ML010650295

Draft Regulatory Guide DG-1105, Procedures and Criteria for Assessing Seismic Soil Liquefaction at Nuclear Power Plant Sites

ML010650295
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Issue date:	03/31/2001
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Thisregulatoryguideisbeingissuedindraftformtoinvolvethepublicintheearlystagesofthedevelopmentofaregulatorypositioninthisarea.It hasnotreceivedcompletestaffrevieworapprovalanddoesnotrepresentanofficialNRCstaffposition.Publiccommentsarebeingsolicitedonthisdraftguide(includinganyimplementationschedule)anditsassociatedregulatoryanalysisorvalue/impactstatement.Commentsshouldbeaccompaniedbyappropriatesupportingdata.WrittencommentsmaybesubmittedtotheRulesandDirectives Branch,OfficeofAdministration,U.S.NuclearRegulatoryCommission,Washington,DC20555-0001.Commentsmaybesubmittedelectronicallyor downloadedthroughtheNRC'sinteractivewebsiteat<WWW.NRC.GOV>throughRulemaking.CopiesofcommentsreceivedmaybeexaminedattheNRCPublicDocumentRoom,11555RockvillePike,Rockville,MD.CommentswillbemosthelpfulifreceivedbyJune15,2001.Requestsforsinglecopiesofdraftoractiveregulatoryguides(whichmaybereproduced)orforplacementonanautomaticdistributionlistforsinglecopiesoffuturedraftguidesinspecificdivisionsshouldbemadetotheU.S.NuclearRegulatoryCommission,Washington,DC20555, Attention:ReproductionandDistributionServicesSection,orbyfaxto(301)415-2289;orbyemailtoDISTRIBUTION@NRC.GOV.ElectroniccopiesofthisdraftguideareavailablethroughNRC'sinteractivewebsite(seeabove),ontheNRC'swebsite<www.nrc.gov>intheReferenceLibraryunderRegulatoryGuides,andinNRC'sPublicElectronicReadingRoomatthesamewebsite,underAccessionNumberML010650295.U.S.NUCLEARREGULATORYCOMMISSIONMarch2001OFFICEOFNUCLEARREGULATORYRESEARCHDivision1DraftDG-1105DRAFTREGULATORYGUIDEContact:J.Philip(301)415-6211DRAFTREGULATORYGUIDEDG-1105PROCEDURESANDCRITERIAFORASSESSINGSEISMICSOILLIQUEFACTIONATNUCLEARPOWERPLANTSITESA.INTRODUCTIONThisregulatoryguideisbeingdevelopedtoprovideguidancetolicenseapplicantsonacceptablemethodsforevaluatingthepotentialforearthquake-inducedinstabilityofsoils resultingfromliquefactionandstrengthdegradation.Itdiscussesconditionsunderwhichthe potentialforsuchresponseshouldbeaddressedinsafetyanalysisreports.Theguidance includesproceduresandcriteriacurrentlyappliedtoassesstheliquefactionpotentialofsoils rangingfromgraveltoclays.In10CFRPart100,"ReactorSiteCriteria,"§100.23,"GeologicalandSeismicSitingCriteria,"setsforththeprincipalgeologicandseismicconsiderationsthatguidetheNRCinits evaluationofthesuitabilityofaproposedsite.Inaddition,10CFR100.23(d)(4)discusses severalsitingfactorsthatmustbeevaluatedandrequiresthatthepotentialforsoilliquefactionbe evaluatedinadditiontoseveralothergeologicandseismicfactors.Safety-relatedsitecharacteristics,includingthoserelatedtotheresponseofsoilstoearthquakes,areidentifiedinRegulatoryGuide1.70,"StandardFormatandContentofSafety AnalysisReportsforNuclearPowerPlants(LWREdition)."RegulatoryGuide4.7,"GeneralSite SuitabilityCriteriaforNuclearPowerStations,"discussesmajorsitecharacteristicsthataffectsite suitability.ProceduresandmethodsofsiteinvestigationsaredescribedinRegulatoryGuide 1.132,"SiteInvestigationsforFoundationsofNuclearPowerPlants."Guidelinesforlaboratory testingaregiveninRegulatoryGuide1.138,"LaboratoryInvestigationsofSoilsforEngineering AnalysisandDesignofNuclearPowerPlants."RegulatoryGuide1.165,"Identificationand CharacterizationofSeismicSourcesandDeterminationofSafeShutdownEarthquakeGround Motion,"definesinvestigationsrelatedtoseismicity,faultsandvibratorygroundmotion.

2Thescopeofthisguideislimitedtoevaluationofthebehaviorofsoilssubjectedtoearthquakeshaking.Itspecificallyexcludesnonseismicfailureofsensitiveclays,failure understaticloads(suchasflowslidesinloosepointbardeposits),andsoilresponseto machinevibrationsandblasting.Theselectionorsynthesisofappropriategroundmotion recordstouseforaresponseanalysisisnotincluded.ThetechnicalbasisforthisregulatoryguideiscontainedinNUREG/CR-5741(1999).NUREG/CR-5741wasdevelopedtocompilecurrentandstate-of-the-art techniquesforevaluatingearthquake-inducedliquefaction.Itsummarizestheprocessof acquiringandusinggeological,geophysical,geotechnical,andotherkindsofrelevant informationthatsupportdesignconsiderationswithrespecttotheliquefactionpotentialof

soils.RegulatoryguidesareissuedtodescribetothepublicmethodsacceptabletotheNRCstaffforimplementingspecificpartsoftheNRC'sregulations,toexplaintechniques usedbythestaffinevaluatingspecificproblemsorpostulatedaccidents,andtoprovide guidancetoapplicants.Regulatoryguidesarenotsubstitutesforregulations,and compliancewithregulatoryguidesisnotrequired.Regulatoryguidesareissuedindraft formforpubliccommenttoinvolvethepublicindevelopingtheregulatorypositions.Draft regulatoryguideshavenotreceivedcompletestaffreview;theythereforedonotrepresent officialNRCstaffpositions.Theinformationcollectionscontainedinthisdraftregulatoryguidearecoveredbytherequirementsof10CFRParts50and100,whichwereapprovedbytheOfficeof ManagementandBudget,approvalnumbers3150-0011and3150-0093.Ifameansused toimposeaninformationcollectiondoesnotdisplayacurrentlyvalidOMBcontrol number,theNRCmaynotconductorsponsor,andapersonisnotrequiredtorespondto, theinformationcollection.B.DISCUSSIONGENERALEverysiteandplantfacilityisunique,andthereforerequirementsforanalysisandinvestigationsvary.Itisnotpossibletoprovideprocedurestodealwithevery contingency.Incircumstancesthatarenotspecificallyaddressedinthisguide,prudent andsoundengineeringjudgmentshouldbeexercised,withdueregardtothedegreeof conservatismneededtoprovidereasonableassuranceoftheadequacyofthedesignand constructionofnuclearfacilities.Inthepresentstateoftheart,theinterpretationofavailablegeotechnicaldataandresultsofanalysesofsoilresponsetoseismicloadingaretemperedby(1)documented experienceandempiricalknowledgeofconditionsunderwhichseismicallyinduced groundfailurehasorhasnotoccurredinthepast,and(2)applicationofadegreeof conservatismthatwillcompensateforuncertaintiesandthusassurethesafetyofthe facilityunderseismicloading.Withadvancesinthestateoftheart,improvementsin methodologywillbeadoptedtominimizetheuncertainties.Themechanismsofliquefactionandtheearlydevelopmentofanalysistechniquesforseismicresponseofsaturatedcohesionlesssoildepositsandthephysical 3mechanismsofliquefactionarediscussedbyCasagrande(1936);Shannon&Wilson,Inc.,andAgbabianandAssociates(1972);Castro(1975);andFinnandMartin(1975).

