【作者】 曹力桥；

【导师】 郑刚；

【作者基本信息】 天津大学 ， 结构工程， 2008， 硕士

【摘要】 国内外岩土工作者对基坑工程的研究已取得了许多重要的成果,基坑工程乃至超深超大基坑在设计、施工上也积累了不少宝贵的经验。随着经济的发展,沿海地区的许多高大建筑只能修建在软土上,导致地基的地质条件变得比较恶劣;在软土区另一个显著的问题就是基坑开挖过程中当开挖面在地下水位以下时会伴随着降水问题。已有研究证明,土的卸荷可产生负的孔隙水压力。同时,基坑降水又会使地下水产生渗流,这两个因素会导致作用在地下连续墙上的土压力随时间产生变化。本课题将研究开挖卸荷产生的孔隙水压力的消散,以及渗流固结耦合作用等因素造成的土压力变化,并对固结效应在分析深基坑变形的方法做一定的探讨。提出考虑孔隙水压力固结、渗流等的土压力计算方法和地面沉降分析的方法。在基坑开挖过程中,孔隙流体压力会逐渐降低,将土层内有效应力的变化,导致土体产生固结变形。土体的固结又造成土体的渗透性参数的变化。在系统归纳、总结前人研究成果的基础上,采用机理分析、算例比较,对经典土压力理论以及对考虑水土相互作用的土压力进行简单介绍和总结。在Prandtl理论基础上推导考虑渗流力的基坑的土压力的改进模型,并利用MATLAB编制适用的基坑挡土墙土压力程序,进行土压力非线性计算理论的研究。总结出一种能反映位移、时间效应的非线性土压力模型,同时系统开展基坑水土压力分布模式及大小的机理分析。并在渗流固结耦合理论的基础上,分析软土地区深基坑的变形特性,包括坑底隆起和周围地层沉降的性状及其影响因素。分析了工程降水对深基坑土体的预压加固作用,并开展对固结效应及挡墙变形引起的基坑变形的研究。并进行了基坑工程降水引起的地表沉降公式的推导。同时用商用数值软件ABAQUS建立两个基坑模型,一个模型是基于总应力法不考虑水的作用,另一个是基于有效应力法考虑基坑降水的流固耦合模型。两者分析结果进行对比,得出基坑开挖降水过程中渗流固结对基坑水土压力和周围地面沉降、基坑底部回弹及地下连续墙变形的影响规律,基坑渗流、工程降水引起围护结构土水压力的变化及地下水对基坑工程支护结构上主、被动土压力的影响,并得出在计算土压力时候,渗流力不可忽略的结论。更多还原

【Abstract】 So far Geotechnical engineers at home and abroad have made many important achievements on foundation pit. Precious design and construction experiences of excavation even ultra-deep and ultra-large foundation pit have also been accumulated. However, with economic developing, large quantity of tall buildings or some important structures have had to build on the soft soil in the areas of Coastal, which leads the foundation geological conditions to become worse. Another significant problem in the soft soil area is that the process of excavation accompanied with the dewatering problems when the excavated surface is under the underground water lever. It has been proved that the earth can produce negative pore water pressure when the pit is excavating and the soil mass excavation unloading. At the same time, dewatering in the pit will also bring about seepage of underground water; these two factors would lead the earth pressure changing over time on the concrete diaphragm wall. This paper deals with that dissipation of excess pore water pressure due to unloading effects which lead by the excavating, and earth pressure changes which is caused by the factors of seepage coupled with the consolidation also called Fluid-solid coupling effects. Do some researches on deformation law of foundation pit which is caused by consolidation. Based on the results, then to get the methods of calculating on the earth pressure and analysis the ground subsidence which considering the fluid-solid coupling effects.In the process of excavation, pore fluid pressure will reduce gradually, and the effective stress in the soil will increase, which leads soil to consolidation settlement and deformation. The consolidation of soil in foundation pit will make the soil permeability change. The article concludes the foundation pit in system, sums up the results of precious studies on the basis of mechanism analysis, examples of comparison. And do a brief introduction and conclusion to the classic earth pressure which is considering fluid and soil interaction. Derivation improved model of the earth pressure which considering the seepage force in foundation pit base on the Prandtl theory. And prepare to use the MATLAB software to write the earth pressure programs for retaining wall in deep excavation, which is to calculate the nonlinear earth pressure in theoretical study. Then to sum up a non-linear model of earth pressure that can reflect displacement and time-effects. At the same time conducts distribution pattern and size of the water pressure and earth pressure in excavation. Based on theoretical analysis of coupling seepage with consolidation, this paper have been made analysis deformation which includes the pit bottom heaving and the character of settlement and its impact factor in deep excavation at the soft soil area. It analyzes the role of soil reinforcement due to the pre-pressure and changing of earth pressure on the retaining wall when dewaters in the foundation pit, and also construes undermine caused by seepage.While carries out the consolidation effects and deformation of the retaining wall in foundation pit. Do the surface subsidence formula derivation due to dewatering and exaction in the excavation works.At the same time, using the general commercially software ABAQUS to found two pit models, one is based on the total stress theory without considering the role of water, another pit method is based on effective stress theory with considering the fluid-solid interaction effect due to dewatering and excavation. Comparison the two results which obtain by finite element analysis, receiving the changing disciplines of water-earth pressure, ground settlement surrounding the foundation pit, pit bottom heaving and the deformation of concrete diaphragm wall, which deduce by the effects of seepage coupled with consolidation during the process of foundation pit excavating accompanying with dewatering. And the change of the water pressure on the retaining structure and analysis active or passive earth pressure on the retaining structure which are also on the impact of groundwater seepage and pit supporting structure. Then get the conclusion is that the seepage force can not be ignored.更多还原