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混凝土重力坝基础流体力学行为分析摘要一个在新的和现有的混凝土重力坝的滑动稳定性评价的关键要求是对孔隙压力和基础关节和剪切强度不连续分布的预测本文列出评价建立在岩石节理上的混凝土重力坝流体力学行为的方法该方法包括通过水库典型周期建立一个观察大坝行为的数据库,并用离散元法(DEM)数值模式模拟该行为一旦模型进行验证,包括岩性主要参数的变化,地应力,和联合几何共同的特点都要纳入分析斯威土地,Albigna大坝坐落在花岗岩上,进行了一个典型的水库周期的特定地点的模拟,来评估岩基上的水流体系的性质和评价滑动面相对于其他大坝岩界面的发展的潜力目前大坝基础内的各种不同几何的岩石的滑动因素,是用德国马克也评价模型与常规的分析方法的裂纹扩展模式和相应扬压力和抗滑安全系数的估计沿坝岩接口与数字高程模型进行了比较得出,由目前在工程实践中使用的简化程序结果发现,在岩石节理,估计裂缝发展后的基础隆起从目前所得到的设计准则过于保守以及导致的安全性过低,不符合观察到的行为因素关键词流体力学,岩石节理,流量,水库设计简介评估抗滑混凝土重力坝的安全要求的理解是,岩基和他们上面的结构是一个互动的系统,其行为是通过具体的材料和岩石基础的力学性能和液压控制大约一个世纪前,Boozy大坝的失败提示工程师开始考虑由内部产生渗漏大坝坝基系统的扬压力的影响,并探讨如何尽量减少其影响今天,随着现代计算资源和更多的先例,确定沿断面孔隙压力分布,以及评估相关的压力和评估安全系数仍然是最具挑战性的我们认为,观察和监测以及映射对大型水坝的行为和充分的仪表可以是我们更好地理解在混凝土重力坝基础上的缝张开度,裂纹扩展,和孔隙压力的发展图.1流体力学行为
(一)机械;
(二)液压本文介绍了在过去20个来自Albigna大坝,瑞士,多年收集的水库运行周期行为的代表的监测数据,描述了一系列的数值分析结果及评估了其基础流体力学行为比较了数值模拟和实际行为在实地的监测结果在此基础上比较了一系列的结论得出了基本孔隙压力在节理岩体的影响可以考虑在其他工程项目,认为那里的岩石节理流体力学行为应予以考虑这些项目包括压力管道,危险废物处置,以及对流动行为的控制断面沿岩石地质遏制依赖的其他情形流体力学的行为自然对先进设备,机械和个别岩石节理的水力特性的概要一个对岩石联合流体力学行为的更详细的描述中可以在阿尔瓦雷斯(1997年)和阿尔瓦雷斯(1995年)和在实验室调查和数值模拟模型进行了乌鸦和Gale
(1985),Gentier(1987年),江崎等人
(1992),和其他人中发现该水力行为的联合可以表示为非线性应用之间的有效正应力双曲线关系,并联合,在装卸,重大的联合封发生在低有效正应力的地方该单位的压力关闭规模迅速下降,但是,随着应力水平增加双曲线的定义是由初始切线刚度定义,,并联合最大的渐近结束,这种关系也是非线性,迟滞的卸载条件,直到成为有效正应力为零(图1a)和的价值观通过对实验数据的回归分析来估计的对于自然和花岗岩裂隙,这些参数都是相互关联的下列限制范围之间的阿尔瓦雷斯等(1995年)这里的单位是Mpa/m,的单位是m粗糙关节展览最大规模的联合最高和最低的封闭初始关节僵硬,关节光滑而有最低和最大的岩石的共同特点是液压行为之间的线性关系液压孔径,,它控制流动规模,关闭和机械联合,,用于水平应力液压孔绘制相应的联合与关闭(图1b),以获取拦截线,,起始水力孔径,边坡系数和耦合,,而“刻画了联合流体力学行为,i.e,两者在液压机械孔径由于孔径的变化变化的关系,鉴于其中是剩余的水力孔径对于给定的岩石节理,两者之间是有粗糙度及耦合系数的关系,因为f的分布和沿关节面流道曲折而定对于理想的平行板,以在整个关节面单流道,f=
1.
