Landslides_White_GM309.ppt

8/15/2019 Landslides_White_GM309.ppt

http://slidepdf.com/reader/full/landslideswhitegm309ppt 1/22

MassMovements/

Wasting



What are they?

Mass movements include:

• Landslides

• Rock falls

• Avalanches• Mud flows

• Debris flows

• Creep



LANDSLIDE HAZARD

•Landslidesencompass allcategories of gravity

related slope fail!res in Eart" materials#



SL$%ES

• Material is constantly

moving on slopes at rates varying fromimpercepti&le creep to

t"!ndering avalanc"esand roc' falls moving at"ig" velocities#



<1 cm/year

>100 km/year

0% ~40%



• Gravity

• Water

• Earth Materials

• Triggering Events

Factors in Slope Stability



• All movement of land masses are referred aslandslides( &!t di)er in many respects( t"ereforeall types of landslides are categori*ed as Eart"

Movements# These are classifed as

Classifcation o EarthMovements

Earth Flow Landslides Subsidence

Solifluction

Creep

Rapid flows

Rock slides

Rock falls

Debris slide or

slump

collapse

Plastic flow



SOLIFUCTI ON

• Soliuction is a

downward movemento wet soil along theslopes under theinuence o gravity.



• Creep is extremely slowdownward movement ofdry surfacial matter.

• Movement of the soil occursin regions which aresubjected to freeze-thawconditions. The freeze liftsthe particles of soil and

rocks and when there is athaw the particles are setback down but not in thesame place as before.

• !t is very important for C"s

to know the rate ofmovement

SOILCREEP



• RAPID FLOWS: Rapid fow is similar to the reep!"#t di$er i% terms o& speed a%d depth' It is &aster'

• Creep is i%(ol(ed #pto shallow depth )app' *+,m-! whereas the rapid fow is i%(ol(ed to .reaterdepth )app' #pto / m or more-



Landslides

• If a mass of earth moves along adefinite plane or surface the failureis termed as Landslide

• Large block known as a slumpblock moves during the landslide.

• The scar above a landslide is easily

visible.• They can occur along a slope

where the internal resistance of therocks are reduced or they loosetheir holding capacity.

•Common after earthquakes or afterremoval of part of the slope due toconstruction, particularly forconstruction of roads.



• During the movement landslide canresult into the Debris slides are

failure of unconsolidated materialon a surface! "ock slide or "ock#all $ where movement of largerock block rolls

• They are also common along thesteep banks of rivers, lakes etc.

• %ore &ater %ressure is the key to

monitoring landslides. 'hearstrength (a resisting force)decreases and the weight (a drivingforce increases).



• Talus – accumulation ormed

y the coarser roc! ragmentsresulted rom the mechanicalweathering along a slopeunder inuence o gravity



• "t represents the downward movement o the surace

• "t may occur due to plastic outow o the underlyingstrata or due to the compaction o the underlyingmaterial

• #$% S#"side%e d#e to Plasti o#tfow: "t may

occur when a plastic layer li!e clay ed is s&uee'edoutward due to overlying heavy load

• #(% S#"side%e d#e to ollapse: "t occur due toe)tensive pull out o large volume o undergroundwater or due to susurace solution activity inlimestone terrain.

Subsidence



CAUSES OF

LANDSLIDES• LANDSLIDES OCCUR DUE OF 0ARIOUS REASONS

• I%ter%al Ca#ses:

• In+!ence of slope %rovides favo!ra&lecondition for landslides, steeper slope areprone to slippage of land# It is 'no-n t"atmost of t"e materials are sta&le !pto

certain angle .ritical angle0 or .angle ofrepose0 1 it varies from 233 for!nconsolidated sediments to 433 formassive roc's and 533433 for partially 6ointed roc's#



• 7ro!nd -ater or associated -ater Mainfactor responsi&le for slippage# S!ppose

t"e "ard or massive roc's are !nderlained&y softer roc's 8s"ale or clay &ed9

• W"en rain -ater percolates t"ro!g" somefract!res or 6oints t"e clayey &eds&ecomes very plastic and acts as slippery&ase( -"ic" en"ance t"e c"ances of looseover&!rden to slip do-n-ard#

• Water is t"e most po-erf!l solvent( -"ic"not only ca!ses decomposition of minerals&!t also leac"es o!t t"e sol!&le matter oft"e roc' and red!ces t"e strengt"#



• Lit"ology roc! which are rich in clay#montmorillonite* entonite%* mica* calcite* gypsum etc

are prone to landslide ecause these minerals areprone to weathering.

• 7eological str!ct!res +ccurrence o inclinededding planes* ,oints* ault or shear 'one are theplanes o wea!ness* which create conditions o

instaility.• H!man In+!ence undercutting along the hill slopes

or laying roads or rail trac!s can result into instaility.

• -eorestation in the uplands* result into more erosionduring the rainy season.



• E:ternal factors

• Most common is the viration resulted due toearth&ua!es lasting to e)plosives volcanic eruption

etc.

• Earth&ua!es oten initiate mass ailures on large scaleeg. $/01 2ssam &ua!e produced gigantic landslide everrecorded in the region.



%RE;EN<I;E

MEAS=RES

• The main actors which contriute to landslides are Slope!water o%te%t! .eolo.ial str#t#re! #%o%solidated or

loose sedime%ts! litholo.1 a%d h#ma% i%ter&ere%e'• Slope: Retaining -all may &e constr!cted against t"e

slopes( -"ic" can prevents rolling do-n of material#<erracing of t"e slope is an e)ective meas!re#

• E$et o& water: Ma'e proper drainage net-or' for>!ic' removal of percolating moist!re or rain -ater &yconstr!cting ditc"es and -ater -ays along t"e slope

• 2eolo.ial str#t#res: Wea' planes or *ones maycovered or gro!ted to prevent percolation of -ater(t"is increases t"e compaction of loose material#



La Conchita, CA

March 1995



It happened again in 2004…in exactly the same place…



3oc! 4alls

Documents

Landslides_White_GM309.ppt