青海上湾特大型红层老滑坡体形成机制研究

青海上湾特大型老滑坡体是一个典型的多期次第四系上更新统黄土与新近系贵德群泥岩切层旋转滑坡，滑动面主要位于新近系贵德群泥岩内。在充分利用现场滑坡勘查和钻探试验所获取资料的基础上，通过对滑坡堆积物中的关键层（黄土状土和砾岩堆积物）与泥岩堆积物的空间位置组合关系的研究，以及对老滑坡体底滑面的形态和黄土状土顶部的淤泥（堰塞湖湖积物）的分析，确定了上湾特大型老滑坡体主要经历了两次规模较大的滑动。利用地下水动力学的理论，计算出两次滑动前的地下水位，并建立了分析滑坡变形与破坏机制的数值模型。综合区域新构造运动特点、地下水位的动态变化、新近系贵德群泥岩在饱水状态下力学强度显著下降的特征以及FLAC3D数值模拟结果，得出老滑坡体第1次滑动主要是由于河流下切作用引起，并给出了河流下切过程中坡体变形的3个阶段。第2次滑动是由于第1次滑动后，斜坡临空面变陡，坡脚剪应力进一步集中，且在其前缘形成一个堰塞湖，导致地下水位上升软化泥岩而发生的累进性牵引滑动。

Study of formation mechanism of giant red bed old landslide in Shangwan of Qinghai province

The Shangwan giant old landslide in Qinghai province, belonging to Upper Pleistocene series loess of Quaternary System and Guide Group mudstone of Neogene System, is a typical multi-stage rotating landslide and the sliding surfaces are mainly in the mudstone of Guide Group. Based on the full use of the materials obtained by the field landslide survey and drilling test, through analyzing the spatial position relation between key layers (loess soil and conglomerate deposits) in the landslide deposits and mudstone deposits, as well as the sliding surface morphology of the old landslide body and the sludge (dammed lake sediment) on the top of the loess, it is confirmed that the Shangwan giant old landslide body had mainly experienced two large-scale slides. And then, with the theory of groundwater dynamics, the groundwater level can be calculated before the two slides, and a numerical model of landslide deformation and destruction mechanism can be established. Combining the regional neotectonic movement characteristics, the dynamic change of underground water level, the feature of significant decrease in strength of mudstone in the saturated state and the FLAC3D numerical simulation results, it is concluded that the first sliding of the old landslide is mainly caused by river incision, and three stages of slope deformation in the process of the river incision are provided. The first sliding results in the steepening of slope’s free face, the concentration of shear stress at the slope toe, and the formation of a dammed lake in the front of the landslide, which leads to an accumulated traction sliding caused by the rising of ground water level and the softening of the mudstone.