土木工程外文翻譯

中文2320字英文文獻(xiàn)：DAMSASETYANDEARTHQUAKESAgreattragedywasavertedinthe1971sanfernandoearthquakejustnorthofLosAngelesinsouthernCalifornia.ThetowerVanNormanDam,lessthan10kilometersfromtherupturedfault,hadbeenbuilt30yearsbeforebyusingcommonmethododcarryingsoilforfillintopositionbywatersluices.Subsequently,additionalhydraulicfillhadbeenplaceintheinteriorportionofthedam,leavingonlyameterorsoofsoilonthedownstreamsidetostopthewaterflowingdownontoadenselypopulatedsuburbanarea.Fortunately,thewaterinthereservoirwadnotattheallowablemaximumatthetimeoftheearthquakeandthesilmearthlipofthedamdidnoterode,butheldthewaterinthereservoiruntilitcouldbedrawndown.Meanwhile,80,000personswereevacuatedfromthedownstreamarea.Theincidentexemplifiestheimportanceofevaluatingprospectivedamsitesforseismicsidk.Notonlyisanearthorconcreatdamanexpensivestructure,utitdirectlyaffectstheeconomyoftheregion,throughpowergeneration,floodcontrol,andirrigation.Asthepopulationcontiuestogrow,structuralfailureofalargedamwillposeincreasinglygreaterdisasterforthesizsblenumbersexposedtothesuddeninundationofthefloodplains,Indeed,invariouscounstriesmajordamsarelocatedinareasthatinthepasthavesufferedlargeearthquakes.Thelikelihoodoffuturedamagingearthquakesmustbemostcarefullystudied.Thenaturallyoccurringearthquakesaside,however,wemustconsideralsoacuriousconnectionsbetween.Reservoirsandearthquakes.Therehavebeenatleast13incidentscountriesinwhichswarmsofearthquakeshaveoccurredunderorverynearalargeteservoirsoonafterithasbeennewlyfiled.Theideathatearthquakesmightbetriggeredbyimpoundingsurfacewaterisnotnew.Inthe1870’s,theU.S.corpsofengineersrejectedproposailsformajorw;storageinthesaltonseainsuothernCaliforniaonthegroundsthatsuchactionmightcauseearthquakes.thefirstdetailedevidenceofsuchaneffcetcamewillthefillingofLakeMeadbehindhooverDam(height221meters),Nevada-Arizona,beginningin1935.Althoughtheremayhavebeenlocalseismicitybefore1935,thefactisthatafter1936earthquakesweremuchmorecommon.Nearbyseismographsinoperationsince1940haveshownthatthelargestearthquake(magnitudeabout5)in1940,theseismicitydeclined.Thefociofhundredsofdetectedearthquakesclusteronsteeplydippingfaultsontheeastsideofthelakeandhavefocaldepthsoflessthan8kilometers.Intheensuringyears,similarcasehistorisehavebeenacumulatedforseveraldozenlargedams,butonlyafewarewelldocumented.Mostofthesedamsaremorethan100metershighand,althoughthegeologicalframeworkatthesitesvaries,themostconvincingexamplesofreservoir-inducedearthquakesoccurintectonicregionswithatleastsomehistoryofearthquakes.Mostofthethousandsoflargedamsaroundtheworldgivenosignofanyonnectionbetweenreservoirfillingandearthquakes;of500largedamssorutinizedintheUnitedStates,apoollin1976showedthatforonly4percentofthemwasanearthquakeroportedwithmagnitudegreaterthan3.0within16kilometersofthedam.Ofparticularinterestarethefollowingfourwell-studiedexamplesofearthquakesinducedbyman-madereservoirs.First