北京XX大學(xué)畢業(yè)設(shè)計(jì)地鐵車(chē)站設(shè)計(jì)模版

北京交通大學(xué)畢業(yè)設(shè)計(jì)地鐵車(chē)站設(shè)計(jì)模版北京交通大學(xué)畢業(yè)設(shè)計(jì)（論文）指導(dǎo)老師評(píng)閱意見(jiàn)附錄附錄一：外文原文1.3TUNNELTYPESTUDIES1.3.1GeneralDescriptionofVariousTunnelTypesTheprincipaltypesandmethodsoftunnelconstructionthatareinuseare:?Cut-and-covertunnels(Chapter5)arebuiltbyexcavatingatrench,constructingtheconcretestructureinthetrench,andcoveringitwithsoil.Thetunnelsmaybeconstructedinplaceorbyusingprecastsections?Boredorminedtunnels(Chapters6through11),builtwithoutexcavatingthegroundsurface.Thesetunnelsareusuallylabeledaccordingtothetypeofmaterialbeingexcavated.Sometimesatunnelpassesthroughtheboundarybetweendifferenttypesofmaterial;thisoftenresultsinadifficultconstructionknownasmixedface(Chapter8).?Rocktunnels(Chapter6)areexcavatedthroughtherockbydrilledandblasting,bymechanizedexcavatorsinsofterrock,orbyusingrocktunnelboringmachines(TBM).Incertainconditions,SequentialExcavationMethod(SEM)isused(Chapter9).?Softgroundtunnels(Chapter7)areexcavatedinsoilusingashieldorpressurizedfaceTBM(principallyearthpressurebalanceorslurrytypes),orbyminingmethods,knownaseitherthesequentialexcavationmethod(SEM)(Chapter9).?Immersedtunnels(Chapter11),aremadefromverylargeprecastconcreteorconcrete-filledsteelelementsthatarefabricatedinthedry,floatedtothesite,placedinapreparedtrenchbelowwater,andconnectedtothepreviouselements,andthencoveredupwithbackfill.?Jackedboxtunnels(Chapter12)areprefabricatedboxstructuresjackedhorizontallythroughthesoilusingmethodstoreducesurfacefriction;jackedtunnelsareoftenusedwheretheyareveryshallowbutthesurfacemustnotbedisturbed,forexamplebeneathrunwaysorrailroadsembankments.PreliminaryroadtunneltypeselectionforconceptualstudyaftertheroutestudiescanbedictatedbythegeneralgroundconditionasillustratedinFigure1-10.Figure1-10PreliminaryRoadTunnelTypeSelectionProcessTheselectionofatunneltypedependsonthegeometricalconfigurations,thegroundconditions,thetypeofcrossing,andenvironmentalrequirements.Forexample,animmersedtunnelmaybemostsuitableforcrossingawaterbody,however,environmentalandregulatoryrequirementsmightmakethismethodveryexpensiveorinfeasible.Therefore,itisimportanttoperformthetunneltypestudyasearlyaspossibleintheplanningprocessandselectthemostsuitabletunneltypefortheparticularprojectrequirements.1.3.2DesignProcessThebasicprocessusedinthedesignofaroadtunnelis:?Definethefunctionalrequirements,includingdesignlifeanddurabilityrequirements;?Carryoutthenecessaryinvestigationsandanalysesofthegeologic,geotechnicalandgeohydrologicaldata?Conductenvironmental,cultural,andinstitutionalstudiestoassesshowtheyimpactthedesignandconstructionofthetunnel;?Performtunneltypestudiestodeterminethemostappropriatemethodoftunneling.?Establishdesigncriteriaandperformthedesignofthevarioustunnelelements.Appropriateinitialandfinalgroundsupportandliningsystemsarecriticalforthetunneldesign,consideringbothgroundconditionsandtheproposedmethodofconstruction.PerformthedesigninPreliminaryandFinaldesignphases.Interimreviewsshouldbemadeifindicatedbyongoingdesignissues.?Establishtunnelalignment,profileandcross-section?Determinepotentialmodesoffailure,includingconstructionevents,unsatisfactorylong-termperformance,andfailuretomeetenvironmentalrequirements.Obtainanynecessarydataandanalyzethesemodesoffailure;?Performriskanalysisandidentifymitigationmeasuresandimplementthosemeasuresinthedesign?Prepareprojectdocumentsincludingconstructionplans,specifications,schedules,estimates,andgeotechnicalbaselinereport(GBR).1.3.3TunnelCross-SectionThetunnelcrosssectiongeometricalconfigurationmustsatisfytherequiredtrafficlanes,shouldersorsafetywalks,suitablespacesforventilation,lights,trafficcontrolsystem,fire/lifesafetysystems,etc.Thecrosssectionisalsodictatedbythemethodoftunnelconstruction.Forexample,boredtunnelsusingTBMwillresultincircularconfiguration,whilecutandcoverconstructionwillresultinrectangularconfiguration.Thestructuralsystemswillalsovaryaccordingly.Theavailablespacesinacircularcrosssectioncanbeusedtohousetunnelsystems,suchastheventilationductorfans,lighting,trafficcontrolsystemsandsigns,closecircuitTV,andthelike.Forrectangularsectionsthevarioussystemscanbeplacedoverhead,invertoradjacenttothetrafficlanesifoverheadspaceislimited.Itisessentialatearlydesignstagestopayattentiontodetailinlayingoutthetunnelcross-sectiontopermiteasyinspectionandmaintenancenotonlyofmechanicalandelectricalequipment,butalsoofthetunnelstructureitself.Thetunnelstructuralsystemsdependonthetypeoftunnel,thegeometricalconfigurationofthecrosssection,andmethodofconstruction.Forexample,incutandcovertunnelsofrectangularcrosssection,castinplaceconcreteisoftentheselectedstructuralsystem,whileforSEM/NATMtunnel,thestructuralsystemcouldbelatticegirdersandshotcrete.ForsoftgroundtunnelsusingTBM,thestructuralsystemisoftenaprecastsegmentalonepasslining.Sometimes,theexcavationsupportsystemcanbeusedasthefinaltunnelstructuralsystemsuchasthecaseintopdownconstruction.Chapter2providesdetaileddiscussionsforthegeometricalconfigurations.1.3.4GroundwaterControlBuildingadrytunnelisaprimaryconcernsoftheowner,user,andoperatoralike.Adrytunnelprovidesasaferandfriendlierenvironmentandsignificantlyreducesoperationandmaintenancecosts.Advancementsintunnelingtechnologyinthelastfewdecadesingeneralandinthewaterproofingfieldinparticularhavefacilitatedtheimplementationofstrictwaterinfiltrationcriteriaandtheabilitytobuilddrytunnels.BasedoncriteriaobtainedfromtheInternationalTunnelingAssociation(ITA),Singapore’sLandTransportAuthority(LTA),Singapore’sPublicUtilitiesBoard(PUB),HongKong’sMassTransitRailCorporation(MTRC)andtheGermanCitiesCommittee,aswellascriteriausedbyvariousprojectsintheUSandabroadforbothhighwayandtransittunnels(e.g.WashingtonDC,SanFrancisco,Atlanta,Boston,Baltimore,Buffalo,Melbourne(Australia),Tyne&Wear(UK)andAntwerp(Belgium),thefollowingITAgroundwaterinfiltrationcriteriaarerecommended;AllowableInfiltrationTunnels≤0.002gal/sq.ft/dayUndergroundpublicspace≤0.001gal/sq.ft/dayInadditionnodrippingorvisibleleakagefromasinglelocationshallbepermitted.Tunnelwaterproofingsystemsareusedtopreventgroundwaterinflowintoanundergroundopening.Theyconsistofacombinationofvariousmaterialsandelements.Thedesignofawaterproofingsystemisbasedontheunderstandingofthegroundandgeohydrologicalconditions,geometryandlayoutofthestructureandconstructionmethodstobeused.Awaterproofingsystemshouldalwaysbeanintegratedsystemthattakesintoaccountintermediateconstructionstages,finalconditionsofstructuresandtheirultimateusageincludingmaintenanceandoperations.Therearetwobasictypesofwaterproofingsystems:drained(open)andundrained(closed).Figures6-40and6-41illustratedrained(open)andundrainedsystem(closed)tunnels,respectively.Variouswaterproofingmaterialsareavailableforthesesystems.Openwaterproofingsystemsallowgroundwaterinflowintoatunneldrainagesystem.Typically,thetunnelvaultareaisequippedwithawaterproofingsystemforminganumbrella-likeprotectionthatdrainsthewaterseepingtowardsthecavityaroundthearchintoadrainagesystemthatislocatedatthebottomofthetunnelsidewallsandinthetunnelinvert.Theopensystemiscommonlyusedinrocktunnelswherewaterinfiltrationratesarelow.Groundwaterinflowistypicallylocalizedtodistinctlocationssuchasjointsandfracturesandtheoverallpermeabilityissuchthatagroundwaterdraw-downinsoillayersoverlyingtherockmasswillnotbeaffected.Thissystemiscommonlyinstalledbetweenaninitialtunnelsupport(initiallining)andthesecondaryorfinalsupport(permanentlining).Theopenwaterproofingsystemgenerallyallowsforamoreeconomicalsecondaryliningandinvertdesignasthehydrostaticloadisgreatlyreducedoreliminated.Closedwaterproofingsystems(closedsystem),oftenreferredtoastankedsystems,extendaroundtheentiretunnelperimeterandaimatexcludingthegroundwaterfromflowingintothetunneldrainagesystemcompletely.Thusnogroundwaterdrainageisprovided.Thesecondaryliningsthereforehavetobedesignedforfullhydrostaticwaterpressures.Thesesystemsareoftenappliedinpermeablesoilswheregroundwaterdischargeintothetunnelswouldbesignificantandwouldotherwisecausealoweringofthegroundwatertableandpossiblycausesurfacesettlements.Forprecastsegmentallining,thesegmentsareusuallyequippedwithgasketstosealthejointsbetweensegmentsandthusprovideawatertighttunnel.Forcutandcovertunnelsunderthegroundwatertableandforimmersedtunnels,waterproofingmembranesencapsulatingthestructuresarerecommended.Thewaterproofingsystemshouldbeaddressedasearlyaspossibleanddesigncriteriaforwaterinfiltrationshouldbeestablishedduringtheprocess.ThisissueisfurtherdiscussedinChapter10-TunnelLinings.1.3.5TunnelPortalsPortalsandventilationshaftsshouldbelocatedsuchthattheysatisfyenvironmentalandairqualityrequirementsaswellasthegeometricalconfigurationofthetunnel.Atportals,itmaybenecessarytoextendthedividingwallbetweentraffictravelinginoppositedirectionstoreducerecirculationofpollutantsfromtheexittunnelintotheentrytunnel.Ifpossible,Portalsshouldbeorientedtoavoiddriversbeingblindedbytherisingorsettingsun.Speciallightingrequirementsattheportalareneededtoaddressthe“blackhole”effect(Chapter2).Theportalshouldbelocatedatapointwherethedepthofthetunnelissuitablycovered.Thisdependsonthetypeofconstruction,thecrossingconfiguration,andthegeometryofthetunnel.Forexample,inacutandcovertunnel,theportalcanbeasclosetothesurfaceastheroofofthetunnelcanbeplacedwithsufficientclearancefortraffic.Ontheotherhand,inTBMminedtunnels,theportalwillbeplacedatalocationwherethereissufficientgroundcovertostarttheTBM.Inmountaintunnelstheportalcanbeasclosetothefaceofthemountainaspracticallyconstructible.1.3.6Fire-LifeSafetySystemsSafetyintheeventofafireisofparamountimportanceinatunnel.Thecatastrophicconsequencesofthetunnelfires(e.g.,theMontBlanctunnel,1999andtheSwissSt.Gotthardtunnel,2001)notonlyresultedinlossoflife,severepropertydamages,butalsogreatconcernsofthelackoffire-lifesafetyprotectioninroadtunnels.DuringtheGotthardTunnelOctober2001fire(Figure1-11)thatclaimed11deaths,thetemperaturereportedlyreached1,832