非稳定渗流作用下基坑支护结构稳定性分析

【作者】 张庆伟；

【导师】 刘忠玉；

【作者基本信息】 郑州大学 ， 工程力学， 2007， 硕士

【摘要】 在地下水位较高的地区开挖基坑时，由于降水可使得基坑内外存在水头差，并且该水头差一般会随时间而变化，因此土体中将发生非稳定饱和-非饱和渗流。大量工程实践表明，渗流对基坑支护结构稳定性的影响十分显著，但目前有关考虑非稳定饱和-非饱和渗流对基坑性状影响的研究尚不多见。本文利用有限元方法模拟了由于基坑降水开挖引起的非稳定渗流，并以水泥土挡土墙为例，初步研究了非稳定渗流对基坑及其支护结构稳定性的影响，主要进展如下。1、在简要介绍非稳定饱和-非饱和渗流的有限元控制方程及定解条件的基础上，利用软件SEEP／W模拟了基坑在降水过程中的瞬态渗流场，分析了作用在水泥土挡土墙前后的水压力及墙底浮力在降水过程中的变化规律，并与静水压力和稳定渗流水压力进行了比较，从水压力方面证明了考虑非稳定渗流的必要性。2、基于库仑土压力理论的假定，利用水平层分析法，推导了考虑非稳定渗流时作用于挡土墙上的土压力强度的计算公式，并编制了Fortran程序，以求得土压力强度的非线性分布解及其合力的作用点位置。重点分析了土体渗透系数、内外摩擦角和降水方案等因素对侧压力分布形式及其作用点位置的影响。在此基础上，研究了降水过程中挡土墙的抗倾覆安全系数和抗水平滑动稳定安全系数的变化规律，并讨论了上述因素对二者的影响。数值分析表明，降水引起的渗流对挡土墙抗倾覆和抗水平滑动稳定性是有利的，按不考虑渗流计算设计是偏于安全的。3、联合应用软件SLOPE／W和SEEP／W，分析了降水过程中基坑整体稳定安全系数的变化规律，并探讨了降水方案、渗透系数对整体稳定性的影响。结果表明，与渗流对挡土墙的抗倾覆和抗滑移稳定性的有利影响正好相反的是，非稳定渗流对基坑整体稳定性是不利的，如果不考虑渗流将使得计算结果偏于危险。因而在设计时只有充分考虑地下水渗流的影响，才能保证设计的合理性。更多还原

【Abstract】 The excavation in the zone of high groundwater table will induce saturate-unsaturated unsteady seepage due to the difference and variation of water head between the both sides of retaining walls of foundation pit. It has been shown by a great amount of engineering practical that the influence of the seepage on the stability of retaining structure is significant. However, there is little relevant study made so far. In this dissertation, the actual unsteady seepage fields in the process of lowering the ground water level is simulated by using the finite element method (FEM), the influence of the unsteady seepage on the stability of retaining structures of foundation pit, for example, the cement-soil retaining wall, is systematically and thoroughly researched. The main original work and results are as follows:1. Based on the fundamental theories of unsteady seepage and finite element, the condition of water pressure acting on the retaining wall is discussed by simulating the unsteady seepage field using the software SEEP/W. The distinct comparisons between the present results with the unsteady seepage and those with the steady seepage or without the seepage indicate that the unsteady seepage condition is very important for the water pressure.2. On the basis of Coulomb’s concept, the calculating formulae for the soil pressure acting on the retaining structure with the unsteady seepage are obtained by using the method of level-layer analysis, and the relevant Fortran programs are developed to find the theoretical answers to the nonlinear distribution of the earth pressure and the position of the application point of the resultant earth pressure. The influence of some parameters such as the project of lowering the ground water level, the coefficient of permeability, the internal friction angle of soils and the angle of wall friction on the distribution of the earth pressure and the application point of its resultant is mainly discussed. Then, the influence of the aforementioned parameters on the safety factors of resisting the wall’s overturn and horizontal slipping in the process of lowering the ground water level is further investigated. Numerical results show that the seepage due to lowering of the ground water level is advantageous to the security of the retaining wall and it is conservative if the seepage is taken no account in the design practice.3. By using the software SLOPE/W and SEEP/W, the condition of the global stability of foundation pit and the influence of the project of lowering the ground water level and the coefficient of permeability on its safety factor are researched. The computed results show that, opposite to its favorable influence on the stability of the wall’s overturn and horizontal slipping, the unsteady seepage is adverse to the global stability of foundation pit, and therefore it is dangerous if the seepage is taken no account in the design practice. In a word, the importance of the seepage should be rightly understood in the deep foundation engineering.更多还原