《专业英语翻译》-Part III Highway Engineering

Unit3一1HighwayConstructionHighwayconstructionhasevolvedovertheyearsandaswithanyindustrytoday，hasbecomefairlysophisticated.Expectationsofthetax-payingcitizenwithrespecttoquality，scheduleandbudgethavealsorisenovertime.Technologyandmodernmachineryhaveraisedthelevelofskillsetsrequiredtounderstandandmanagehighwayconstructionprojects.Theskillsetrequiredvariesbasedonthenatureandcomplexityoftheproject;differencesbetweennewconstructionandreconstructionprojects;anddifferencesforprojectsinurbansettingsandthoseinruralregions.下一页返回Unit3一1HighwayConstructionThequalityofaprojectdependsonmaterialquality，skillandcommitmentoftheworkforce.Themajorityofmaterialsusedinhighwayconstruction，suchasfillmaterialsforembankmentconstruction，aggregatesforhaleandsurfacecoursesarenaturallyoccurringmaterials.Thesematerialsareusuallyavailablewithincertainproximitytotheprojectandmeetingcertainphysicalandchemicalcharacteristics.Thebehaviorofthesematerialsunderthelocalenvironmentoftrafficloads，ambienttemperatures,上一页下一页返回Unit3一1HighwayConstructionannualrainfallandlocalpracticeofkeepinghighwayserviceableduringadverseweatherconditionswillhavetoheunderstood.Basedonthisunderstanding，themethodsandmeansofconstructingahighwaywillhavetobeadoptedaccordingly.HighwayElementsandLayoutConstructionofahighwaytodayrequiresbroadknowledgeofanumberofelementswhichcouldbedividedintotechnicalandcommercialelementsofthesystemsee(Fig.1)andprocess.Thetechnicalelements上一页下一页返回Unit3一1HighwayConstructionincludematerials，materialquality，installationtechniques，andtrafficcontrolsystems，etc.Thecommercialelementsincludeunderstandingofthecontract;environmental，politicalandlegalaspectsofaproject;andpublicconcerns.Thecontractor'sprojectorganizationforhighwayconstructionisstructuredaroundtrades，projectmanagement，gradingorearthwork上一页下一页返回Unit3一1HighwayConstructionStructurestrafficcontrolsystemslandscapingandpaving.Projectmanagementcoversschedulingcostestimatingprocurement，qualitycontrol，safetyandenvironmentalcontrol.Agoodprojectmanagementapproachwillincludeawell-definedstructureoutliningrolesandresponsibilitiesandensuregoodcommunicationamongthevariousgroups.Anumberofagenciesarebeginningtorequirethebuilderprovideindependentqualitycontrolandqualityassurance.上一页下一页返回Unit3一1HighwayConstructionTheenvironmentalaspectsofaprojectarenotlimitedtotheelementsoftheprojectandtotheprojectlimits.Permitrequirementsand

commitmentswillhavetobeunderstoodtoavoidexpensivefinesandshutdowns.Impactstoadjacentpropertiessurfaceandsub一surfacedrainage，noiseandlightpollutionduringandafterconstructionwillhavetobeunderstoodandimplemented.Politicalaspectsofaprojectcanbecomplex，dependingonthelocationsizeoftheproject，fundingfortheproject，etc.