,LakeKaribainZambiabeganfillingin1985behinda128-meterhighdam.Althoughthereissomeevifenceforminorearthquakesinthevivinitybefortheconstruction,uptill1963,whenthereservoirwasfull,morethan2,000localshocks,mostunderthereservoir,werelocatedwiththeuseofnearbyseismographs.ThelargestshockinSeptember1963hadamagnitude5.8;sincethentheactivityhasdecreased..TheninKoyna,Iniaanearthquake(magnitude6.5)centeredclosetothedam(height103meters)causedsignificantdamageonDecember11,1967.Afterimpoundingbeganin1962,reportsoflocalshakingbecameprevalentinaprevlouslyalmostaseismicarea.Seismographsshowesthatfoclwereconcentraewdatshallowdepthsunderthelake.In1967anumberofsizeableearthquakesoccurred,leadinguptotheprincipalearthquakeofmagnitude6.5onDecember11.Thistemblorcausedsignificantdamagetobuildingsnearby,killed177persons,andinjuredmorethan1,500.Astrongmotionseismographinthedamgalleryregisteredamaximunaccelerationof0.63g.TheseriesofearthquakesrecordedatKoynahasapattertthatseemstofollowtherhythnoftherainfall.Atleastacomparisonofthefrequencyofearthquakesandwaterlevelsuggeststhatseismicityincreasesafewmonthsaftereachrainyseaonwhentheresercoirlevelishighest.Suchcorrelationsarenotsocleainotherexamplesnowknown.Anotherseriesofearthquakes,whichwerequiteconclusivelyreservoirinducedoccurredinChinanorthofCanton.TheHsingfengkiangDam(height105meters)wascompletedin1959.Thereafterincreasingnumbersoflocalearthquakeswererecorded,thegrandtotalin1972amountingtomorethan250,000.Ofcourse,mostwereverysmall,butonMarch19,1962,astrongshockofmagnitude6.1occurred.Theenergureleasedwasenoughtodamagetheconcretedamstructure,whichrequiredpartialdewateringandstrengthen-ing.Mostearthquakefociwereatdeepest,andsomeofthefocicoincidedwithintersectionsofthemainnearbyfaults.Thedataarenotyetcompleteforthefinalexample:themassiveNurekDam(height317meters)inTadzhikistan,USSR,thehighestearthfilldamintheworld.Evenin1972,beforeitscompletionbutafterwaterimpoundingbegan,signsofincreasedlocalseismicitywerereported.Atthiswritingtheplanisforthefullloadofstoredwatertogoontothecrustin1978;thefewyearsfollowingwillbeanxiousonesasmanywaittoseeifalargenearbyearthquakeshakesthefacilty.Howdoeswaterinalargereservoirstimulateearthquakes?Itishardtobelivethatitisentirelytheeffectoftheaddedweightontherocks;theactualadditionalpressureafewkilometersbelowthereservoirisasmallfractionofthenaturaltectonicstressesalreadypresend.(Calculationsindicatethatafewkilometersdowntheaddedstresstosheartherockisonlyafractionofabar.)AmoreplausibleexplanationisthetriggermechannismthatinducedtheDenverandRangelyearthquankesdiscussedearlierinthechapter.Inbrief,thismechanismwouldbeasfollows,Extrapressureproducedbythereserovoirloadingspreadsoutasapressurewaveorpulseintothecrust.Itsslowrateofspreadingmaytaleitmonthsoryearstotraveladistanceof5kilometers,dependingonthepermeabilityanamountoffracturingoftherock.Butifthepressurepulsefinallyreachesazoneofmicrocracksitmightforcewaterintothemandsodecreasetheforcesthatarepreventingthealreadypresenttectonicstrainfrominitiatingslidingandelasticreboundalongthefaults.Inanareawherethereisalikelihoodofseismicactivity,certainpreliminarystepsmustbetakenbeforeconstrctionofadam.First,whetherthecauseforconcernisanaturaloraninducedearthquake,itisessentialatthedesignstagestoestimatetheintensityofgroundshakingthestructurewillsustainduringitslifetime.Alsopreconstructiongeodeticsurveysoftheregionareusefulforpurposesofdetectinganychangsincrustaldeformationsassociatedwithreservoirloading.Furthermore,inorderthatearthquakeeffectscanbestudied,seismographsandotherinstrumentationshouldbeinstalledatanearlytime.Hydrographsformeasuringlargewaterwaves(seiches)inthereservoirarealsoimportant.Intheabsenceofsuitablerecordinginstrumentstomeasuretheseverityofearthquakemotionsandofthedamresponse,theadventofastrongearthquakenearbywillposequestionsthatcannotbeanswered.If,forexample,structuraldamagehasoccurred,andnosuchmeasurementshasbeentaken,itisimpossibletocomparebehaviorwithdesignearthquakeconditionsandthustoestimateperformanceforotherandperhapslargershocks,ortomakedesigndecisionsforrepairandstrengtheningofthesructure.英文文獻(xiàn)翻譯：壩的安全與地震1971年,在南加利福尼亞洛衫磯以北的圣非南多發(fā)生的地震中，避免了一場巨大的災(zāi)難。里斷裂帶不到10公里遠(yuǎn)的下游處是凡。諾爾曼壩.這座壩是30年前用水槽把土運(yùn)到壩址出填筑起來的,這是一種常用的填筑方法。隨后在壩上又補(bǔ)充進(jìn)行了水力充填。1971年地震期間，壩內(nèi)側(cè)出現(xiàn)了一個大的滑坡，壩的下游一側(cè),只剩下一米左右的土墻阻止水流向人口稠密的郊區(qū)流去，幸運(yùn)的是地震時水庫中的水沒有達(dá)到允許的最高水位，而且極其薄弱的壩體沒有被侵蝕。因此在水能夠排放前，一直把水擋在水庫內(nèi)，當(dāng)時有八萬人從下游撤離。這次事故可作為一個例子,說明從地震危險的角度來評價未來壩址是十分重要。土壩或混凝土壩不僅是花錢多的建筑物，而且是通過發(fā)電防洪和灌溉也是直接影響著這一地區(qū)的經(jīng)濟(jì)，由于人口不斷增長，大壩失事會給突然泛濫的洪泛平原的大量人口帶來日益增大的禍患。確實，在許多國家里，都建在過去曾發(fā)生過大地震的地區(qū)。為了確保下游居民區(qū)的安全,在壩的規(guī)劃過程中，以及竣工之后都要考慮到未來出現(xiàn)的破壞地震的可能性。當(dāng)然，對壩址附近的地質(zhì)條件，包括滑坡和斷層，都必須仔細(xì)研究。然而,撤開自然發(fā)生的地震不談，我們還必須考慮水庫和地震之間的奇妙關(guān)系。至少已有13起發(fā)生在不同國家的事故可以表明:大水庫剛蓄水后，水庫下邊或靠近水庫的地方就發(fā)生了多次地震。地表蓄水可以激發(fā)地震的觀點(diǎn)并不新鮮。19世紀(jì)70年代，美國陸軍工程師團(tuán)曾拒絕在加利福尼亞南部索爾頓湖大量蓄水。其根據(jù)就是認(rèn)為這種舉動可能引起地震。內(nèi)華達(dá)一亞利桑那的胡佛壩（壩高221米）上游的麥德水庫在1935年開始蓄水，隨之就首次獲得了這種作用的詳細(xì)資料，雖然1935年前,那里可能就有局部地震，但事實是1936年以后，地震頻繁的多了，1930年開始使用附近的地震儀表明，1940年的大地震（震級約為5級）后地震便減少了，檢測到幾百次的地震的震源都在麥德水庫東側(cè)急劇下陷的斷層出，而震源的深度不到八公里。在以后的幾年里，幾十座大壩都有類似的記載，但只有幾座有完整的書面材料。這些壩中，絕大多數(shù)都高于100米。雖然壩址的構(gòu)造各不相同，但水庫誘發(fā)地震的最有說服力的的例子都發(fā)生在至少都有地震史的構(gòu)造地區(qū)，全世界幾千座大壩中的大部分并沒有跡象可以表明水庫蓄水和地震之間有任何關(guān)系,1976年的一次民眾調(diào)查表明，美國仔細(xì)審查的500座大壩中，只有%4的離壩16公里的區(qū)域以內(nèi)發(fā)生過三級以上的地震。卜面仔細(xì)研究的人工水庫誘發(fā)地震的四個例子尤為有趣。第一個例子是贊比亞的卡里巴湖，壩高128米，1958年開始蓄水.雖然在建壩前就有證據(jù)表明附近有小地震，但直到1963年水庫蓄滿水時，附近的地震儀測到過2000多次局部地震，大部分發(fā)生在水庫下面。1963年9月發(fā)生的最大的一次地震，震級為5.8級,從那以后,地震的活動性就減小了。第二個例子發(fā)生在印度的庫依納。1967年12月11日，震中靠近大壩（壩高103米）的一次6.5級地震造成了嚴(yán)重破壞。1962年水庫開始蓄水以后，在這個先前幾乎無地震的地區(qū)里，局部地震的報告頻繁了。地震儀顯示出震源都在水庫下面很求淺的地方，1967年發(fā)生了一連串相當(dāng)大的地震，導(dǎo)致了12月11日的6.5級的主震。這次地震造成附近餓建筑物嚴(yán)重破壞，177人死亡，1500多人受傷。大壩廊道里的一臺強(qiáng)動地震儀記錄的最大加速度為0.63g。庫依納的一連串地震記錄