水利水电工程专业毕业设计外文翻译.docx

水利水电工程专业毕业设计外文翻译.docx

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水利水电工程专业毕业设计外文翻译

附录一外文翻译

英文原文

AssessmentandRehabilitationofEmbankmentDams

NasimUddin,P.E.,M.ASCE1

Abstract:

Aseriesofobservations,studies,andanalysestobemadeinthefieldandintheofficearepresentedtogainaproperunderstandingofhowanembankmentdamfitsintoitsgeologicsettingandhowitinteractswiththepresenceofthereservoiritimpounds.Itisintendedtoprovideanintroductiontotheengineeringchallengesofassessmentandrehabilitationofembankments,withparticularreferencetoaCrotonDamembankment.

DOI:

10.1061/（ASCE）0887-3828（2002）16:

4（176）

CEDatabasekeywords:

Rehabilitation;Dams,embankment;Assessment.

Introduction

Manymajorfacilities,hydraulicorotherwise,havebecomeveryoldandbadlydeteriorated;moreandmoreownersarecomingtorealizethatthecostofrestoringtheirfacilitiesistakingupasignificantfractionoftheiroperatingbudgets.Rehabilitationis,therefore,becomingamajorgrowthindustryforthefuture.Inembankmentdamengineering,neitherthefoundationnorthefillsarepremanufacturedtostandardsorcodes,andtheirperformancecorrespondinglyisnever100%predictable.Damengineering—inparticular,thatrelatedtoearthstructures—hasevolvedonmanyfrontsandcontinuestodoso,particularlyinthecontextoftheeconomicaluseofresourcesandthedeterminationofacceptablelevelsofrisk.Becauseofthis,therefore,thereremainsawidevarietyofopinionandpracticeamongengineersworkinginthefield.Manyaspectsofdesigningandconstructingdamswillprobablyalwaysfallwithinthatgroupofengineeringproblemsforwhichtherearenouniversallyacceptedoruniquelycorrectprocedures.

Inspiteofadvancesinrelatedtechnologies,however,itislikelythatthebuildingofembankmentsandthereforetheirmaintenance,monitoring,andassessmentwillremainanempiricalprocess.Itis,therefore,difficulttoconceiveofasetofrigorous

assessmentproceduresforexistingdams,iftherearenodesigncodes.Manyagencies（theU.S.ArmyCorpsofEngineers,USBR,TennesseeValleyAuthority,FERC,etc.）havedevelopedchecklistsforfieldinspections,forexample,andsuggestedformatsandtopicsforassessmentreporting.However,thesecannotbetakenasprocedures;theyserveasguidelines,reminders,andexamplesofwhattolookforandreporton,buttheyserveasnosubstituteforanexperienced,interested,andobservantengineeringeye.Severalkeyfactorsshouldbeexaminedbytheengineerinthecontextofthemandateagreeduponwiththedamowner,andthesetogetherwithrelevantandappropriatecomputationsofstaticanddynamicstabilityformthebasisoftheassessment.Itisonlysensibleforanengineertocommittotheevaluationoftheconditionof,ortheassessmentof,anexistingandoperatingdamifhe/sheisfamiliarandcomfortablewiththedesignandconstructionofsuchthingsandfurthermorehasdemonstratedhis/herunderstandingandexperience.

RehabilitationMeasures

Themainfactorsaffectingtheperformanceofanembankmentdamare

（1）seepage;

（2）stability;and（3）freeboard.Foranembankmentdam,allofthesefactorsareinterrelated.Seepagemaycauseerosionandpiping,whichmayleadtoinstability.Instabilitymaycausecracking,which,inturn,maycausepipinganderosionfailures.Themeasurestakentoimprovethestabilityofanexistingdamagainstseepageandpipingwilldependonthelocationoftheseepage（foundationorembankment）,theseepagevolume,anditscriticality.Embankmentslopestabilityisusuallyimprovedbyflatteningtheslopesorprovidingatoeberm.Thisslopestabilizationisusuallycombinedwithdrainagemeasuresatthedownstreamtoe.Ifthestabilityoftheupstreamslopeunderrapiddrawdownconditionsisofconcern,thenfurtheranalysisand/ormonitoringofresultingporepressuresormodificationsofreservoiroperations

mayeliminateorreducetheseconcerns.Finally,raisinganearthfilldamisusuallyarelativelystraightforwardfillplacementoperation,especiallyiftheextentoftheraisingisrelativelysmall.Theinterfacebetweentheoldandnewfillsmustbegivencloseattentionbothindesignandconstructiontoensurethecontinuityoftheimperviouselementandassociatedfilters.Relativelynewmaterials,suchastheimperviousgeomembranesandreinforcedearth,havebeenusedwithsuccessinraisingembankmentdams.Rehabilitationofanembankmentdam,however,israrely

achievedbyasinglemeasure.Usuallyacombinationofmeasures,suchastheinstallationofacutoffplusapressurereliefsystem,isused.Inrehabilitationwork,theeffectivenessoftherepairsisdifficulttopredict;often,aphasedapproachtotheworkisnecessary,withmonitoringandinstrumentationevaluatedastheworkproceeds.Intherehabilitationofdams,thesecurityoftheexistingdammustbeanoverridingconcern.Itisnotuncommonforthedamtohavesufferedsignificantdistress—oftenduetothedeficienciesthattherehabilitationmeasuresaretoaddress.

