稳定分析中的强度指标问题

Strength Parameters in Stability Analysis

稳定分析一般可以分为三类:①不排水的稳定问题,以总应力法进行分析;②排水的稳定问题,以有效应力法分析;③部分排水的稳定问题,以有效固结应力法分析。实际上,土坡或地基的失稳通常都是在一些不利因素的触发下突然发生的,其破坏过程基本上由不排水条件控制,故用有效应力法得出的安全系数往往偏高,而总应力法给出的安全系数则又大多偏低。比较合理的是采用有效固结应力法进行分析,它既能考虑土体在施工过程中有效应力增长的有利因素,又不忽视不排水破坏过程中剪切引起孔压的不利影响,弥补了上述两种方法的不足。但是,在现行方法中,对于固结不排水三轴压缩试验得出的强度指标的定义及其实际应用,还存在着一些明显的误解和不协调。本文对此进行讨论并提出改进。最后,以一个工程实例说明现行方法可能引起的误差及其影响。

Stability problems have been divided into three categories: (1) undrained (2) drained and (3) partially drained. Actually failures usually occur without significant drainage, conventional effective stress analyses give unsafe estimates of potential instability. On the other hand, the factors of safety obtained by total stress analyses are always underestimated. Therefore the so-called effective consolidation stress analysis, that treats in-situ effective stresses before failure as equal to consolidation stresses in order to evaluate variations in undrained shear strength during construction, is more rational than the above-mentioned two analyses. Inconsistencies in the conventional definition and the practical application of the angle of shearing resistance obtained from consolidated-undrained biaxial compression tests were discussed and clarified. Finally a case history was presented to illustrate the possible errors induced by the mentioned ambiguity.