上一页下一页返回Unit3一1HighwayConstructionThoughthecontractingagencyisresponsibletokeepthewheelsturningtheconstructorhasalotatstakeifthefundingfortheprojectisnotinplaceornotassuredforthefutureyears.Additionally，theconstructorwillneedtobeawareofotherpoliticalpressuressuchasuseoflocalworkforcespecialneedsofacommunityorgroup，etc.Legalaspectsoftheprojectcouldincludemeetingcommitmentsofthecontract，subcontracting，claims，changedconditions，safetyoftravelingpublic，etc.上一页下一页返回Unit3一1HighwayConstructionTheseincludetherequiredlevelofparticipationofdisadvantagedbusinesses，prescribedminimumwages，bettermentsestablishedtoplacatelocalmunicipalities，andenvironmentalrequirements，etc.上一页下一页返回NewWordsandExpressionstax-paying n.纳税urban adj.城市的;都市的;城镇的commitment n.委托;交钾;承担义务embankment n.河堤;路基aggregate n.合计，总计;聚集体，骨料，集料adj.合计的，聚集的proximity n.接近，附近;近似;接近度;rainfall n.降雨量，降雨commercial dj.商业的，商品化的;商用的earthwork n.土方(工程);土木工事landscape n.陆上风景，山水(风景画);地表(形、貌)上一页下一页返回NewWordsandExpressionspave vt.铺(路等)，作铺设……之用;铺设安排，准备agency n.代理机构，办事处，代理处independent n.独立自主者，无党派者subcontract n.转包合同，分包合同placate vt.安抚，抚慰;使和解municipality 治区;自治市;市或区的政府当局;直辖市skillset技能ambienttemperature环境温度;室温;周围温度publicconcern公众关注，大众关注(的事)atstake在危急关头.在危险中上一页下一页返回ExercisesI.WriteTinfrontofastatementifitistrueandwriteFifitisfalseaccordingtothetext.1.Theskillsetrequiredbetweennewconstructionandreconstructionprojectsaresame.2.Themajorityofmaterialsusedinhighwayconstructionarenaturallyman-madematerials.3.Inanyproject，theenvironmentalaspectsarenotlimitedtotheelementsoftheproject.4.Politicalaspectsofaprojectsometimesbecomplex，whileitdependonthelocationsizeoftheproject，fundingfortheprojectetc.上一页下一页返回ExercisesII.TranslatethefollowingsentencesintoChinese.1.Thequalityofaprojectdependsonmaterialquality，skillandcommitmentoftheworkforce.2.Constructionofahighwaytodayrequiresbroadknowledgeofanumberofelementswhichcouldbedividedintotechnicalandcommercialelementsofthesystem.3.Politicalaspectsofaprojectcanbecomplex，dependingonthelocation，sizeoftheproject,fundingfortheprojectetc.上一页下一页返回ExercisesIII.TranslatethefollowingsentencesintoEnglish.1.在现代的典型公路横断面设计中，每一个要素的尺寸大小都是在对交通量、交通特性车速以及对机动车和驾驶员特点的仔细分析的基础上确定下来的。2.在双向行驶的交通流之间设置明显的分隔带是一种减少多车道公路上车前灯引起的炫日、交通冲突和事故的有效措施。上一页返回Unit3一2HighwayAlignmentDesignThealignmentofahighwayisathree-dimensionalproblembecausethehighwayitselfnegotiatesthroughtheterraininconnectingtwopoints.Thehighwaymaybevisualizedassegmentsofconnectedhorizontalandverticalcurves（ortheircombination

）.Thealignmentofahighwayisbestrepresentedbyitscentrelineinathree-dimensionalcoordinatesystem.However,fortheeaseofinterpretationoftheconstructiondrawing.theconventionofplanandprofileviewshavebeenadopted.下一页返回Unit3一2HighwayAlignmentDesignTheplanviewgivesthehorizontalalignmentofahighway.Thelengthofthehighwayismeasuredalongtheplanviewonahorizontalplane.Thelengthisexpressedintermsofdistancefromareferencestation，intermsofstations.Eachstationis100m.Ahighwaynormallystartsfromafixedreferencestation.Thedistancefromthereferencestation，togetherwiththedirectionfromthereferencestationorsubsequentstations,spellsoutthehorizontalalignment.