Thedammaybeinpoorconditionattheoutsetandmaypossiblybeinamarginallystablecondition.Therefore,howtherehabilitationworkmaychangethepresentconditions,bothduringconstructionandinthelongterm,mustbeassessed,toensurethatitdoesnotadverselyaffectthesafetyofthedam.Inthefollowingtext,acasestudyispresentedasanintroductiontotheengineeringchallengesofembankmentrehabilitation,withparticularreferencetotheCrotonDamProject.

CaseStudy

TheCrotonDamProjectislocatedontheMuskegonRiverinMichigan.TheprojectisownedandoperatedbytheConsumerPowerCompany.Theprojectstructuresincludetwoearthembankments,agatedspillway,andaconcreteandmasonrypowerhouse.Theearthembankmentsofthisprojectwereconstructedofsandwithconcretecorewalls.Theembankmentswerebuiltusingamodifiedhydraulicfillmethod.Thismethodconsistedofdumpingthesandandthensluicingthesandintothedesiredlocation.CrotonDamisclassifiedasa‘‘high-hazard’’damandisinearthquakezone1.AspartoftheFERCPart12Inspection（FERC1993）,anevaluationoftheseismicstabilitywasperformedforthedownstreamslopeoftheleftembankmentatCrotonDam.TheCrotonDamembankmentwasanalyzedinthefollowingmanner.Soilparameterswerechosenbasedonstandardpenetration（N）valuesandlaboratorytests,andaseismicstudywascarriedouttoobtainthedesignearthquake.Usingthechosensoilproperties,astaticfinite-elementstudywasconductedtoevaluatetheexistingstateofstressintheembankment.Thenaone-dimensionaldynamicanalysiswasconductedtodeterminethestressinducedby

thedesignearthquakeshaking.Theavailablestrengthwascomparedwithexpectedmaximumearthquakeconditionssothatthestabilityoftheembankmentduringandimmediatelyafteranearthquakecouldbeevaluated.Theevaluationshowedthatthe

embankmenthadastrongpotentialtoliquefyandfailduringthedesignearthquake.Theminimumsoilstrengthrequiredtoeliminatetheliquefactionpotentialwasthendetermined,andarecommendationwasmadetostrengthentheembankmentsoilsbyinsitudensification.

SeismicEvaluation

Twomodesoffailurewereconsideredintheanalyses—namely,lossofstabilityandexcessivedeformationsoftheembankment.Thefollowinganalyseswerecarriedoutinsuccession:

（1）Determinationofporewaterpressurebuildupimmediatelyfollowingthedesignearthquake;

（2）estimationofstrengthfortheloosefoundationlayerduringandimmediatelyfollowingtheearthquake;（3）analysisofthelossofstabilityforpostearthquakeloadingwheretheloosesandlayerintheembankmentiscompletelyliquefied;and（4）liquefactionimpactanalysisfortheloosesandlayerforwhichthefactorofsafetyagainstliquefactionisunsatisfactory.

LiquefactionImpactAssessment

BasedontheaverageofthecorrectedSPTvalueandcyclicstressratio（TokimatsuandSeed1987）,atotalsettlementofthe4.6m（15ft）thicklooseembankmentlayerduetocompleteliquefactionwasfoundtobe0.23m（0.75ft）.

PermanentDeformationAnalysis

BasedonaprocedurebyMakdisiandSeed（1977）,permanentdeformationcanbecalculatedusingtheyieldacceleration,andthetimehistoryoftheaveragedinducedacceleration.Sincethefactorofsafetyagainstflowfailureimmediatelyfollowingthe

earthquakefallswellshortofthatrequiredbyFERC,theNewmarktypedeformationanalysisisunnecessary.Therefore,itcanbeconcludedthattheembankmentwillundergosignificantpermanentdeformationfollowingtheearthquake,duetoslopefailureinexcessoftheliquefaction-inducedsettlementof0.23m（0.75ft）.

EmbankmentRemediation

Basedontheforegoingresults,itwasrecommendedtostrengthentheembankmentbyinsitudensification.Ananalysiswascarriedouttodeterminetheminimumsoilstrengthrequiredtoeliminatetheliquefactionpotential.Theanalysiswasdividedintothreeparts,asfollows.First,aslopestabilityanalysis@usingthecomputerprogramPCSTABL（Purdue1988）#ofthedownstreamslopeoftheleftembankmentwasconducted.Strengthandgeometricparameterswerevariedinordertodeterminetheminimumresidualshearstrengthandminimumzoneofsoilstrengtheningrequiredforapostearthquakestabilityfactorofsafety,（FS）>1.Second,SPTcorrectionsweremade.Theminimumresidualshearstrengthcorrelatestoacorrected/normalizedpenetration

resistancevalue（N1）of60.Fromthisvalue,abackcalculationwasperformedtodeterminetheminimumfieldmeasurestandardpenetrationresistanceNvalues（blowsperfoot）.Third,liquefactionpotentialwasreevaluatedbasedontheminimumzoneofstrengtheningandminimumstrengthinordertoshowthatiftheemb