M 3-4 or greater) or construction
activity

4.2.3     Human Intervention
Landslides may result directly or indirectly from the activities of people. Slope
failures can be triggered by construction activity that undercuts or overloads
dangerous slopes, or that redirects the flow of surface or ground-water.

4.3 Combination of Slope Characteristics and Triggering Factors
    for Landslides
In general a landslide occurs due to the combination of the morphological
characteristics of the terrain and some kind of triggering factor. In Table 2 the
most common combinations of slope characteristics and triggering factors are
shown for both dry and wet conditions.




Landslide Hazard Manual                    22        www.engineering4theworld.org/LAP
    Table 2: Slope characteristics and triggering factors for landslides (F.Ferrando).
TYPES        SLOPE                          TRIGGERING FACTORS          PROCESS
             CHARACTERISTICS
Dry          -Very steep slopes             -Seismicity                 Localized
Conditions   -Highly fractured rocks        -Volcanic eruptions         - Stone fall and
             -Low friction angle of the     -Human intervention          crumbling
             soil                           -Strong winds               - Mud and debris flow
             -Permeability of sediments     -Human interventions        Localized
             -Slope angle                   -Prolonged rainfall         - Landslides
Assisted     -Thickness of                  -Intense rainfall
                                                                        Extended area
by water      unconsolidated sediments      -Seismicity
                                                                        - Mud and debris
             -Clay content in the subsoil   -Accelerated snow melting
                                                                         flows
             -Low roughness of subsoil
                                                                        - Jokül-laups




Landslide Hazard Manual                        23        www.engineering4theworld.org/LAP
5     How to Minimize Landslide Hazards


5.1 Passive Intervention
       Choose a safe location to build your home
       Prevent deforestation and vegetation removal
       Avoid weakening the slope

5.2 Active Preventive Intervention
       Reforestation: Root systems bind materials together (Figure 5-1) and
       plants do both prevent water percolation and take water up out of the slope.




    Figure 5-1: Tree roots help holding the different soil layers together and hinder
                                       landslides.


       Proper water runoff must be ensured, especially where houses and roads
       have disrupted the natural flow patterns. This can be achieved by providing a
       proper canalization network.
       Drainage: good ground drainage is essential to prevent is saturation and
       consequent weakening. Drainage is also needed when any kind of civil work,
       like retaining walls, has been done. As it can be observed in Figures 5-2 A) &
       B) the introduction of drainage ducts




Landslide Hazard Manual                    24       www.engineering4theworld.org/LAP
Figures 5-2: A) High pore water pressures weaken the ground and push down the
retaining wall; B) By providing proper drainage the pore water pressures are reduced as
well as the forces on the retaining wall.


       Nets (Figure 5-3) are a common and cost-effective solution. However, it is
       still too costly (and technically complicated) to be used in small villages or to
       protect private homes.




                Figure 5-3: Net used to prevent stone fall on a roadway.

       Retaining walls efficiently reduces localized landslide hazards, like in the
       case where cuts into the slopes are needed to build a house or a road.
       However, they have to be used with precaution because they might also
       increase the hazard when the soil is not allowed to drain properly. In Figure
       5-4 a number of low-cost ways to build retaining walls are shown.




Landslide Hazard Manual                    25       www.engineering4theworld.org/LAP
                    Figure 5-4: A number of low-cost retaining walls


In addition, gabions can also effectively replace the more expensive reinforced
concrete retaining walls (Figure 5-5).




Landslide Hazard Manual                   26        www.engineering4theworld.org/LAP
                          Figure 5-5: Retaining wall built with gabions



       Proper construction practice: It is often the case that some landslide
       mitigation works are conducted but these are insufficient or not properly
       planned. As seen in Figure 5-6 the retaining wall constructed was
       insufficient for the earth pressures developed in rainy conditions.




                            Figure 5-6: Insufficient retaining wall



       Major civil works: The undertaking of major civil works is mostly not a
       feasible solution because of their high cost and technical complexity. In
       addition, such works are often unnecessary if the land is properly managed
       and its use takes into account the local hazards. The pictures in Figure 5-7
       show part of a massive US$50 million landslide mitigation project in
       Antofagasta/Chile with a dubious necessity and functionality.


Landslide Hazard Manual                        27        www.engineering4theworld.org/LAP
         Figure 5-7: Massive landslide mitigation project in Antofagastga, Chile.