Empiricaltechniquesbasedonfieldperformancedataweresubsequentlydevelopedand promoted.TheseincludepublicationsbySeed(1976,1979a,1979b),Finn(1981),and SeedandIdriss(1971,1982).Hynes(1988)extendedthestateofknowledgeon liquefactionmechanismswithregardtolarge-particlesizedsoils;Kaufman(1981),Puri (1984),WalkerandStewart(1989),Koester(1992),andothersexaminedmechanismsof earthquake-inducedliquefactionofsandscontainingfinesandbothplasticandnonplastic mixturesofsiltandclay.DEFINITIONSDuringanearthquake,soilsmayundergoeithertransientorpermanentreductioninundrainedshearresistanceasaconsequenceofexcessporewaterpressuresor disruptionofthesoilstructureaccompanyingcyclicloading.Suchstrengthdegradation mayrangefromslightdiminutionofshearresistancetothecatastrophicandextreme caseofseismicallyinducedliquefaction,whichisatransientphenomenon.Theword"liquefaction"meansachangeinstatefromasolidtoliquid.Asappliedtoasoil,thetermreferstoachangefromasolidorstableassemblageofsoilparticlesto acompleteorsubstantiallycompletesuspensionofthesolidparticlesinafluid,suchthat thesuspensionhasaverylowshearstrength.Somepractitionersrestricttheuseofthe termliquefactiontodescribeflowfailure,asisobservedtooccurinafailedslopewhen drivingshearstressescausedbyanearthquakeremainhigherthanthepost-failureshear strengthofthesoilmaterials(CastroandPoulos,1977).Othersusetheterminitial liquefactiontodescribethebuildupofporewaterpressureinlaboratorytestswithinan undrainedsoilspecimentoalevelequaltothetotalconfiningstress.Liquefaction-inducedgroundfailure,intheextremesenseofsurfacemanifestation,maytaketheform offlowfailure,lateralspreadasmentioned,andgroundoscillation(Youd,1993).Inthisguide,thetermseismicallyinducedliquefactionincludesanydrasticlossofundrainedshearresistance(stiffnessand/orstrength)resultingfromrepeatedrapid straining,regardlessofthestateofstresspriortoloading.Thetermisinterchangeably appliedtothedevelopmentofeitherexcessivecyclicstrainsorcompletelossofeffective stresswithinanundrainedlaboratoryspecimenundercyclicloading(sometimesreferred toasinitialliquefaction).SITECHARACTERIZATIONPreliminaryassessmentsaretobemadetodeterminewhetherthesiteisclearlylikelyornotlikelytoliquefyinresponsetoearthquakeshaking.Thefollowinginformation isessentialtoaninitialassessmentofthepotentialforearthquake-inducedgroundfailure.1.Topographyofthesite.2.Asoilprofile,includingclassificationofsoilpropertiesandtheoriginofsoilsatthesite,andathree-dimensionalsubsurfacesoilstratigraphyshouldbe developedtosupportthesiteconceptualmodel.3.Water-levelrecords,representativeofbothcurrentandhistoricalfluctuations.

44.Evidenceobtainedfromhistoricalrecords,aerialphotographs,orpreviousinvestigationsofpastgroundfailureatthesiteoratsimilar(geologicallyand seismologically)nearbyareas(includinghistoricalrecordsofliquefaction, topographicalevidenceoflandslides,sandboils,effectsofgroundinstability ontreesandothervegetation,subsidence,andsandintrusionsinthe subsurface).5.Seismichistoryofthesite.SiteinvestigationsfornuclearfacilitiesandproceduresforinvestigationsaredescribedinRegulatoryGuide1.132,"SiteInvestigationsforFoundationsofNuclear PowerPlants."Significantstepsinthesiteinvestigations,asrelatedtotheevaluationof thepotentialforseismicallyinducedgroundfailure,occurinboththeinitialexploration phaseandthedetailedexplorationphase.Theinitialphaseshouldincludeboringswith standardpenetrationtests(SPTs)formeasuringpenetrationresistanceandforobtaining disturbedsplit-spoonsamplesforsoilclassificationandwatercontentdetermination.The SPTsshouldbecomplementedbyconepenetrationtesting(CPT).AlthoughtheSPTistheroutinemethodofdeterminingpenetrationresistanceforthepurposeofevaluatingthepotentialforseismicallyinducedgroundfailure,becauseof theavailabledatabaseforcorrelatingSPTvalueswithseismicresponse,CPTsoundings shouldalsobeperformedsincetheyprovidebetterstratigraphicdetailforpenetration resistanceandsoilcharacteristics.CPTresultsshouldbeverifiedusingpublished(e.g.,

Olsen,1994,1988,1984,andOlsenandFarr,1986)andsite-determinedcorrelationwith SPTvaluesandrelevantsoilparameters.Fortheinsituinvestigationofthestrengthofsoilscontaininggravelsorcobblesandtheirpotentialforliquefaction,thetoolofchoiceshouldbetheBeckerHammerTool.

