针对汶川地震中边坡的破坏形式与坡体结构密切相关的问题,以"5·12"汶川地震中安县高川乡大竹坪滑坡和干磨房滑坡失稳工点为原型,在充分分析滑坡地区工程地质条件及其动力变形特征的基础上,提出采用3维离散元数值模拟技术进行失稳机理对比分析的思路.结果表明:陡倾顺层硬岩斜坡的动力破坏形式以崩滑为主,陡倾顺层软硬互层斜坡的动力破坏形式以滑移弯曲为主;在相同地震作用下,峰值地面加速度(peak ground acceleration,PGA)放大系数与坡体高程总体成正相关,斜坡同一高度处的PGA放大系数由坡表向坡内总体呈现先增大后减小的趋势;陡倾顺层硬岩斜坡的PGA放大系数总体小于陡倾顺层软硬互层斜坡,硬岩斜坡的PGA放大系数范围在2~3,最大值在坡表的3/4处;软硬互层斜坡的PGA放大系数范围在2.5~4.0,最大值在斜坡顶部.此外,陡倾顺层硬岩斜坡的破坏机制为4个阶段:层面部分贯通滑移—锁固段震荡松弛—上部抛射—底部滑面贯通并失稳,而软硬互层斜坡的失稳机理则为:层面错动–部分贯通滑移—下部局部抛出–局部弯曲—高位横向扩展滑移—下部弯曲折断–整体失稳.研究成果可为西南地区高陡顺层岩质斜坡失稳评价及机理分析提供相应的技术支持.%In order to reveal the relationship between failure modes and slope structures, the field investigation aftershock in Wenchuan area was conducted, especially for the dynamic instability of steep slopes. This study takes two typical slope failure sites, namely, Dazhuping landslide at Gaochuan county and Ganmofang landslide at an county in Sichuan province as the example, by considering the landslide related engineering geological condition and dynamic deformation characteristic, a three-dimensional discrete element numerical simulation on instability mechanism of the two slopes was conducted. The results showed that the mode of hard rock steep bedding slope destruction was a slippage type, while the failure of interbedded steep bedding slope was by a sliding bending.Under the same earthquake,PGA amplification coefficient and the slope height was positively correlated,and PGA amplification coefficient turned a first increasing and then decreasing phenomenon with the increase of elevation.The PGA amplification coefficient of steep bedding hard rock slope was smaller than that of steep bedding interbed slopes.While the amplification coefficient in hard rock slope PGA ranges from 2 to 3,the maximum was in 3/4 of slope surface.The PGA amplification coefficient of interbedded slope ranges from 2.5 to 4.0, with the maximum value located at the top of the slope. In addition, the damage mechanism of hard rock bedding slope could be divided into four stages: the first stage was a slip partly through the locking section; the second stage was shock re-laxation; the third stage was the ejection phase; and the fourth stage was a overall instability. For the interbed slope, the first stage was a layer dis-location, the second stage was local lower ejection, the third stage was a continuous crack spreading in the high location, and the fourth stage was a bottom bending failure. The research results can provide technical support for the instability evaluation and mechanism analysis of high steep bedding rock slope in Southwest China.
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