【作者】 尹宏磊；

【导师】 李仲奎；

【作者基本信息】 清华大学 ， 水利工程， 2009， 博士

【摘要】 边坡中的初始地应力长期处于不受重视的地位,即使考虑初应力,也只是用重力场来代替。传统的极限平衡方法与新近流行的强度折减法都不能考虑初始地应力的作用。增量有限元虽然可以考虑初应力,但它一般给出的是极限载荷;即使它借用极限平衡的概念,能给出一个基于过载定义的安全系数,但这个定义的物理意义不明确。本文研究了两种数值计算方法,既能考虑地应力的影响,又能给出一个工程师关心的安全系数。本文在工程地质概念和经验的基础上,明确提出研究初始地应力状态和边坡稳定性之间的关系,并且找到了有效的定量分析方法(而不仅仅是靠概念性的分析)对这一问题进行研究。发展完善了边坡稳定极限分析的单元集成法,发现这种方法对于需要考虑一个分布场变量对边坡稳定性的影响时所具有的特殊优越性。采用单元集成法对膨胀土边坡的稳定性,以及不同水平构造应力条件下边坡的稳定性进行了分析,得出在考虑土体膨胀变形和水平构造应力条件下,边坡稳定安全系数会显著降低的结果。这与实际工程中遇到的情况相符,并且避免了以稳定结果凑强度参数的人为性。当考虑土体膨胀变形和水平构造应力条件时,按照相同优化条件得到的临界破坏模式由普通的深层滑动变成了在浅层出现的一个局部滑动,它会牵动其上部的土体也相继出现局部滑动,从而形成一个较长范围的浅层滑动。这与膨胀土滑坡时所具有的牵引性的特点以及高地应力区一些水电工程的坝基和坝址岸坡开挖后出现的浅层破坏现象(岩层鼓曲)正好是相符合的。把弹性补偿法引入到岩土工程领域,并对其算法过程进行了改造,特别是弹性模量调整公式中名义应力与等效应力的确定。通过编写用户子程序,在ABAQUS中成功实现了弹性补偿法的计算过程。在弹性迭代的过程中,可以同时生成满足极限定理的静力场和机动场,从而求出相应的极限载荷(安全系数)。弹性补偿法可以方便地考虑初始地应力的影响。通过本文的研究,给初始地应力影响的边坡提供了一种有效的评价方法。更多还原

【Abstract】 Initial stresses do not receive their deserved consideration in slope stability analysis for a long time. Engineers are used to considering gravity field instead of initial stresses. Initial stresses can not be included in conventional Limit Equilibrium Method (LEM) and recently popular Strength Reduction Method. Although incremental Finite Element Method (FEM) can take initial stresses into account, it only gives a limit load, not a Factor of Safety (FOS). Combining FEM and LEM can give a FOS based on an overload concept, but this definition does not have a straightforward physical meaning. Based on the two numerical methods proposed in this dissertation, both initial stresses and FOS concerned by engineers can be considered.With the help of the concept and experience of engineering geology, research on the relationship between initial stresses and slope stability is done, and an efficient quantitative method (not conceptual analysis only) is also found.The Element Integration Method (EIM) for limit analysis of slope stability is perfected. When considering the influence of a distributed field on the slope stability, EIM has an outstanding advantage. After stability analysis of expansive slopes and slopes under different horizontal tectonic stresses, it is found that the FOS of slopes could decrease dramatically. This agrees with the factual things, and avoids the arbitrariness of inferring strength parameters by results. Taking expansive deformations and horizontal tectonic stresses into consideration, the critical collapse pattern from the same optimization transforms from ordinary deep slide to local shallow slide, which will induce the upside soil mass into another small range of shallow slide. As a result, a larger range of shallow slide comes into being. This agrees well with the traction character of expansive soil slope and the phenomenon of shallow collapse after the excavation of slopes in some hydraulic engineering with high initial stresses.Elastic Compensation Method (ECM) is introduced to geotechnical area. The author modifies the formulation of ECM, particularly in the determination of nominal stress and equivalent stress. By virtue of compiling user subroutines, the procedures of ECM are realized successfully in ABAQUS. In the elastic iterations, statically admissible stress and kinematically admissible velocity can be derived in the same time. Thus limit load or FOS can be attained by limit theorem. ECM can take initial stresses into consideration easily.The research of this dissertation provides an efficient appraisable method for slopes influenced by initial stresses.更多还原