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LANDSLIDES – Module 2 02-04-2019
Compiled by Shimi Lawrence, SCTCE 1
Module 2b Landslides , Types, causes &
effects
CE 488
LANDSLIDES – Module 2 02-04-2019
Compiled by Shimi Lawrence, SCTCE 2
DefinitionLandslides – the movement of a mass of rock, debris or earth downthe slope, when the shear stress exceeds the shear strength of thematerial
Earth movements – all movement of land masses are referred aslandslides. All types of landslides are categorized as earth movements.(eg : Earth flow, landslides, subsidence)
A process by mainly gravitational forces – Mass movement of rock,debris or earth down the slope.
LANDSLIDES – Module 2 02-04-2019
Compiled by Shimi Lawrence, SCTCE 3
Landslides
The occurrence of slope movements is the consequence of a complex field offorces (stress is a force per unit area) which is active on a mass of rock or soilon the slope.
The consequence of these forces in conjunction to the slope morphology andthe geotechnical parameters of the material define together the specific typeof landslide which might occur.
Landslides -Increase in shear strength (causes landslides)
➢ Removal of lateral and underlying support (erosion, previousslides, road cuts and quarries)
➢ Increase of load (weight of rain/snow, fills, vegetation)
➢ Increase of lateral pressures (hydraulic pressures, roots,crystallisation, swelling of clay)
➢ Transitory stresses (earthquakes, vibration of trucks, machinery,blasting)
➢ Regional tilting (geological movements)
LANDSLIDES – Module 2 02-04-2019
Compiled by Shimi Lawrence, SCTCE 4
Causes - Natural1. Ground water pressure acting to destabilize the slope
2. Loss or absence of vertical vegetative structure, soil nutrients, andsoil structure
3. Erosion of the toe of a slope by rivers or ocean waves
4. Weakening of a slope through saturation of snow melt, glaciersmelting or heavy rains
5. Earthquakes adding loads to barely stable slopes
6. Earthquake caused liquefaction destabilizing slopes
7. Volcanic eruptions
Causes - human1. Vibrations from machinery or traffic
2. Blasting
3. Earthwork which alters the shape of the slope or which imposesnew loads on an existing slope
4. In shallow soils, the removal of deep rooted vegetation that bindscolluvium to bed rock.
5. Construction , agricultural or forestry activities which change theamount of water which infiltrates into the soil
LANDSLIDES – Module 2 02-04-2019
Compiled by Shimi Lawrence, SCTCE 5
Landslides – on earth movements
LANDSLIDES – Module 2 02-04-2019
Compiled by Shimi Lawrence, SCTCE 6
Causes of landslides /landslipsGeological Morphological Physical Human
Weathered material due to Heavy rainfall
Slope angle Intense rainfall Excavation
Shearing of soil Uplift Rapid snow melt Loading
Jointed or fissured materials
Rebound Prolonged precipitation Draw- down
Adversely oriented discontinuities
Fluvial erosion Earthquake Land use pattern change (road, house)
Permeability contrasts Wave erosion Volcanic eruption Water management
Material contrasts Glacial erosion Thawing Mining
Rainfall. Snow fall Erosion of lateral margins
Freeze – thaw Quarrying
Working of machinery Subterranean erosion
Ground water changes Vibration
Earthquakes Slope loading Soil pore water pressure Water leakage
Vegetation change Surface run off Deforestation
erosion Seismic activity Land use pattern
Soil erosion Pollution
Classification of Earth Movements – Earth FlowsAre down the slope, viscous flows of saturated, fine-grained materials, which move at any speed from slow to fast.
Reasons – heavy rains, volcanic eruptions, earthquakes
LANDSLIDES – Module 2 02-04-2019
Compiled by Shimi Lawrence, SCTCE 7
Munnar 2018 – earth flow
Photograph from aerial survey showing the upper parts of the landslidethat occurred in northwest Washington on March 22, 2014.
LANDSLIDES – Module 2 02-04-2019
Compiled by Shimi Lawrence, SCTCE 8
Mud flow & LaharMudflow (mudslide) Lahar
A mudflow, when the soil becomes so saturated with water that it speeds down the hill in a muddy river carrying debris
Lahar is the volcanic debris flow.
