洞室開挖穩(wěn)定分析、如何建設隧洞-畢業(yè)論文外文文獻翻譯(四篇)

TunnelStabilityAnalysisofTunnelExcavationAspillwaytunnelforanembankmentdamistobeconstructedinapoorqualitysandstone.Theexcavateddiameterofthetunnelisabout13mandthecoverovertheroofis8m.Thetunnelistohavea1.3mthickun-reinforcedconcreteliningand,afterplacementofthislifting,a28tohighportionoftherockfilldamwillheovertheconstructedtunnel.Thequestionstobeaddressedare:(1)Whatsupportisrequiredinordertoexcavatethetunnelsafelyundertheveryshallowcover?(2)Istheproposedtopheadingandbenchexcavationsequence,usingdrillandblastmethods,appropriateforthistunnel?(3)Howwilltheconcreteliningrespondtotheloadingimposedbytheplacementof28mofrockfilloverthetunnel?Inordertoanswerthesequestionsaseriesoftwo-dimensionalfiniteelementanalyseswerecarriedusingtheprogramPHASE'`.Thefirstoftheseanalysesexaminedthestabilityandsupportrequirementsforthetopheadingexcavation.Thefinalanalysisincludedtheentireexcavationandsupportsequenceandtheplacementoftherockfilloverthetunnel.Therockmassisapoorqualitysandstonethat,beingclosetosurface,isheavilyjointed.ThemechanicalpropertiesassumedforthisrockmassareacohesivestrengthC=0.04Mpa,africtionangleof40andamodulusofdeformationE=1334MPa.Noinsitustressmeasurementsareavailablebut,becauseofthelocationofthetunnelinthevalleyside,ithasbeenassumedthatthehorizontalstressnormaltothetunnelaxishasbeenreducedbystressrelief.Themodelisloadedbygravityandaratioofhorizontaltoverticalstressor0.5isassumed.Asimplifiedversionofthemodelwasusedtoanalysethestabilityandsupportrequirementsforthetopheading.Thismodeldidexcludetheconcreteliningandthebenchexcavations.Thefirstmodelwasusedtoexaminetheconditionsforafull-faceexcavationofthetopheadingwithoutanysupport.Thisisalwaysausefulstartingpointinanytunnelsupportdesignstudysinceitgivesthedesigneraclearpictureofthemagnitudeoftheproblemsthathavetobedealtwith.Themodelwasloadedintwostages.Thefirststageinvolvedthemodelwithoutanyexcavationsandthiswascreatedbyassigningthematerialwithintheexcavationboundarythepropertiesofthesurroundingrockmass.Thisfirststageiscarriedoutinordertoallowthemodeltoconsolidateundergravitationalloading.Itisrequiredinordertocreateareferenceagainstwhichsubsequentdisplacementsinthemodelcanbemeasured.TheresultsoftheanalysieareillustratedinFigure18.1,thatshowntheextentofyieldintherockmasssurroundingthetopheading,andFigure18.2thatshowstheinduceddisplacementsaroundthetunnel.Thelargeamountofyieldintherockmassoverlyingthetopheadingsuggeststhatthisexcavationwillbeunstablewithoutsupport.ThisviewissupportedbythedisplacementsshowninFigureI8.2.Thereadermaybesurprisedthatthedisplacementintheroofofthetunnelisonly26mmwhentheextentoftheyieldzonesuggestscompletecollapseoftheroof.