1.4 landslide
TRANSCRIPT
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 11
LANDSLIDELANDSLIDE
Presented byPresented byCT.Lakshmanan B.Arch., M.C.P.CT.Lakshmanan B.Arch., M.C.P.
SRM School of ArchitectureSRM School of ArchitectureSRM UniversitySRM University
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 22
What is Landslide ?What is Landslide ?
downward and outward movement of slope forming materials composed of rocks, soils, artificial fills or combination of all these materials along surfaces of separation by falling, sliding and flowing, either slowly or quickly from one place to another.
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 33
An idealized slump-earth flow showing commonly used nomenclature for labeling the parts of a landslide.
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 44
Classification with respect to depth Classification with respect to depth of slideof slide
Type Maximum depth (m)
Surface slide < 1.5
Shallow slide 1.5 – 5
Deep slide 5 – 20
Very deep slide > 20
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 55
Types of landslides
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 66
Rotational and Translational Rotational and Translational landslidelandslide
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 77
Block slide & RockfallBlock slide & Rockfall
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 88
Topple & Debris flowTopple & Debris flow
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 99
Debris Avalanch & Earth flowDebris Avalanch & Earth flow
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 1010
CreepCreep
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 1111
Lateral spreadLateral spread
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 1212
Types of rapid mass movementTypes of rapid mass movement
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 1313
SlumpSlump
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 1414
Factors that control slope stabilityFactors that control slope stability
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 1515
Factors that control slope stabilityFactors that control slope stability
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 1616
Factors that control slope stabilityFactors that control slope stability
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 1717
Factors that control slope stabilityFactors that control slope stability
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 1818
CAUSES OF LANDSLIDESCAUSES OF LANDSLIDES
• Geological Weak material
• Erosion
• Intense rainfall
• Human Excavation
• Earthquake shaking
• Volcanic eruption
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 1919
Causes of LandslidingCauses of Landsliding
Geologists use a variety of classification schemes to describe causes of landslides. Because of wide variety of causes, no single scheme has yet been developed that address or describe all types of landslides.
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 2020
ExternalExternalGeometrical change
1. Gradient2. Height3. Slope length
Unloading 1. Natural2. Human-induced
Loading 1. Natural2. Human-induced
Shocks and Vibrations 1. Single2. Multiple/continuous
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 2121
InternalInternalProgressive failure (internal response to unloading, etc.)
1. Expansion, swelling 2. Fissuring3. Strain softening 4. Stress concentration
Weathering 1. Physical property changes, swelling 2. Chemical changes
Seepage Erosion 1. Removal of cements 2. Removal of fines
Water Regime Change
1. Saturation2. Rise in water table 3. Excess pressures 4. Drawdawn
Source: The Royal Academy of Engineering. 1995. Landslides Hazard Mitigation. Westminster, London: The Royal Academy of Engineering.
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 2222
Human causesHuman causes
a. Excavation of slope or its toeb. Loading of slope or its crestc. Drawdown (of reservoirs)d. Deforestatione. Irrigationf. Miningg. Artificial vibrationh. Water leakage from utilities
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 2323
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 2424
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 2525
Major Landslides of India
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 2626
Major Landslides of India
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 2727
Major Landslides of India
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 2828
MAIN MITIGATION STRATEGIES
Hazard mapping
Land use
Retaining Walls
Surface Drainage Control Works
Engineered structures
Increasing vegetation cover
Insurance
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 2929
MAIN MITIGATION STRATEGIES
Hazard mapping will locate areas prone to slope failures. This will permit to identify avoidance of areas for building settlements.
These maps will serve as a tool for mitigation planning.
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 3030
MAIN MITIGATION STRATEGIESLand use practices such as:• Areas covered by degraded natural vegetation in upper slopes are
to be afforested with suitable species. Existing patches of natural vegetation (forest and natural grass land) in good condition, should be preserved
• Any developmental activity initiated in the area should be taken up only after a detailed study of the region and slope protection should be carried out if necessary.
