地震边坡破坏机制及其破裂面的分析探讨

 地震作用下边坡破坏机制是边坡动力稳定性分析的前提，目前主要采用拟静力与动力有限元时程分析的方法进行分析，认为地震边坡破坏机制为剪切破坏，并以极限平衡法计算得到的剪切滑移面作为地震动力作用下的破裂面，而不考虑地震荷载作用下的拉破坏，从而使地震边坡稳定性分析失真。汶川地震边坡调研发现，滑坡上部多数发生拉破坏，甚至有些岩土体被抛出，这是一个很好的启示，为此，采用FLAC动力强度折减法，结合具有拉和剪切破坏分析功能的FLAC3D软件对地震边坡破坏机制进行数值分析。计算表明，地震边坡的破坏由边坡潜在破裂区上部拉破坏与下部剪切破坏共同组成，而不是剪切滑移破坏，通过多种途径给出地震边坡破裂面位置的确定方法，为边坡动力稳定性分析提供更加准确的基础。

ANALYSIS AND DISCUSSION OF FAILURE MECHANISM AND FRACTURE SURFACE OF SLOPE UNDER EARTHQUAKE

The failure mechanism of slope under earthquake is the premise of slope¢s dynamic stability analysis. Presently，pseudo-static method and dynamic time-history analysis method are commonly used，which regard the failure mechanism of slope under earthquake as shear failure，and take the shear sliding surface obtained by limit equilibrium method as failure surface under dynamic effect of earthquake without considering the tension failure under seismic load. It may lead to inaccuracy in the stability analysis of slope under earthquake. Investigation of the slopes during Wenchuan earthquake shows that tension failures mostly appear in the upper part of the landslides，and even some rock and soil masses are thrown out，which is an obvious enlightenment. So the FLAC dynamic strength reduction and program of FLAC3D with the function of tensile and shear failure analysis are adopted to study failure mechanism of slope under earthquake numerically. The study shows that the failure of slope under earthquake is made up of the tension failure in the upper part of the fracture zone and the shear failure in the lower part instead of shear sliding failure. A method of locating the fracture surface of slope under earthquake through several ways is provided，which is an accurate foundation for dynamic stability analysis of slopes.