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,thecontractoronthisdamprojectdidnothaveagreatdealofexperienceinusingshotcreteintunnelsanditwasunlikelythattheworkerswouldhavebeenpreparedtooperateunderacoverofshotcreteonly.Anotheralternativethatiscommonlyusedinexcavatingtunnelportalsistousesteelsetstostabilisetheinitialportionofthetunnelunderlowcover.Thissolutionworkswellinthecaseofsmalltunnelsbut,inthiscase,a13mspantunnelwouldrequireveryheavysets.Anadditionaldisadvantageinthiscaseisthattheinstallationofsetswouldpermittoomuchdeformationintherackmass.Thisisbecausethesteelsetsareapassivesupportsystemandtheyonlycarryaloadwhentherockmasshasdeformedontothesets.Sincethistunnelisindeformationofadam,excessivedeformationisclearlynotacceptablebecauseoftheadditionalleakagepathswhichwouldbecreatedthroughtherockmass.Thesolutionfinallyadoptedwas"borrowed"fromtheminingindustrywhereuntensionedfullygrouteddowelsarefrequentlyusedtopre-supporttherockmassaboveundergroundexcavations.Inthiscase,apattern3mx3mpatternof15mlong60toncapacitycableswereinstalledfromthegroundsurfacebeforeexcavationofthetopheadingwascommenced.Whenthesecableswereexposedintheexcavation,faceplateswereattachedandtheexcesscablelengthwascutoff.Inaddition,a2mx2mpatternof6mlongmechanicallyanchoredrockboltswereinstalledradiallyfromtheroofofthetopheading.TheresultsofananalysisofthissupportsystemareillustratedinFigure18.3andFigure18.4whichshowtheextentoftheyieldzoneandthedeformationsintherockmassabovethetopheading.ComparingFigure18.1andFigure18.3showsthattheextentoftheyieldzoneisonlyreducedbyasmallamountbytheenstallationofthesupportsystem.Thisisnotsurprisingsincesomedeformationoftherockmassisrequiredinordertomobilizethesupportingloadsintheuntensionedcables.Thisdeformationoccursasaresultoffailureoftherockmass.Figure18.4showsthatthedisplacementsintheroofofthetopheadinghavebeenreducedsubstantiallyasaresultoftheplacementofthesupport.However,asmallproblemremainsandthatistheexcessivedisplacementoftherockbetweentherockboltfaceplateswhicharespacedona2mx2mgrid.Unlessthisdisplacementiscontrolleditcanleadtoprogressiveravellingoftherockmass.Onlyasmallsurfacepressureisrequiredtocontrolthisravellingandthiscouldbeachievedbymeansofalayerofmeshorshotcreteofbytheinstallationoflightsteelsets.Inthiscasethelattersolutionwasadoptedbecauseofthesenseofsecuritywhichthesegavefortheworkersinthetunnel.洞室開挖穩(wěn)定分析某土石壩工程在質量差的砂巖區(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程序進行了一系列的平面有限元分析。首先對上導洞開挖的穩(wěn)定性及所需要的支護形式進行分析，然后對全斷面開挖、支護順序和堆石對隧洞襯砌的影響進行分析巖體為質量差的砂巖，近地表淺部節(jié)理發(fā)育。其力學特性建議為:黏聚力c=0.04Mpa.內摩擦角為40度，變形模量E=1334MPa。沒有現場地應力量測資料，由于隧洞位于谷坡，可以假定垂直隧洞軸線的水平應力由于應力釋放而減小，并且認為水平與垂直應力之比為0.5，計算模型考慮自重荷載.一簡化的計算模型可用于洞室頂拱穩(wěn)定性分析和支護要求。該模型不包括混凝土襯砌和臺階開挖。初始模型用來檢查在沒有任何支護情況下的上導洞全斷面開挖的情況。該模型常用于隧洞支護設計研究開始階段，因為模型可以為設計者提供較清楚的將要處理問題的難度。模型的加載分兩個階段。首先是沒有開挖情況下的模型，此模型是在開挖邊界內用給定巖石材料特性建立起來。第一階段實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。分析結果如圖18.1所示，圖中顯示了上導洞圍巖的屈服范圍;而圖18.2則顯示了旋隧洞次生位移的情況。上導洞洞頂巖體的大范圍屈服說明在沒有支護條件下的開挖是不穩(wěn)定的。圖18.的位移也說明了這一點。大家感到奇怪的是當屈服帶的范圍被暗示洞頂會全部坍塌時，隧洞頂部僅有26mm的位移。但應記住PHASE“是一個關于小應變模型的有限元程序，并不適用于隧洞整體塌落的應變工況。從圖18.2可看出，考慮整體位移形狀遠比位移量重要，而且?guī)r體將不能承受圖所示的差異性位移，上導洞不做支護開挖，由于漸進式剝落.最終導致洞石完全塌落是肯定。經驗豐富的隧洞建設者采用的經驗法則是隧洞上部覆蓋層厚度大于1.5倍洞室跨度，地下開挖才可達到自承支護。對所涉及的問題來說，當開挖洞日有幾種選取方案時，上面情況才會發(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(單軸壓縮強度30MPa)對于隧洞的穩(wěn)定已經足夠。