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8RCCasaNewConstructionMethod（RCC作为一种新的施工方法）8.1GeneralConstructionConsiderations(一般情况下施工过程需考虑的因素)·Thereareconsiderabledifferencesbetweenvertical,block-by-blockconstruction（垂直块状浇筑）ofdamswithconventionalmassconcreteandhorizontal,lift-by-liftconstruction（水平通仓浇筑）ofdamswithRCC.·TheconstructionplantforRCCisusually,lesscostly,andutilizedatahighercapacityfactor（利用率）thanthatrequiredforconventionalconcretegravitydams.·ButthefastpaceofplacementrequiredtoachievetheeconomiespossiblewithRCCimposesagreaterdiscipline(要求)ontheplanning,scheduling(进度),andcoordination(协调)inthefieldbetweendesigner(设计)andcontractor(承包商).·TheRCCdesignapproachesdescribedinChaps.4,5,and6diverge(不同点在于….)insomeconstructionprocedures.·Inallcases,however,themixing(拌合),transporting(运输),spreading(摊铺),andcompacting(碾压)ofrelativelylargevolumesofmaterialareconcentratedintoashorttimeinterval.IntheUnitedStates,thetimelimitfrommixingplanttofinalcompactionisabout45min.ItisabouttwicethatinJapan.Inaddition,theJapaneseRCDmethodrequiresthatliftsbecured(养护)foraslongas36hbeforeplacement(浇筑)ofthenextlayerofRCC.IntheUnitedstatesandelsewhere,thegoalhasnearlyalwaysbeentocomeascloseaspossibletocontinuousplacementofRCC.8.1.1SchedulingConstructionschedulingforRCCislessforgivingthanformassconcrete(大体积混凝土).Althoughsomemixdesignscanhavegreatertolerancesthanconventionalconcrete,RCCisstillasensitiveconcreteandthecriticalpath(关键路线)forplacingRCCisfocusedoncompletingoneliftatatime.Therearenoalternatemonolithic(整块的、独块的)blockstoformorplacewhileproblemsarebeinganalyzed.Toavoidcostlydelaysoverdisputesonspecification（规范）compliance（执行）,theauthoritytoresolveengineeringproblemsmustbevestedinawelltrainedfieldorganization.Linesofcommunicationbetweentheprojectengineer（项目工程师）andcontractormustbeclearlyestablishedandusedfrequently.Clarity(廉洁),candor（坦诚）,andcooperationareveryimportantinachievingthespeedofplacementpossiblewithRCC.Thoroughfieldandclassroomtrainingofconstructioncrews（施工队伍）andinspectors（检查员）inthehandlingandplacementofRCCisessential.Lean,dryRCCmixesresembledamp（潮湿的）gravel（砂砾石）andareoftenplacedbyroad-buildingorearth-damcrewsusingearthmovingequipment.However,allthedesiredcharacteristicsoftheproductarethoseofconcrete.MeetingthespecificationsrequireseducatingworkerstothespecificrequirementsofRCCasanewconstructionmaterialrequiringspecificconstructionmethods.Becausesomuchdependsonfast,efficientplacementoftheRCC,allrelatedactivitiessuchasfoundationcleanup,access,assemblyofembeddedcomponents(预埋件),andstockpiling（贮存、堆存）ofmaterialsmustbemeticulouslyplannedandscheduledwellbeforeconstructionstarts.Constructionofformsandassemblyofembeddeditemsshouldbeplannedandscheduledsothatasmuchoftheworkaspossibleisdoneoffthedam,orifnecessary,fromthetopofalift（升程）duringshift（工作班）changes.Liftschedulingisoftencomplicatedbyconcernsoverheatbuildup.BecausetheproductionrateofRCCcanbeveryhigh,controlstolimitthermalcracking（温度裂缝）mayrestricttheseasonortimeofdaythatplacementisallowedaswellastherateofplacement.AtUpperStillwaterDam,alloftheRCCwasplacedduringafive-monthweatherwindoweachyearfromMaytoOctoberandonlyduringtwo8-hshiftsstartingat8p.m.Thiswasnecessaryinordertokeepplacementtemperaturesbelowthe50oF(10oC)specificationlimit.AtWillowCreekandGalesvilledams,placementwaslimitedtonomorethanthreeandfourlifts,respectively,each24h..Conversely,atElkCreekandStagcoachdams,thecontractorwasencouragedtoplaceRCCasfastaspossible.Atpeakplacement,six1-ft(0.3-m)liftswereplacedinadayatStagecoach.The150-ft-high(46-m)damrequired44,500yd3(34,000m3)ofRCCwhichwasplacedduring37daysinthesummerof1988.TokeepplacementtemperatureslowatElkCreek,thespecificationsrequiredthatthemostmassivesectionsbeconstructedduringthelatewinterandearlyspring.8.2AggregateProductionandPlantLayout(砂石料生产和混凝土工厂布置)MaintainingadequatesuppliesofacceptableaggregateisparticularlyimportanttoRCCscheduling.Morethanhalfoftheaggregaterequiredforanentireconstructionseasonmayneedtobestockpiledwellaheadofthestartofconstructioninordertokeepupwithextraordinarilyhighdemandduringtheplacementseason.Thiscanalsoprovidesomeeasing(缓解)ofcashflow（现金流）andschedulingrequirementsduringtheplacementseason.Largestockpilesalsoallowformoreeconomicalsizingofproductionfacilitiesandforblendingofmaterialthatmaybeoutofspecification.Ifprecoolingofaggregateisdesiredtokeepplacementtemperatureslow,stockpilinginthewinterprovidesthatopportunity.ContinuousrawfeedtostockpilesisnecessarythroughouttheconstructionseasontokeepupwithRCCproduction.AtUpperStillwaterDam,thelargestintheUnitedStates,thecontractorhadtoproduce9000tons/day(8160metrictons)of3/4-and2-in.(19-to50-mm)aggregatefromsoftsandstonetokeepupwithitsRCCplacementscheduleof7200yd3/day(5500m3/day)duringthefinalconstructionseasonin1987.Thelocation,size,andshapeofaggregatepilesmustbecoordinatedwiththeconcreteplantlocationandmethodoffeed.Ifconveyors(传送带、皮带机)arenotused,severallargeloadersmayberequiredtofeedthemixersonlargeRCCprojects.ToachieveRCCproductionof900yd3/h(690m3/h),forinstance,four12-yd3(9m3)front-endloaderscouldbeneededtoallowforareasonableintervalbetweenlo