上一页下一页返回Unit3一2HighwayAlignmentDesignTheverticalalignment(includingthegradientsandverticalcurves)arerepresentedinaprofileview.Theprofileviewistheviewalongthelength(includingthetruelengthofhorizontalcurve)ofthehighway.Theelevationsofallthepointsatregularintervalsarespecifiedintheprofileview.HorizontalAlignmentAhorizontalcurveprovidesthedirectionaltransitiononthehorizontalplane，betweentwostraightsectionsofthehighwayrunningindifferentdirections.上一页下一页返回Unit3一2HighwayAlignmentDesignHorizontalcurvesareexpressedascircularcurveswithconstantradiiorsuccessivecurveswithdifferentradii.Spiralcurveswithconstantrateofchangeofradiuscanalsobefound.Acurvecanbedescribedbyitsradiusorbyitsdegreeofcurvature.Fig.1showsthepropertiesofacurvewithaconstantradius(R)connectingtwostraightsectionsofahighway.Thecurvestartsatpointofcurvature(PC)，endsatpointoftangent(PT).Thepointofintersection(PI)istheintersectingpointifthetwostraightlinesareextended.上一页下一页返回Unit3一2HighwayAlignmentDesign△isthecentralangleofthecurve，expressedindegrees.Thelengthoftangent(T)isTheexternaldistance(E)isVerticalAlignmentAverticalcurveprovidesasmoothtransitionbetweentwotangentgrades.Therearetwotypesofverticalcurves:crestverticalcurvesandsagverticalcurves.上一页下一页返回NewWordsandExpressionsthree-dimensional adj.三维的，立体的，有立体感的

horizontal n.水平线.水平面.水平位置radii n.半径curvature n.弯曲，曲率tangent adj.接触的，正切的，离题的crest n.波峰;振幅;峰值，最大值，山顶，羽冠sag vi.下垂，倾抖，姜靡，萧条上一页下一页返回NewWordsandExpressionsspelloutv.讲清楚，清楚地说明horizontalcurve 平面曲线horizontalplane水平面上一页下一页返回ExercisesI.Accordingtothetext，answerthefollowingquestionsinEnglish.1.Whydowethinkthealignmentofahighwayisathree-dimensionalproblem?2.Whatdoesahorizontalcurveprovideinhighwayalignmentdesign?3.Whatdoesaverticalcurveprovidesinhighwayalignmentdesign?4.Howmanytypesofverticalcurvesarethere?Whatarethey?上一页下一页返回Exercises1.我们用同定半径的圆曲线或不同半径的连续曲线来表示平面曲线。2.公路线形最好在空间坐标系(如经度、纬度和海拔)用道路中线表示出来。3.纵断面线形在两个纵向坡度间提供一个平滑的过渡区间。它包括两种类型:凸形竖曲线和凹形竖曲线。上一页返回Unit3一3HighwayCrossSection(一)Atypicalcrosssectionofahighwayconsistsofthefollowingcomponents:traveledwayshoulders.Importantelementsinthegeometricdesignarecrossslopeoftravellane，lanewidth，widthandslopeofshoulder，andcurb.ForthepurposeofcrosssectioninhighwaygeometricdesignAASHTOclassifiespavementsintohigh-typeandlow-type.High-typepavementsretaintheirshapeanddonotravelattheedgeifplacedonatablesubgrade.下一页返回Unit3一3HighwayCrossSection(一)Theirsurfacesareusuallysmooth.Low-typepavementshaveatendencytowardravelingandareusuallyusedforlowvolumeroad.Thistypeofpavementisnormallyconstructedfromgravel，earth，orcrushedstone.CrossSlopeUndividedhighwaysontangents，oronflatcurveshavetwotypesofcrossslopedesigns:acrownorhighpointinthemiddleandacrossslopedownwardtowardbothedges;ahighpointatoneedgeandacrossslopeacrossslopeacrosstheentirewidth.上一页下一页返回Unit3一3HighwayCrossSection(一)Ondividedhighway，eachone-wayroadwaymaybetreatedasanundividedhighwayasmentionedabove.Fig.1showsafewpossibledesigns.Acrosssectionwitheachroadwaycrownedseparatelyprovidesamorerapiddrainageofstormwater，butattheexpenseofmoredrainageinletsandundergroundlines.Thistypeofcrosssectionaldesignshouldbelimitedtoareawithheavyrainfall.