基于可靠性理论的基坑稳定与变形研究

发布时间：2018-03-07 12:49

本文选题：基坑　切入点：可靠性理论　出处：《武汉理工大学》2015年硕士论文　论文类型：学位论文

【摘要】：基坑稳定性验算及变形验算的目的是对基坑支护设计方案的安全性做出评价,避免由于设计不当而造成事故。当前,由于设计原因造成基坑事故的比例占30%~45%,说明现有的基坑稳定性及变形验算方法存在一定的缺陷。本文将可靠性理论运用于基坑的稳定性和变形验算中,充分考虑了土体或支护结构等因素的变异性,对基坑稳定可靠性和变形可靠性的计算方法进行研究。主要的工作内容及结论如下:(1)分析了可靠度的三种表述方式:可靠概率、失效概率、可靠指标;论述了不确定因素的三种处理方法:χ2检验法、K-S检验法、A2检验法;总结了几种常用的可靠度计算方法:一次二阶矩法、蒙特卡洛法、随机有限元法、优化算法;阐述了体系可靠度的计算方法。(2)研究了基坑稳定可靠性的计算方法:在极限平衡法的基础上,将基坑的抗力效应与荷载效应的差值作为可靠性功能函数。由于不同形式支护结构的受力不同,在考虑土层性质的差异和受力分析的基础上,分别建立了土钉墙支护结构的整体稳定性功能函数、抗滑移稳定性功能函数、抗倾覆稳定性功能函数,悬臂式支护结构的抗倾覆功能函数,桩(墙)撑式支护结构的抗倾覆功能函数,重力式支护结构的抗倾覆功能函数、抗滑移功能函数;将各层土体的粘聚力和内摩擦角作为随机变量,根据功能函数的特点,选择改进的一次二阶矩法计算稳定可靠度,并用MATLAB编制了通用的计算程序。(3)研究了基坑变形可靠性的计算方法:根据可靠性理论,提出将基坑的深层土体位移、坑底隆起及周边沉降值的警戒值与相应的实际最大变形值的差值作为可靠性功能函数,功能函数大于零的概率即为可靠度。针对基坑的变形很难用显式方程式表达出来的特点,选择随机有限元法计算变形可靠度,将土体的粘聚力和内摩擦角作为随机变量,深层土体位移的最大值、坑底隆起的最大值、周边沉降的最大值作为随机输出变量,研究了运用ANSYS-PDS模块计算基坑变形可靠度的方法。(4)将基于可靠性理论的基坑稳定和变形评价方法应用于某支护形式为两道支撑+排桩的基坑工程中,对该方法的适用性进行验证。对桩撑式支护结构进行受力分析,建立了抗倾覆稳定性功能函数,将具体的数据代入编制的通用计算程序,计算出了抗倾覆可靠度;采用ANSYS的APDL编制了基坑开挖的分析文件,运用PDS模块计算出基坑的深层土体位移、坑底隆起及周边沉降变形可靠度,并根据系统可靠性理论计算出基坑的变形可靠度。结果显示基坑的稳定可靠度和变形可靠度均大于目标可靠度,表明基坑是安全的,与实际相符,说明基于可靠性理论的基坑稳定和变形评价方法具有适用性。
[Abstract]:The purpose of checking calculation of foundation pit stability and deformation is to evaluate the safety of foundation pit support design scheme and avoid accidents caused by improper design. The proportion of foundation pit accidents caused by design reasons accounts for 30%, which indicates that the existing methods for checking foundation pit stability and deformation have certain defects. In this paper, reliability theory is applied to check the stability and deformation of foundation pit. Taking fully into account the variability of soil or supporting structure, the calculation methods of stability reliability and deformation reliability of foundation pit are studied. The main work contents and conclusions are as follows: 1) the three expressions of reliability are analyzed: reliability probability, reliability probability, and so on. Failure probability, reliability index, three methods to deal with uncertain factors are discussed: 蠂 2 test method and K-S test method and A2 test method, and several commonly used reliability calculation methods are summarized: first order second moment method, Monte Carlo method, stochastic finite element method, the first order second moment method, the Monte Carlo method, the stochastic finite element method, the first order second moment method, the Monte Carlo method and the stochastic finite element method. The calculation method of stability reliability of foundation pit is studied, which is based on the limit equilibrium method. The difference between the resistance effect of foundation pit and the load effect is regarded as the function of reliability. Because the stress of different support structures is different, considering the difference of soil properties and the analysis of force, The overall stability function, the anti-slip stability function, the anti-overturning stability function and the overturning function of the soil nailing wall supporting structure are established, respectively. The anti-overturning function function of pile (wall) supporting structure, the anti-overturning function function and anti-slip function function of gravity support structure, the cohesive force and internal friction angle of each layer of soil are taken as random variables, according to the characteristics of function function, The improved first-order second-moment method is chosen to calculate the stability reliability, and the general calculation program .Xi ~ 3 is compiled by MATLAB. The method of calculating the deformation reliability of foundation pit is studied. According to the reliability theory, the displacement of the deep soil of the foundation pit is put forward. The difference between the warning value of pit bottom uplift and surrounding settlement value and the corresponding maximum actual deformation value is regarded as the reliability function, and the probability that the function function is greater than zero is the reliability degree. In view of the characteristic that the deformation of foundation pit is difficult to express by explicit equation, Random finite element method is selected to calculate the reliability of deformation. The cohesive force and the angle of internal friction of soil are taken as random variables, the maximum displacement of deep soil, the maximum value of uplift at the bottom of the pit, and the maximum value of settlement around the soil are taken as random output variables. The method of calculating the deformation reliability of foundation pit by using ANSYS-PDS module is studied. The method of foundation pit stability and deformation evaluation based on reliability theory is applied to the foundation pit engineering with two braced piles. The applicability of this method is verified. The stress analysis of pile-braced supporting structure is carried out, the function function of anti-overturning stability is established, the specific data is added into the general calculation program, and the anti-overturning reliability is calculated. The analysis document of foundation pit excavation is compiled by APDL of ANSYS, and the reliability of deep soil displacement, uplift of pit bottom and surrounding settlement deformation is calculated by PDS module. According to the system reliability theory, the deformation reliability of the foundation pit is calculated. The results show that the stability reliability and deformation reliability of the foundation pit are higher than the target reliability, which indicates that the foundation pit is safe and consistent with the practice. It shows that the method of foundation pit stability and deformation evaluation based on reliability theory is applicable.
【学位授予单位】：武汉理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU753

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