0.对于集中流道蜿蜒穿过关节面,f
1.0因此,用经典的立方定律表示通过岩石节理流率其中Q是流量;是水的单位重量;是沿岩石节理头部下降;μ是水(
11.005×p•s)的动力粘度;是联合液压孔径而G是形状因子,由水流几何而定直流地下G=W/L(其中W和L是宽度和长度,分别联合),为不同径向流,G=2π/lnre/其中和re分别为内外圆柱面半径裂隙岩体渗透性随深度变化另外,岩体等效渗透,公里,可以以同样的形式作为修改后的定律,或在液压口径计算,同样的形式占关节间距,S:在裂隙岩体渗透性的变化,由于覆盖层和围应力,计算
[1]-
[3]岩体的渗透性,K,理论的深度关系的结果高达1000米,采用当量
[5]载于图2孔的液压随覆盖减少强调在岩体渗透性,随深度的增加,从cm/s到附近的水面在600厘米深度/秒-1000米的结果估计岩体渗透性得到假设f=
1.0,=和=10,这是在实验室测试中取得的值与(阿尔瓦雷斯等al.1995)相似,巴西在这一测试中描述位置的花岗岩编队部分覆盖层讲估计使用的是
26.0kN/m3单位重量在这种情况下,它的假设是横向和纵向应力大致相同(土压力系数Ko=
1.0),这也被认为将在巴西的测试位置的火成岩地层的代表,但其他价值在原位强调可以预计,如对高e.g.forKo
1.0,垂直节理将有较大的渗透率在深露天矿在巴西花岗岩开采项目获得的场渗透率测量在图2中绘制与理论的关系比较联合间距从钻孔岩心观察值都在数米范围内,从而产生了一个5米间距是常数的计算假设阿霍的价值在300-1000μm范围被用来确定公里=f的理论关系(z)的,其中Z是深度,以实地测量和比较这两个钻孔测量值相对渗透率在100至200米深处的高,可能表明的一个区或剪切节理岩带更多的存在所测岩石渗透率稳步下降,在深度的增加,然而,它们的值与对应的岩体渗透性的理论与模型估计趋势良好典型液压孔径400-500μm的和后关节僵硬=10V的双曲线关系,与三菱商事和=似乎同意这些结晶岩体观测场行为良好图.
2.裂隙岩体渗透性随深度的关系虽然真正的流体力学节理岩体的行为是需要考虑具体的地点和地质因素,该方法提供了一个框架,但在设计阶段,其中岩石资料尚未提供大规模渗透Hydromechanical____ysisofflowbeh__iorinconcretegr__itydamfoundationsAbstract:Akeyrequirementintheevaluationofslidingstabilityofnewandexistingconcretegr__itydamsisthepredictionofthedistributionofporepressureandshearstrengthinfoundationjointsanddiscontinuities.Thispaperpresentsamethodologyforevaluatingthehydromechanicalbeh__iorofconcretegr__itydamsfoundedonjointedrock.Themethodologyconsistedofcreatingadatabaseofobserveddambeh__iorthroughouttypicalcyclesofreservoirfillingandsimulatingthisbeh__iorwithadistinctelementmethodDEMnumericalmodel.On__themodelisvalidatedvariationsofkeyparametersincludinglithologyinsitustressjointgeometryandjointcharacteristicscanbeincorporatedinthe____ysis.Asite-specificsimulationofatypicalreservoircyclewascarriedoutforAlbignaDamSwitzerlandfoundedongraniticrocktoassessthenatureoftheflowregimeintherockfoundationsandtoevaluatethepotentialforslidingsu_____sotherthanthedam–rockinte_____todevelop.ThefactorofsafetyagainstslidingofvariousrockwedgesofdifferinggeometrypresentwithinthedamfoundationswasalsoevaluatedusingtheDEMmodelandconventional____yticalpro__dures.Esti__tesofcrackpropagationpatternsandcorrespondingupliftpressuresandfactorsofsafetyagainstslidingalongthedam–rockinte_____obtainedwiththeDEMwerealsocomparedwiththosefromsimplifiedpro__durescurrentlyusedinengineeringpracti__.Itwasfoundthatinajointedrockfoundationupliftesti__tesaftercrackdevelopmentobtainedfrompresentdesignguidelinescanbetooconservativeandresultinfactorsofsafetythataretoolowanddonotcorrespondtotheobservedbeh__ior.Keywords:Hydromechanicaljointedrockflowdamdesign.Introduction:Evaluatingthesafetyofconcretegr__itydamsagainstslidingrequiresanunderstandingthatrockfoundationsandthestructureabovethemareaninteractivesystemwhosebeh__ioriscontrolledbythemechanicalandhydraulicpropertiesofconcrete__terialsandrockfoundations.Abouta__nturyagothefailureofBoozyDamprompteddamengineerstostartconsideringtheeffectofupliftpressuresgeneratedbyseepagewithinthedam–foundationsystemandtoexplorewaystominimizeitseffect..Todaywithmoderncomputationalresour__sandmuchmorepre__dentitisstillmostchallengingtodeterminethepore-pressuredistributionalongfoundationdiscontinuitiestoassesspertinentstressesandevaluatefactorsofsafety.Itisouropinionthatobservingandmonitoringthebeh__ioroflargedamsonwell__ppedandadequatelyinstrumentedfoundationscanbringimportantinsightsforabetterunderstandingoffactorscontrollingjointopeningcrackpropagationandpore-pressuredevelopmentinfoundationsofconcretegr__itydams.Fig.