上一页下一页返回Unit3一3HighwayCrossSection(一)Roadwayswithunidirectionalcrossslopestendtoprovidemorecomfortfordriverswhentheychangelanes.Downwardslopestowardthemedianhavetheadvantageofrequiringonlyonedrainageconduitatthemedian.Therateofcrossslopeisanimportantelementincrosssectiondesign.Theslopeshouldbesteepenoughtodirecttherainfallrunofftoflowtowardstheedgeoftheroadway(insteadofalongtheslopeofaverticalcurve),providesufficientdrainagecapacityforthedesignstorm上一页下一页返回Unit3一3HighwayCrossSection(一)butatthesametime，avoidthetendencyforvehiclestravelingstraighttodrifttowardsthelowpointofthecrosssection(unlesscorrectedbysteeringcontrol).Crossslopeofupto2%arenormallynotnoticeablebydriversintermsofsteeringcontrol，morethan2%willnormallyrequiresteeringcorrection.Excessivecrossslopealsopresentsdangerforlateralskiddingwhenvehicleapplyemergencybrakeevenondrypavement.Thedesignofcrossroadmaybeusedtocounterconsistentcrosswind.上一页下一页返回Unit3一3HighwayCrossSection(一)Ifaroadwayhasacrownatthecentre，thecrossslopesonbothsidesofthecrownlineshouldrangefrom1.5%to2%.Inanycase，theslopesonbothsidesofthecrownlineshouldnotbemorethan2%.Usingslopesofmorethan2%onbothsidesofthecrownwillsubjectdriverstomorethan4%differentialslopewhenmovingacrossit.Subsequentlanestowardtheedgemayhavethesameslope，orhavetheslopeincreasedby0.5%to1%.Theaboveguidelineappliesforhigh-typepavements.上一页下一页返回Unit3一3HighwayCrossSection(一)Low-typepavementsarerelativelyporous.Topreventwaterfromabsorbingintothematerialsthatmakeupthesurfacelayer，highslopesof2%to6%areapplicable.上一页下一页返回NewWordsandExpressionscurb n.抑制;勒马绳;边石vt.抑制，束缚，勒住pavement n.路面;人行道;铺面路;铺路材料ravel vt.使纠缠，使错综复杂subgrade n.路基，地基gravel n.砂砾.碎石undivided adj.未分开(割)的;(利润等)未分配的;连绵的;完整的;专心的，专一的crown n.王冠，王权，顶点上一页下一页返回NewWordsandExpressionsdrainage n.排水(法);逐步流出;排水装置inlet n.进口，插入物slope n.倾抖，抖坡(度)，抖面runoff n.径流(量);决赛;决定性竞选guideline n.指导路线，方针，指标，准则上一页下一页返回ExercisesI.Fillintheblankswithsuitablewordsandexpressionsfromthelist，chancingtheformwhennecessary.上一页下一页返回ExercisesII.Accordingtothetext，answerthefollowingquestionsinEnglish.1.Howmanyimportantelementsinthegeometricdesignarethere?Whatarethey?2.Howmanytypesofcrossslopedesignsarethereinundividedhighwaysontangents?Whatarethey?3.Whycouldn'thighwaydesignersdesignexcessivecrossslopeevenondrypavement上一页下一页返回ExercisesIII.TranslatethefollowingsentencesintoEnglish.1.横向坡度是横断面设计的一个重要因素。2.横向坡度在达到2%以前，通常对司机转向控制影响并不明显，坡度超过2%，通常需要转向纠正.上一页返回Unit3一4PavementDistressesandPerformance(一)Differenttypesofdistresscanoccurinasphaltpavement.Thesedistressescouldbedevelopedduetotrafficloadrepetitions，temperature,moisture,aging,constructionpractice,orcomhinations,Thecommontypesofdistressesinflexiblepavementsarediscussedbelow.FatigueCrackingFatiguecracksareaseriesoflongitudinalandinterconnectedcrackscausedbytherepeatedapplicationsofwheelloads.