降雨促发黄土滑坡的启动机制模拟

Simulation of the Initiation Mechanism of Loess Landslide Promoted by Rainfall

黄土滑坡和降雨关系尤为密切。为深入研究降雨入渗对滑坡的促发作用,在对陕西西安地区“9·17”灞桥滑坡现场勘察的基础上,利用数值模拟方法系统研究了黄土边坡在降雨入渗条件下土体相关物理力学指标的变化响应特征及时空分布规律;从滑动面安全系数变化的角度分析了边坡的失稳过程,并揭示了该类滑坡的启动机制。结果表明:①降雨入渗首先引起坡面土体的基质吸力逐渐降低,而且不同分布位置的降幅不同;②滑坡启动前,坡体的高体积含水量范围随降雨明显扩大,且体积含水量表现出从古土壤层向邻近黄土层递减的规律;③边坡的水平方向位移自坡面中部向坡体的上下部呈放射状递减特征,垂直方向位移由上至下逐渐减小,而临界滑动面的安全系数也随降雨入渗过程逐步递减;④节理处土体的孔隙水压力和体积含水量的变化响应时间及幅度都早于且强于坡体其他区域,坡体内最大剪应变的区域分布与坡面基本平行,模拟结果与原型滑坡一致;⑤基于黄土独特的水敏性、地质构造和人类工程活动等诱因的影响,加上节理裂隙为水的入渗和运移提供了优势通道,降雨加速了黄土潜蚀和坡体结构破坏过程,改变了边坡内部应力场、位移场和水文地质条件,进而促发了滑坡。

The occurrence of loess landslides is particularly closely related to rainfall.In order to deeply understand the promotional effect of rainfall infiltration on landslides,based on the investigation of“9·17”Baqiao landslide in Xi'an area of Shaanxi,the numerical simulation methods were used to systematically study the change response characteristics and spatial-temporal distribution laws of the relevant physical and mechanical parameters of the loess slope under the rainfall infiltration conditions,analyze the destabilization process of the slope from the perspective of the change of the safety factor of sliding surface,and reveal the initiation mechanism of this type of landslide.The results show that①the action of rainfall causes a gradual decrease in the matrix suction of the slope soil,and the magnitude of the decrease varies at different distribution locations;②before the initiation of the landslide,the range of high volume moisture of the slope body expands significantly with rainfall,and the volume moisture shows the law of decreasing from paleosoil layer to the adjacent loess layer;③the horizontal displacement of the slope is radially decreasing from the middle to the upper and lower parts of the slope body,while the vertical displacement gradually decreases from the top to the bottom,and the safety coefficient of its critical sliding surface gradually decreases with the process of rainfall infiltration;④the response time and magnitude of pore water pressure and the change of volume moisture in the soil at the nodal development site are earlier and stronger than those in other areas of the slope,and the regional distribution of the maximum shear strain within the slope is basically parallel to the slope surface,and the simulation results are consistent with the prototype landslide;⑤based on the unique water-sensitive nature of loess,and the influence of causal factors such as geological structure or human engineering activities,the existence of loess joints and fissures provides an advantageous channel for water infiltration and transport,and rainfall accelerates the process of loess subduction and slope structure destruction,changing the internal stress field,displacement field and hydrogeological conditions of the slope,which in turn promotes the occurrence of landslides.