电力水利 外文文献 文献翻译 英文文献 涵洞设计.docx
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电力水利 外文文献 文献翻译 英文文献 涵洞设计.docx
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电力水利外文文献文献翻译英文文献涵洞设计
CulvertDesign
Introduction:
Culvertshavebeenutilizedforthousandsofyearsasameanstotransmitwaterunderwalkwaysorroads. Often,aculvertissimplyinstalledwithoutmuchthoughttohowmuchwateritneedstoconveyunderextremeconditions. Ifaculvertcannotconveyalloftheincomingwater,thenthewaterwillflowoveroraroundthepipe,orsimplybackupbehindtheculvertcreatingapondorreservoir. Ifanyoftheseconditionsareunacceptable,thentheproperculvertdiameterandnumberofculvertsmustbeselectedpriortoinstallationinordertoconveyalloftheanticipatedwaterthroughthepipe(s). Thiscalculationhelpsthedesignersizeculvertsaswellaspresentaheadwaterdepthvs.dischargeratingcurve.
TheLMNOEngineeringcalculationisprimarilybasedonthemethodologypresentedinHydraulicDesignofHighwayCulvertsbyNormann(1985)andpublishedbytheU.S.DepartmentofTransportation'sFederalHighwayAdministration. ItisalsoknownasHDS-5(HydraulicDesignSeriesNo.5). HDS-5focusesonculvertdesign. Culvertdesignisusuallybasedonthemaximumacceptabledischarge-thustheHDS-5methodologyisgearedtowardculvertsflowingfullwithwaterpossiblyflowingovertheroadabovetheculvert. InadditiontoprogrammingtheHDS-5methodology,LMNOEngineeringwishedtocomputeheadwaterdepthsforlesserflows. Therefore,inadditiontotheHDS-5methodology,wehaveaddedtheManningequationforculvertsflowingpartiallyfull. TheHDS-5methodologyalsoassumesthattheuserknowsthetailwaterdepth(Yt)beforeusingthemethodology. ThoughYtcanbefoundbyfieldmeasurements,itisoftencomputedintheofficeusingManning'sequationbasedonbottomwidth,sideslopes,channelroughness,andchannelslope. Therefore,LMNOEngineeringaddedtheadditionalfeatureofabuilt-insubroutineforcomputingYtfortrapezoidalchannels. Notethatforthegraphingportionofourcalculation,Ytisre-computedfortheentirerangeofflows(Qt)shownonthegraph(unlesstheuserspecificallyinputsYt).
DesignCulvertAndDesignRequirementsforCulvertJoints
TheCulvertcommandletsyoumodelthebehaviourofaculvertundervariousconditionsofflow.Aculvertisashort,closed(covered)conduitthatconveysstormwaterrunoffunderanembankment,usuallyaroadway.Theprimarypurposeofaculvertistoconveysurfacewater,butproperlydesigneditmayalsobeusedtorestrictflowandreducedownstreampeakflows.Inadditiontothehydraulicfunction,aculvertmustalsosupporttheembankmentand/orroadway,andprotecttrafficandadjacentpropertyownersfromfloodhazardstotheextentpracticable.Mostculvertdesignisempiricalandreliesonnomographsandstandardprocedures.Thepurposeofthissectionistoprovideanoverviewofculvertdesignstandardsandprocedures.Becauseofthemanyvariablesinvolved,theprocessislargelyoneoftrialanderrorandMIDUSSdoesnotsuggestinitialfeasiblevaluesforthedesign.
Culvertdesigncanbecarriedoutforeithersteady,(i.e.timeinvariant)floworforaninflowhydrograph.Wheninflowisintheformofahydrographthehydraulicdesigncanbefollowedbyaroutingprocessthatshowstheattenuationoftheinflowhydrographcausedbypondingthatoccursupstreamoftheembankment.Insuchcasesthepeakoutflowfromthebarrelwillbelessthanthepeakinflowandyoucanrefinethebarreldesignforthereducedflowifdesired.Thedesignofaculvertshouldtakeintoaccountmanydifferentengineeringandtechnicalaspectsattheculvertsiteandadjacentareas.Thelistbelowpresentsthekeyconsiderationsforthedesignofculverts.
25-yeardesignstormevent.Theallowableheadwateristhedepthofwaterthatcanbepondedattheupstreamendoftheculvertduringthe100yreventwithcloggedconditions,whichwillbelimitedbyoneormoreofthefollowingconstraintsorconditions.
(1)Theallowableheadwatermustnotdamageupstreamproperty.
(2)Thepondingdepthistobenogreaterthanthelowpointintheroadgrade.
(3)Thepondingdepthistobenogreaterthantheelevationwhereflowdivertsaroundtheulvert.
(4)Headwaterelevationsshallbeestablishedtodelineatepotentialfloodzones.
YourCulvertdesigncanbeprecededbyaChanneldesignwitheitheratrapezoidalorcomplexcross-section.Whenthisisdonethecross-sectionalshapeofthechannelis‘inherited’bytheculvertdesignandusedtodescribetheflowcross-sectionupstreamoftheculvert.Iftheinflowisaflowhydrograph,achanneldesignmaybefollowedbyaChannelroutingprocessfromwhichthechanneloutflowformstheinflowtotheculvert.
