基于PFC^(3D)位移判据的低渗堆积层滑坡临界降雨阈值反演

Back analysis of critical rainfall threshold for landslide in low permeable stacking based on displacement criteria on PFC^(3D)

贵州省罗甸县纳缝堆积体滑坡体具有吸水性强、低渗透性、易饱和的特点,目前处于蠕滑变形阶段。通过堆积体颗粒级配试验及室内大剪试验结果,运用PFC^(3D)离散元数值软件建立反映颗粒相对大小的三维数值试验模型,反演对应于滑坡土体材料宏观力学特征的细观参数。通过现场无人机勘测摄像(UAV)生成数字高程模型(DEM),建立纳缝滑坡的三维数值模型,模拟该滑坡在自重及不同地下水位静水压力作用下的变形和运动过程,监测模拟过程中颗粒的位移,将位移突增点(计算不收敛)对应的地下水位作为临界过渡参数。基于Pradel&Raad提出的降雨入渗土坡深度的算法,反演临界降雨强度、降雨时长及降雨量;结合该滑坡体的位移监测数据、年降雨量的变化情况以及斜坡所处的稳定状况,验证降雨预警阈值的合理性。研究结果表明,纳缝滑坡地下水静水压力的大小与坡体的稳定性关系紧密,其破坏的临界静水位高度在1.70-1.75 m之间,反演得到的降雨预警参数阈值为降雨强度5.73×10^(-5)cm/s,降雨量439.13 mm。其工作思路和方法可为类似滑坡提供参考和借鉴。

The landslide in Nafeng talus slope in Luodian County,Guizhou Province is characterized by strong water absorption,low permeability and easy saturation,and is in the creep deformation stage at present.Based on the results of the grain grading test of the talus and the indoor large-scale shearing test,the discrete element numerical software(PFC^(3D))is used to establish a three-dimensional numerical test model reflecting the relative size of the particles,and the microscopic parameters corresponding to the macro-mechanical characteristics of the landslide soil material are inverted.The digital elevation model(DEM)is generated by UAV survey camera(UAV),and the PFC 3D numerical model of Nafeng landslide is established to simulate the deformation and movement process of the slope under the action of its own weight and hydrostatic pressure with different groundwater level.The displacement process is monitored,and the groundwater level corresponding to the sudden increase displacement point(calculation does not converge)is taken as the critical transition parameter.Based on the algorithm of rainfall infiltration depth proposed by Pradel&Raad,the critical rainfall intensity,rainfall duration and rainfall capacity are inversed.Combined with the displacement monitoring data of the landslide,the change of annual rainfall and the stability of the slope,the rationality of rainfall warning threshold is verified.The research results show that the magnitude of the hydrostatic pressure of the groundwater in the Nafeng landslide is closely related to the stability of the slope.The critical static water level of its damage is between 1.70-1.75m,and the rainfall warning parameter threshold obtained by the inversion is the rainfall intensity 5.73×10^(-5) cm/s,rainfall 439.13mm.Its working ideas and methods can provide reference for similar landslides.