洞室開挖穩(wěn)定分析、如何建設(shè)隧洞 外文文獻(xiàn)翻譯(四篇)

StabilityAnalysisofTunnelExcavationAspillwaytunnelforanembankmentdamistobeconstructedinapoorqualitysandstone.Theexcavateddiameterofthetunnelisabout13mandthecoverovertheroofis8m.Thetunnelistohavea1.3mthickun-reinforcedconcreteliningand,afterplacementofthishighportionoftherockfilldamwillheovertheconstructedtunnel.Thequestionstobeaddressedare:(1)Whatsupportisrequiredinordertoexcavatethetunnelsafelyundertheveryshallowcover?(2)Istheproposedtopheadingandbenchexcavationsequence,usingdrilmethods,appropriateforthistunnel?(3)Howwilltheconcreteliningrespondtotheloadingimposedbytheplacementof28mofrockfilloverthetunnel?Inordertoanswerthesequestionsaseriesoftwo-dimensionalfiniteelementanalyseswerecarriedusingtheprogramPHASE'`.Thefirstoftheseanalysesexaminedthestabilityandsupportrequirementsforthetopheadingexcavation.Thefinalanalysisincludedtheentireexcavationandsupportsequenceandtheplacementoftherockfilloverthetunnel.Therockmassisapoorqualitysandstonethat,beingclosetosurface,isheavilyjointed.ThemechanicalpropertiesassumedforthisrockmassareacohesivestrengthC=0.04Mpa,africtionavailablebut,becauseofthelocationofthetunnelinthevalleyside,ithasbeenassumedthatthehorizontalstressnormaltothetunnelaxishasbeenreducedbystressrelief.Themodelisloadedbygravityandaratioofhorizontaltoverticalstressor0.5isassumed.Asimplifiedversionofthemodelwasusedtoanalysethestabilityandsupportrequirementsforthetopheading.Thismodeldidexcludetheconcreteliningandthebenchexcavations.Thefirstmodelwasusedtoexaminetheconditionsforafull-faceexcavationofthetopheadingwithoutanysupport.Thisisalwaysausefulstartingpointinanytunnelsupportdesignstudysinceitgivesthedesigneraclearpictureofthemagnitudeoftheproblemsthathavetobedealtwith.Themodelwasloadedintwostages.Thefirststageinvolvedthemodelwithoutanyexcavationsandthiswascreatedbyassigningthematerialwithintheexcavationboundarythepropertiesofthesurroundingrockmass.Thisfirststageiscarriedoutinordertoallowthemodeltoconsolidateundergravitationalloading.Itisrequiredinorwhichsubsequentdisplacementsinthemodelcanbemeasured.TheresultsoftheanalysieareillustratedinFigure18.1,thatshowntheextentofyieldintherockmasssurroundingthetopheading,andFigure18.2thatshowstheinduceddisplacementsaroundthetunnel.Thelargeamountofyieldintherockmassoverlyingthetopheadingsuggeststhatthisexcavationwillbeunstablewithoutsupport.ThisviewissupportedbythedisplacementsshownThereadermaybesurprisedthatthedisplacementintheroofofthetunnelisonly26mmwhentheextentoftheyieldzonesuggestscompletecollapseoftheroof.IthastoberememberedthatPHASEisasmallstrainfiniteelementmodelandthatitcannotaccommodatetheverylargestrainsassociatedwiththecompletecollapseofatunnel.InexaminingFigure18.2itismoreimportanttolookattheshapeoftheoveralldisplacementprofilethanthemagnitudeofthedisplacements.Arockmasswillnottoleratethedifferentialdisplacementsillustratedandprogressiveravellingleadingtoultimatecollapsewouldalmostcertainlyresultfromexcavationofanunsupportedtopheading.Ageneralruleofthumbusedbyexperiencedtunnellersisthatanundergroundexcavationwillnotbeself-supportingunlessthecoveroverthetunnelexceeds1.5timesthespanoftheopening.Thisisatypicalsituationthatoccurswhenexcavatingtunnelportalsarethereareseveraloptionsavailablefordealingwiththeproblem.Oneoftheseoptionsistouseashotcreteliningtostabilizetherockmassabovethetunnel.Afiniteelementanalysisofthisoptionshowsthata50mmthicklayeroffullyhardenedshotcrete(uniaxialcompressivestrengthof30MPa)issufficienttostabilizethetunnel.Theproblemishowtogetofshotcreteintoanadvancingtunnelheading.Asecondproblemiswhethertheworkerswouldhavesufficientconfidenceinsuchasolutiontoworkinthetunnel.Oneprojectonwhichthissolutionwasusedwastheconstructionofan8mspandiversiontunnelforadam.Therockmasswasaveryweaklycementedlimestonethatcouldbeexcavatedbyhandbutwhichhadsufficientstrengththatitwasmarginallyself-supporting.TheScandinaviancontractorontheprojecthadusedshotcreteformanyyearsandtheveryexperiencedtunnellershadcompleteconfidenceinworkingunderacoverofshotcrcte.Thetunnelwasnotonthecriticalpathoftheprojectandsoconstructioncouldproceedatasufficientlyslowpacetoallowtheshotcretetosetbeforethenextadvance.Alayerofun-reinforcedshotcretewasthesolesupportusedinthistunnel,withoccasionalsteelsetsembeddedintheshotcretewheregroundconditionswereparticularlydifficult.Inthecaseofthetopheadinginsandstoneunderconsiderationhere,theshotcretesolutionwasrejectedbecause,inspiteofthefiniteelementanalysis,thedesignersdidnothavesufficientconfidenceintheabilityoftheshotcretelayertosupportthelargespanofblockysandstone.Inaddition,thecontractoronthisdamprojectdidnotshotcreteintunnelsanditwasunlikelythattheworkerswouldhavebeenpreparedtooperateunderacoverofshotcreteonly.Anotheralternativethatiscommonlyusedinexcavatingtunnelportalsistousesteelsetstostabilisetheinitialportionofthetunnelunderlowcover.Thissolutionworkswellinthecaseofsmalltunnelsbut,inthiscase,a13mspantunnelwouldrequireveryheavysets.Anadditionaldisadvantageinthiscaseisthattheinstallationofsetswouldpermittoomuchdeformationintherackmass.Thisisbecausethesteelsetsareapassivesupportsystemandtheyonlycarryaloadwhentherockmasshasdeformedontothesets.Sincethistunnelisindeformationofadam,excessivedeformationisclearlynotacceptablebecauseoftheadditionalleakagepathswhichwouldbecreatedthroughtherockmass.Thesolutionfinallyadoptedwas"borrowed"fromtheminingindustrywhereuntensionedfullygrouteddowelsarefrequentlyusedtopre-supporttherockmassaboveundergroundexcavations.Inthiscase,ainstalledfromthegroundsurfacebeforeexcavationofthetopheadingwascommenced.Whenthesecableswereexposedintheexcavation,faceplateswereattachedandtheexcesscablelengthwascutoff.Inaddition,a2mx2mpatternof6mlongmechanicallyanchoredwereinstalledradiallyfromtheroofofthetopheading.TheresultsofananalysisofthissupportsystemareillustratedinFigure18.3andFigure1whichshowtheextentoftheyieldzoneandthedeformationsintherockmassabovethetopComparingFigure18.1andFigure18.3showsthattheextentoftheyieldzoneisonlyreducedbyasmallamountbytheenstallationofthesupportsystem.Thisisnotsurprisingsincesomedeformationoftherockmassisrequiredinordertomobilizethesupportingloadsintheuntensionedcables.Thisdeformationoccursasaresultoffailureoftherockmass.Figure18.4showsthatthedisplacementsintheroofofthetopheadinghavebeenreducedsubstantiallyasaresultoftheplacementofthesupport.However,asmallproblemremainsandthatistheexcessivedisplacementoftherockbetweentherockboltfaceplateswhicharespacedona2mx2mgrid.UnlessthisdisplacementiscontrolleditcanleadtoprogressiveravellingofOnlyasmallsurfacepressureisrequiredtocontrolthisravellingandthiscouldbeachievedbymeansofalayerofmeshorshotcreteofbythlattersolutionwasadoptedbecauseofthesenseofsecuritywhichthesegavefortheworkersinthetunnel.洞室開挖穩(wěn)定分析某土石壩工程在質(zhì)量差的砂巖區(qū)開挖溢洪隧洞。其開挖直徑13m,頂部理深8rn。隧洞有1.3m厚的普通混凝土襯砌。襯砌澆筑后在隧洞上修建28m高的土石壩出水口。面臨的問題是:(1)在淺部開挖時，為保證溢洪隧洞的安全所需的支護(hù)形式?(2)在隧洞開挖時比較適用的是鉆爆法施工，開挖過程中如何確定頂部上導(dǎo)洞和分步開挖的順序?(3)混凝土襯砌與隧洞上28m高的堆石荷載之間的作用是怎樣的?為解決上述問題，采用PHASE2程序進(jìn)行了一系列的平面有限元分析。首先對上導(dǎo)洞開的影響進(jìn)行分析摩擦角為40度，變形模量E=1334MPa。沒有現(xiàn)場地應(yīng)力量測資料，由于隧洞位于谷坡，可以假定垂直隧洞軸線的水平應(yīng)力由于應(yīng)力釋放而減小，并且認(rèn)為水平與垂直應(yīng)力之比為0.5，計(jì)算模型考慮自重荷載.一簡化的計(jì)算模型可用于洞室頂拱穩(wěn)定性分析和支護(hù)要求。該模型不包括混凝土襯砌和初始模型用來檢查在沒有任何支護(hù)情況下的上導(dǎo)洞全斷面開挖的情況。該模型常用于隧洞支護(hù)設(shè)計(jì)研究開始階段，因?yàn)槟Ｐ涂梢詾樵O(shè)計(jì)者提供較清楚的將要處理問題的難度。巖石材料特性建立起來。第一階段實(shí)施是為了在重力荷載條件下對模型加固相對于模型其后的位移可以量測到，則創(chuàng)建一個參考系是必要的。上導(dǎo)洞洞頂巖體的大范圍屈服說明在沒有支護(hù)條件下的開挖是不穩(wěn)定的。圖18.的位移也說明了這一點(diǎn)。大家感到奇怪的是當(dāng)屈服帶的范圍被暗示洞頂會全部坍塌時，隧洞頂部僅有26mm的應(yīng)變工況。從圖18.2可看出，考慮整體位移形狀遠(yuǎn)比位移量重要，而且?guī)r體將不能承受圖經(jīng)驗(yàn)豐富的隧洞建設(shè)者采用的經(jīng)驗(yàn)法則是隧洞上部覆蓋層厚度大于1.5倍洞室跨度，地才會發(fā)生。這些方案之一是采用噴混凝土襯砌來維持隧洞頂部巖體的穩(wěn)定。這一方案有限元分析表明，50mm厚的充分硬化噴混凝土層(單軸壓縮強(qiáng)度30MPa)對于隧洞的穩(wěn)定已經(jīng)足夠。問題是如何把充分硬化的噴射混凝土注人到前方的洞室端部。其次是施工者是否有信心來解決隧洞的這一問題。某工程在為大壩建一條8m跨度的導(dǎo)流洞時采用了噴混凝土襯砌。圍巖為弱膠結(jié)的灰?guī)r?？捎檬止ぞ蜻M(jìn)，但有足夠的強(qiáng)度在一定程度上達(dá)到自承作用。斯堪的納維亞(Scandinavian)承包商在工程上采用噴混凝土技術(shù)已多年，非常有經(jīng)驗(yàn)的隧道建設(shè)者完全有信心在噴射過混凝土層中的鋼拱架支護(hù)。但設(shè)計(jì)者沒有充分的信心認(rèn)為噴混凝土層可以對塊狀砂巖大跨度洞室進(jìn)行支護(hù)。除此以外，大壩項(xiàng)目的承包商沒有隧洞噴混凝土施工的豐富經(jīng)驗(yàn)，施工人員也不準(zhǔn)備在僅有噴混凝土支在開挖洞口時另一個通常采用的方法是在洞頂覆蓋層較薄的地方用鋼架來支護(hù)隧洞的進(jìn)口部分。在小型隧洞中常用此法，但本工程情況13m跨度的隧洞需要高強(qiáng)度的鋼架。另一個不利因素是安裝鋼架時要預(yù)留有巖體較大的變形量。這是因?yàn)殇摷苁且粋€被動的支護(hù)系過大的變形會增多滲漏通道。最終采取的方案借鑒采礦工程的經(jīng)驗(yàn)，即對地下開挖以上的巖體一般采用非張拉注漿錨索進(jìn)行預(yù)支護(hù)。具體施工時，在上導(dǎo)洞室開挖前，從地表安裝裝間距3m*3m、長15m、錨固力60t的錨索。當(dāng)錨索在開挖面出露時，焊上面板并把多余的錨索切掉。此外，在洞室頂部安裝放射狀間距2mx2m、長6m的機(jī)械錨固的巖石錨桿。支護(hù)系統(tǒng)的分析結(jié)果見圖18.3和圖18.4，圖中表明了屈服帶的發(fā)展程度和上導(dǎo)洞之上因?yàn)閹r體的某些變形要協(xié)調(diào)非張拉錨索的支護(hù)荷載，而且這些變形是巖體破裂的結(jié)果。在巖石錨桿面板(以2mx2m的網(wǎng)格布設(shè))之間的巖石仍存在較大位移。如果不對這些位移進(jìn)行控制，就可能導(dǎo)致巖體的漸進(jìn)式剝落破壞?？