高速黄土滑坡前缘冲挤效应颗粒流模拟

    PARTICLE FLOW SIMULATION OF RAPID LOESS LANDSLIDES WITH FRONTAL PLOWING EFFECT

    • 摘要: 一些高速黄土滑坡在运动过程中对其前缘的松散阶地物质存在冲挤作用,造成阶地物质大范围隆起和运移。此类滑坡的运动过程非单一黄土的滑移,而是两种不同物质的相互作用过程。为研究此类滑坡前缘冲挤效应的运动演化机理,本文以陕西咸阳塬北缘的西庙店高速黄土滑坡为对象,开展了滑坡堆积体地貌和地层变形特征的现场调查,在此基础上建立滑坡的二维颗粒流模型,分析了前缘冲挤效应的形成过程,探讨了斜坡坡度对其演化模式的影响。结果表明: 高陡黄土斜坡发生突发性破坏而高速下滑为前缘冲挤效应的形成提供了动能条件; 黄土滑体冲挤阶地物质使其产生隆起变形和水平推移,此过程中两者基本不发生混合; 前缘冲挤效应的演化过程可分为俯冲铲起、多级冲剪破坏、推移隆起和减速停止4个阶段,其中冲剪破坏是导致阶地地层形成多级逆冲推覆式构造的主要原因; 不同滑前斜坡坡度黄土滑坡的前缘冲挤模式不同,随坡度增加,黄土滑体披覆于阶地物质上的程度变大,堆积结构逐渐由推挤式过渡为披覆式。本文研究可为预测此类滑坡的致灾范围提供方法。

       

      Abstract: During the run-out process of certain rapid loess landslides, loose terrace materials at the slope toe can be plowed and pushed forward by the loess sliding mass, resulting in significant upheaval deformation and horizontal transport of the terrace materials, leading to the enlargement of the landslide impact area. This phenomenon is referred to as the frontal plowing effect in the literature. To investigate the dynamic evolution mechanism of the frontal plowing effect of rapid loess landslides, we conducted a case study on the Ximiaodian landslide that occurred on the northern margin slopes of the loess tableland in Xianyang City, Shaanxi Province. Field investigations were carried out to study the depositional geomorphology of the landslide and the deformation characteristics of the terrace material. Subsequently, we developed a particle flow model to analyze the frontal plowing effect formed during the run-out process of this landslide. Finally, we discussed the influence of the pre-failure slope angle on the frontal plowing mode of the landslide. The results indicate that the rapid movement of the loess landslide provides the kinematic conditions for the formation of the frontal plowing effect. The upheaval deformation and horizontal transport of the front terrace material are caused by the squeezing of the loess landslide, and during this process, the loess sliding mass does not significantly mix with the terrace materials. Based on the simulated run-out characteristics of the landslide, the frontal plowing process can be divided into four stages: (1)shoveling stage in which the landslide plows into the topsoil of the terrace, (2)squeezing-shearing stage when multiple spiral shear failure surfaces form in the terrace, (3)pushing-upheaval stage in which the pushing-induced upheaval deformation of the terrace in the front part continues, and (4)decelerating-stable stage when the frontal plowing process stops. The squeezing-shearing stage plays an important role in the formation of the multiple thrust-nappe structure in the disturbed terrace area. Additionally, it also indicates that the pre-failure slope angle determines the frontal plowing mode of the landslide. With the increase in slope angle, more loess sliding mass will cover the disturbed terrace material, and the frontal plowing mode transforms from a pure horizontal pushing mode to a covering-pushing mode. The research results of this paper could provide a useful reference for the prevention and mitigation of this type of landslide in loess areas.

       

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