Liquefactionresistanceandresidualstrengthofgravellysoilsshouldbeestimatedby convertingBeckerHammerPenetrationTest(BPT)blowcountstoequivalentSPTblow count(e.g.,HarderandSeed,1986).RecommendationswithrespecttoBPT performanceandresultinterpretationarediscussedinNCEER(1997).Duringtheinitialfieldinvestigations,thefollowingconditionswouldbecausetosuspectapotentialforseismicallyinducedgroundfailure:(1)lowpenetrationresistance asmeasuredbySPTsorCPTsinsandsandfinergrainedsoils,orBPTsingravelsor cobbles,(2)artesianheadconditionsorexcessporepressures,(3)persistentinabilityto retainsoilsamplesinconventionalsamplingdevices,(4)saturatedzonesofgranularsoils withimpededdrainage,and(5)thepresenceofanyclean,finesandbelowtheground-watertable.Anyoftheseoccurrencesshouldbenotedontheboringloganddescribedin thereportofthesiteinvestigations.Ifdepositsareidentifiedthatshowapotentialfor seismicallyinducedgroundfailurethatwouldaffectthesafetyofthefacility,theyshould beexploredindetailtodefinetheirthicknessandarealextent,andfurtherinvestigations shouldbeconductedtodefinethethreatthatthosedepositsmayposetothefacility.Thenextphasefollowingtheinitialphaseofsubsurfaceinvestigationsshouldincludesurveysandundisturbedsamplingboringsto:(1)refinethepreliminary interpretationofthestratigraphyandtheextentofpotentiallyliquefiablesoils,(2)measure insitudensitiesanddynamicpropertiesforinputtodynamicresponseanalyses,and(3) 5recoverundisturbedsamplesforlaboratorytestingwhensitesoilsarenotadequatelyrepresentedintheavailabledatabase.SCREENINGTECHNIQUESFOREVALUATIONOFLIQUEFACTIONPOTENTIALOnthebasisoftheinformationobtainedduringtheinitialsiteinvestigations,anearlyevaluationofthepotentialforseismicallyinducedgroundfailurecanbemadein somecases.Thegoaloftheseevaluationsistodeterminewhetherthesiteisclearlysafe orwhethersoilsclearlywillliquefy.Iftheresultsofthescreeningevaluationareunclear, however,moredetailedanalysisshouldbeconducted.Thefollowingparagraphsdiscuss somescreeningtechniquesforevaluationofliquefactionpotential.Earthquake-inducedliquefactionismostcommonlyobservedin(butnotrestrictedto)thefollowingtypesofsoils:(i)fluvial-alluvialdeposits,(ii)eoliansandsandsilts,(iii) beachsands,(iv)reclaimedland,and(v)uncompactedhydraulicfills.Cohesivesoilswithfinescontentgreaterthan30percentandfinesthateither(i)classifyasclaysbasedontheUnifiedSoilClassificationsystemor(ii)haveaPlasticity Index(PI)greaterthan30percentshouldgenerallynotbeconsideredsusceptibleto liquefaction.SandshavingdualUnifiedSoilClassificationsystemdesignationssuchasCL-ML,SM-SC,orGM-GCarepotentiallyliquefiable(Youd,1998).Otherdesignationsinvolving the"C"description,iftheclaycontentisgreaterthan15percentbyweightandtheliquid limitisgreaterthan35percentandoccursatnaturalwatercontentslowerthan90percent (Wang,1979),canbeconsiderednonliquefiable.Somegravellysoilsarepotentiallyvulnerabletoliquefaction(CoulterandMigliaccio,1986;Ishihara,1984;Harder,1988;AndrusandYoud,1987;Andrusand Youd,1989;Andrusetal.,1992)when(i)theirvoidsarefilledwithfinerparticlesor(ii) theyaresurroundedbylessporoussoilswheretheirdrainageisimpededandtheymay bevulnerabletocyclicporepressuregenerationorliquefactionorboth.Liquefactionresistancecanberoughlycorrelatedwithgeologicage,depositionalenvironment,andpriorseismichistory(Youd,1998,afterYoudandPerkins,1978).Most liquefactionriskisassociatedwithrecentHolocenedepositsanduncompactedfills.

Therehave,however,beenafewobservedcasesofliquefactionofPleistoceneandeven Pre-Pleistocenedeposits.Particularcautionshouldbeusedindealingwithveryloose typesofthesesoils(e.g.,dunesands,talus)andwithextremelyloosecollapsiblesoils (e.g.,loess).Ifitcanbedemonstratedthatanypotentiallyliquefiablesoiltypespresentatasite(i)arecurrentlyunsaturated(e.g.,areabovethewatertable),(ii)havenotbeensaturated previously(e.g.,areabovethehistorichighwatertable),and(iii)cannotreasonablybe expectedtobecomesaturated,suchsoilscanbeconsideredtoposenopotential liquefactionhazard.Youd(1998)hassummarizedhistoricaldatathatrelatewatertable depthtoliquefactionsusceptibility.

6Potentiallyliquefiablesoilsmaynotposealiquefactionrisktothefacilityiftheyareinsufficientlythickandoflimitedlateralextent.If,however,theyareverylooseand continuelaterallyoverasufficientarea,theycanrepresenthazardousplanesof weaknessandslidingandmaythusposeotherhazardswithrespecttotranslationalsite instability,lateralspreading,orrelatedgrounddisplacement.Whensuitablysoundlateral containmentisprovidedtoeliminatepotentialslidingonliquefiedlayers,potentially liquefiablezonesoffinitethicknessoccurringatanydepthmaybedeemedtoposeno significantslidingriskbutmay,however,besusceptibletodifferentialsettlement.Where considerationsofsuchdifferentialsettlementorrelativeplacementbetweenstructuresor componentsofthefacilityhavesafetysignificance,quantitativeanalysesofthesettlement ofthedeformations,includingeffectsofearthquakes,willberequiredeventhoughthe soilsinvolvedmaybejudgedseismicallystabletoliquefactioneffects.Probabilisticmethodologiescansometimesbeusedasascreeningtechniquetoidentifypotentiallyliquefiablesoils(e.g.,NUREG/CR-6622).PROCEDURESFOREVALUATINGLIQUEFACTIONSUSCEPTIBILITYGeneralIfthegeologicsiteevaluationindicatesthepresenceofpotentiallyliquefiablesoils,theresistanceofthesesoilstoliquefactionorsignificantstrengthlosstocyclicpore pressuregenerationshouldbeevaluated.FactorofSafetyAgainstLiquefactionLiquefactionsusceptibilitycanbeexpressedintermsofafactorofsafetyagainsttheoccurrenceofliquefactionas:FSFS CRR CSRagainstliquefaction

==whereCRR(cyclicresistanceratio)istheavailablesoilresistancetoliquefaction,expressedintermsofthecyclicstressesrequiredtocauseliquefaction,andCSR(cyclic stressratio)isthecyclicstressgeneratedbythedesignearthquake.Theabovedefinitionofthefactorofsafetyisusedinempiricalproceduresfortheevaluationofliquefactionpotential.Interpretationsofthefactorofsafety,FS,are providedbyMarcuson,Hynes,andFranklin(1990)forlevelgroundconditions,Tokimatsu andYoshimi(1983)forsandysoils,Evans(1987),andHynes(1988)forgravellysoils.AnalyticalMethodsThesemethodstypicallyrelyonlaboratoryteststodetermineeitherliquefactionresistanceorsoilpropertiesthatcanbeusedtopredictthedevelopmentofliquefaction.