下一页返回Unit3一4PavementDistressesandPerformance(一)Thistypeofcrackinggenerallystartsasshortlongitudinalcracksinthewheelpathandprogresstoanalligatorcrackingpattern(interconnectedcracks)asshowninFig.1.ThistypeofcrackinghappensbecauseoftherepeatedbendingactionoftheHMAlayerwhentheloadisapplied.Thisgeneratestensilestressesthateventuallycreatecracksatthebottomoftheasphaltlayer.Cracksgraduallypropagatetothetopofthelayerandlaterprogressandinterconnect.Thistypeofdistresswilleventuallyleadtoalossofthestructuralintegrityofpavementsystem.上一页下一页返回Unit3一4PavementDistressesandPerformance(一)Recentstudieshavedemonstratedthatalesscommonfatiguecrackingmayinitiatefromthetopofthepavementsurfaceandpropagatesdownward(top-downcracking).Thistypeoffatigueisnotaswelldefinedfromamechanicalviewpointasthemoreclassical“bottom-up”fatigue.Itishypothesizedthatcriticaltensileandshearstressesdevelopatthesurfaceandcauseextremelylargecontactpressuresatthetypeedges一pavementinterface，coupledwithhighlyaged(stiff)surfacelayerandtheseareresponsiblefactorsforthiskindofcracking.上一页下一页返回Unit3一4PavementDistressesandPerformance(一)Top-downcrackingfirstshowsupasrelativelylonglongitudinalcracksadjacenttothetyreswithinthewheelpaths.RuttingRuttingisdefinedaspermanentdeformationinthewheelpathasshowninFig.2.

Ruttingcanoccurdueto:(a)unstableHMA(b)densificationofHMA，(c)deepsettlementinthesubgradeasdemonstratedinFig.3.上一页下一页返回Unit3一4PavementDistressesandPerformance(一)RoughnessRoughnessisdefinedastheirregularitiesinthepavementprofilewhichcausesuncomfortable，unsafe，anduneconomicalriding.Roughnessaffectsthedynamicsofmovingvehicles，increasingthewearonvehiclepartsandthehandlingofvehicles.Thus，roadroughnesshasanappreciableimpactonvehicleoperatingcostsandthesafetycomfort，andspeedoftravel.Italsoincreasesthedynamicloadingimposedbyvehiclesonthesurface,acceleratingthedeteriorationofthepavementstructure.上一页下一页返回Unit3一4PavementDistressesandPerformance(一)ThermalCrackingAsthetemperaturedecreasestheHMAmaterialcontracts.Sincethematerialisrestrainedfrommovementduetothefrictionwiththeunderlyingmaterial，tensilestressesdevelopwithintheHAMmaterial.IfthetensilestressexceedsthetensilestrengthofthematerialthermalcracksdevelopasshowninFig.4.Thermalcrackstypicallyoccurinthetransversedirectionperpendiculartothedirectionoftraffic.上一页下一页返回Unit3一4PavementDistressesandPerformance(一)Thistypeofcrackingisusuallyequallyspaced.Thisisanon-loadassociatedtypeofcrackinganditstartsduringthewinterseason.Thewidthofthethermalcracksusuallychangesfromsummertowinter.ShovingShovingisaformofplasticmovementresultinginalocalizedbulgingofthepavementsurface.Shovingcantakeanumberofdifferentformssuchasupheaval(showninFig.5)，“wash-boarding”orripplesacrossthepavementsurface，orcrescentshapedbulging.上一页下一页返回Unit3一4PavementDistressesandPerformance(一)ShovingoccursintheasphaltlayersthatlackstabilitybecauseoftoomuchasphaltbinderintheHMAmix，toosoftasphaltbinder，roundedaggregateparticlessmoothaggregatetextureortoomanyfinesinthemix.