EVALUATION OF LIQUEFACTION POTENTIAL OF ROORKEE REGION AND ITS INDUCED EFFECTS ON DYNAMIC STABILITY OF LEVEE CONSIDERING SEDIMENT EJECTA MANIFESTATION

Abstract

Liquefactionofsoilisaphenomenonwheretheeffectivestressesgetsreducedduetothegen- eration ofexcesspore-waterpressures(EPP)duringearthquakeshaking.Thisismanifestedby loss ofsoilstiffnessandshearstrength.Liquefactionisoneofthemostsignificantandremark- able causesofgroundfailureingeotechnicalearthquakeengineering.Thephenomenonmostly occurs insaturatedcohesionlesssoilswhensubjectedtoseismicloading.Thetendencyofasoil to getliquefyisdefinedasitsliquefactionpotential.Itisageneralpracticetoevaluatethelique- factionpotentialusingEPPgenerationandsingleordoubleamplitudeshearstrainof3%or5% respectivelyusingstress-based,strain-basedorenergy-basedapproach.Bothfieldandlaboratory investigationssupportstheevaluationofliquefactionpotentialanditsinducedeffects. Manifestation carriedoutinthepresentstudyisfocusedonthesoilofRoorkeeregion, Uttarakhand, India.DuetothepresenceoftheSolaniriver,thewatertableisatashallowdepthin the regionunderconsideration.Both,siteinvestigationandelementleveltestinghavesupported the findingthatSolanisandismorepronetoliquefaction.Thestudyareaalsoliesinseismiczone IV,altogethersignifyingthevulnerabilityofRoorkeeregionagainstseismicevents.Thus,itisof paramount importancetostudythebehaviourofregionalsoilandidentifyitseffectsondynamic stability ofbuiltenvironment.Forthispurpose,overallstudyiscategorizedintofourmajor sections: (a)GeotechnicalinvestigationusingfieldtestsandEarthquakesourcecharacterisation using paleo-liquefactionstudies,(b)Laboratoryinvestigationtoexaminethebehaviorofsoil under differentloadconditions,(c)Liquefactionpotentialofsoilusingtheenergy-basedapproach and relatingitwithearthquakeenergy,and(d)Sedimentejectamanifestationanditseffecton leveeconstructedoverplainterrain. In thepresentstudy,ninesiteslocatedinRoorkeeregionofUttarakhand,Indiaarese- lected namely,Bhagwanpur,Bahadrabad,ConvocationhallIITR,DEQcampusIITR,Haridwar, Hospital IITR,Solaniriverbed,SolanikunjIITRandSwimmingpoolIITR.Geotechnicalinves- tigationcarriedoutforeachsiteusingStandardPenetrationTest(SPT)by Muleyetal.,2022 are utilized inthepresentstudyandtheliquefactionpotentialisevaluatedfollowingthreeapproaches viz, IS1893:Part1,2016, Boulanger &Idriss,2014 and Youd&Idriss,2001a. Siteinvestigationis followedbytheprobabilisticearthquakesourcecharacterization.Theinverseanalysistechniques is utilizedonpaleo-liquefactionstudiestoestimatetheprobableseismicsourcelocationandmag- nitude fortheselectedRoorkeeregion.Accordingly,therelativelikelihoodofthesourcelocation and magnitudeisestimated.Amongst,alltheninesites,onesitefromalltheliquefactionsus- ceptible sitesi.eSolaniriverbedischosenforfurtherinvestigation.Thesamplescollectedfrom Solani riverbedaretakentolaboratorytodeterminetheindexproperties.BehaviourofSolani sand isexaminedundermonotonicandcyclicloadingsbothindryandsaturatedconditionsin the laboratory.Forthispurposefoursetoftestsareconductedviz.(a)drysamplessubjectedto monotonic loading,(b)saturatedsamplessubjectedtomonotonicloading,(c)drysamplessub- jected tocyclicloading,and(d)saturatedsamplessubjectedtocyclicloading.Resultsfromall the fourcasesarediscussedtofindtheeffectofsaturationandthedifferenceinbehaviourofsoil under bothstaticanddynamicconditions.Thetestsconductedarestrain-controlledundrained cyclictriaxialtestssubjectedtovaryingeffectiveconfiningstresses(50,100,150and200kPa). Further,measurementofliquefactionpotentialofSolanisandusinglaboratorytestsis also carriedout,followingtheenergy-basedapproach.Forthispurpose,aseriesofcyclictriaxial experimentsconductedinprevioussectionareutilizedtodeterminetherelationshipbetweenthe generated excessporewaterpressureandtheenergyrequiredbythesoiltoliquefy(WL). Cu- mulativedissipatedenergyperunitvolumeduringeachloadingcycleisequaltothecumulative enclosed areaofthehysteresisloop.Soil’sliquefactionenergyisdefinedasthesumoftheener- gies ineachcycleuptothecommencementofliquefaction.Anumericalapproachisdesignedto imitate theexperimentalresults.Theproposednumericalmodelisvalidatedandfurtherutilized to simulatethefieldconditions.Forthispurpose,asetofsixnear-fieldandsixfar-fieldground motions correspondingtothetargetteddesignedspectrumareselected,andtheenergyexperi- enced ontargettedsoilsampleduringtheseearthquakesisevaluated.Ifanearthquakeimparts energyequivalenttothecalculatedenergy,thesoilisconsideredtoliquefy. Lastly,tostudytheimpactofliquefactioninducedeffectsonthedynamicstabilityof builtenvironment,sedimentejectamanifestationonliquefiableSolanisandusingeffectivestress analysis (ESA)iscarriedoutinOPENSEES.TheparametersforthePM4Sandsoilconstitutive model usedinOPENSEESfornumericalstudyareevaluatedusingthenumericalapproachde- signed andcalibratedtoimitatetheexperimentalresults.Theeffectondynamicperformanceof leveeduetosedimentejectaisalsoexamined.Forthispurpose,aleveestructureisconstructedon the site,surroundedbytheSolanirivertoitsrightandaresidentialslumareatoitsleft.Ifseismic waveshitthisearthquake-pronearea,Solanisandismorelikelytoliquefywithsubsequentejecta of sedimentandaffecttheadjacentlivelihood.Thepresentstudyaimsatestimatingthehydraulic demand toproducesubsequentsedimentejectaforthelevelgroundandfinditseffectonlevee constructed overtheterrain.Basedonthefindings,severityofgroundfailureisalsoassessed.