Cs Varnavrat land Slide

Geological Survey of India

ContributedbyNorthernRegion1

TreatmentandStabilisationofVarunavatParvatLandslide,Uttarkashi

District,Uttarakhand

Uttarkashi town (Long.7826E,Lat.3044N) is locatedat the toeof thehillslopesof

the Varunavat Parvat (Photo1), on the right bank of Bhagirathi river, at an elevation of

1150m.s.l.Itislocatedatadistanceof155kmfromRishikeshonRishikeshGangotriNational

Highway (NH108).RiverBhagirathi ispassing through the centreof the town almosthalfof

whichislocatedatthebaseofVarunavatParvat.

Amassive landslide on Varunavat Parvat started on 24 Sept. 2003 subsequent to the

incessantrainsinthearea.ThelandslideactivityprogressedeastwardfromRamLilagroundto

MasjidMohalla.Theslideactivityburiedanumberofcivilstructures likehouses,govt.offices,

hotels,etc.whichwerelocatedbythesideofNH108atthetoeofthehill.Almost3000people

wereaffectedbytheVarunavatslidesandpropertyworthRs50croreswasdamaged.However,

it isworthmentioning thatno lossofhuman lifeoccurredduring thisdisastrousslideactivity

because of timely proactive action taken by the district administration on the basis of early

warninggivenbyGSI.TheNationalHighway (NH108)wascompletelyblockedbydebris flow.

Due to blockade of this highway a 145m long alternate routewas opened between Sanskrit

MahavidyalayaMahisasurMardini temple areas. During sliding activity and blockade in

TambakhaniareathetrafficwasdivertedviaJoshiyaraTilothCollectorateDurgatempleroute.

GSIgeologistswhileworkinginthisareaaboutonemonthbeforethelandslidenoticed

some indicationsof slopemovementonVarunavatParvaton2124August2003andadvised

thedistrictadministrationforimmediateevacuationofthehighriskzoneatthetoeofthehill,

i.e.VarunavatParvat.Thepromptaction takenby thedistrictauthoritieson thisadvice from

24.09.03onwardsbywarning /evacuating the residents from identifiedhigh risk zone saved

humanliveswhenthedisasterstruckthearea.Atotalof293buildingsincluding23government

buildingswere identified.The landslidedamaged81buildingscompletely.212buildingsprone

todamagehavebeenidentifiedinbufferzone.

As soon as the enormity of the hazardwas realised byUttarakhandGovernment an

expert committee was formed by Chief Secretary, Uttarakhand in Sept.2003 to suggest

immediate remedialmeasureswithGSIas itsmember.Thereafter,aCentralComposite team

was formed by theMinistry ofHomeAffairs,Govt. of India,NewDelhi vide letterNo.D27

05/2003NDM1dated21.10.2003withDirector,GSIascoordinatorof the team toassess the

situation and to find out possibilities of the stabilisation of Varunavat Parvat as an interim



measure and also to explore the feasibility of permanent stabilisation for habitation.

Subsequently,aTaskForcewassetupunderthechairpersonshipofJointSecretary,Ministryof

Home Affairs (MHA), Government of India. Under the aegis of this Task Force, a Technical

Committee was formed for which Director, Geological Survey of India, Uttarakhand Unit,

Dehradunwasmadethechairman.

GeologyandTectonics

UttarkashitownislocatedintheLesserHimalayangeotectonicblockanditisbounded

bytwomajorthrustfaultsMainCentralThrust(MCT)andSrinagarThrust(ST).TheMCTexists

inthenortheastofUttarkashi,separatingrocksofGarhwalGroupandCentralCrystalline.The

Srinagar Thrust lies in the southwest of Uttarkashi and along this tectonic plane rocks of

Garhwal Group and Jaunsar Group are juxtaposed. The Garhwal Group (Proterozoic age)

comprisesquartzite,phylliteandmetabasicrockandthesedip1545 inN1040Edirection

i.e.intothehill.TherocksformingVarunavathillarecomposedofthinlybeddedquartziteand

phyllitewhich arehighlyweathered,destressed,decomposed, jointed and fractured.Thehill

slopes areof theorderof 4560 except at the topof thehillwhere the slopes are gently

sloping.ThetopportionoftheVarunavathillisoccupiedbyloose,unconsolidated,overburden

mass,exhibitinggentletopography.ThetopisatEl.1800mwhereasthetoepartofthehillisat

El.1100abovemsl.

The interfaceofoverburdenmassandunderlyingrocks isatEl.1650m.Uttarkashi lies

inZoneVofSeismicZoningMapofIndiaandithasarecordedseismichistory.