• In construction of roads, irrigation canals etc. proper care is to be taken to avoid blockage of natural drainage
• Total avoidance of settlement in the risk zone should be made mandatory.
• Relocate settlements and infrastructure that fall in the possible path of the landslide
• No construction of buildings in areas beyond a certain degree of slope.
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 3131
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 3232
MAIN MITIGATION STRATEGIES
Retaining Walls can be built to stop land from slipping (these walls are commonly seen along roads in hill stations). It’s constructed to prevent smaller sized and
secondary landslides that often occur along the toe portion of the larger landslides.
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 3333
MAIN MITIGATION STRATEGIES
Surface Drainage Control Works. The surface drainage control works are implemented to control the movement of
landslides accompanied by infiltration of rain water and spring flows.
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 3434
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 3535
MAIN MITIGATION STRATEGIES
• Engineered structures with strong foundations can withstand or take the ground movement forces.
• Underground installations (pipes, cables, etc.) should be made flexible to move in order to withstand forces caused by the landslide
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 3636
MAIN MITIGATION STRATEGIES
Increasing vegetation cover is the cheapest and most effective way of arresting landslides. This helps to bind the top layer of the soil with layers below, while preventing excessive run-off and soil erosion.
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 3737
MAIN MITIGATION STRATEGIES
Insurance will assist individuals whose homes are likely to be damaged by landslides or by any other natural hazards. For new constructions it should include standards for selection of the site as well as construction technique.
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 3838
Flattening of the slopeFlattening of the slope
Slope at the point of failure may be stabilised by grading the slope to a flatter angle on the basis of proper geotechnical investigation
Done either by regarding the slope from bottom to the top with benching, wherever necessary or cut in upper hills.
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 3939
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 4040
Stitching of the debris cover to the rockStitching of the debris cover to the rock
Movement of surface soil can be controlled by stitching the debris to the base rock with help of micro-piles (e.g. timber piles)
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 4141
Retaining wallsRetaining walls
Built at the bottom of the slope but the base of the wall should be properly anchored into the rock.
Big landslides cannot be controlled by retaining walls
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 4242
GroutingGrouting
Effective method of improving the shear strength and decreasing the permeability of coarse-grained soil. Suitable for filling voids in the rock mass.
Cement grouts are injected under pressure to close the voids in the rock
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 4343
GeotextilesGeotextiles
Geotextiles wrapped filler drains are inserted into the slope extending beyond the estimated slip surface.
They are connected to a crib wall at the base which is made of crushed rock to provide drainage of water from the transverse drain.
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 4444
Rockfall ProtectionRockfall ProtectionIn many areas rock faces are ‘stitched’ with massive steel bolts to try to keep material from being lost to active weathering.
Alternately, surfaces can be covered with strong mesh or boulder catching nets can be used.
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 4545
Mudflow BarriersMudflow BarriersThese kinds of barriers are
designed to catch most
sediment, but are not capable
of stopping very large and very
fast moving debris.
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 4646
Debris BasinsDebris Basins
debris flowhead ing tow ard neighborhood
debris trappedin concre te-lined
basin
These require periodic (regular) removal of trapped material.
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 4747
The hazard from landslides can be reduced
by avoiding construction on steep slopes
and existing landslides, or by stabilizing the
slopes.
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 4848
Stability increases when ground water is Stability increases when ground water is prevented from rising in the landslide mass byprevented from rising in the landslide mass by
(1) covering the landslide with an impermeableMembrane(2) directing surface water away from the landslide(3) draining ground water away from the landslide(4) Minimizing surface irrigation.
Slope stability is also increased when a retaining structure and/or the weight of a soil/rock berm are placed at the toe of the landslide or when mass is removed from the top of the slope.
Prepared by CT.LakshmananPrepared by CT.Lakshmanan 4949
Thank you