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跨度的導流洞時采用了噴混凝土襯砌。圍巖為弱膠結的灰?guī)r?？捎檬止ぞ蜻M，但有足夠的強度在一定程度上達到自承作用。斯堪的納維亞(Scandinavian)承包商在工程上采用噴混凝土技術已多年，非常有經驗的隧道建設者完全有信心在噴射過混凝土的隧道中施工。該隧洞并不是工程的關鍵隧洞，建設者有充分的時間進行噴混凝土施工。在隧洞中噴混凝土技術是常用的支護措施，對隧洞地質條件特別差的地段，采用預埋在噴混凝土層中的鋼拱架支護。在砂巖中進行上導行洞開挖，未采用噴混凝土方案，盡管有限元分析結果表明是可以的，但設計者沒有充分的信心認為噴混凝土層可以對塊狀砂巖大跨度洞室進行支護。除此以外，大壩項目的承包商沒有隧洞噴混凝土施工的豐富經驗，施工人員也不準備在僅有噴混凝土支護條件下施工。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隧洞的進口部分。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度的鋼架。另一個不利因素是安裝鋼架時要預留有巖體較大的變形量。這是因為鋼架是一個被動的支護系統(tǒng)，只有當巖體變形并與之接觸時才可承重。由于隧洞位于壩基中。過大然不能接受，因為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驗，即對地下開挖以上的巖體一般采用非張拉注漿錨索進行預支護。具體施工時，在上導洞室開挖前，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的機械錨固的巖石錨桿。支護系統(tǒng)的分析結果見圖18.3和圖18.4，圖中表明了屈服帶的發(fā)展程度和上導洞之上巖體的變形情況。對比圖18.1和圖18.3看出，在安裝支護系統(tǒng)后，屈服帶范圍有少量減小。這并不奇怪，因為巖體的某些變形要協(xié)調非張拉錨索的支護荷載，而且這些變形是巖體破裂的結果。圖18.4表明，上導洞頂拱的位移隨著支護的安裝顯著地減少。然而.仍存在一些小問題，在巖石錨桿面板(以2mx2m的網格布設)之間的巖石仍存在較大位移。如果不對這些位移進行控制，就可能導致巖體的漸進式剝落破壞?？刂茙r體的剝落作用只需要很小的表面壓力，可通過掛網或安裝輕型鋼架噴混泥土來實現。例中采用第二種方案，因為隧洞施工者對安全較為敏感。HowTunnelsAreBuiltAfterthegeneraldirectionforatunnelhasbeendetermined,thenextstepsareageologicalsurveyofthesiteandaseriesofboringstoobtainspecificinformationonthestratathroughwhichthetunnelmaypass.Thelengthandcrosssectionofatunnelgenerallyaregovernedbytheuseforwhichitisintended,butitsshapemustbedesignedtoprovidethebestresistancetointernalandexternalforces.Generally,acircularornearlycircularshapesischoosen.Ineveryhardrock,excavationusuallyisaccomplishedbydrillingandblasting.Insoftmedium-hardrock,atunnel-boringmachinetypicallydoestheexcavationwork.Insoftground,excavationusuallyisaccomplishedbydiggingorbyadvancingashieldandsqueezingthesoftmaterialintothetunnel.Inallcases,theexcavatedrockorearth,calledmuck,iscollectedandtransportedoutofthetunnel.Inunderwatertunneling,ashieldisusedtoadvancethework.Anothermethodofbuildinganunderwatertunnelistosinktubularsectionsintoastrengthdugatthebottomofariverorotherbodyofwater.Hard-rocktunnelingShorttunnelsthroughhardrockaredrivenonlyFromtheportalsbutlongeronesusuallyaredrivenalsofromoneormoreintermediateshafts.Somelongtunnelshavebeenbuiltwiththeaidofasmallpilottunneldrivenparalleltothemaintunnelandconnectedwithitbycrosscutsatintervals.Thepilottunnelnotonlyfurnishesadditionpointsofaccessbutalsoarouteforremovingmuckandforventilationductsanddrainagelines.Anothermethodistheheading-and-benchsystem,formallyusedonmostlargefunnel.becauseitrequiredsmalleramountsofpowerandpermittedsimultaneousdrillingandmucking(removalofexcavatedmaterial).Theupperportionofthetunnelisdrivenaheadofthelowerpartwhichiscalledthebench.Aseparatecrewisthusabletomuckinthelowerportionofthetunnelwhiletheupperportionisbeingdrilled.Withimprovementsintunnelingmethodsandmachinery,thefull-facemethodofattack,previouslyusedonlyinsmalltunnels,cameintocommonuseinbuildinglargeones.Thischangewaspartlybroughtaboutbythejumbo,amovableplatformonwhichnumerousrockdrillsaremounted.Bythisdevice,alargepartofthetunnel’sfacecanhedrilledatonetime.Thefullfacemethodbecamethecommonestandfastestwaytodriveatunnel.Soft-groundtunnelingSometunnelsaredrivenwhollyormostlythroughsoftmaterial.Inverysoftground,littleornoblastingisnecessarybecausethematerialiseasilyexcavated.Atfirst,forepolingwastheonlymethodforbuildingtunnelsthroughverysoftground.Forepolesareheavyplanksabout1.5mlongandsharpenedtoapoint.Theywereinsertedoverthetophorizontalbarofthebracingatthefaceofthetunnel.Theforepolesweredrivenintothegroundofthefacewithanoutwardinclination.Afteralltheroofpolesweredrivenforabouthalfoftheirlength,atimberwaslaidacrosstheirexposedendstocounteranystrainontheouterends.Theforepolesthusprovidedanextensionofthetunnelsupport,andthefacewasextendedunderthem.Whentheendsoftheforepoleswerereached,newtimberingsupportwasadded,andtheforepolesweredrivenintothegroundforthenextadvanceofthetunneling.Theuseofcompressedairsimplifiedworkinginsoftground.Anairlockwasbuilt,thoughwhichmenandequipmentpassed,andsufficientairpressurewasmaintainedatthetunnelfacetoholdthegroundfirmduringexcavationuntiltimberingorothersupportwaserected.Anotherdevelopmentwastheuseofhydraulicallypoweredshieldsbehindwhichcast-ironorsteelplateswereplacedonthecircumferenceofthetunnels.Theseplatesprovidedsufficientsupportforthetunnelwhiletheworkproceeded,aswellasfullworkingspaceformeninthetunnel.UnderwatertunnelingThemostdifficulttunnelingisthatundertakenatconsiderabledepthsbelowariverorotherbodyofwater.Insuchcases,waterseepsthroughporousmaterialorcrevices,subjectingtheworkinprogresstothepressureofthewaterabovethetunnelingpath.Whenthetunnelisdriventhroughstiffclay,theflowofwatermaybesmallenoughtoberemovedbypumping.Inmoreporousground,compressedairmustbeusedtoexcludewater.Theamountofairpressurethatisneededincreasesasthedepthofthetunnelincreasesbelowthesurface.Acircularshieldhasprovedtobemostefficientinresistingthepressureofsoftground,somostshield-driventunnelsarecircular.Theshieldonceconsistedofsleetplatesandanglesupports,withaheavilybraceddiaphragmacrossitsface.Thediaphragmhadanumberofopeningswithdoorssothatworkerscouldexcavatematerialinfrontoftheshield.Inafurtherdevelopment,theshieldwasshovedforwardintothesiltymaterialofariverbed,therebysqueezingdisplacedmaterialthroughthedoorsandintothetunnel,fromwhichthemuckwasremoved.Thecylindricalshelloftheshieldmayextendseveralfeetinfrontofthediaphragmtoprovideacuttingedge.Arearsection,calledthetail,extendsforseveralfeetbehindthebodyoftheshieldtoprotectworkers.Inlargeshields,anerectorarmisusedintherearsideoftheshieldtoplacethemetalsupportsegmentsalongthecircumferenceofthetunnel.Thepressureagainsttheforwardmotionofashieldmayexceed48.8Mpa.Hydraulicjacksareusedtoovercomethispressureandadvancetheshield,producingapressureofabout245MPaontheoutsidesurfaceoftheshield.Shieldscanbesteeredbyvaryingthethrustofthejacksfromleftsidetorightsideorfromtoptobottom,thusvaryingthetunneldirectionleftorrightorupordown.Thejacksshoveagainstthetunnelliningforeachforwardshove.Thecycleofoperationisforwardshove,line,muck,andthenanotherforwardshove.Theshieldusedabout1955onthethirdtubeoftheLincolnTunnelinNewYorkCitywas5.5mlongand9.6mindiameter.Itwasmovedabout81.2cmpershove,permittingthefabricationofa81.2cmsupportringbehindit.Cast-ironsegmentscommonlyareusedinworkingbehindsuchashield.Theyareerectedandboltedtogetherinashorttimetoprovidestrengthandwatertightness.InthethirdtubeoftheLincolnTunneleachsegmentis2mlong,81.2cmwide,and35.5cmthick,andweighsabout1.5tons.Thesesectionsformaringof14segmentsthatarelinkedtogetherbybolts.Theboltsweretightenedbyhandandthenbymachine.Immediatelyaftertheywereinplace,thesectionsweresealedatthejointstoensurepermanentwatertightness.Sunken-tubetunnelsWheretheriverbedsubsoilisfirmandtherivercurrentisnotexcessive,shore-fabricatedtunnelsectionscanbetowedoverapreparedtrenchintheriverbottomandsunkintoplacetoformaunderwatertunnel.Thefirstmajorprefabricated,floated.andsunkentunnelwastheDetroitRiverTunnelbetweenDetroitandWindsor,Ontrio.Thisvehiculartunnelwasbuiltin1906~1910.ThenextimportantvehiculartunnelbuiltbythismethodwasthePosey'tube,whichwascompletedin1928,ItrunsunderasaltwaterarmbetweenOaklandandAlameda.Calif.Sincethenmanyothersunken-tubetunnelshavebeenbuiltunderriversandsaltwaterbodies,notablytheTranshayTunnelbetweenOaklandandSanFrancisco.Thecylindricaltunnelsectionsusuallyaremadeofsteelinanonshoreyard.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.如何建設隧洞對隧洞來說，總體方向被確定之后，下一步是現場地質測繪和一系列的鉆探以獲得遂洞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.但其形狀必須設計成所給予的內外阻力最小。一般說來，圓形或近似圓形受到歡迎。在各種堅硬的巖石中，開挖常用鉆探和爆破來完成。在軟到中等堅硬的巖石，一種專門的隧洞掘進機用于開挖施工。在軟巖中，通常利用掘進或先進的盾構來完成開挖。并用盾構把軟巖擠人隧洞。在所有的情況下，把開挖的巖石或土(也叫碎屑)收集起來并運到洞外。在地下水位以下隧洞，盾構可提高工作效率。建設地下水位以下的隧洞另一種辦法是用沉管刃口進行掘進，這適合于河床和其他有水體的地方。堅硬巖石隧洞對于通過堅硬巖石的短隧洞僅從進口開挖，但隧洞較長時可從一個或多個中間斜井開挖。一些長隧洞借助小的導航隧洞建設，而這樣導洞和主洞平行，且在一定間距上用橫導洞與主洞連起來。這樣的導洞不僅增加了出人口，同時為棄渣、通風和排水增加了通道。另外一種方法是用上導洞和階梯式開挖，過去常用于大斷面隧洞，因為它要求的動力小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械的改進，受到質疑的全斷而開挖(以前在小斷面隧洞使用在建設大斷面隧洞中得到普遍使用。這一變化部分來源于鑿巖臺車的使用，它是在臺車可移動平臺上安裝了數個巖石鉆。利用這一裝置.一個大的隧洞工作面可進行一次性鉆孔全斷面法在隧洞開挖中成.為最普遍和進尺最快的方法。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，因為它很容易被開挖。最初，矢板是用于軟巖建設隧洞的唯一方法。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入且向外傾斜。在所有的頂桿被導入其長度的一半后，放置肋木，它橫過頂桿外露端以計量外端的變形。矢板可提供隧洞支撐延展，而矢板下的工作面會膨脹。當矢板到了板的末端，加上新的肋木支撐，為了隧洞下一步進尺，再把矢板沿隧洞面導入。利用壓縮空氣可以簡化軟巖開挖工作。在隧洞內裝上氣塞孔，人和設備可通過氣塞孔，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撐被安裝上。另外一種方法使用液壓作為盾構動力，它的后面沿隧洞圓周安裝鑄鐵板或鋼板。這樣在開挖時鋼板對隧洞提供了充分支撐，除此之外在洞內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深處。在這種情況下，水會通過孔隙和裂隙滲漏，開挖則是在隧洞以上水位的水壓下進行。在硬黏土中開挖隧洞，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。對阻止軟巖壓力來說，圓形盾構大部分是有效的，因而盾構開挖的隧洞是圓形的。盾構一度由鋼板和角支撐構成，而且有很重的拉桿隔板橫過工作面，隔板上有數個帶門的通道，以至于工人在盾構前面可進行開挖。更進一步發(fā)展，盾構可以向前推壓進入河床泥沙物質中，這樣通過門把泥排出并進入隧洞，最后把碎屑泥移走。盾構的圓形套管在隔板前可伸出幾英尺以切割隧洞周邊。后部或尾部在盾構體后仲延幾英尺以保護作業(yè)工人。在大的盾構中，在盾構后部沿隧洞周邊使用升降臂來裝配金屬支撐扇形片。盾構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，這時在盾構的外表面產生約245MPa的壓力。