强震作用下中倾外层状岩质边坡动力失稳机理研究

Study on dynamic instability mechanism of moderate outward dipping stratified rock slope under strong earthquake

中倾外层状岩质边坡在静力条件下的稳定性一般较好,但是在对"5·12"汶川地震中失稳边坡调查的过程中,却发现了大量的中倾外层状岩质边坡动力失稳案例。为了得出该类型斜坡动力变形失稳机理,采用三维离散元数值模拟技术,对该类型边坡在地震作用下失稳机理进行数值模拟。结果表明:在地震荷载作用下,坡表各监测点PGA放大系数随高程增加呈现非线性增大且均大于1。在边坡水平剖面上PGA放大系数先增大,在距坡表50 m后逐渐降低;而竖直剖面上PGA放大系数在1/2高度下整体变化不大,超过该高度其急剧增大。地震作用下整个边坡的失稳机理为:边坡顶部优势层面逐渐张开,缓倾坡外的结构面发生剪切变形;随着变形的发展,坡体上部拉张裂缝向深处扩展,坡内锁固段岩层被破坏,控制性结构面贯通;滑坡沿贯通滑面快速滑下,摧毁坡脚铁路线并堵塞河道,整个边坡发生拉裂-滑移-剪断型失稳破坏。研究成果为类似地区的边坡工程地震失稳分析提供参考和依据。

The stability of the moderate outward dipping stratified rock slope is generally better under static condition. However,a lot of the cases of dynamic instablity of moderate outward dipping stratified rock slope are found during the investigation of the unstable slope occurred in the 5·12 Wenchuan Earthquake. In order to find out the mechanism of the instablity from dynamic deforamtion of such inclined slop,the instability mechnism of that kind of slope under sismic effect is numerically simulated with the technique of 3-D discrete element numerical simulation. The result shows that the PGA amplification coefficients of all the monitoring points on the slope surface under seismic loading non-linearly increase along with the elevation and all are over 1. On the horizontal profile of slope,the PGA amplification coefficient increases at first and then gradually decreases after the distance of50 m from the slope surface,while the overall variation of the PGA amplification coefficient is not so large at the 1/2 height on the vertical profile and then is sharply increased if the height is exceeded. The instability machanism of a whole slope under seismic effect is that the dominate bedding plane at the slope crest gradually expands and then shear deformation occurs at the structure plane outside of the moderate inclined slope,while the tensile crack of the upper part of slope deeply expands along with the development of the deformation,and then the rock formation of the locked section inside of the slope is destroyed and the dominate structure plane is broken through,thus landslide mass rapidly slips down along the breaking-through slipping plane,which destroys the railway at the slope toe and blocks the river channel therein,from which a tensile-cracking-slipping instability failure finally occurs. The study result provides reference and basis for the analysis on the instability caused by earthquake for the slope project within the similar regions concerned.