LANDSLIDES-CAUSES, EFFECTS AND CONTROLS

Contents:

I nt roduct i on- Mas s was t i ng proces s esWhat are l ands l i des ?Part s of s l opes – i s s ues of s t abi l i t yCharact eri s t i c of l ands l i deCaus es of l ands l i desHazard of l ands l i de i n al l as pectZonat i on map of Lands l i de(I ndi a)Lands l i des hazards areas i ndi cat orsprevent i onConcl us i on.Ref erence.

I t ref ers t o t he s l i di ng or di s l odgi ng of a l arge mas s of rocks

mat eri al s , s oi l s et c… down t he s i de of a mount ai n or c l i f fl ands l i des repres ent t he mos t

ext reme hazards , es peci al l y i n t erms of l os s of l i f eOverpopul at i on and s oci o-economi c

pres s ures have f orced s ome of t he mos t vul nerabl e popul at i ons i nt o areas of hi gh ri s k (hi l l s i des )Furt her, l and degradat i on and

cl i mat e change have exacerbat ed t he probl emI t caus es permanent def ormat i on

Parts of a typical landslide

landslide model in various places

Characteristic of Landslide:Lands l i de are charact er by s t eep s carp i n t hei r upper part s and i rregul ar l obat e

r i dges and f urrow at l ower part s . Lands l i de vary i n ext end f rom s everal

s quare met er t o s everal s quare ki l omet er and f rom l es s t han a met er t o s everal hundred of met er i n t hi cknes s .

Lands l i de vel oci t i es range f rom i mpercet abl e movement t o more t han 100kmph.

Causes of landslides

The f act ors af f ec t i ng t he l ands l i de can be of vari ous ways by bot h nat ural and human i nduced act i vi t ySome of t he f act ors are as f ol l ows :-

The geol ogys t ruct ure, l i t hol ogy, and t ect oni c act i vi t yRai nf al l amount , i nt ens i t y and durat i onGeomorphol ogyrel i ef , s l ope (amount , nat ure s l ope morphol ogy and as pect )Hydrol ogys urf acenat ural and art i f i c i al and s ubs urf aceLandus eagri cul t ure, s et t l ement s , f ores t , mi ni ng, quarryi ng, grazi ng and barren l andsSoci o-economi cpopul at i on dens i t y, educat i on, economi c condi t i on and devel opment act i vi t i es

fall

topple

torrent slump

creep

flow

slide

landslide

Classification of types of landslides

ToppleTopple

Toppl e I t ref ers t o t he end-over-end mot i on of rock down a s l ope.

SlideSlide

Sl i de When t he movement i s paral l el t o pl anes of weaknes s and occas i onal l y paral l el t o s l ope.

Creep

Creep Gradual movement of s l ope mat eri al s i s ref erred t o as creep

SlumpSlump

Sl ump The compl ex movement of mat eri al s on a s l ope; i ncl udes rot at i onal s l ump.

Fall

Fal l f ree f al l i ng of mat eri al s f rom cl i f f s .

Flow

Fl ow Vi s cous t o f l ui d-l i ke mot i on of debri s .

Torrent

Torrent A s poradi c and s udden channel i zed di s charge of wat er and debri s .

Landslide hazard

I nt roduct i on :-Lands l i de hazards ref ers t o t he

l os s or damage produced by t he Lands l i de i .e. t he af t er ef f ec t

Lands l i de l ocks or des t roy hi l l roads , hi ghways , rai l ways , canal s , bri dgesI t des t roys agri cul t ural f i el ds , pl ant at i ons , habi t at i onsI t bl ocks ri vers val l eys f l oodi ngI t al s o has advers e af f ect t o t he envi ronment as wel l as t he s oci et y

Landslide hazard indexDefined using seven parameters :

Sl opeGeol ogi cal condi t i onSoi l moi s t ure condi t i onVeget at i on coverPreci pi t at i on Sei s mi c condi t i onPopul at i on dat a

Slopes

Figure 9.3

Environmental EffectsEnvironmental Effects

Eros i onEros i on

Uproot i ngUproot i ng

Sl ope degradat i onSl ope degradat i on

Effects on SocietyEffects on Society

Des t ruct i on of Propert yDes t ruct i on of Propert y

Los s t o human l i f eLos s t o human l i f e

Creat es anxi et yCreat es anxi et y

The landslide susceptible zones of India

landslide hazards in roadways

landslide in settlements

landslide along the railroads

Oct ober 1990 Ni l gri s 36 peopl e ki l l ed and s everal i nj ured. Several bui l di ngs and communi cat i on net work damagedJul y 1991 As s am 300 peopl e ki l l ed, road and bui l di ngs damaged, Mi l l i ons of rupees l os tNovember 1992 Ni l gi r i s Road net work and bui l di ngs damaged, Rs .5 mi l l i on damage es t i mat edAugus t 1993 Kohi ma, Nagal and = 200 hous es des t royed, 500 peopl e di ed, about 5km road s t ret ch was damaged 8,Augus t 1998 Mal pa,Kal i r i ver =205 peopl e ki l l ed road net work t o Mans arovar di s rupt ed Augus t 2003 Ut t arkas hi =Heavy l os s of i nf ras t ruct ures

Some major landslide hazard

some landslide effects

Recent landslides in Uttarakhand:

Kal i yas aur l ands l i de (al ong NH-58) react i vat ed due t o heavy rai nf al l

i n Sept ember 2010.

Personal PreparationsGet a geologic evaluation of property

Avoid homes at mouth of valley or canyon

Consult local agencies

Monitor small landslides on property

Look for cracks in house walls, leaning retaining walls, doors or windows that stick

Personal Preparations, cont.Beware of leaks in swimming pools or septic tanks, trees

or fences that tilt, or sagging or taut utility wires

Beware of small springs

Look for surface features

Don’t buy a home that has a landslide hazard

Prevention of LandslidesDrainage control

Keeps water from infiltrating a slopeDrains can divert water Impermeable layers

Prevention of Landslides, cont.Grading can increase slope

stability.Material from upper slope

can be moved to base.

Slope supports.Retaining walls – Concrete

or filled wire baskets.Vegetation

Conclusion:-

Lands l i de i s a nat ural proces s whi ch has occurred under t he i nf l uence of gravi t yThe human act i vi t y however i nduces t he proces s and t ri ggers more hazardsThus l ands l i de hazard ref ers t o t he af t ermat h of t he l ands l i deI t has t remendous hazards on t he hi l l roads , hi ghways , rai l ways , bri dges , canal s , agri cul t ural f i el ds , s et t l ement s , r i ver val l eys et c gi vi ng ri s e t o i nconveni enceThe s us cept i bi l i t y i s more t owards t he nort h and nort heas t part of I ndi a as wel l as s ome part s al ong Keral a and s o on.

Reference:

Engi neeri ng Geol ogy by Qui do zaruba & Voj ech Mencl . (pp-163-171)Geomorphol ogy & Engi neeri ng- Donol d.R. Coat es . (pp-273-279)Engi neeri ng Geol ogy by H.Ri es & Thomas L Wat s on. (pp-365-378)