重庆小南海滑坡形成机制离散元模拟分析

重庆小南海滑坡是烈度相对较低地区发生的地震高位滑坡，其成因一直令人费解。基于重庆黔江小南海相关研究资料，通过对复原的小南海坡体进行失稳分析，计算得出使岩体产生崩滑破坏的地震力临界条件，即只有当地震波地形放大后滑坡才能启动。为了进一步验证计算所得的结论，运用UDEC软件建立小南海典型二维场地模型，施加相应的地震力对坡体失稳崩滑的全过程进行模拟，以研究地震作用下地形放大效应触发具平行坡面陡倾控制性结构面的高位岩质斜坡地震机理。研究结果表明，在地震波传播过程中，具平行坡面陡倾控制性结构面的高陡突出地形对地震波有明显的放大作用。该坡体运动模式为：峰值加速度放大-增加的振幅迫使岩体顺平行坡面陡倾控制性结构面迅速拉裂-沿缓倾层面滑移-高速脱离滑源区-巨大的势能和动能驱动坡体做长距离运动，其间伴随解体、颗粒间相互碰撞、铲刮作用，具有二相甚至三相流体性质。分析揭示地震力作用下斜坡体中质点加速度具有地形放大效应。对比结构面监测点和基岩监测点加速度放大系数，表明，滑坡启动时具有较大的加速度，当遇到平行坡面的不连续结构面时，斜坡动力响应强烈，最终导致坡体失稳。

Discrete element simulation analysis of formation mechanism of Xiaonanhai landslide in Chongqing city

Xiaonanhai landslide in Chongqing city is a high landslide occurred in relatively low seismic intensity regions, its causes have been puzzled. This paper is based on the related research materials of Qianjiang Xiaonanhai, through the recovery of the Xiaonanhai slope instability analysis, to calculate the seismic force’s critical conditions that make rock mass collapse sliding. Only after the topographic ampliflcation effects of seismic waves can landslide start. In order to further validate the calculated conclusions, by using UDEC software, a typical two-dimensional space model of the Xiaonanhai is established. Applying the corresponding seismic force on the slope to simulate the whole process of landslide, as to research in the mechanism that a steep slope parallel to the surface of the structure controlling the high rocky slopes triggered by topographic amplification effect under earthquake. The results show that, in the process of seismic wave propagation, the high and steep terrain with a parallel slope controlled by steep structure plane, have a significant amplified effect on seismic wave. Amplify peak acceleration-the increasing amplitude forces rock mass along the controlling structure planes which parallel with slope to crack quickly-slip along the gently dipping levels-high-speed detach from the slipping source region-huge potential and kinetic energy drive rock mass to do long-distance movement; meanwhile, accompanied by disintegration, collisions between particles and scraping effect, even with two-phase or three-phase fluid properties, which is the movement mode of this slope. Analysis reveals that the particle acceleration in the slope body has terrain amplification effects under the action of seismic force. Comparing the speed amplification factor of monitoring points between structural surface and bedrock, it is proved that the slide starts with a greater acceleration, when faces with discontinuities structural surface which parallels, to the slope, the dynamic response of slope becomes strong and eventually lead to slope’s instability.