微承压水作用下深基坑稳定的有限元分析.pdf

摘要基坑开挖是一个综合性的岩土工程问题,涉及到土力学、水力学等许多相关理论。土中水的问题是土压力计算的难点,环绕基坑的土体既是应力场、位移场,同时还是一个复杂的渗流场。从基坑事故的分析中可知,大多数事故直接或间接与地下水有关。天津市基坑工程中,对基坑有影响的土层范围及相应土层中影响基坑稳定的地下水的土层厚度小于50m,在此范围内除去表层地下水埋藏于地面下1-2m随季节有变化外,在地面下15—30m范围内,存在含水的粉、细砂层,此层被上覆粘性土层隔开,钻探时发现此层水表现一定承压性质,工程中常称之为微承压水。工程实践表明此承压水对基坑安全稳定危害较大,常造成基坑工程事故。在地铁工程中表现得尤为突出。地铁南楼基坑涌砂事故就是典型实例。本文在总结地下微承压水对工程危害的基础上,分析了承压水渗流对基坑工程的影响,尤其是支护上被动土压力的影响。编制极限平衡法计算程序,对基坑安全系数进行分析。利用PLAXIS有限元程序计算了考虑基坑中微承压水作用下支护结构变形和整体稳定,重点突出了承压水对有效应力和稳定性的影响,将各种计算方法的成果进行对比,绘制承压水影响下基坑周边和下部土质中的渗流场,结合工程实例进行分析,通过与实测值进行比较,得到了承压水影响下的基坑稳定分析的量化结果,为完善设计理论和工程决策提供了科学依据。分析成果表明,承压水的存在可明显降低有效应力和整体安全系数,在实际工程设计和施工方案的确定中需高度重视,以避免工程事故的发生。关键词:基坑工程、微承压水、渗流、有限元、安全系数 Abstract Foundations excavation is acomplicated geotechnical engineering is related tolotsofknowle如e on SoilMechanics magnitude of thewater’Sinfluence isdifficulty pute,but isveryimportant tothefoundations Soilaround thefoundationpit posed ofstressfield,displacements fieldandalso acomplex seepage beknown from many failureoffoundations thatmany ofthem are direct orindirect tothegroundwater. The scaleofgroundwater influence onfoundations’stablity inTianjin is not more than shallow groundwater changing withthe seasons below theground I=2meters,there are siltand fine sandlayers below theground 15-30meters,which were founded thewaterintheselayersexpresses some charactersofconfined water intheselayers iscalledmicro- thepractising themicor-artesian has agreat influence on thestability theunderground engineering isdevastating. The pipingphenomenon inNanlou subway stationisjust atypicalexample. Inthisartical,summarizing themicro-artesian’Sdamaging totheconstruction,1 will analyse thestability ofthefoundationunder theinfluenceofthemicro— discuss indetail theconfined water seepage’S influence on thefoundation,especially thepassive earthpressure on thesoftware—·PLAXIS,I analyse thebracing structure’S