利用可變推力千斤頂會使盾構行駛，從左到右、從上到下都可做到.這樣隧洞可左、右、上、下改變它的方向。每次前移千斤頂要對隧洞襯砌加反力。每次循環(huán)是前推、襯砌、出渣，然后是另一次循環(huán)。盾構開始應用于1955年紐約(NewYork)城林肯隧洞的第三條管線，其長度5.5m，直徑9.6m。前移一次達81.2cm，在其后可裝配81.2cm支撐環(huán)。鑄鐵扇形片在盾構后面隧洞裝配中得到普遍使用。把鑄鐵片在洞內進行裝配并用螺栓固定在一起，這樣在不長時間內起到加固隧洞和防水作用。在林肯隧洞第三管道，每一扇片長2m，寬8l.2cm，厚35.5cm。重大約1.5噸。每環(huán)有14個扇片組成，它們之間用螺栓固定。螺栓是先用手工然后用機械擰緊。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。沉管式隧洞當河床土層膠結。水流不時，在岸上裝完的管道可搬運到河床已挖好的溝槽處，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間的咸水海灣下運行。從此在河流或咸水體下建了許多沉管式隧道，特別在此要提出的是奧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。在溝槽開挖后，鋼管兩端用剛悶頭封起來，用船裝運準備下水。一旦下水用重混凝土塊對鋼管加以穩(wěn)定，直到它受的浮托力最小為止，然后把這一條鋼管拖到隧洞的現場。在鋼管運到現場前，用挖泥機和水下開挖器開挖溝槽到隧洞適當的深度。當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的部位。在前一段和后一段放入水后，潛水員要檢查凸緣并擰緊螺栓。在兩個合攏悶頭間，鋼板周圍接口要扣好。接口用凝固物封好以確保兩端之間連接不漏水。在所有部分被裝配和連接后，在進行埋填使整個管道處于穩(wěn)定和保護狀態(tài)。沉管技術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口進入并切除鋼悶頭，知道鋼管中央處。最后用混凝土做鋼管內襯，這樣使鋼管內壁光滑且更安全。瓦片、導管、套筒導線、水泵、膠管最后組裝。ShieldsAtunnelshieldisastructuralsystem,normallyconstructedofsteel,usedduringthefaceexcavationprocess.Theshieldhasanoutsideconfigurationwhichmatchesthetunnel.Theshieldprovidesprotectionforthemenandequipmentandalsofurnishedinitialgroundsupportuntilstructuralsupportscanbeinstalledwithinthetailsectionoftheshield.Theshieldalsoprovidesareactionbaseforthebreast-boardsystemusedtocontrolfacemovements.Theshieldmayhaveeitheranopenorclosedbottom.Inaclosed-bottomshield,theshieldstructureandskinprovide360-degreegroundcontactandtheweightoftheshieldrestsupontheinvertsectionoftheshieldskin.Theopenshieldhasnobottomsectionandrequiressomeadditionalprovisiontosupportitsweightandthesuperimposedweightofgroundpressurebeatingontheskin;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.In1869thefirstcircularshieldwasdevisedbyBarlowandGreatheadinLondonandisreferredtoastheGreathead-typeshield.Laterthatsameyear,BeachinNewYorkCityproducedasimilarshield.Thefirstuseofthecircularshieldcameduring1869whenBralowandGreatheademployedtheirdeviceintheconstructionofthe2.1mdiameterTowerSubwayundertheRiverThames.Despitethenameofthetunnel,itwasusedonlyforpedestriantraffic.Beachalsoputhiscircularshieldtoworkin1869toconstructademonstrationprojectforaproposedNewYorkCitysubwaysystem.Theprojectconsistedofa2.4mdiametertunnel,90mlong,usedtoexperimentwithasubwaycarpropelledbyairpressure.Shieldsaremostcommonlyusedingroundconditionwhereadequatestand-uptimedoesnotexist.Theadvantageoftheshieldinthistypeofground,inadditiontotheprotectionaffordedmenandequipment,isthetimeavailabletoinstallsteelribs,linerplates,orprecastconcretesegmentsunderthetailsegmentoftheshieldbeforegroundpressureandmovementbecomeadversefactors.Oneoftheprincipleproblemsassociatedwithshielduseissteering.Nonuniformgroundpressureactingontheskintendstoforcetheshieldofflineandgrade.Thisproblemisparticularlyacutewithclosedbottomshieldthatdonotrideonrailsorskidtracks.Steeringisaccomplishedbyvaryingthehydraulicpressureinindividualthrustjacks.Iftheshie