Fastest and wettest type of flow Rapidly flowing – contains rock debris and water
SOLIFUCTIONSolifuction is a downward movement of wet soil along the slopes under the influence of gravity
LANDSLIDES – Module 2 02-04-2019
Compiled by Shimi Lawrence, SCTCE 9
SOIL CREEP (depth 1-2m)Creep is extremely slow downward movement of dry surficial matter.Movement of the soil occurs in regions which are subjected to freeze-thaw conditions. The freeze lifts the particles of soil and rocks and whenthere is a thaw, the particles are set back down, but not in the sameplace as before. It is very important for Civil Engineers to know the rateof movement (few centimetres per day)
Can be slowed down by afforestation
LANDSLIDES – Module 2 02-04-2019
Compiled by Shimi Lawrence, SCTCE 10
LANDSLIDES – Module 2 02-04-2019
Compiled by Shimi Lawrence, SCTCE 11
LANDSLIDES – Module 2 02-04-2019
Compiled by Shimi Lawrence, SCTCE 12
Snow meltCold countries
Sudden increase in temperature leads to rapid melting of snow pack.This water try to infiltrate to ground, which may have impermeablelayers below the surface (still frozen soil, rock water)
Leading to increase in pore water pressure and landslides.
A serious phenomenon
When warmer weather is followed by precipitation, (precipitation andmelting of water – add water pressure), accelerating thawing.
RiversUndercutting of slopes, during floods in rivers.
Increases gradient of slope, reducing stability, and toe removal –accelerating instability of slopes.
LANDSLIDES – Module 2 02-04-2019
Compiled by Shimi Lawrence, SCTCE 13
SeismicityAs a result of seismic shaking and pore water pressure generation
Seismic shaking
The passage of the earthquake waves through the rock and soil produces a complex set of accelerations that try to change the gravitational load on the slope.
Vertical accelerations successively increases the or decreases the normal load on the slope,
Horizontal accelerations induce shearing force due to inertia of the landmass.
LiquefactionThe passage of the earthquake waves through a granular material such as soil induce liquefaction.
Pores inside the soil reduces and density of soil increases.
Sometimes, the material can generate FLOW SLODES that can be rapodand creating damages.
The increase in the pore pressure can reduce the normal stress in the slope allowing the activation of translational and rotational failures
LANDSLIDES – Module 2 02-04-2019
Compiled by Shimi Lawrence, SCTCE 14
IS recommended remedial measures
1. Restraining structures
2. Easing of pressure by excavation
3. Reconstruction of slope using reinforced earth
4. Rock reinforcement
Are the direct methods
Indirectly – erosion control measures, and improving in surface and sub-surface drainage can reduce land slides
LANDSLIDES – Module 2 02-04-2019
Compiled by Shimi Lawrence, SCTCE 15
Restraining Structures (ht <=4m)
Dry, banded and mortar masonry walls
Gabions/ sausage walls
Concrete retaining walls
Restraining piles
Excavation methodsTo increase stability of the soil mass beneath a slope.
The main methods◦ Removal of unstable materials
◦ Flattening of slopes
◦ Benching of slopes,
◦ Change of line or grade and
◦ Alteration of slope geomety
LANDSLIDES – Module 2 02-04-2019
Compiled by Shimi Lawrence, SCTCE 16
Reconstruction of slope using reinforced earthReinforced earth using metallic stripes
Geofabric reinforcement structures on slopes
Slope reinforcement by soil nailing
Micro-piles, root piles for slope stabilisation
Erosion control measuresGrass plantation and shrubs to restore vegetative cover
Jute / coir netting
LANDSLIDES – Module 2 02-04-2019
Compiled by Shimi Lawrence, SCTCE 17
DrainageSurface drainage : Control of surface water flow
• Collection of runoff at the uphill boundary of any unstable area
• Maximixing runoff from the unstable area and controlling and collecting the run off.• Catch water or interceptor drains
• Road side drains
• Cross drains
Subsurface drainage : more effective for deep seated landslide, because it leads to a decrease in pore water pressure directly at the failure plane and tends to produce a more stable condition of slide area
1. Horizontal drains
2. Deep trench drains.
LANDSLIDES – Module 2 02-04-2019
Compiled by Shimi Lawrence, SCTCE 18
Landslide warning signs1. Sticking or jamming of doors or windows
2. Appearance of cracks in plaster, tile, brick or foundations
3. Pulling away from the building of outside walls or stairs
4. Slow development of widening cracks on the ground or an paved areas such as streets
5. Breakage of underground utility lines
6. Appearance of bulging ground at the base of a slope
7. Emergence of flowing ground water in new sites
8. Sudden decrease in creek water levels through rain is still falling or just recentlystopped
9. Tilting or moving of fences, retaining walls, utility poles or trees
10. Faint rumbling sound that increases in volume as the landslide nears. The groundslopes downward in one specific direction and may begin shifting in that directionunder his/her feet
LANDSLIDES – Module 2 02-04-2019
Compiled by Shimi Lawrence, SCTCE 19
64
Landslides Prediction
The development of a landslide is a temporal process◦ takes as long as a year to develop
◦ Movement speed, several cm per month
Landslides are spatial in nature.◦ Position
◦ Movement direction
67
System Architecture
Deployment◦ A network of sensor columns
◦ Placed in vertical holes drilled over the hill surface
Using sensor columns to detect movements
LANDSLIDES – Module 2 02-04-2019
Compiled by Shimi Lawrence, SCTCE 20
What was the biggest landslide in the world?
