基于偏应力增量的边坡开挖松动区的确定方法

对于开挖卸荷效应导致的边坡破坏现象,传统的极限平衡法无法给出合理的稳定性评价结果。以松动区作为开挖破坏型边坡的稳定性分析对象,选取偏应力增量为主要评判指标,归纳了通过数值分析法确定边坡开挖松动区范围的方法。首先将松动区定义为连续分布且对稳定性存在不利影响的弹性松弛区和塑性流动区的总和,认为开挖后偏应力场的调整是边坡变形破坏的主要原因。基于FILAC~(3D)软件平台编制了偏应力及其增量的计算程序。以某顺倾层状路堑边坡为案例,计算了开挖卸荷作用下偏应力场与位移场的动态发展过程。结果表明:岩土体偏应力与变形演化具有较敏感的相关关系,在松动区形成过程中偏应力增量等值线会相应地出现局部凸起、正负分区等异常现象。不同等值线凸起顶点的顺次连线即为偏应力变化异常与否的分界线,可作为松动区的内边界。所述方法可为堑坡稳定性分析、预加固设计等工作提供一定参考。

A Method to Determine the Disturbed Zone of Cutting SlopeBased on Deviatoric Stress Increment

For the slope failure caused by excavation unloading effect, the reasonable stability analyses result always can not be obtained by the traditional limit equilibrium method. With loosened zone as the stability analysis object for cutting slope, deviatoric stress increment was chosen as the analysis indicator and its numerical analysis method to determine the range of loosened zone was put forward. The loosened zone was definedas the sum of elastic relaxation zone and plastic flow zone which should distribute continuously and have adverse effect on slope stability. The adjustment of deviatoric stress field is the main reason for slope failure after excavation. Calculation program of deviatoric stress and its increment was written in FLAC^3D software. Taking a dip bedded cutting slope as example, the development process of deviatoric stress and displacement during the excavation was calculatedby the FLAC^3D. The results indicate that there exists a remarkable correlativity between the deviatoric stress and displacement. The deviatoric stress increment contours were characterized by abnormal phenomena which contain local salience and partition of positive and negative values etc. The sequential connection line of salience vertexes is the boundary line between zones in which deviatoric stress redistribution is abnormal or not, and so it can be considered the inner boundary of loosened zone. The proposed method can provide some referencesfor the stability analyses and pre-reinforcement design of cutting slopes.