软土地区深基坑坑底抗隆起稳定性分析

发布时间：2018-07-20 12:38

【摘要】：我国长江流域及沿海地区多为软土平原地区,这些地区土质承载力低、地下水位高,容易发生基坑失稳事故,基坑隆起是基坑失稳的常见形式之一。在深基坑工程安全评估中,深基坑坑底抗隆起破坏分析具有重要参考价值,同时也是基坑工程设计中的一项重要内容。深基坑坑底抗隆起稳定性分析方法主要有三种：极限平衡法、极限分析法和数值分析法。本文以极限平衡法中的圆弧滑动模式为理论基础,认为现有圆弧滑动简化公式应考虑分层土的土体参数、挡墙参数以及加固土参数的影响,提出了考虑这三类影响因素的深基坑坑底抗隆起稳定性安全系数计算公式,并通过力矩相等原则推导了等效土体参数的取值方法。同时,分析了圆弧滑动模式和极限承载力模式计算公式的适用条件。通过对工程实例的计算,验证了不同公式在不同条件下的适用性和准确性。然后,对Prandtl极限承载力模式计算公式及圆弧滑动模式公式,利用MATLAB进行编程,把土体参数、挡墙参数以及加固土参数对深基坑坑底抗隆起稳定性的影响程度进行对比分析。最后,通过极限承载力模式结合Vesic理论,推导了存在软弱下卧层深基坑坑底抗隆起稳定安全系数计算公式,并提出了可以不考虑软弱下卧层影响的临界厚度概念,分析了不同参数影响下临界厚度的大小。得到以下几项主要研究成果： (1)本文推导公式与国家规范公式对比,考虑了基坑内外主被动土压力系数的区别、加固土的影响以及挡墙提供弯矩的作用,并详细推导了等效土体参数的取值方法。通过工程算例,分析对比了本文推导公式与其他公式计算结果的区别。当挡墙底部以上土质较差时,本文推导公式比Prandtl极限承载力模式公式更加合理。 (2)在深基坑坑底抗隆起稳定性各影响因素中,土体内聚力、土体内摩擦角及土体重度和挡墙插入比对深基坑坑底抗隆起稳定性影响很大。通过计算分析对比,各参数影响程度从大到小排序为：土体内摩擦角,土体重度,土体内聚力,挡墙插入比,加固土无侧限抗压强度,地面超载。 (3)在分析存在软弱下卧层的基坑坑底抗隆起稳定性时,当挡墙底部离软弱下卧层顶部的厚度小于临界厚度时,需要考虑软弱下卧层对基坑抗隆起稳定性的影响；当挡墙底部离软弱下卧层顶部的厚度大于临界厚度时,可不考虑软弱下卧层对基坑抗隆起稳定性的影响。
[Abstract]:The Yangtze River Basin and the coastal area are mostly soft soil plain area. The soil bearing capacity is low and the groundwater level is high, the foundation pit instability is easy to occur. The foundation pit bulge is one of the common forms of the foundation pit instability. In the safety assessment of deep foundation pit engineering, the analysis of the foundation pit bottom anti uplift failure is of important reference value, and it is also a foundation pit. There are three main methods for analyzing the uplift stability of deep foundation pit bottom: limit equilibrium method, limit analysis method and numerical analysis method.
Based on the theory of circular arc sliding mode in the limit equilibrium method, this paper considers that the existing simplified formula of circular arc sliding should take into account the soil parameters of the layered soil, the parameters of the retaining wall and the influence of the reinforced soil parameters. The formula for calculating the safety factor of the stability of the bottom of the deep foundation pit with these three factors is considered, and the original moment is equal to the original moment. The method of obtaining the equivalent soil parameters is derived. At the same time, the applicable conditions for the calculation formula of the circular arc sliding mode and the ultimate bearing capacity model are analyzed. The applicability and accuracy of the different formulas under different conditions are verified by the calculation of the engineering examples. Then, the calculation formula of the Prandtl extreme limit bearing capacity model and the circular slip mode are given. The formula is programmed with MATLAB. The influence degree of soil parameters, retaining wall parameters and reinforcement parameters on the stability of deep foundation pit at the bottom of the pit is compared and analyzed. Finally, the calculation formula of stability safety factor for the foundation pit bottom of deep foundation pit with weak substratum is derived through the ultimate bearing capacity model and the Vesic theory. The critical thickness can be considered without consideration of the influence of soft substratum, and the critical thickness under the influence of different parameters is analyzed.
(1) the comparison between the derived formula and the national standard formula, the difference between the dynamic soil pressure coefficient of the main ground inside and outside of the foundation pit, the effect of reinforcement soil and the effect of the retaining wall providing bending moment, and the value method of the equivalent soil parameters are derived in detail. The difference between the derived formula and the calculation results of the other formulas is analyzed and compared by an engineering example. When the soil quality above the bottom of the retaining wall is poor, the formula deduced in this paper is more reasonable than the formula of Prandtl ultimate bearing capacity formula.
(2) among the factors affecting the stability of the deep foundation pit, the cohesive force, the friction angle of the soil and the gravity of the soil and the insertion of the retaining wall have a great influence on the stability of the bottom of the deep foundation pit. By the calculation and analysis, the degree of influence of the parameters from the large to small is the internal friction angle, the soil mass, the cohesive force of the soil and the retaining wall. The insertion ratio has no unconfined compressive strength of the reinforced soil, and the ground is overloaded.
(3) when analyzing the stability of foundation pit bottom in soft substratum, when the thickness of the bottom of the retaining wall is less than the critical thickness at the top of the weak substratum, it is necessary to consider the influence of the soft substratum on the stability of the foundation pit against the bulge. The effect of lying layer on the stability of foundation pit anti uplift.
【学位授予单位】：武汉理工大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：TU473.2

【参考文献】