CausesofLandslides

Thecontinuousheavyrainsinthearea ledtosaturationoftheoverburden/loosemass

occupying the topof thehillsabove theEl.1650m supporting luxuriantvegetativecoverand

restingondenselyvegetatedrockyslopesofweatheredquartzite.Thesaturationbyrainwater

increased the increase inporepressure in theoverlyingoverburdenmassand lubricated the

underlying fracturedweathered rockmass. This had in fact reduced shear resistance of the

slopematerialsandthustriggeredtheslides.Oncetheslidesweretriggered,thefastmovement

ofdebris flowcarriedalong themuprootedpine treesdown theslopeandburied thehuman

settlements located at the toe of the hill around Ram Lila ground, Horticulture colony and

MasjidMohalla.Theslopemovementcontinuedforaboutamonthwithdustcloudsandthen



subsided.Pastanthropogenicactivitiesespeciallyinthetoeofthehillhavealsorenderedthehill

slopesvulnerable.

Immediateinitiativesundertaken/ActionPlanbyGSI

Immediately after the slide activity an action plan was proposed and adopted for

immediateimplementationwhichincluded:i)creationofabufferzone,closetothetoeofthe

Varunavat.ItwasredemarcatedbyexpertsfromGSIandCBRIashighriskzone; ii)removalof

slidematerialaccumulatedclosetoRamLilagroundalongtheNHforresumingvehiculartraffic;

iii) startingof geologicalmapping byGSI in the area as andwhen site conditionspermitted

amidst intermittent slide activity in the area.Themappingwas confined to accessible slopes

onlyandtherockconditionswereinterpretedfromnearbyexposedarea;andiv)constructionof

an approach track to the crown of the slide for taking up initial stabilisation of overburden

slopes.

GeotechnicalInvestigations

For suggesting permanent stabilisation measures in the slide area, the site specific

geological/geotechnicalstudiesproposedare:i)Surveyingandcontouringoftheslideareaon

1:1,000 scale using Total Station; ii)geological and structural mapping on 1:1,000 scale;

iii)geophysicalsurveys;iv)geomechanicaltestingofoverburdenmass;v)slopestabilityanalysis

numerical modeling (by NIRM); vi) monitoring of slope movement by Automatic Target

Recognition(ATR);andvii)studiesforbiorestorationofoverburdenslopes(byForestResearch

Institute,Dehradun).

TreatmentsandStabilisationMeasures

Followingmain treatmentsweredecided for theVarunavatParvat: i) removalofslide

massandgradingoftheslopesaboveEl1670m;ii)treatmentoftheCrownPortionEl1895m

El1670mwiththehelpofrockboltingandshotcreting intherockandbiorestoration inthe

overburden mass; iii) cable anchoring in two rows above El 1670m, iv) grading of slopes

betweenEl1670m El1550mandstabilisationbymeansofgeosynthetics/geojute, rock

boltingandshotcretinginareaswhererockisencountered;v)treatmentalongthethreechutes,

viz.RamlilaGround,MasjidMohallaandTambakhanichutes;vi)constructionofgeogridwallat

thetoeofTambakhanichute;vii)constructionofaconcretewallatthetoeofRamlilaGround

Chutesothatacatchpit iscreatedbackof it;viii)constructionofamaincatchdrainallalong



thetoeofVarunavatParvattocollectthedrainageflowingdownthethreechutesandthrough

theinterveningareas;andix)constructionofabyepasstunnelbelowTambakhanichute.

CurrentStatusofLandslide

ThemaintreatmentworksoftheVarunavatParvatlandslideareahavebeencompleted

in2008and it isworthhighlighting that there isnosliding from the treatedparts for the last

threeyears,despiteunusuallyhighrainfall(maximuminthelastthreedecades)inUttarakhand

intheyear2010.ThecontributionofGSI inthe forwarningofVarunavatParvat landslidehas

beendulyreflected inthePressReleaseofMinistryofMines,Govt.of Indiadated12.01.2005

(copy enclosed) which itself is the testimony to the importance of the role which GSI,

UttarakhandUnit,DehradunhasplayedinthetreatmentofVarunavatParvatLandslide.

GSI has recommended for posttreatment monitoring of the treated part of the

Varunavat Parvat landslide through a comprehensive monitoring scheme with the help of

instrumentsandanAutomatedRadarsystem,inordertoassesstheeffectivenessofthesupport

measures.

Photo1:ViewofVarunavatParvatbeforeLandslide



Photo2:ViewofVarunavatParvatafterLandslideandDevelopmentofthreeChutes(GoogleEarth)

Photo3:StabilisationinrockbymeansofRockbolting,ChainlinkShotcretingandCableAnchoringin

easedslope



Photo4SupportbymeansofConcretewallandWirecratewallintheCrownPortion

Photo5SlopeStabilisationinOverburdenMaterialbymeansofGeojute



Photo6ViewofCatchpitatRamlilaGroundattheRoadLevel

Photo7ViewofGeogridWallatMasjidMohalla

Cs Varnavrat land Slide

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