Variousequivalentlinearandnon-linearcomputermethodsareusedwiththelaboratory datatoevaluatethepotentialforliquefaction.Analyticalmethodsneedaccurate measurementsofconstitutivesoilproperties.Ifreliablescreeningprocedureshavenot ruledoutthepossibilityofliquefaction,acomprehensivelaboratorytestingprogram 7shouldbeconducted.GuidelinesforlaboratorytestingaredescribedinRegulatoryGuide1.138,"LaboratoryInvestigationsofSoilsforEngineeringAnalysisandDesignofNuclear PowerPlants."LaboratoryCyclicStrengthTestingThecyclictestsusedtoevaluatetheresponseofsoilstoearthquakeshakingshouldcorrectlysimulatetheloadingtowhichthesoilwouldbesubjectedinsitu.Cyclic simplesheartestsmaybestreproducethestraininginasoilspecimencausedby upwardlypropagatingearthquakewaves.Variousconfigurationsofcyclicsimpleshear, cyclictriaxial,large-scaleshaketable,andcyclictorsionalshearapparatuseshavebeen employedtostudyliquefactionresistance(Woods,1981;Wood,1982;andDepartmentof theArmy,1986).Researchstudieshavedemonstratedthatlaboratory-determinedcyclictriaxialstrengths(infact,strengthsdeterminedfromanyunidirectionalloadingtest)arehigher thanthoseexpectedtoproduceequivalenteffectsinthefield(Seed,1976).Research hasalsoshownthatestimationoffieldliquefactionresistancefromlaboratorytestresults maynotbepossiblebyuniversalapplicationofsimplefactors,e.g.,gradation,density, andsoiltype(Koester,1992).PhysicalModelingInphysicalmodelingbytheuseofacentrifuge,asmall-scalephysicalmodelofasoildepositissubjectedtoanincreasedaccelerationfieldsuchthatthestresslevel causedbyselfweightinthemodelwouldbethesameasthecorrespondingstresslevel intheprototype.Numerousstudiesbymanyresearchershavedemonstratedthebenefits ofcentrifugemodelingforseismicsimulationstudiesandliquefactionpotentialevaluation (Whitman,Lambe,andKutter,1981;Schofield,1981;Scott,1983;Arulanandan, Anandarajah,andAbghari,1983;Steedman,1984;Coe,Prevost,andScanlan,1985; Hushmand,Scott,andCrouse,1988;Ketchman,Ko,andSture,1991;andArulanandan andScott,1993).EmpiricalProceduresEmpiricalmethodshavebecomewidelyusedinroutineengineeringpractice.Proceduresforcarryingoutaliquefactionassessmentusingempiricalmethodsarein SeedandIdriss(1971);Seed(1983);NationalResearchCouncil(1985);(BSSC,1991);

andNCEER(1997).RecommendedrelationshipsbetweencorrectedSPTpenetrationresistanceandtheliquefactionresistanceCRR(normalizedforoverburdenstress)arediscussedin NCEER(1997).ThemeasuredSPTblowcountismodifiedforvariousparametersto yieldthecorrectedSPTpenetrationresistance.ModificationsforCRRincludethosefor earthquakemagnitudesgreaterthan7.5andotherparameters(NCEER,1997).CPT-derivedestimationsofCRRfollowproceduresdiscussedinNCEER,1997;Olsen,1994,1988,and1984;OlsenandFarr,1986;OlsenandMitchell,1995;Olsenand Koester1995;Olsen,Koester,andHynes,1996;andSeedandDeAlba,1986.BPT 8blowcountareconvertedtoequivalentcorrectedSPTvalues(HarderandSeed,1986),whichinturnareusedtoestimateCRR.Bycomparingthecalculatedequivalent,uniform, earthquake-inducedcyclicstressratio,CSR,withtheuniformcyclicstressrationecessary tofullytriggerliquefaction,CRR,thefactorofsafetyagainst"triggering"ofliquefactioncan becalculated.SeismicWaveVelocityMeasurementsChartsrelatingshearwavevelocitytomaximumsurfaceaccelerationhavebeendevelopedbyStokoeetal.(1988)topredictliquefactionpotential.Otherapplicationsof shearwavevelocityincludethoseinNCEER(1997).Thesemethods,atpresent,have limitedapplicabilityexceptforsoilsandconditionsrepresentedinthedatabaseusedin thedevelopmentofthesetechniques.C.REGULATORYPOSITION1.SITECHARACTERIZATION1.1GeneralTheinitialphaseofthesitecharacterizationprogramshouldincludeboringswiththeirlocationsanddepthschosensothatthesitegeologyandfoundationconditionsare sufficientlydefinedinlateralextentanddepthtoprovidethedataforthedesignsforall structuresandexcavations.Thisphaseshouldinclude(1)boringswithSPTtestsfor measuringpenetrationresistanceandobtainingdisturbedsplit-spoonsamplesfor measuringclassificationandwatercontentdeterminationsand(2)CPTfordetermining penetrationresistance.CPTshouldbethetoolofchoiceforinitialsitecharacterizationstudiesinsupportofliquefactionpotentialassessment.TheCPTresultsshouldbeusedtoselectlocalities anddepthsforsubsequentSPTboringsandothersamplingefforts.Coverageofthesite withCPTsandSPTboringsshouldbeadequateto(1)establishgeneralsoilconditions, distributionofsoiltypes,homogeneity,andground-waterelevation;(2)identifysoilsthat mightliquefy;and(3)assistinspecifyingthelocationsofadditionalboringsand geophysicalsurveysaimedatdetailedseismicresponseevaluation.Fortheinsituinvestigationofthestrengthofsoilscontaininggravelsorcobblesandtheirpotentialforliquefaction,thetoolofchoiceistheBeckerHammerTool.1.2PerformanceofStandardPenetrationTestsTheproceduresandapparatususedinperformingSPTsshouldconformtoapplicablepublishedindustryconsensusstandardsandshouldbedescribedinsufficient detailtopermittheevaluationoftheresultsbytheNRCstaff.Becauseoftheimportance ofthedetailsoffieldprocedure,fieldtestsmadefortheevaluationofseismicstabilityof soilsshouldbeperformedunderaqualityassuranceprogram,inaccordancewith requirementsofAppendixB,"QualityAssuranceCriteriaforNuclearPowerPlantsand 9FuelReprocessingPlants,"to10CFRPart50,"DomesticLicensingofProductionandUtilizationFacilities."1.2.1Adjustmentof"N"'ValuesProceduresusedforadjustingorcorrecting"N"valuesfromSPTsforvariousparametersforuseintheevaluationofliquefactionpotentialmustbediscussedand justified.Adjustmentsforthe"N"valuesarediscussedintheliterature,e.g.,NCEER (1997).1.2.2SPTCorrelationsInevaluatingtheseismicstabilityofsitesoilsonthebasisofcorrelationofSPTdata,wherecorrelationsorcomparisonsaremadewithotherthanrawmeasureddata (i.e.,withparameterssuchasrelativedensityoroverconsolidationratioderivedor computedfromthe"N"values),themethodofderivationshouldbedescribedinsufficient detailthatthestaffcanretracethederivation.Whenderivedparametersareusedin correlations,the"N"valuesshouldalsobeprovided.1.3PerformanceofConePenetrationTestsForCPT-basedevaluations,soilsamplingusingtheSPTshouldbeperformedtoobtaindisturbedsamplesforconfirmationofsoiltypeandforsoilindextesting.CPTsoil characterizationcharts(e.g.,OlsenandKoester,1995)forestimatingliquefaction resistanceshouldbeusedinconjunctionwithlaboratory-measuredsoilindextests.

