武隆鸡尾山滑坡形成机理数值模拟研究

2009年发生的重庆武隆鸡尾山滑坡,因滑源区斜坡岩层整体缓倾山内,缺乏有效的临空面和滑移空间,因此,在滑坡孕育过程中存在前缘岩溶带压缩变形、底部剪切滑移、后缘拉裂以及最终前缘关键块体(岩溶带)侧向剪断滑出等一系列的复杂动力学行为。这一过程存在显著的连续变形向非连续变形的过渡与转化,单纯用连续介质的有限元和离散介质的离散元来分析模拟都很难取得较好的效果。为探究鸡尾山滑坡的孕育过程和失稳机理,运用将连续–非连续单元有机耦合的大型数值模拟软件CDEM,模拟鸡尾山滑坡的失稳过程和形成机制。研究表明:滑体前方岩溶发育带具有"可压缩性",为滑体运动提供了一定的变形空间;滑源区下方的采矿活动产生应力重分布,滑带抗剪强度降低,滑体沿其底部软弱带发生剪切蠕滑,并逐渐形成滑体后缘拉裂缝;滑动块体在向前滑移过程中不断挤压向前缘"易压缩带",坡体应力自组织调整,并逐渐在前部三角区形成垂直的第二破裂面,前缘抗力体(关键块体)形成,最后剪断岩溶带个别与稳定山体咬合岩块,整体失稳破坏。数值模拟结果较好地揭示了武隆鸡尾山滑坡前缘视倾向展布岩溶带"软基效应"所提供"准临空面",重现了鸡尾山滑坡"蠕滑—拉裂—压缩(压碎)—剪切滑出"的致灾机理。

Numerical simulation for formation of Jiweishan landslide in Wulong County,Chongqing City of China

Because of the gently-inclined rock in the hill sliding source area and the lack of the effective free surface and sliding space, there were a series of complicated dynamic behaviors during the process of Jiweishan landslide in Wulong County, Chongqing City of China in 2009, such as compression deformation, bottom shear sliding, trailing edge rupture and lateral cutting and sliding of the leading key blocks (karst zone). There exists a remarkable transition and transformation from continuous deformation to discontinuous one. It is difficult to obtain good results simply by using the finite elements of continuous media or the discrete elements of discrete media. The instability process and formation mechanism of Jiweishan landslide are simulated by use of the large numerical simulation software CDEM with the organic coupling continuous-discontinuous elements. The results show that the bottom sliding surface is cut through and the shearing creep occurs along the bottom surface in the process of the formation of landslide. The stresses on the slope concentrate towards the "easy compression zone" at the leading edge of the slope, and they are slope stress automatically adjusted. The slope along the "easy compression zone" creeps, and the second fracture face perpendicular to the slope (cliff) is formed. Finally, the karst rock is cut to induce instant instability of land slide and high-speed remote debris flows. The numerical results reveal the “quasi free surface provided by soft foundation effects” in karst zone in the viewpoint of apparent dip distribution, and the disaster-causing mechanism of “creep-crack-