1.Hydromechanicalbeh__iorofnaturaljoints:amechanical;bhydraulic.Thispaperpresentsbeh__iorrepresentativeofcyclesofreservoiroperationinthelast20yearscollectedfrommonitoreddataofAlbignaDamSwitzerlandandalsodescribestheresultsofaseriesofnumerical____ysescarriedouttoassessthehydromechanicalbeh__iorofitsfoundations.Comparisonsare__debetweenresultsofnumericalmodelingandtheactualbeh__iormonitoredinthefield.Basedonthesecomparisonsaseriesofconclusionsaredrawnregardingbasicpore-pressurebuildupmechani__sinjointedrock__sseswithimplicationsthat__ybeconsideredinotherengineeringprojectswherethehydromechanicalbeh__iorofjointedrockshouldbeconsidered.Suchprojectsincludepressuretunnelshazardouswastedisposalandothersituationsdependentongeologiccontai__entcontrolledbyflowbeh__ioralongrockdiscontinuities.Hydromechanicalbeh__iorofnaturaljointsAbriefsum__ryofthestate-of-the-artofmechanicalandhydraulicbeh__iorofindividualrockjointsispresentedhere.AmoredetaileddescriptionofrockjointHydromechanicalbeh__iorcanbefoundinAlvarez1997andAlvarezetal.1995andininvestigationsinlaboratoryandnumericalmodelsimulationscarriedoutbyR__enandGale1985Gentier1987Esakietal.1992andothers.Themechanicalbeh__iorofthejointcanberepresentedbyanonlinearhyperbolicrelationshipbetweentheappliedeffectivenor__lstress,andjointclosureDuringloadingsignificantjointclosuretakespla__atloweffectivenor__lstresses.The__gnitudeoftheclosureperunitofstressdecreasesrapidlyhoweverasthestresslevelincreases.Thehyperbolaisdefinedbytheinitialtangentstiffnessandtheasymptote__ximumjointclosure.Thisrelationshipisalsononlinearandhystereticfortheunloadingconditionuntileffectivenor__lstressesbecomezeroFig.1a.Thevaluesofandareesti__tedbyregression____ysisonexperimentaldata.Fornaturalandindu__dfracturesingranitetheseparametersareinterrelatedandrangebetweenthefollowinglimitsAlvarezetal.1995:WhereisinMpa/mandisinmRoughjointsexhibitthelargestjoint__ximumclosureandthelowestinitialjointstiffnesswhereas__oothjointsh__ethelowestandthelargestThehydraulicbeh__ioroftherockjointischaracterizedbythelinearrelationshipbetweenhydraulicaperturewhichcontrolsthe__gnitudeofflowandmechanicaljointclosurewhichdependsonstresslevels.HydraulicaperturesareplottedversustheircorrespondingjointclosureFig.1btoobtainthelineinter__ptinitialhydraulicapertureandthecoupledslopecoefficientwhichcharacterizesthehydromechanicalbeh__iorofthejointi.e.therelationshipbetweenchangesinhydraulicapertureduetochangesinmechanicalaperturegivenbyWhereistheresidualhydraulicaperture.Foragivenrockjointthereisarelationshipbetweenroughnessandthecoupledcoefficientbecausefdependsonthedistributionandtortuosityofflowchannelsalongthejointsu_____.Foridealparallelplateswithasingleflowchannelalongtheentirejointsu_____f=
1.