WhenconvertingCPTmeasurementsintoequivalentSPTblowcountvaluesfor estimatingliquefactionresistanceCRR,site-determinedcorrelationsshouldsupplement publisheddata,particularlyifsitesoilsarenotadequatelyrepresentedinthedatabase.1.4PerformanceofBeckerHammerPenetrationTestsUncertaintiesshouldbeminimizedintheinsitutestingofgravellysoilsusingBPTtests.Recommendations,suchasinNCEER(1997),shouldbefollowedcloselywith respecttoBPTperformanceandresultsinterpretation.1.5SeismicWaveVelocityMeasurementsAlimiteddatabaseexistsforrelatingshearwavevelocitytomaximumsurfaceaccelerationtopredictliquefactionpotentialinsoils,particularlyforsoils>8metersdeep anddensersoilsshakenbystrongergroundmotions(Andrusetal.,1992,andNCEER, 1997).Thus,useofthismethodshouldbelimitedstrictlytosoilsandconditionsinthe databaseandprimarilyasascreeningtool.2.SCREENINGTECHNIQUESFOREVALUATINGLIQUEFACTIONPOTENTIALBasedontheinitialsitecharacterization,anearlyevaluationofthepotentialforseismicallyinducedgroundfailureshouldbemade.Theliquefactionhazardevaluation shouldaddressthreebasicquestions:(1)Arepotentiallyliquefiablesoilspresent?(2)If so,aretheysaturatedorcouldtheybecomesaturatedatsomefuturedate?and(3)Ifso, aretheyofsufficientthicknessorlateralextenttoposearisktothesurvivalorfunctionof theproject?Theseevaluationsshouldmakeassessmentsastowhetherthesiteis 10clearlysafeorifsoilsclearlywillliquefy.Iftheresultsofthescreeningevaluationareunclear,moredetailedevaluationsshouldbeconducted.3.PROCEDURESFOREVALUATINGLIQUEFACTIONSUSCEPTIBILITY3.1GeneralIfevaluationsofthesiteinvestigationsindicatethepresenceofpotentiallyliquefiablesoils,theresistanceofthesesoilstoliquefactionmustbeevaluated.Itshould alsobedeterminedwhetherthepotentiallyliquefiablesoilsshouldberemoved,whether remedialactionshouldbeundertaken,whetherfurtherfieldandlaboratoryinvestigations areneeded,orwhetherdetailedstabilityanddeformationanalysiscoulddemonstratethat anacceptablemarginofsafetyismaintainedforthedesignstructuresevenifliquefaction isassumedtooccur.3.2FactorofSafetyAgainstLiquefaction

.Thefactorofsafety,FS,isusedinempiricalproceduresfortheevaluationofliquefactionpotential.InterpretationsoftheFSshouldbeusedwithcaution.Ingeneral:

1.SoilelementswithlowFSs(FS1.1)wouldachieveconditionswhereinsoilliquefactionshouldbeconsideredtohavebeentriggered.Conservativeundrainedresidualstrengths,S r,fromlaboratoryandfieldtestsshouldbeassignedtothesezonesforfurtherstabilityanddeformationanalyses.

2.SoilelementswithahighFS(FS1.4)wouldsufferrelativelyminorcyclicporepressuregenerationandshouldbeassignedsomelargefractionoftheir(drained)staticstrength,obtainedfromlaboratorytests,forfurtherstabilityanddeformation analysis.3.SoilelementswithintermediateFSs(FS1.1to1.4)shouldbeassignedstrengthvaluesbetweenthevaluesappropriatetoconditions1and2aboveforfurtherstabilityanddeformationanalyses.Instronglycontractivesoils,thepossibilityof progressivefailureordeformationshouldbeconsideredandmobilizationof undrainedresidualstrengthsshouldbeassumed.ForcomputingtheFSwithrespecttoseismicallyinducedgroundfailure,cyclicresistancescorrespondingtostresslevelscausing5percentpeak-to-peakcyclicstrainor 2-1/2percentstrainincompression,whicheveroccursfirst,shouldbeused.These criteriarefertodataobtainedinconsolidated-undrained,stress-controlled,cyclictriaxial tests.Whenothermethodsoftestareused,consistentcriteriashouldbeapplied.3.3AnalyticalMethodsAnalyticalmethodsrelyonaccuratemeasurementsofconstitutivesoilproperties.Manyofthematerialpropertiesandotherinputparametersusedintheanalysesas discretevaluesareactuallyknownonlywithinsomerangeofvalues.Somefactors relatedtoinputparameters,assumptions,andmethodsofanalysesthatshouldbe addressedfollow.

113.3.1UncertaintyinGeotechnicalInputParametersThenormalvariabilityinsoilandrockmaterialsissuchthatgeotechnicalengineeringparameters,suchassoiltypes,layerthicknesses,andsoilstrengths,are usuallyknownasrangesofvaluesratherthanasdiscretevalues.Toensurethatreliably conservativeresultsareobtainedfromtheanalyses,valuesrepresentingtheconservative sideoftherangeofaninputparameterordinarilyareused.Ifameanvalueisused,orif itisnotknownwhichsideoftherangeisthemoreconservative,analysesshouldbe performedtodeterminethesensitivityoftheanalysistothatvariable.3.3.2SeismicInputMotionsThecharacterandformoftheearthquakemotionaresignificanttosoilresponseanalysesanddirectlyaffecttheresults.Indynamicanalysesofsoilorsoil-structure systems,theearthquakenormallymustbespecifiedasanaccelerationversustime record,whichisevent-specific.Analysesshouldbeperformedusinganensembleof recordssuchthatasawholetheyconservativelyrepresentthefrequencies,amplitudes, anddurationofshakingthatarecriticaltothefoundationsandearthstructuresofthe facility.3.3.3TimeStepinDigitizationofEarthquakeRecordTimeintervalsusedindigitizationofgroundmotionrecordsshouldbesmallenoughtoadequatelyrepresentthehighestfrequenciesthataresignificanttothe analysis.Ingeneral,200samplespersecondisanappropriatesamplingrate.3.3.4Ground-WaterLevelForanalysis,ground-watertablesorpoolelevationsshouldbeassumedtolieatthemaximumortheminimumoftherangethatcanbeexpectedatthesiteofthefacility, inthedirectionthatismostcriticaltotheanalysis.Inanalysisofseismicallyinduced groundfailure,thehigherwaterlevelsnormallywillbethemostcritical.Normalwater levelsshouldbechoseninaccordancewithRegulatoryGuide1.135,"NormalWaterLevel andDischargeatNuclearPowerPlants,"andwaterlevelsgovernedbyfloodconditions shouldbechoseninaccordancewithAppendixAtoRegulatoryGuide1.59,"'Design BasisFloodsforNuclearPowerPlants."Intheabsenceofadditionalsupportingdatafromtheprojectsiteitself,extrapolationofdataregardingwatertableelevationsfromadjacentsiteswillnot,byitself, usuallysufficetodemonstratetheabsenceofliquefactionhazard,exceptinthosecases inwhichacombinationofuniformityoflocalgeologyandverylowregionalwatertables permitsveryconservativeassessmentofwatertabledepths.Preliminarygeologicsite investigationsshouldalsoaddressthepossibilityoflocalwatertablesorlocallysaturated soilunitsatthesite.3.4LaboratoryCyclicStrengthTesting,PhysicalModeling,andUseofData3.4.1EffectsofSampleDisturbanceInlaboratoryteststodeterminetheresponseofgranularsoilstocyclicstresses,theuseofundisturbedsamplesofgoodqualityispreferredtotheuseofreconstituted materials.However,researchandexperiencehasshownthattheeffectsofdisturbance duringsamplingincludeanincreaseindensityinthecaseofloosesands,andadecrease indensityinthecaseofdensesands.Tominimizethechangesofdensityand 12consequentdegradationofstrengthinsamplesofrelativelydensesands,itisadvisabletousecarefullycontrolledandexecutedfieldsamplingmethodsinordertoobtainsamples ofthebestqualitypossible.Alessdesirablealternativeistheuseoftestspecimensthat arereconstitutedtotheirinsitudensities.Ifthismethodisused,caremustbetakento ensurethatthereisnomixingofmaterialsfromdifferentstrata.MarcusonandFranklin (1979)havereviewedtechniquesandapparatuscommonlyappliedtosamplegranular

soils.3.4.2EquivalenceBetweenEarthquakeStressHistoryandPeriodicStressHistoryintheLaboratoryThestressexcitationproducedatthesitebyanearthquakeresemblesinmanyrespectsarandommotion,anddynamicstressanalysesareperformedwithexcitation inputsresemblingasnearlyaspossibletheexpectedearthquakemotionsatthesite.

Laboratorycyclicloadtestingisconventionallyperformedusinguniformperiodicload cycling.Tomakeavalidcomparisonbetweenstressesinthefieldandsoilresponsein testswithuniformperiodicloads,itisnecessarytodevelopanequivalencebetweenthe quasi-randomstressrecordobtainedfromadynamicanalysisandsomenumberof uniformloadcyclesatsomeloadorstresslevel.Theequivalenceismaterial-dependent andshouldbecomputedonacase-by-casebasisusingtheresultsofcyclicmaterial responsetestshavingappropriaterangesofcyclicstressandnumberofappliedload cycles.Therangesinthesetestparametersshouldcovertherangesofinterestinthe field,sothatextrapolationisnotrequired.3.4.3OverconsolidatedSoilsAnyadjustmentoflaboratory-derivedcyclicstrengthvaluestoaccountforoverconsolidationorlateralearthpressureconditionsshouldbeadequatelysupportedby appropriatefieldandlaboratoryinvestigationstodemonstratetheexistenceofthose conditions.3.4.4ApplicationofCyclicTriaxialTestDataThecyclictriaxialtestdoesnotaccuratelymodelthestressconditionsinsitu.Cautionshouldbeexercisedwhenusinglaboratory-obtainedsoilcyclicstrengths.There shouldbeappropriatedownwardadjustmentsofcyclicstressvaluesobtainedfromtriaxial testsasappropriate.Therationalebehindtheadjustmentandthedatasupportingits magnitudeshouldbepresentedandreferenced.Laboratorycyclictestsshouldbeused onlytoestablishparametriceffectsoncyclicstrengthbehavior.3.4.5PhysicalModelingCentrifugemodeltestingpermitscorrectmodelingofthestressesandstrainsthroughtheincreasedgravityfield.However,particlesizesinthemodeltocompensate forscalingeffectsareincorrect.Further,thetestsdonotreplicateinsitusoilconditions andloadinghistory.Suchtests,therefore,shouldonlybeusedforverificationoftheories, parametricstudies,verificationofnumericalanalysis,orstudyofsoilresponse phenomena.3.5EmpiricalMethodsEmpiricalmethodshavebecomewidelyacceptedinroutineengineeringpractice.TheDiscussionsectionofthisguidediscussestheuseofSPT,CPT,andBPTteststo 13evaluateliquefactionpotential,whileRegulatoryPosition1discussesproceduresthatshouldbefollowedintheperformanceofthesetests.4.FINALEVALUATIONOFSEISMICSTABILITYInevaluatingthepotentialforseismicallyinducedgroundfailureatanuclearfacilitysite,theNRCstaffwillreviewthemethodsofanalysisorevaluationused,the assumptions,theinputparameters,andtheoriginaldataobtainedinthefieldand laboratoryinvestigations.TheexpositionofthesefactorsintheSafetyAnalysisReport shouldbeadequatetopermitthestafftoperformanindependentanalysisandtoverify theanalysispresented.Inthefinalevaluationofthesite'ssafetywithrespecttoseismicstabilityofsoils,thecollectiveinformationandthestudiesappliedshouldbeconsideredasawholein determiningwhetherthemarginofsafetyisacceptable.Anacceptablemarginofsafety applicabletoallcasescannotbefixed.Itshouldbedeterminedonacase-by-casebasis byusingengineeringjudgment,considering(1)thedegreeofconservatismintheinput parameters,(2)theassumptionsintheanalysis,(3)theanalyticalmethodsused,(4)the extentofandreliabilityofthedatabasefortheinputparameters,(5)thedefinitionof failureused,(6)thecriticalmodeoffailure,(7)thedefinitionoffactorofsafetyused,(8) thesafetysignificanceoftheproblem,(9)casehistoryevidenceoffieldperformance undersimilarsoilconditions,and(10)thedegreeofconsistencyintheresultsofthe analysesandcorrelations.D.IMPLEMENTATIONThepurposeofthissectionistoprovideguidancetoapplicantsandlicenseesregardingtheNRCstaff'splansforusingthisregulatoryguide.Thisdraftguidehasbeenreleasedtoencouragepublicparticipationinitsdevelopment.Exceptinthosecasesinwhichanapplicantorlicenseeproposesan acceptablealternativemethodforcomplyingwiththespecifiedportionsoftheNRC's regulations,themethodstobedescribedintheactiveguidereflectingpubliccomments willbeusedintheevaluationofapplicationsforconstructionpermits,operatinglicenses, earlysitepermits,orcombinedlicensessubmittedafterJanuary10,1997.Thisguide wouldnotbeusedintheevaluationofanapplicationforanoperatinglicensesubmitted afterJanuary10,1997,iftheconstructionpermitwasissuedbeforethatdate.