刂茙r體的剝落作用只需要很小的表面壓力，可通過掛網(wǎng)或安裝輕型鋼架噴混泥土來實(shí)現(xiàn)。例中采用第二種方案，因?yàn)樗矶词┕ふ邔Π踩^為敏感。Afterthegeneraldirectionforatunnelhasbeendetermined,thenextstepsareageologicalsurveyofthesiteandaseriesofboringstoobtainspecificinformationonthestratathroughwhichthetunnelmaypass.Thelengthandcrosssectionofatunnelgenerallyaregovernedbytheuseforwhichitisintended,butitsshapemustbedesignedtoprinternalandexternalforces.Generally,acircularornearlycircularshapesischoosen.Ineveryhardrock,excavationusuallyisaccomplishedbydrillingmedium-hardrock,atunnel-boringmachinetypicallydoestheexcavationwork.Insoftground,excavationusuallyisaccomplishedbydiggingorbyadvancingashieldandsqueematerialintothetunnel.Inallcases,theexcavatedrockorearth,calledmuck,iscollectedandtransportedoutofthetunnel.Inunderwatertunneling,ashieldisusedtoadvancethework.Anothermethodofbuildinganunderwatertunnelistosinktubularsectionsintoastrengthdugatthebottomofariverorotherbutlongeronesusuallyaredrivenalsofromoneormoreintermediateshafts.Somelongtunnelshavebeenbuiltwiththeaidofasmallpilottunneldrivenparalleltothemaintunnelandconnectedwithitbycrosscutsatintervals.Thepilottunnelnotonlyfurnishesadditionpointsofaccessbutalsoarouteforremovingmuckandforventilationductsanddrainagelines.Anothermethodistheheading-and-benchsystem,formallyusedonmostlargefunnel.becauseitrequiredsmalleramountsofpowerandpermittedsimultaneousdrillingandmucking(removalofexcavatedmaterial).Theupperportionofthetunnelisdrivenaheadofthelowerpartwhichiscalledthebench.Aseparatecrewisthusabletomuckinthelowerportionofthetunnelwhiletheupperportionisbeingdrilled.Withimprovementsintunnelingmethodsandmachinery,thefull-facemethodofattack,previouslyusedonlyinsmalltunnels,cameintocommonuseinbuildinglargeones.Thischangewaspartlybroughtaboutbythejumbo,amovableplatformonwhichnumerousrockdrillsaremethodbecamethecommonestandfastestwaytodriveatunnel.Soft-groundtunnelingSometunnelsaredrivenwhollyormostlythroughsoftmaterial.Inverysoftground,littleornoblastingisnecessarybecausethematerialiseasiAtfirst,forepolingwastheonlymethodforbuildingtunnelsthroughverysoftground.Forepolesareheavyplanksabout1.5mlongandsharpenedtoapoint.Theywereinsertedoverthetophorizontalbarofthebracingatthefaceofthetunnel.Theforepolesweredrivenintothegroundofthefacewithanoutwardinclination.Afteralltheroofpolesweredrivenforabouthalfoftheirlength,atimberwaslaidacrosstheirexposedendstocounteranystrainontheouterends.Theforepolesthusprovidedanextensionofthetunnelsupport,andthefacewasextendedunderthem.Whentheendsoftheforepoleswerereached,newtimberingsupportwasadded,andtheforepolesweredrivenintothegroundforthenextadvanceofthetunneling.Theuseofcompressedairsimplifiedworkinginsoftground.Anairlockwasbuilt,thoughwhichmenandequipmentpassed,andsufficientairpressurewasmaintainedatthetunnelfacetoholdthegroundfirmduringexcavationuntiltimberingorothersupportwaserected.Anotherdevelopmentwastheuseofhydraulicallypoweredshieldsbehindwhichcast-ironorsteelplateswereplacedonthecircumferenceofthetunnels.Theseplatesprovidedsufficientsupportforthetunnelwhiletheworkproceeded,aswellasfullworkingspaceformeninthetunnel.UnderwatertunnelingThemostdifficulttunnelingisthatundertakenatdepthsbelowariverorotherbodyofwater.Insuchcases,waterseepsthroughporousmaterialorcrevices,subjectingtheworkinprogresstothepressureofthewaterabovethetunnelingpath.Whenthetunnelisdriventhroughstiffclay,theflowofwatermaybesmallenoughtoberemovedbypumping.Inmoreporousground,compressedairmustbeusedtoexcludewater.Theamountofairpressurethatisneededincreasesasthedepthofthetunnelincreasesbelowthesurface.Acircularshieldhasprovedtobemostefficientinresimostshield-driventunnelsarecircular.Theshieldonceconsistedofsleetplatesandanglesupports,withaheavilybraceddiaphragmacrossitsface.Thediaphragmhadanumberofopeningswithdoorssothatworkerscouldexcavatematerialinfrontoftheshield.Inafurtherdevelopment,theshieldwasshovedforwardintothesiltymaterialofariverbed,therebysqueezingdisplacedmaterialthroughthedoorsandintothetunnel,fromwhichthemuckwasremoved.Thecylindricalshelloftheshieldmayextendseveralfeetinfrontofthediaphragmtoprovideacuttingedge.Arearsection,calledthetail,extendsforseveralfeetbehindthebodyoftheshieldtoprotectworkers.Inlargeshields,anerectorarmisusedintherearsideofthetoplacethemetalsupportsegmentsalongthecircumferenceofthetunnel.Thepressureagainsttheforwardmotionofashieldmayexceed48.8Mpa.Hydraulicjacksareusedtoovercomethispressureandadvancetheshield,producingapressureofabout245MPaontheoutsidesurfaceoftheshield.Shieldscanbesteeredbyvaryingthethrustofthejacksfromleftsidetorightsideorfromtoptobottom,thusvaryingthetunneldirectionleftorrightorupordown.Thejacksshoveagainstthetunnelliningforeachforwardshove.Thecycleofoperationisforwardshove,line,muck,andthenanotherforwardshove.Theshieldusedabout1955onthethirdtubeoftheLincolnTunnelinNewYorkcmpershove,permittingthefabricationofa81.2cmsupportringbehindit.Cast-ironsegmentscommonlyareusedinworkingbehindsuchashield.Theyareerectedandboltedtogetherinashorttimetoprovidestrengthandwatertightness.InthethirdtubeoftheLincolnTunneleachsegmentis2mlong,81.2cmwide,and35.5cmthick,andweighsabout1.5tons.Thesesectionsformaringof14segmentsthatarelinkedtogetherbybolts.Theboltsweretightenedbyhandandthenbymachine.Immediatelyaftertheywereinplace,thesectionsweresealedatthejointstoensurepermanentwatertightness.excessive,shore-fabricatedtunnelsectionscanbetowedoverapreparedtrenchintheriverbottomandsunkintoplacetoformaunderwatertunnel.Thefirstmajorprefabricated,floated.andsunkentunnelwastheDetroitRiverTunnelbetweenDetroitandWindsor,Ontrio.Thisvehiculartunnelwasbuiltin1906~1910.ThenextimportantvehiculartunnelbuiltbythismethodwasthePosey'tube,whichwascompletedin1928,ItrunsunderasaltwaterarmbetweenOaklandandAlameda.Calif.Sincethenmanyothersunken-tubetunnelshavebeenbuiltunderriversandsaltwaterbodies,notablytheTranshayTunnelbetweenOaklandandSanThecylindricaltunnelsectionsusuallyaremadeofsteelinanonshoreyard.Eachsectionisshout300feet(90meters)longand28to48feet(8.5~14.6meters)indiameterAftertheopeningsateachendofasectionareclosedwithsteelbulkheads,thetubeisreadyforlaunchinginthemannerofaship.Onceinthewater,asectionisballastedwithconcreteuntilaminimumbuoyancyisattained.Thenthesectionistowedtothetunnelsite.Beforethearrivalofthesection,dredgesandunderwaterexcavatorsdigatrenchtotheproperdepthofthetunnel.Whenthetubesectionispositionedpreciselyaveritsfinallocation,additionalconcreteisaddeduntilthesectionsinksintothepreparedtrench.Allsectionsofritetunneltransportedasunkinplaceinthesameway.Eachsectionhasprojectingplatesorflangesthatfitoverorintotheprecedingsectioninthemannerofamaleandfemaleelectricalconnection.Afteronesectionandasucceedingonehavebeensunk,diversengagetheflangesandtightenthebolts.Steelplatesaresliddownaroundthejointbetweenthetwoclosedbulkheads.Thejointisthensealedwithconcretetoensurewatertightlinksbetweenthesections.Afterallofthesectionsareplacedandjoined,theyarecoveredoverwithfilltogivethemstabilityandprotection.Thusthesunken-tuteetechniqueisanunderwaterversionoftheoldcut-and-covermethod.Incompletingthework,crewsenterfromtheportalsateachendofthetunnelandcutawaythesteelbulkheadsastheyapproachthecenterofthetube.Concretethenisplacedfortheinteriorliningofthetube,providingagoodappearanceandgreatersafety.Tiles,duct,liningswiring,pumps,andpipingarethenadded.通過巖層的各種信息。隧洞的長度和斷面形狀一般受隧洞用途的控制.但其形狀必須設(shè)計(jì)成把軟巖擠人隧洞。在所有的情況下，把開挖的巖石或土(也叫碎屑)收集起來并運(yùn)到洞外。在口進(jìn)行掘進(jìn)，這適合于河床和其他有水體的地方。堅(jiān)硬巖石隧洞對于通過堅(jiān)硬巖石的短隧洞僅從進(jìn)口開挖，但隧洞較長時可從一個或多并且允許鉆探和出渣(把開挖材料移走)可同時作業(yè)。先開挖L面部分，當(dāng)上部被鉆孔時，施工人員可在下而部分出清。隨著隧洞開挖方法和機(jī)械的改進(jìn)，受到質(zhì)疑的全斷而開挖(以前在小斷面隧洞使用在建臺上安裝了數(shù)個巖石鉆。利用這一裝置.一個大的隧洞工作面可進(jìn)行一次性鉆孔全斷面法在隧洞開挖中成.為最普遍和進(jìn)尺最快的方法。軟巖隧洞一些隧洞全部地或部分地通過軟巖石在這種非常軟的巖石中，很少或不需要爆破，因?yàn)樗苋菀妆婚_挖。最初，矢板是用于軟巖建設(shè)隧洞的唯一方法。矢板是極重的厚板，大約有1.5m長，端部被削尖。在掌子面它被插人水平撐桿頂部。這樣矢板沿著巖面導(dǎo)入且向外傾斜。在所有的隧洞下一步進(jìn)尺，再把矢板沿隧洞面導(dǎo)入。利用壓縮空氣可以簡化軟巖開挖工作。在隧洞內(nèi)裝上氣塞孔，人和設(shè)備可通過氣塞孔，在隧洞工作面氣壓保持不變.這樣在開挖時，使洞室面不致發(fā)生破壞，一直到肋木或其他支開挖時鋼板對隧洞提供了充分支撐，除此之外在洞內(nèi)人員有一個充分的工作空間。水下隧洞施工最困難的隧洞可以斷言是在河流或其他水體以下相當(dāng)深處。在這種情隧洞，水量很小，可用水泵抽水。在孔隙發(fā)育的地方，用壓縮空氣方法以隔斷水流。隨著隧洞深度的增加空氣壓力也要增加。一度由鋼板和角支撐構(gòu)成，而且有很重的拉桿隔板橫過工作面，隔板上有數(shù)個帶門的通道，盾構(gòu)后部沿隧洞周邊使用升降臂來裝配金屬支撐扇形片。盾構(gòu)前移所受到的壓力會超過48.8Mpa。液壓千斤頂可克服這樣大的壓力向前推動盾構(gòu)，這時在盾構(gòu)的外表面產(chǎn)生約245MPa的壓力。度5.5m，直徑9.6m。前移一次達(dá)81.2cm，在其后可裝配81.2cm支撐環(huán)。鑄鐵扇形片在盾構(gòu)后面隧洞裝配中得到普遍使用。把鑄鐵片在洞內(nèi)進(jìn)行裝配并用螺栓固螺栓是先用手工然后用機(jī)械擰緊。在鑄鐵片被裝配后立即對連接處加以封堵以確保永久隔水。溝槽處，并沉人溝槽形成地下管道第一個大的裝配式、浮動的沉管隧道是Detroit河隧洞，位于Detroit和Winsor,Ontario之間這一車輛隧洞建于1906}1910年之間。用這一方法建成的另一條重要的車輛隧道是Posey隧道于是于1928年完成。它在位于Oakland和Alamed,Calif克蘭和舊金山之間的Transbay隧洞。在岸上工地，圓筒形管道通常用鋼板制成。每條約長90m，直徑8.5~14.6m。在溝槽用挖泥機(jī)和水下開挖器開挖溝槽到隧洞適當(dāng)?shù)纳疃?。?dāng)鋼管在整個最終位置上精確定位后，增加水泥重塊一直把鋼管沉到相應(yīng)的溝槽。