上一页下一页返回NewWordsandExpressiondistress n.病害interconnect vt.使互相连接;使互相联系propagate vt.繁殖，传播，传送hypothesize v.假设，假定rutting n.车辙densification n.压实，填密，夯实subgrade n.地基;路基roughness n.粗糙;未加工;粗糙程度上一页下一页返回NewWordsandExpressionwear n.使用;耗损，磨损appreciable adj.可感知的，可评估的deterioration n.恶化，衰退，退化transverse adj.横向的，横断的perpendicular adj.垂直的;成直角的bulge n.胀，膨胀flexiblepavement柔性路面fatiguecracking疲劳裂缝HMAlayer沥青混合料层tensilestress拉伸应力coupledwith加上alligatorcracking路面龟裂上一页下一页返回ExercisesI.Fillintheblankswithsuitablewordsandexpressionsfromthelistlivenbelow，chancingtheformwhennecessary.1._______cracksareaseriesoflongitudinalandinterconnectedcracks.2.Thestudieshave_______thatalesscommonfatiguecrackingmayinitiatefromthetopofthepavementsurfaceandpropagatesdownward.3.Ruttingisdefinedaspermanent______inthewheelpath.上一页下一页返回Exercises4.Asthetemperature_____theHMAmaterialcontracts.5.Shovingisaformofplasticmovementresultinginalocalized_______ofthepavementsurface.II.AnswerthefollowingquestionsinEnglish.1.Howmanytypesofdistresscanoccurinasphaltpavement?2.WhatisthereasonforthetensilestressesdevelopingwithintheHAMmaterialinthe“ThermalCracking"paragraph?上一页下一页返回Exercises3.Howmanyformsofshovingintheasphaltlayers?III.TranslatethefollowingsentencesintoChinese.1.ThistypeofcrackinghappensbecauseoftherepeatedbendingactionoftheHMAlayerwhentheloadisapplied.Thisgeneratestensilestressesthateventuallycreatecracksatthebottomoftheasphaltlayer.Cracksgraduallypropagatetothetopofthelayerandlaterprogressandinterconnect.Thistypeofdistresswilleventuallyleadtoalossofthestructuralintegrityofpavementsystem.上一页下一页返回Exercises2.AsthetemperaturedecreasestheHMAmaterialcontracts.Sincethematerialisrestrainedfrommovementduetothefrictionwiththeunderlyingmaterial，tensilestressesdevelopwithintheHAMmaterial.Ifthetensilestressexceedsthetensilestrengthofthematerial，thermalcracksdevelop.上一页返回Unit3一5HighwayDrainageSystemsandDesignOneofthemostimportantfactorsinbuildingaroadisdrainage.Ifeveryotheraspectofhighwaydesignandconstructionisdoneperfectlybutthedrainagedoesnotworkwell，theroadwillfailquickly.Fig.1isapictureofaroadlessthanayearoldthatdidnothaveadequatedrainageinthefilluponwhichthepavementstructurewasbuilt.Evenwhenthefailureisnotcatastrophic，waterinthehighwaystructurewillinevitablyleadtoprematurefailure下一页返回Unit3一5HighwayDrainageSystemsandDesign.Theyarecalled“highways”becauseearlyroadbuildersknewitwasnecessarytoconstructroadsabovethegroundandawayfromwater.Highwaydrainageandsubdrainagesystemsarecomplexandlocationspecific.Therearemanyfactorstoconsiderwhendesigningdrainagesystems.Mostofthedesignguidesandequationsavailablecomefromempiricalstudiesapplicableonlytolimitedgeographicregions.Yetprocessesderivedfromempiricalstudiesareoftenusedindiscriminately.