14 REFERENCESAndrus,R.D.,etal.,"InsituVsofGravellySoilsWhichLiquefied,"Proceedingsofthe10 thWorldConferenceonEarthquakeEngineering,,Madrid,Spain,19-25July,pp.1447-1452, 1992.Andrus,R.D.,andT.L.Youd,"SubsurfaceInvestigationofaLiquefaction-InducedLateralSpread,ThousandSpringsValley,Idaho,"MiscellaneousPaperGL-87-8,U.S.A.E.

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16NationalResearchCouncil,LiquefactionofSoilsDuringEarthquakes,NationalAcademyPress,Washington,DC,1985.NCEER,"ProceedingsoftheNCEERWorkshoponEvaluationofLiquefactionResistanceofSoils,"NationalCenterforEarthquakeEngineeringResearch,ReportNo.NCEER 0022,StateUniversityofNewYorkatBuffalo,Buffalo,NY,viewableontheWorldWide Webathttp://nceer.buffalo.edu., 1997.NUREG/CR-5741,"TechnicalBasesforRegulatoryGuideforSoilLiquefaction,"J.P.Koester,M.K.Sharp,M.E.Hynes,Editors,USNRC,March2000.NUREG/CR-6622,"ProbabilisticLiquefactionAnalysis,"USNRC,November1999.

Olsen,R.S.,"LiquefactionAnalysisUsingtheConePenetrometerTest,"ProceedingsoftheEighthWorldConferenceonEarthquakeEngineering,Vol.III,Prentice-Hall,Inc.,EnglewoodCliffs,NJ,pp.247-254,1984.Olsen,R.S.,"SoilClassificationandSiteCharacterizationUsingtheConePenetrometerTest,"ProceedingsoftheFirstInternationalSymposiumonPenetrationTesting(ISOPT-1)(ed.J.DeRuiter),A.A.Balkema,Rotterdam,Netherlands,pp.887-893,1988.Olsen,R.S.,"NormalizationandPredictionofGeotechnicalPropertiesUsingtheConePenetrometerTest(CPT),"Ph.D.DissertationsubmittedtotheUniversityofCalifornia, Berkeley,May1994(alsoavailableasTechnicalReportGL-94-29,USAEWaterways ExperimentStation,Vicksburg,MS39180,August1994),1994.Olsen,R.S.,andJ.V.Farr,"SiteCharacterizationUsingtheConePenetrometerTest,"Proceedings,InSitu'86,AmericanSocietyofCivilEngineers,SpecialtyConferenceonUseoftheInSituTestinginGeotechnicalEngineering,June22-25,1986,VirginiaPolytechnic InstituteandStateUniversity,Blacksburg,VA,pp.854-868,1986.Olsen,R.S.,andJ.P.Koester,"PredictionofLiquefactionResistanceUsingtheCPT,"Proceedings,InternationalSymposiumonConePenetrometerTesting-CPT'95,Linkopping,Sweden,October1989,1995.Olsen,R.S.,J.P.Koester,andM.E.Hynes,"EvaluationofLiquefactionPotentialUsingtheCPT,"Proceedingsofthe28 thJointMeetingoftheU.S.-JapanCooperativePrograminNaturalResources-PanelonWindandSeismicEffects,U.S.NationalInstituteofStandardsandTechnology,Gaithersburg,Maryland,May1996.Olsen,R.S.,andJ.K.Mitchell,"CPTStressNormalizationandPredictionofSoilClassification,"ProceedingsoftheInternationalSymposiumonConePenetrometerTesting-CPT'95,Linkopping,Sweden,October1989,1995.Puri,V.K.,"LiquefactionBehaviorandDynamicPropertiesofLoessial(Silty)Soils,"Ph.D.Thesis,UniversityofMissouri-Rolla,MO,1984.RegulatoryGuide1.59,"DesignBasisFloodsforNuclearPowerPlants,"USNRC,Revision2,August1977.

17RegulatoryGuide1.70,"StandardFormatandContentofSafetyAnalysisReportsforNuclearPowerPlants(LWREdition),"USNRC,Revision3,November1978.RegulatoryGuide1.132,"SiteInvestigationsforFoundationsofNuclearPowerPlants,"Revision1,USNRC,March1979.RegulatoryGuide1.135,"NormalWaterLevelandDischargeatNuclearPowerPlants,"USNRC,September1977.RegulatoryGuide1.138,"LaboratoryInvestigationsofSoilsforEngineeringAnalysisandDesignofNuclearPowerPlants,"USNRC,April1978.RegulatoryGuide1.165,"IdentificationandCharacterizationofSeismicSourcesandDeterminationofSafeShutdownEarthquakeGroundMotion,"USNRC,March1997.RegulatoryGuide4.7,"GeneralSiteSuitabilityCriteriaforNuclearPowerStations,"USNRC,Revision2,April1998.Schofield,A.N.,"DynamicandEarthquakeGeotechnicalCentrifugeModeling,"Proceedings,InternationalConferenceonRecentAdvancesinGeotechnicalEarthquakeEngineeringandSoilDynamics,(ed.Prakash,S.),UniversityofMissouri,Rolla,MO,Vol.3,pp.1081-1100,1981.Scott,R.F.,"CentrifugeModelTestingatCaltech,"SoilDynamicsandEarthquakeEngineering,Vol2(4),pp.188-198,1983.Seed,H.B.,"EvaluationofSoilLiquefactionEffectsonLevelGroundDuringEarthquakes,"LiquefactionProblemsinGeotechnicalEngineering,PreprintNo.2752,AmericanSocietyofCivilEngineersNationalConvention,Philadelphia,pp.1-104,1976.Seed,H.B.,"19 thRankineLecture:ConsiderationsintheEarthquakeResistantDesignofEarthandRockfillDams,"Geotechnique,vol.29(3),pp.215-263,1979a.Seed,H.B.,"SoilLiquefactionandCyclicMobilityEvaluationforLevelGroundDuringEarthquakes,"JournaloftheGeotechnicalEngineeringDivision,NewYork,Vol.105(GT2),pp.201-255,AmericanSocietyofCivilEngineers,1979b.Seed,H.B.,"Earthquake-ResistantDesignofEarthDams,"Proceedings,SymposiumonSeismicDesignofEmbankmentsandCaverns,"pp41-64,May6-10,AmericanSocietyofCivilEngineers,1983.Seed,H.B.,andP.DeAlba,"UseofSPTandCPTTestsforEvaluatingtheLiquefactionResistanceofSoils,"Proceedings,SpecialityConferenceontheUseofInSituTestsinGeotechnicalEngineering,Blacksburg,VA,AmericanSocietyofCivilEngineersGeotechnicalSpecialPublicationNo.6,pp.120-134,1986.Seed,H.B.,andI.M.Idriss,"SimplifiedProcedureforEvaluatingSoilLiquefactionPotential,"JournaloftheSoilMechanicsandFoundationsDivision,Vol.97(SM9),pp.1249-1273,AmericanSocietyofCivilEngineers,1971.