Landslide Hazard Manual                    28        www.engineering4theworld.org/LAP
6     Dos and Don’ts

6.1 Prior to a Potential Landslide due to Intense Storms

       Stay alert and stay awake! Many debris-flow fatalities occur when people
       are sleeping. Listen to a radio for warnings of intense rainfall. Be aware that
       intense short bursts of rain may be particularly dangerous, especially after
       longer periods of heavy rainfall and damp weather.
       If you are in areas susceptible to landslides and debris flows, consider
       leaving if it is safe to do so.
       Listen for any unusual sounds that might indicate moving debris, such as
       trees cracking or boulders knocking together. A trickle of flowing or falling
       mud or debris may precede larger flows. If you are near a stream or channel,
       be alert for any sudden increase or decrease in water flow and for a change
       from clear to muddy water. Such changes may indicate debris flow activity
       upstream, so be prepared to move quickly. Don’t delay! Save yourself, not
       your belongings.
       Contact your local fire, police, or public works department. Local
       officials are the best persons able to assess potential danger.
       Inform affected neighbors. Your neighbors may not be aware of
       potential hazards. Advising them of a potential threat may help save lives.
       Help neighbors who may need assistance to evacuate.
       Evacuate. Getting out of the path of a landslide or debris flow is your
       best protection.


6.2 What to Do During a Landslide

       Quickly move out of the path of the landslide or debris flow. Moving
       away from the path of the flow to a stable area will reduce your risk.
       If escape is not possible, curl into a tight ball and protect your head.
       A tight ball will provide the best protection for your body.


6.3 What to Do After a Landslide




Landslide Hazard Manual                  29        www.engineering4theworld.org/LAP
       Stay away from the slide area. There may be danger of additional
       slides.
       Go to the established meeting point and follow instructions by the
       assigned responsible person.
       Check for injured and trapped persons near the slide, without entering
       the direct slide area. Direct rescuers to their locations.
       Help a neighbor who may require special assistance — infants, elderly
       people, and people with disabilities. Elderly people and people with
       disabilities may require additional assistance. People who care for them or
       who have large families may need additional assistance in emergency
       situations.
       Listen to local radio or television stations for the latest emergency
       information.
       Watch for flooding, which may occur after a landslide or debris flow.
       Floods sometimes follow landslides and debris flows because they may
       both be started by the same event.
       Look for and report broken utility lines to appropriate authorities.
       Reporting potential hazards will get the utilities turned off as quickly as
       possible, preventing further hazard and injury.
       Check the building foundation, chimney and surrounding land for damage.
       Damage to foundations, chimneys or surrounding land may help you assess
       the safety of the area.
       Replant damaged ground as soon as possible since erosion caused by loss
       of ground cover can lead to flash flooding.
       Seek the advice of a geotechnical expert for evaluating landslide hazards
       or designing corrective techniques to reduce landslide risk. A professional
       will be able to advise you of the best ways to prevent or reduce landslide
       risk, without creating further hazard.

6.4 Construction Don’ts

   Do not build on or at the base of unstable slopes (Figure 6-1 & Figure 6-2)




Landslide Hazard Manual                  30       www.engineering4theworld.org/LAP
                    Figure 6-1: Avoid building under very steep slopes




  Figure 6-2: Buildings on a very steep slope… and damaged houses due to slope failure.

   In or at the base of minor drainage hollows
   At the base or top of an old fill slope
   At the base or top of a steep cut slope




                 Figure 6-3: Slope destabilized by a cut ends up failing.


   Developed hillsides where leach field septic
   Minimize the number of trees and vegetation removed from the slope.


Landslide Hazard Manual                      31      www.engineering4theworld.org/LAP
7     Workshop Teaching Procedure

-Use local examples
-Concentrate on local hazard properties
The one-day workshop will consist of a theoretical and a hands-on session. The
theory will be taught with the help of graphics, pictures, and videos where possible.
It will present the basic shortcomings of how the construction site is currently
chosen (the workshops will have to be modified for different locations) and show
how to improve them. The hands-on session will be used to show them how to
implement the recommended improvements and show them how easy they can be.
The workshops should be run at a village level and organized by local NGOs that
already have an established network in the targeted region and already have the
infrastructure in place to create a grassroots initiative.


Note: These workshops should not be fully free. The community should provide a
donkey (if needed) to transport materials to the village, or a guide, or food. The
NGO could donate the posters.




Landslide Hazard Manual                   32      www.engineering4theworld.org/LAP
8      Additional Resources and Annexes

Landslide Research Card




Figure 8-1




Landslide Hazard Manual      33    www.engineering4theworld.org/LAP