上一页下一页返回Unit3一5HighwayDrainageSystemsandDesignItisimportanttobeawareofthesituationsforwhichaparticulardesignprocessisapplicable.Inallbutthesimplestapplications，acombinationofappropriatemethodsandsuitablematerialsisusedtomovewaterawayfromthepavementstructure.Erosioncontrolisanintegralpartofhighwaydrainage.Excessiveerosionmayplugculvertsleadingtosaturationofthepavementstructureandfailureofdrainagesystems，andfinallyresultingtopavementfailure。Environmentalconsiderationsthatthedictateerosionmusthecontrolled.上一页下一页返回Unit3一5HighwayDrainageSystemsandDesignSurfacedrainagemustbeprovidedtodrainprecipitationawayfromthepavementstructure.Inasimpleexample，crossslopedirectswatertotheshoulderwhereitflowsintoaditch，thendowntheditchtoaculvertandfinallyintoanexistingnaturaldrainage.Waterontheroadsurfacecanleadtohydroplaningandskiddingwhichmayresultinaccidentsandfatalities.Surfacedrainagedesignincludesthepredictionofrun-offinfiltration，aswellasopenchannelanalysisandculvertdesignformovementofsurfacewatertoconvenientlocationsornaturallyoccurringwaterpaths.上一页下一页返回Unit3一5HighwayDrainageSystemsandDesignDuringthedesignprocess，culvertsmustbeanalyzedtodeterminecapacity，control，andperformance.Liningsmustbeaddedtoopenchannelstominimizeerosionand，insomecases，todecreasethevelocity.Highwaydesignusesacombinationofsurfaceandsubsurfacedrainagesolutions.Subsurfacedrainageproblemsoftenleaddirectlytopavementfailure.Theymayalsoleadtoslopefailures，suchastheoneinFig.1particularlywhenfillsareconstructedonexistingslopesorwhenroadsareconstructedthroughsteepcuts.上一页下一页返回Unit3一5HighwayDrainageSystemsandDesignTherearemanysourcesofsubsurfacewaterandjustasmanysolutions.Forexample，longitudinalandtransversedrainsusedinconjunctionwithdrainageblanketscanremovegroundwaterandwatermeltingfromicelenses.Subsurfacedrainagedesignhasprogressedrapidlyinrecentyears，leadingtoincreasedavailabilityofproductsandimprovedpavementperformance上一页下一页返回Unit3一5HighwayDrainageSystemsandDesign.Subsurfacedrainagethatremovesexcesswaterfromthepavementstructureincreasestheperformanceandlifeofapavementsectionbuttheyarenoteconomicallyfeasibleinallsituations.Propercost-benefitanalysisshouldbeperformedbeforedrainagesystemsareinstalled.Selectingadesignapproachforwaterflowrequiressoundengineeringjudgment.Consequencesandlikelihoodoffailureandeconomicconstraintsarethemainconsiderations.上一页下一页返回Unit3一5HighwayDrainageSystemsandDesignTemporaryconstructiondrainagefacilitiesaredesignedtoalowerflowratesincetheprobabilityof,forexample，a50yearfloodisslimduringthedurationofconstruction.Permanentfacilitiesontheotherhandaremuchmorelikelytosuffera50-yearflood.Onemustuseamoreconservativedesignapproachwhenputtingplanstogetherforacriticalroadwaythanforaroadthatcaneasilybebypassed.上一页下一页返回Unit3一5HighwayDrainageSystemsandDesignTheonlyroadtoresidencesismorecriticalthantheonlyroadtoagravelpit.Selectingadesignflowisacriticalchoicethatmustbemadeearlyinthedesignprocess.Thesedecisionsdonoteasilylendthemselvestorigorousengineeringanalysisbuttheymustbemadewithconsiderablecareandforethought.上一页下一页返回Unit3一5Highway