其他鋼管施工過程是一樣的。每一段凸板或翼緣以凸形或凹形電焊接的形式裝入相應(yīng)的部位。在前一段和后一段放入處于穩(wěn)定和保護(hù)狀態(tài)。沉管技術(shù)是古式切割和掩埋方法的水下形式。完成這一工作后，工作人員從隧道的每一端進(jìn)口進(jìn)入并切除鋼悶頭，知道鋼管中央處。最后用混凝土做鋼管內(nèi)襯，這樣使鋼管內(nèi)壁光滑且更安全。瓦片、導(dǎo)管、套筒導(dǎo)線、水泵、膠管最后組裝。Atunnelshieldisastructuralsystem,normallyconstructedofsteel,usedduringthefaceexcavationprocess.Theshieldhasanoutsideconfigurationwhichmatchesthetunnel.Theshieldprovidesprotectionforthemenandequipmentandalsofurnishedinitialgroundsupportuntilstructuralsupportscanbeinstalledwithinthetailsectionoftheshield.Theshieldalsoprovidesareactionbaseforthebreast-boardsystemusedtocontrolfacemovements.Theshieldmayhaveeitheranopenorclosedbottom.Inaclosed-bottomshield,theshieldstructureandskinprovide360-degreegroundcontactandtheweightoftheshieldrestsupontheinvertsectionoftheshieldskin.Theopenshieldhasnobottomsectionandrequiressomeadditionalpsupportitsweightandthesuperimposedweightofgroundpressurebeatingontheskin;normallythisprovisionisapairofsidedriftsdriveninadvanceofshieldexcavation.Railsorskidtracksareinstalledwithinthesesidedriftstoprovidebearingsupportfortheshield.Shieldlengthgenerallyvariesfrom1/2to314ofthetunneldiameter.Thefrontoftheshieldisgenerallyhoodedsothatthetopoftheshieldprotrudesforwardfurtherthantheinvertportion;thisprovidesadditionalprotectionforthemenworkingatthefaceandalsoeasepressureonthebreast-boards.Thesteelskinoftheshieldmayvaryfrom1.3to10cminthickness,dependingontheexpectedgroundpressures.Thetypeofsteelusedintheshieldisthesubjectofmanyargumentswithinthetunnelingfraternity.SomeprefermildsteelintheA36categorybecauseofitsductilityandcaseofweldingintheundergroundenvironmentwhereprecisionworkisdifficult.Otherspreferahigh-strengthsteelsuchasT-1becauseofitshigherstrength/weightratio.Shieldweightmayrangefrom5to100tons.MostoftheheaviestshieldsarefoundintheformerSovierUnionbecauseoftheirpreferenceforcast-ironinbothstructuralandskinelements.Propulsionfortheshieldisprovidedbyaseriesofhydraulicjacksinstalledinthetailoftheshieldthatthrustagainstthelaststeelsetthathasbeeninstalled.Thetotalrequiredthrustwillvarywithskinareaandgroundpressure.Severalshieldshavebeenconstructedwithtotalthrustcapabilitiesinexcessof10000tons.Hydraulicsystemsareusuallyself-contained,air-motorpowered,andmountedontheshield.Workingpressuresinthehydraulicsystemmayrangefrom20to70MPa.Toresistthethrustoftheshieldjacks,ahorizontalstructuremember(collarbrace)mustbeinstalledoppositeeachjacklocationandbetweentheflangesofthesteelset.Inadditionsomestructuralprovisionmustbemadefortransferringthisthrustloadintothetunnelwalls.Withoutthisprovisionthethrustwillextendthroughthecollarbracestothetunnelportal.AnEnglishman,MarcBrunel,iscreditedwithinventingtheshield.BrunelsupposedlygothisideabystudyingtheactionoftheTeredonavalis,ahighlydestructivewoodworm,whenhewasworkingattheChathamdockyard.In1818BrunelobtainedanEnglishpatentforhisrectangularshieldwhichwassubsequentlyusestoconstructthefirsttunnelundertheRiverThamesinLondon.In1869thefirstcircularshieldwasdevisedbyBarlowandGreatheareferredtoastheGreathead-typeshield.Laterthatsameyear,BeachinNewYorkCityproducedasimilarshield.Thefirstuseofthecircularshieldcameduring1869whenBralowandGreatheademployedtheirdeviceintheconstructionofthe2.1mdiameterTowerSubwayundertheRiverThames.Despitethenameofthetunnel,itwasusedonlyforpedestriantraffic.Beachalsoputhiscircularshieldtoworkin1869toconstructademonstrationprojectforaproposedNewYorkCitysubwaysystem.Theprojectconsistedofa2.4mdiametertunnel,90mlong,usedtoexperimentwithasubwaycarpropelledbyairpressure.Shieldsaremostcommonlyusedingroundconditionwhereadequatestand-uptimedoesnotexist.Theadvantageoftheshieldinthistypeofground,inadditiontotheprotectionaffordedmenandequipment,isthetimeavailabletoconcretesegmentsunderthetailsegmentoftheshieldbeforegroundpressureandmovementbecomeadversefactors.Oneoftheprincipleproblemsassociatedwithshielduseissteering.Nonuniformgroundpressureactingontheskintendstoforcetheshieldofflineandgrade.Thisproblemisparticularlyacutewithclosedbottomshieldthatdonotrideonrailsorskidtracks.Steeringisaccomplishedbyvaryingthehydraulicpressureinindividualthrustjacks.Iftheshieldistryingtodive,additionalpressureontheinvertjackswillresistthistendency.Itisnotushieldwanderingseveralfeetfromtherequired.Althoughlasersarefrequentlyusedtoprovidecontinuouslineandgradedatatotheoperator,oncetheshieldwandersoffitscourse,itssheerbulkresistseffortstobringitback.Heterogeneousgroundconditions,suchasclaywithrandomboulders,alsopresentssteeringproblems.Onetheoreticaldisadvantageoftheshieldistheannularspaceleftbetweenthesupportsystemandthegroundsurface.Whenthesupportsystemisinstalledwithinthetailsectionoftheshield,theindividualsupportmembersareseparatedfromthegroundsurfacebythethicknessofthetailskin.Whensteelribsareused,theannularspaceisfilledwithtimberblockingastheforwardmotionoftheshieldexposestheindividualribs.Acontinuoussupportsystempresentsadifferentproblem.Inthiscase,afillermaterial,suchaspeagravelorgrout,ispumpedbehindthesupportsystemtofillthevoidbetweenitandthegroundsurface.Themainenemyoftheshieldisgroundpressure.Asgroundpressurebeginstobuild,twothingshappen,morethrustisrequiredforshieldpropulsionandstressincreasesinthestructuralmembersoftheshield.Shieldsaredesignedandfunctionunderapreselectedgroundpressure.Designerswillselectthispressureasapercentageofthemaximumgroundpressurecontemplatedbythepermanenttunneldesign.Insomecases,unfortunately,theshieldjustgetsbuiltwithoutspecificconsiderationofthegroundpressuresitmightencounter.Whengroundpressureexceedsthedesignlimit,theshieldgets“stuck”.Thefrictioncomponentofthegroundpressureontheskinbecomesgreaterthanthethrustcapabilityofthejacks.Severalmethods,includingpumpingbentoniteslurryintotheskin,groundinterface,pushingheavyequipment,andbumpingwithdynamite,havebeenappliedtostuckshields