oF(1,000oC)infewminutes,andthicksmokeandcombustibleproductpropagatedover1.5mile(2.5km)within15minutes.Figure1-11GotthardTunnelFireinOctober2001(FHWA2006)Forplanningpurposes,itisimportanttounderstandthefire-lifesafetyissuesofaroadtunnelandconsidertheirimpactsonthealignments,tunnelcrosssection,emergencyexits,ventilationprovisions,geometricalconfiguration,right-of-way,andconceptualcostestimates,NationalFireProtectionAssociation(NFPA)502–StandardforRoadTunnels,Bridges,andOtherLimitedAccessHighwaysprovidesthefollowingfireprotectionandlifesafetyrequirementsforroadtunnels:?ProtectionofStructuralElements?FireDetection?CommunicationSystems?TrafficControl?FireProtection(i.e.,standpipe,firehydrants,watersupply,portablefireextinguisher,fixedwaterbasefire-fightingsystems,etc.)?TunnelDrainageSystem?EmergencyEgress?Electric,and?Emergencyresponseplan.In2005,theFHWA,AASHTO,andtheNationalCooperativeHighwayResearchProgram(NCHRP)sponsoredascanningstudyofequipment,systemsandproceduresusedinEuropeantunnels.Thestudyconcludedwithnine(9)recommendationsforimplementationincludeconductingresearchontunnelemergencymanagementthatincludeshumanfactors;developingtunneldesigncriteriathatpromoteoptimaldriverperformanceduringincidents;developingmoreeffectivevisual,audible,andtactilesignsforescaperoutes;andusingarisk-managementapproachtotunnelsafetyinspectionandmaintenance.AppendixApresentstheexecutivesummaryofthescanstudy.ThescanstudyreportisavailableentiretyontheFHWAwebsiteathttp://I/uts/uts.pdf(FHWA,2006).EmergencyEgressEmergencyegressforpersonsusingthetunneltoaplaceofrefugeshouldbeprovidedatregularintervals.Throughoutthetunnel,functional,clearly-markedescaperoutesshouldbeprovidedforuseinanemergency.AsshowninFigure1-12,exitsshouldbeclearlymarked,andthespacingofexitsintoescaperoutesshouldnotexceed1000feet(300m)andshouldcomplywiththelatestNFPA502-StandardforRoadTunnels,Bridges,andOtherLimitedAccessHighways.Emergencyexitsshouldbeprovidedtosafe,securelocations.Figure1-12EmergencyExit(FHWA,2006)Theemergencyegresswalkwaysshouldbeaminimumof3.6ftwideandshouldbeprotectedfromoncomingtraffic.Signageindicatingbothdirectionanddistancetothenearestescapedoorshouldbemountedabovetheemergencywalkwaysatreasonableintervals(100to150ft)andbevisibleinanemergency.Theemergencyescaperoutesshouldbeprovidedwithadequatelightinglevelandconnectedtotheemergencypowersystem.Wheretunnelsareprovidedintwintubes,crosspassagestotheadjacenttubecanbeconsideredsafehaven.Thecrosspassageshouldbeofatleasttwo-hourfireratingconstruction,shouldbeequippedwithselfclosingfirerateddoorsthatopeninbothdirectionsorslidingdoors,andthecrosspassagesshouldbelocatednotmorethan656ft(200m)apart.Anemergencywalkway”atleast3.6feet(1.12m)wideshouldbeprovidedoneachsideofthecross-passageways.Inlongtunnels,sometimesbreakdownemergencyalcoves(localwidening)forvehiclesareprovided.SeeFigure1-13.SomeEuropeantunnelsalsoprovideatintervalsanemergencyturn-aroundforvehiclesintotheadjacentroadwayductwhichturn-aroundwouldnormallybeclosedbydoors.Figure1-13EmergencyAlcoveEmergencyVentilation,LightingandCommunicationAnemergencyventilationsystemshouldbeprovidedtocontrolsmokeandtoprovidefreshairfortheevacuationofpassengersandforsupporttotheemergencyresponders.Theemergencyventilationsystemisoftenthenormalventilationsystemoperatedathigherspeeds.Emergencyventilationscenariosshouldbedevelopedandtheoperationofthefanswouldbebasedonthelocationofthefireandthedirectionofthetunnelevacuation.Thefansshouldbeconnectedtoanemergencypowersourceincaseoffailureoftheprimarypower.Emergencytunnellighting,firedetection,firelines,andhydrantsshouldbeprovided.Incertaininstallations,firesuppressionmeasuressuchasfoamordelugesystemhavebeenused.Theriskoffirespreadingthroughpowercableductsshouldbeeliminatedbydividingcableductsintofireproofsections,placingcablesincast-inducts,usingfireproofcableswhereapplicable,andotherpreventativemeasures.Vitalinstallationsshouldbesuppliedwithfire-resistantcables.Materialsusedshouldnotreleasetoxicoraggressivegasessuchaschlorine.Waterforfire-fightingshouldbeprotectedagainstfrost.Firealarmbuttonsshouldbeprovidedadjacenttoeverycross-passage.Emergencyservicesshouldbeabletoapproachatunnelfireinsafety.Emergencytelephonesshouldbeprovidedinthetunnelsandconnectedtotheemergencypowersupply.Whensuchatelephoneisused,thelocationofthecallershouldbeidentifiedbothatthecontrolcenterandbyawarninglightvisibletorescuingpersonnel.Telephonesshouldbeprovidedatcross-passagedoorsandemergencyexits.Communicationsystemsshouldgivethetravelingpublicthepossibilityofsummoninghelpandreceivinginstructions,andshouldensurecoordinatedrescue.Systemsshouldraisethealarmquicklyandreliablywhenunusualoperatingconditionsoremergencysituationsarise.Radiocoverageforpolice,fireandotheremergencyservicesandstaffshouldextendthroughoutthetunnel.Itisnecessaryforpolice,fireandemergencyservicestousetheirmobileradioswithintunnelsandcross-passages.Radiosystemsshouldnotinterferewitheachotherandshouldbeconnectedtotheemergencypowersupplytocommunicatewitheachother.Itisalsorecommendedthatmobiletelephonecoveragebeprovided.1.3.7TunnelDrainageGooddesignanticipatesdrainageneeds.Usuallysump-pumpsystemsareprovidedattheportalsandatlowpoints.Roadwaydrainagethroughoutthetunnelusingdraininletsanddrainagepipesshouldbeprovided.Thedrainagesystemshouldbedesignedtodealwithsurfacedrainageaswellasanygroundwaterinfiltrationintothetunnel.Otherareasofthetunnels,suchasventilationductsandpotentiallocationsforleakage,shouldhaveprovisionfordrainage.Accumulationoficeduetoinadequatedrainageprovisionsmustbeavoidedforsafepassage.1.4OPERATIONALANDFINANCIALPLANNING1.4.1PotentialFundingSourcesandCashFlowRequirementsTraditionallyState,Federal,andLocalfundsarethemainfundingsourcesforroadtunnels.However,recentlyprivateenterprisesandpublic-privatepartnership(PPP)arebecomingmoreattractivepotentialsourcesforfundingroadtunnelprojects.Forexample,thePortofMiamiTunnelhasbeendevelopedusingthePPPapproach.VariousformsoffinancinghavebeenappliedinvariouslocationsintheUSandtheWorld.Tollsareoftenleviedonuserstohelprepayconstructioncosts,andtopayoperatingcosts,especiallywhentheroadsarefinancedbyprivatesources.Insomecases,bondissueshavebeenusedtoraisefundingfortheproject.Indevelopingthefundingstrategy,itisimportanttoconsiderandsecurethecashflowrequiredtocompletetheproject.Inassessingthecashflowanalysis,escalationtotheyearofexpenditureshouldbeused.Variousindicesofescalationratesareavailable.Itisrecommendedthatescalationratescomparabletothistypeofconstructionandfortheareaoftheprojectshouldbeused.Factorssuchasworkloadinthearea,availabilityofmaterials,availabilityofskilledlabor,specialtyequipment,andthelike,shouldbetakenintoconsideration.Repaymentofloansandthecostofthemoneyshouldbeconsidered.Theymaycontinueforasubstantialnumberofyearswhiletheoperationandmaintenancecostsofthetunnelalsohavetobecovered.1.4.2ConceptualLevelCostAnalysisAttheconceptuallevel,costanalysesareoftenbaseduponthecostsperunitmeasurementforatypicalsectionoftunnel.Thehistoricalcostdataupdatedforinflationandlocationisalsocommonlyusedasaquickcheck.However,suchdatashouldbeusedwithextremecautionsinceinmostcases,theexactcontentofsuchdataandanyspecialcircumstancesarenotknown.Inaddition,constructionoftunnelsisaspecialtyworkandinvolvesasignificantlaborcomponent.Laborexperienceandproductivityarecriticalforproperestimatingofatunnelconstructioncost.Furthermore,thetunnelbeingalinearstructure,itscostishighlydependentontheadvancerateofconstruction,whichinturnisdependentonthelaborforce,thegeologicalconditions,thesuitabilityofequipment,thecontractor’smeansandmethods,andtheexperienceoftheworkers.Sincetunnelingishighlydependentonthelaborcost,issuessuchasadvancerates,constructionschedule,numberofshifts,laborunionrequirements,localregulationssuchaspermissibletimeofwork,environmentalfactorssuchasnoiseandvibrations,andthelikeshouldbetakenintoconsiderationswhenconstructioncostestimatesaremade.Itisrecommended,evenattheplanningphase,toprepareabottomupconstructioncostestimateusingestimatematerials,labor,andequipment.Theuseofexperiencefromothersimilarprojectsintheareaisusuallydoneforpredictinglaborforceandtheadvancerates.Attheconceptuallevel,substantialcontingenciesmayberequiredattheearlystagesofaproject.Asthedesignadvancesandtherisksidentifiedanddealtwith,contingencieswouldbereducedgraduallyasthelevelofdetailanddesignincreases.Softcostssuchasengineering,programandconstructionmanagement,insurance,ownercost,thirdpartycost,rightofwaycosts,andthelikeshouldbeconsidered.Thecostestimateshouldprogressivelybecomemoredetailedasthedesignisadvanced.MoredetaileddiscussionsonthissubjectarepresentedinChapterProjectDeliveryMethodsGenerally,twocategoriesofdeliverymethodshavebeenusedinthepastforundergroundconstruction,withvariouslevelsofsuccess.Theyare:?Design-Bid-Build?Design-BuildThecontractualtermsofthesetwodeliverymethodsvarywidely.Themostcommonisthefixedpriceapproach,althoughfortunneling,theunitpricesapproachisthemostsuitable.Othercontracttermsusedinclude:?FixedPricelumpsum?Lowbidbasedonunitprices?Qualitybasedselection?BestandFinalOffer(BAFO)?CostplusfixedfeeThetraditionalprojectdeliverymodelisthedesign-bid-build.Inthismethod,theclientfinancestheprojectanddevelopsanorganizationtodealwithprojectdefinition,legal,commercial,andlandaccess/acquisitionissues.Itappointsaconsultingengineerunderaprofessionalservicescontracttoactonitsbehalftoundertakecertaindesign,procurement,constructionsupervision,andcontractadministrationactivities,inreturnforwhichtheconsultingengineerispaidafee.Theclientplacesconstructionhilstthistypeofcontracthasitsadvantages,itsshortfallsparticularlyonlargeinfrastructureprojectsadesign-buildprocess,theprojectisawardedtoadesign-buildentitythatdesignandconstructtheheprocurementoptionsofthedesign-buildapproachvarybasedontheprojectgoalsandtheowners’Competitivebid(lowprice)sponsibilitystandards(costandqualifications)cluding“BestandFinalOffer”heallocationofriskbetweentheownerandthecontractorwillhaveadirectrelationshiptotheesign-buildhastheadvantagethatthedesigncanbetailoredtofittherequirementsofthecontractor‘scontractsfollowingacompetitivetenderingprocessforafixedprice,withtheselectionareoftenbasedonlowbid.Thistypeofcontractissimple,straightforwardandfamiliartopublicowners.However,inthisprocessthemajorityofconstructionriskispassedtothecontractorwhooftenuseshighercontingencyfactorstocoverthepotentialconstructionrisks.Theclienteffectivelypaysthecontractorfortakingontherisk,irrespectiveofwhethertheriskactuallytranspires.Whilstthistypeofcontracthasitsadvantages,itsshortfallsparticularlyonlargeinfrastructureprojectscouldbesignificant.Adversarialrelationshipsbetweenprojectparticipants,potentialcostoverruns,anddelaystoprojectschedulesarebynomeansunusual.Withthetraditionalcontractforms,thereissignificantpotentialforprotracteddisputesoverresponsibilityforevents,tothedetrimentoftheprogressofthephysicalworks.Theclient,itsagents,andthecontractorsaresubjecttodifferentcommercialrisksandpotentiallyconflictingcommercialobjectives.Inadesign-buildprocess,theprojectisawardedtoadesign-buildentitythatdesignandconstructtheproject.Theowner’sengineerusuallypreparesbiddingdocumentsbasedonapreliminary-leveldesignidentifyingtheowner’srequirements.Contracttermsvaryfromfixedpricetounitprices,tocostplusfee.Fortunnelingprojects,thegeotechnicalandenvironmentalinvestigationsshouldbeadvancedtoahigherlevelofcompletiontoprovidebetterinformationandunderstandingoftheconstructionrisks.Theselectedcontractorthenpreparesthefinaldesign(usuallywithconsultationwiththeowner’sengineer)andconstructstheproject.Thisprocessisgaininginterestamongownersofundergroundfacilitiesinordertoreducetheoveralltimerequiredtocompletetheproject,avoiddealingwithdisputesoverchangedconditions,andavoidpotentiallengthyandcostlylitigations.Theprocurementoptionsofthedesign-buildapproachvarybasedontheprojectgoalsandtheowners’objectives.Examplesoftheprocurementoptionsinclude:?Competitivebid(lowprice)?Competitivebidwithhighresponsibilitystandards(costandqualifications)?Competitivebidswithalternativeproposals?Priceandotherfactors?Priceafterdiscussionincluding“BestandFinalOffer”?Qualitybasedselection?SolesourcenegotiationTallocationofriskbetweentheownerandthecontractorwillhaveadirectrelationshiptothecontractorcontingencyaspartofthecontractor’sbid.Therefore,itisimportanttoidentifyarisksharingmechanismthatisfairandequitableandthatwillresultinareasonablecontingencybythecontractorandsufficientreservefundtobeprovidedbytheownertoaddressunforeseenconditions.Forexampleunforeseenconditionsduetochangesintheanticipatedgroundconditionsarepaidforbytheownerifcertaintestsaremet,whilethemeansandmethodsaregenerallythecontractor’sresponsibilityandhisinabilitytoperformunderprescribedconditionsareriskstobeabsorbedbythecontractor.Withpropercontractingformandequitableallocationofrisksbetweentheownerandthecontractor,thecontractorcontingency,whichispartofitsbidprice,willbereduced.Similarly,theowner’sreservefundwillbeusedonlyifcertainconditionsareencountered,resultinginanoveralllessercosttotheowner.ThisisfurtherdiscussedinChapter14ConstructionEngineering.Design-buildhastheadvantagethatthedesigncanbetailoredtofittherequirementsofthecontractor‘smeansandmethodssinceboth,thedesignerandtheconstructorworkth