黄土高原渭河宝鸡段北岸大型深层滑坡动力学机制研究

Research on Kinematics and Dynamic Mechanism of Large-Scale Deep-Seated Landslide on the North Bank of Baoji Stream Segment of Weihe River in Loess Plateau

为研究渭河盆地黄土塬边大型深层滑坡运动机制,通过对渭河宝鸡段北岸斜坡构造地貌过程解析、滑体地质剖面平衡计算与运动过程的动态数值模拟,结合黏土岩滑动带发育的宏观力学背景、物理结构变化特征与剪切蠕变、滑动力学行为特征研究,确定了渭河北岸大型深层滑坡的几何学、运动学特征,初步揭示了黏土岩质滑带塑性流动挤出的控滑机制。研究表明:①大型深层滑坡的运动变形由后缘向坡脚传递,后缘下降、前缘隆起,整体变形由底部泥岩控制,具有一定的水平位移,是旋转-平移复活式滑坡;②黏土岩滑动带结构损伤形成蠕变变形带,滑动过程中,塑性变形区在滑体下方呈倾斜三角形状,产生塑性流动变形,逆冲向上运动中形成翻卷结构,滑体前缘以流动状态隆起挤出;③黏土岩的塑性流动变形是黏土矿物含量增加、活性增强的结果,滑带土内的粘粒含量(<2μm)由初始的17.94%增加到50.22%,蒙脱石的绝对含量从初始的13.19%增加至26.38%,而其比表面积平均由124.55增加至215.08,从而降低滑动带的强度、恶化水理性质,引起滑体剧烈变形,而滑体内赋存的高孔隙水压力可推动滑体滑动。

In order to investigate the mechanism how the movement of large scale deep-seated landslide develops at the edge of loess tableland in Weihe River basin,balance computation of geological section of landslide mass and dynamic numerical simulation of movement process are conducted,together with the analysis of the tectono-geomorphologic process of slope on the north bank Combined with research on the macromechanics background,characteristics of physical structure changes and characteristics of shear creep and sliding mechanics of clay rock slip band development,this paper identifies the characteristics of geometry and kinematics of deep-seated landslide and reveals the sliding-control mechanism for plastic flow extruded from clay rock slip band.The research indicates that：（1） The deformation of large-scale deep-seated landslide initiates at the trailing edge,then transfers to the slope toe,leading to a descent at the trailing edge and ascent at the front edge.The overall deformation is controlled by the mudstone located at the bottom.With the horizontal displacement,it could be categorized as rotatory-translational revived landslide; （2） The clay rock slip band evolves to be a creep deformation band due to tectonic damage.During the failure process of landslide,the plastic deformation zone below the sliding mass presents a diagonaltriangle.It takes reverse overthrust movement to form the overturned structure and it presents plastic flow deformation and flow extrusion damages; （3） The increase of clay mineral content and activity enhancement have been identified as the cause of plastic flow deformation of clay rock.The clay content （＜ 2 μm） within the slip soil increases from 17.94％ to 50.22％,and the absolute content of montmorillonite increases from 13.19％ to 26.38％.The average of specific surface area of clay rock increases from 124.55 to 215.08,which could easily deteriorate the strength and water-physical properties,and cause severe deformations of the sliding mass.The sliding mass would be pushed by the high pore water pressure.