0.Forcon__ntratedflowchannelsmeanderingacrossthejointsu_____f
1.
0.Hen__theclassiccubiclawexpressesflowratethrougharockjoint:WhereQistheflowrate;istheunitweightofthewater;istheheaddropalongtherockjoint;μisthedynamicviscosityofthewater
1.005×Pa·s;Isthejointhydraulicaperture;andGistheshapefactorwhichdependsonthegeometryofflow.ForstraightflowG=W/LwhereWandLarethewidthandlengthrespectivelyofthejoint;andfordivergentradialflowG=2π/lnre/whereandrearetheboreholeandexternalcylindricalsu_____radiusesrespectively.Jointedrock__sspermeabilitychangewithdepthAlternativelytherock__ssequivalentpermeabilitykmcanbeexpressedinthesameformasthemodifiedcubiclaworintermsofhydraulicaperturetoaccountforspacingofthejointsS:Changesinjointedrock__sspermeabilityduetooverburdenandconfiningstresseswerecalculatedusingeqs.
[1]–
[3].Theresultsofatheoreticalrelationshipofrock__sspermeabilitykfordepthsupto1000musingeq.
[5]arepresentedinFig.
2.Thereductionofhydraulicapertureswithincreasingoverburdenstressesresultsinarock__sspermeabilitythatdecreaseswithanincreaseindepthfromcm/snearthesu_____tocm/satdepthsof600–1000m.Therock__sspermeabilityesti__teswereobtainedassumingf=
1.0=and=10whicharerepresentativeofthevaluesobtainedinlaboratorytestscarriedoutingraniticfor__tionsAlvarezetal.1995similartothoseoftheBraziliantestlocationdescribedinthissection.Overburdenstresseswereesti__tedusingaunitweightof
26.0kN/m
3.InthiscaseitwasassumedthathorizontalandverticalstressesareaboutthesamecoefficientofearthpressureatrestKo=
1.0whicharealsoconsideredtoberepresentativeoftheigneousfor__tionsattheBraziltestlocationbutothervaluesofinsitustressescouldbeesti__tede.g.forKo
1.0verticaljointswouldh__elargerpermeabilities.FieldpermeabilitymeasurementsobtainedinPackertestsatadeepopen-pitminingprojectingraniticrockinBrazilarealsoplottedinFig.2forcomparisonwiththetheoreticalrelationship.Valuesofjointspacingobservedfromboreholecoresareintherangeofafewmetersandthusaconstantspacingof5mwasassumedinthecomputations.Valuesofahointherangeof300–1000μmwereusedtodeterminethetheoreticalrelationshipsofkm=fzwherezisthedepthandcomparewithfieldmeasurements.Measuredpermeabilityvaluesinthetwoboreholesarerelativelyhighatdepthsbetween100and200mprobablydenotingthepresen__ofashearedzoneorazoneofmorejointedrock.Themeasuredrockpermeabilitiesdecreasesteadilywithanincreaseindepthhoweverandtheirvaluescorrespondwellwiththetheoreticaltrendofrock__sspermeabilityesti__tedwiththemodel.Typicalhydraulicaperturesof400–500μmandjointstiffnessfollowingahyperbolicrelationshipwith=10Vmcand=seemtoagreewellwithobservedfieldbeh__iorforthesecrystallinerock__sses.Fig.
2.Theoreticaljointedrock__sspermeabilityrelationshipwithdepth.AlthoughrealHydromechanicalbeh__iorofjointedrock__ssesissitespecificanddependsongeologicfactorswhichneedtobetakenintoaccounttheproposedapproachprovidesaframeworktoesti__terock__sspermeabilityduringdesignstageswhereinfor__tionisnotyet__ailable.。