The world's biggest historic landslide occurred during the 1980 eruptionof Mount St. Helens, a volcano in the Cascade Mountain Range in theState of Washington, USA. The volume of material was 2.8 cubickilometers (km).
The world's biggest prehistoric landslide (discovered so far and on land),is in southwestern Iran, and is named the Saidmarreh landslide. Thelandslide is located on the Kabir Kuh anticline in Southwest Iran at 33degrees north latitude, 47.65 degrees east longitude. The landslide hasa volume of about 20 cubic kilometers, a depth of 300 m, a traveldistance of 14 km and a width of 5 km. This means that about 50 billiontons of rock moved in this single event!
Effects &
Consequences of Landslides
LANDSLIDES – Module 2 02-04-2019
Compiled by Shimi Lawrence, SCTCE 21
Effects & consequences of landslides
Effect Type Such as
Direct & indirect
Direct Effects just after the event Death, damage
Indirect Events after the event Psycho-social impacts, bereavement and evacuation
Tangible & intangible
Tangible Possible to assign reasonable reliable monetary values
Replacement of damaged property
Intangible Cannot be satisfactorily assessed in monetary terms
Loss of human life (difficult to assess financially)
Built & natural env
Built Agricultural land, infrastructure
Water supplies, fisheries, sewage disposal systems, dam
Natural Forest
Effects on landslides on Built environment
Residentialbuildings onunstableslopes
Partial damage tocompletedestruction
Landslides destabilize or destroyfoundations, walls, floors,surrounding property, utilities suchas water pipelines, power lines,communication lines, transportroutes.
Commercialstructures
Access routesdamaged.
Disruption in business
LANDSLIDES – Module 2 02-04-2019
Compiled by Shimi Lawrence, SCTCE 22
Impact of Landslides (1/2)Effect of Landslides on
Buildings
Development of cracks
Collapse of buildings, or complete damage/ burial. ( Slowmoving/ creep)
Burial of buildings (Fast moving landslides)
Transportation system (roads & railways)
Blockages of highways , temporary diversion of traffic or evenclosure of road traffic or a major excavation.
State and National highways affected.
Risk to vehicles and passengers on road side.
Essential services (power, communication, water supply)
Rigid pipelines and structures more affected when comparedwith flexible/elastic pipelines and structures.
Health and education sectors Patients, pregnant ladies, school children, very small childrenand elderly persons.
Natural environment Morphology of earth system – mountain valley system,continents, beneath oceansForest and grass land cover, wild life, rivers.Dams
Impact of Landslides (2/2)Effect of Landslides on
Cultural heritage Damage to the heritage structures (Utharakhand), pine trees (>300 trees) uprooted in 2014
National/ Border security Blockage of roads in international border areas.Movement of army vehicles and troupes on road.
Economic effect Cost of repair, loss of property value, distruption oftransportation routes, medical costs (injury), wateravailiability(non) , quality and quantityIllhealth
Interrelationship of landslides and other hazards (THE MULTIPLE HAZARD EFFECT)
Floods, EQ, Volcanic eruptions can cause landslides. One cantrigger other.
EQ, triggered landslide in ocean can cause Tsunami. (if largeqty of soil displaced)
Volcanic eruption induced landslides, can block river way andflooding upstream.
Landslide in dams – can cause flooding downstreamLandslide in dam, if dam fails, flooding downstream. Riverbank damage, coastal erosion,
LANDSLIDES – Module 2 02-04-2019
Compiled by Shimi Lawrence, SCTCE 23
Fast moving landslides –
Rockfalls/topples,debris flow
Occur without precursors and warnings, move too quickly –for any safety measures to be taken, with high momentumdue to its mass and velocity, that can destroy anything thatcomes in its way.
Slow movinglandslides
Slight damage and its slow pace may allow implementationof mitigation measures as well. Can destroy structures overtime.
Nature of landslidemovement
Can continue after days, weeks, or months preclude(preventing from happening) rebuilding on the affectedarea, unless mitigation measures are taken appropriately.
Increase of Population
People tend to move to new lands, which deemed to be toohazardous in the past.
Poor / non – existent land use policies allow buildingconstructions to take place on the land that might be betterfor agriculture, parks.
Unsafe building practices and may not have legitimate oradequate means/ expertise to do so.