【作者】 包旭范；

【导师】 吕和林；

【作者基本信息】 西南交通大学 ， 岩土工程， 2008， 博士

【摘要】 软土地基超大型基坑工程的关键所在是基坑的变形控制,变形控制主要与围护体系选型和施工方法的选择有关,其涉及到许多因素,因此需要通过研究才能获得合理的设计和施工参数。本文以铁路上海南站南广场主基坑为背景,通过室内土工离心模拟试验、数值分析计算方法结合现场实测资料针对围护体系和施工方法带来的相关工程问题进行系统研究,涉及土坡在施工期的蠕变变形规律、影响土体蠕变的因素、预留土台的大小和作用以及土块的跳挖方法,主要研究工作、成果和结论包括:(1)根据软土超大型基坑的变形特点,研究分析了围护体系和施工方法的选择及其所带来的问题,指出了软土超大型基坑变形控制的关键在于合理的设计和施工参数。(2)通过离心试验对土坡的蠕变变形进行了模拟分析,在此基础上,根据土体的剪切蠕变特性、采用等效应力和时间的分维数描述土体的蠕变方程,结合现有的上海地区软土的蠕变试验曲线,拟合出蠕变计算参数;采用时间硬化模型对该基坑放坡和围护相结合的施工过程中土坡的蠕变变形、剪应力松弛和蠕应变变化规律进行了计算分析,结果表明采用幂指数形式的蠕变方程进行软土放坡开挖基坑土坡长期暴露下的蠕变计算是可行的。此外,对临近基坑的超载大小和位置、围护结构背后的防渗墙的宽度和高度、中板支撑与否对土坡蠕变的影响规律进行了计算分析,为超大型软土基坑施工参数的优化设计提供了依据。(3)为有效控制超大型基坑施工过程中的变形,针对比选工法后带来的预留土台宽度、开挖顺序等问题进行了离心模拟试验和数值计算分析。研究分析了预留土台在控制大面积软土基坑变形中的作用机理,推导了土台临界宽度的计算公式以及连续墙水平变形与土台宽度之间的关系;采用有限元模拟方法,通过基坑变形、连续墙的受力和变形对比,计算分析了中心岛土块、预留土台的开挖顺序,对于软土超大型基坑中心岛法结合部分逆作的施工方法具有一定的指导意义。(4)根据前述研究结果,结合大量工程经验,总结提出了三种较适合于软土超大型基坑的设计施工方案,并从控制开挖对周围环境的影响和基坑自身的变形控制两个方面,分析总结了软土地基超大型基坑变形控制的一些关键措施。更多还原

【Abstract】 The key of super-large foundation pit engineering in soft soil is to control the deformation, the deformation control is mainly related with the selection of supporting and bracing system and construction method, which involved many factors. therefore we need to do some research so as to acquire the reasonable design and construction parameters. With the background of main excavating foundation pit of Shanghai Nan railway station of South Square project ,this paper studied systemically the problems brought by supporting and bracing system and construction method through centrifuge model test, numerical analysis calculation combined with actual data, the creep deformation rules of slope during the construction process, factors that affect the creep deformation, dimension and function of pre-remained mound also with the stepped excavation method of clod are all involved in the problems. The research work done and results include as follows:(1) According to the characteristic of deformation of foundation pit in soft soil, problems brought by selection of supporting and bracing system and construction method were studied, thee keys of the deformation control of foundation pit in soft soil was presented,which were reasonable design and construction parameters .(2) The centrifuge model test was used to simulate and analyze the creep deformation of slope, based on the test, the creep equation was described by fractal dimension of equivalent stress and time according to the shear creep properties of soil, the calculated creep parameters were fitted combing with experimental creep curves of soil in Shanghai; the time hardening model was used to calculate the creep deformation、shear stress relaxation and creep strain change rules of slope during the construction process based on the combination of excavating slope and supporting, The results shows that it is feasible to adopt exponential creep equation to calculate the long-exposure creep of cutting slope in soft soil foundation pit. Besides, the variation rules of the creep of slope were calculated and analyzed under the influence of factors which include the amount and location of overload near the foundation pit、the width and height of leakageproof wall behind the supporting structure and whether it has middle board as a brace, these studies provide gist to the optimizing design of construction parameters. (3) In order to control the deformation of large excavated foundation pit during the construction process, in this paper, centrifuge model test and numerical calculation analysis was done aimed at the problems of the width of pre-remained mound、the construct order of clod and etc, which were brought by the selected construction method. The action mechanism of pre-remained mound in the deformation control of large excavated foundation pit in soft soil was studied, thereby the calculation formula of critical width and the relationship between horizontal deformation of wall and the mound width were deduced; the FEM was used to calculate and analyzed the construction order of central island clod and pre-remained mound through comparison of the deformation of foundation pit、the inter force and deformation of underground diaphragm wall, the results in a sense be guidance to the central island with partly top-down construction method in large excavated foundation pit in soft soil.(4) Based on the results of chapaters before,combined with much experience in projects, three designing and construction schemes were presented and somekey measures to control the deformations of super-large foundation pit engineering in soft soil were analyzed and summarized from two aspects,which are the control of influence to surroundings and the deformation of foundation pits.更多还原