Theculvertisassumedtobelocatedbelowasagpointinahighwayembankmentthatwillformanoverflowweirintheeventthatthebarrelflowcapacityissufficientlysurcharged.Flowseparationbetweenbarrelandweirflowisassumedtoberecombineddownstreamofthebarrel.Thecross-sectionofthebarrelconduitmaybeacircularpipe,arectangularbox,ahorizontalorverticalellipseorapipearch.Multiplebarrelsmaybeusedbutcross-sectionandotherhydraulicparametersareassumedtobethesameforallbarrels.
ⅠResearchProblemStatement
Traditionalmethodsforthestructuraldesignofburiedculvertsignoreculvertdistressemanatingfromlongitudinal,shearandgasketcircumferentialstressesatthejoint.Typically,itispresumedthatalignmentandbeddingstiffnessisuniforminthelongitudinaldirectionofthepipeandthegasketinsertionpressuresminimal.Accordingly,thestructuraldesignoftheculvertjointisbasedontheassumptionofin-planeloadingofthepipescrosssection,thatis,in-planebending(ovaling,yielding,andcracking)andin-planethrust(crushing&buckling).Longitudinalbendingmomentsandshearresultingfromnon-uniformloadingand/orvariationsinthebeddingsupportalongthelengthofthepipeorinternalringtensionforcesfromgasketsarenottraditionallyconsideredinthedesignprocess.
Contrarytotraditionaldesignpractice,fieldobservationsrevealthatlongitudinaleffectsmayberesponsibleforalargenumberofcostlyculvertfailures.Oneveryprevalentfailuremodeisinitiatedbylongitudinalvariationsinbeddingstiffnessresultingindifferentialsettlementofthepipe,whichinturngenerateslongitudinalculvertstressesandrelativejointmovements.IntherecentNCHRPProject4-24forHDPEplasticpipe,pipecrackingfromthejointintegrityofburieddrainagepipewasobservedtobeextremelysensitivetodifferentialsettlement.Thesuppositionisthatnon-uniformbeddingstiffnessincludedjointdistress,allowingleakageofgroundwaterandsoilintotheculvert,therebylosingvastamountsofsoilsupport,andultimately,collapseofpipeanddestructionofpavement.Inlikefashion,ifajointiscracked,shearedorover-deflectedandopenedduetocircumferentialtensionforcesfromagasket,theresultingleakagehasthesameeffect.
Anotherwell-knownlongitudinalproblemoccurswheneverculverts(concrete,corrugatedmetalorplastic)arejoinedintomanholesorheadwalls.Herethediscontinuityofsoilsupporttothestiffermanhole/headwallsupportisevenfurtheraggravatedbythesofterthannormalsoilsupportduetodeeperexcavationsandpoorcompactioninthevicinityofthemanhole/headwall.
Moreinstallationsarebecominggasketedinordertopreventinfiltrationofbackfillintotheculvert.Insertionforcefromthecompressionofarubbergasketduringtheconnectionoftwopipeexertstensileforcesonthebellandspigotendofthematingpipe.Ifthepipeisnotstructurallyadequatetoresisttheseforces,eitherthebellorspigotwilldeform,crackorshear.Theconsequentialopeningtothebackfillwillpermitfurtherunderminingoftheculvertandembankment.Conversely,areductionofconfiningstressovertimeinjointsduetothenatureofthevisco-elasticmaterialsutilizedforjointsmustalsobeassessedwithrespecttothetypeofgasketandpipeemployed.
Ithaslongbeenarguedthatlongitudinaldistressresultingfromlessthanperfectbeddingalignmentandstiffnessisaproblemthatshouldbecuredbyplacingtightercontrolsontheconstruction/installationmethods.Althoughitiscorrectthattheengineeringcommunityshould
Srivetoenforceproperconstructionprocedures,realityandlongexperiencehasshownthatconstructionwillalwaysbelessthanperfect.Thus,inordertoavoidcostlyrepairs,itisprudenttoincorporateintheculvertdesignprocesssomedesignrequirementstoaccountforlongitudinaldistressresultingfromlessthanperfectconstructionpractices.
ⅡObjective
Theobjectiveofthisresearchistodevelopjointdesignrequirementsforculvertjointstowithstandreasonablevariationsinbeddingstiffnessandothernon-uniformeffectsthatareanticipatedformactualconstructionandinstallationpractice.Allculvertmaterialsareincludedinthisobjective,e.g.corrugatedmetal,reinforcedconcrete,andplasticpipe.
Stepstoachievetheobjectiveinclude:
Surveyliteratureandexistingculvertinstallationstoquantifyallmechanismsandpracticesthatpromotelongitudinal,jointandsheardistressatculvertjoints.
Establishdesigncriteriaforeachfailuremechanism,pipetype,andassociatedjointtype,includingmaterialtimeeffects.Thesedesigncriteriaaretobebased,inpart,onthedevelopmentofanticipatedloadingconditionsfromresearchfieldandlaboratorytesting.
Developageneraldesignmodelapplicabletoallpipetypesandjoints(suchasbeamsegmentswithspecializedjointsonyieldingfoundation).Asensitivityanalysistoincorporatevariationsinmaterialproperties,stiffness,rotationalmovementandinsertionforc
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