18Seed,H.B.,andI.M.Idriss,GroundMotionsandSoilLiquefactionDuringEarthquakes

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W-7405-eng-26,1972.Steedman,R.S.,"ModelingtheBehaviorofRetainingWallsinEarthquakes,"Ph.D.Thesis,CambridgeUniversity,Cambridge,UK,1984.Stokoe,K.H.,etal.,"LiquefactionPotentialofSandsfromShearWaveVelocity,"Proceedings,NinthWorldConferenceonEarthquakeEngineering,Tokyo-Kyoto,Japan,Vol.III,pp.213-218,August1988.Tokimatsu,K.,andY.Yoshimi,"EmpiricalCorrelationofSoilLiquefactionBasedonSPT-ValueandFinesContent,"SoilsandFoundations,Vol15(4),pp.81-92,JapaneseSocietyofSoilMechanicsandFoundationEngineering,1983.Walker,A.J.,andH.E.Stewart,"CyclicUndrainedBehaviorofNonplasticandLowPlasticitySilts,"TechnicalReprotNCEER-89-0035,NationalCenterforEarthquake EngineeringResearch,StateUniversityofNewYorkatBuffalo,NY,July1989.Wang,W.S.,"SomeFindingsonSoilLiquefaction,"WaterConservancyandHydroelectricPowerScientificResearchInstitute,Beijing,China,1979.Whitman,R.V.,P.C.Lambe,andB.L.Kutter,"InitialResultsFromaStackedRingApparatusforSimulationofaSoilProfile,"Proceedings,InternationalConferenceonRecentAdvancesinGeotechnicalEngineeringandSoilDynamics(ed.S.Prakash),UniversityofMissouri,Rolla,MO,Vol.III,pp.1105-1110,1981.Wood,D.M.,LaboratoryInvestigationsoftheBehaviorofSoilsunderCyclicLoading:AReview,"SoilMechanics-TransientandCyclicLoads,"JohnWileyandSons,Ltd.,1982.

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19 20REGULATORYANALYSIS1.STATEMENTOFTHEPROBLEMNewregulationswereissuedunderSubpartB,"EvaluationFactorsforStationaryPowerReactorSiteApplicationsonorAfterJanuary10,1997,"in10CFRPart100.Thenew regulationshaveamajorimpactonseismicsitingcriteria.Animportantconsequenceof seismicityisthepotentialforearthquake-inducedliquefactioninsoils.Itisthestaff'sview thatguidanceisneededtoprovidefortheuseofstate-of-the-artmethodsinassessing liquefactionpotential.Abetterbasisisneededtoevaluatethestabilityanddeformationof soilsatnuclearpowerplantsites.Ifguidanceisnotavailable,licenseeswouldhaveto extractinformationonliquefactionpotentialfromwidelydispersedliteratureanddata bases,noteasilyaccessible.Aregulatoryguide,"ProceduresandCriteriaforAssessingSeismicSoilLiquefactionatNuclearPowerPlants,"wouldprovideguidancetolicenseapplicantsonmethods acceptabletotheNRCstaffforevaluatingthepotentialforearthquake-inducedinstability ofsoilsresultingfromliquefactionandstrengthdegradation.Theguideshoulddiscusses conditionsunderwhichthepotentialforliquefactionresponseshouldbeaddressedin safetyanalysisreports.2.OBJECTIVETheobjectiveofthisregulatoryactionistoprovideguidancethatisacceptabletotheNRCstafftolicenseesonassessingthepotentialforearthquake-inducedliquefactionof soilsforthedesignoffoundationsandearthworksatnuclearpowerplantsites.3.ALTERNATIVESANDCONSEQUENCESOFTHEPROPOSEDACTION3.1Alternative1(DoNotIssueGuidance)Underthisalternative,newlicenseapplications(submittedafterJanuary10,1997)fornuclearpowerplantswouldhavenoguidanceonmethodsacceptabletotheNRCstafffor assessingtheearthquake-inducedliquefactionpotentialofsoilsatnuclearpowerplant sites.Practicesintheareaofliquefactionpotentialassessmenthavebeenevolving rapidlyoverthepast20years.Futureapplicantsmay,ontheirowninitiative,researchthe widelydispersedliteratureonthelatestacceptableproceduresandcriteria,buttheymay notdoso,resultinginalessthanadequatebasisfordesign.Thisalternativeis consideredthebaselineornoactionalternative.3.2Alternative2(IssueGuidance)3.2.1ConsequencesThestaffhasidentifiedthefollowingconsequencesrelatedtoAlternative2:(1)Guidancewouldpromotestate-of-the-artmethodsfortheassessmentofliquefactionpotentialinonedocument.Informationonearthquake-induced liquefactionpotentialispresentlywidelydispersedinworldwideliteratureandthe 21databasesarenoteasilyaccessible.Licenseeswouldbeabletousetheguidanceforamoreefficientassessmentofliquefactionofsoils.(2)Useoftheguidancebylicenseeswouldresultinsubstantialcostreductionsandimprovedefficiencies(comparedtonoguidancebeingprovided)toboththe licenseeandtoNRCinitsreviewofthelicensees'application.(3)Useoftheguidancebythelicenseewouldresultinabetterbasisforconductingstabilityanddeformationanalysesoffoundationsandearthworksatnuclearpower plants.4.CONCLUSIONAregulatoryguideonproceduresandcriteriaforassessingseismicsoilliquefactionatnuclearpowerplantsitesshouldbeissued,withprovisionforpubliccomment.This regulatoryguideshouldbebeneficialbecauseitmayleadtosaferplantdesignsatlower cost.Thestaffseesnoadverseeffectsassociatedwithissuanceofthisguide.BACKFITANALYSISThisguidedoesnotrequireabackfitanalysisasdescribedin10CFR50.109(c)becauseitwouldnotimposeaneworamendedprovisionintheCommissionrulesoraregulatory staffpositioninterpretingtheCommissionrulesthatiseithernewordifferentfroma previousapplicablestaffposition.DraftRegulatoryGuideDG-1105wouldapplyonlyto siteapplicationssubmittedafterJanuary10,1997.Becausenoapplicationsofthistype arepending,abackfitanalysisisnotrequiredaccordingtotherequirementslistedunder 10CFR50.109(a)(1),items(i)through(iv).Inaddition,thisregulatoryguidedoesnot requirethemodificationoradditiontosystems,structures,components,ordesignofa facilityortheproceduresororganizationrequiredtodesign,construct,oroperatea facility.Rather,alicenseeorapplicantcanselectapreferredmethodforachieving compliancewithalicenseortherulesortheordersoftheCommissionasdescribedin10 CFR50.109(a)(7).Thisregulatoryguideprovidesanopportunitytousestate-of-the-art-methods,availableinonedocument,ifthatisalicensee'sorapplicant'spreferred method.