降雨诱发反粒序堆积体破坏的冲蚀-潜蚀-渗流耦合作用机理研究

The accumulation with inverse grading characteristics can always be formed from the high-speed and long-runout landslide, and rainfalls are the most important inducing factor of the progressive instability of these inverse grading accumulations. In consideration of a lack of deeply understanding the mechanism of erosion-internal erosion-permeation of the inverse grading accumulation failure induced by the rainfall, taking several inverse grading accumulations formed from typical high-speed and long-runout landslides as the research objects, based on the investigation and study of their hydrogeology and engineering geological characteristics, an artificial rainfall physical model experiments will be executed in this object. The technologies of 3D laser scanning, PIV system monitoring and acoustic emission can revealed the influence rules of the erosion-internal erosion on permeation, deformation, failure and particle migration. A mathematical model of slope runoff and unsaturated seepage will be established. The coupled numerical method based on material particle method (MPM) and discontinuous deformation analysis (DDA) will be developed, and the numerical simulation results will reveal the mechanisms of the particle migration and coupling hydro-mechanics of inverse grading accumulation failure induced by rainfalls, and a dynamic model of pore-water pressure considering internal particle migration and porosity will be established. A dynamic stability evaluation method of the inverse grading accumulation under the coupling effect of erosion-internal erosion-permeation during rainfall will be presented. The expected results will deepen our understanding of mechanisms of the rainfall-induced accumulation landslide, and provide theoretical support for stability evaluation of the accumulation.

高速远程滑坡通常形成具有反粒序堆积结构特征的堆积体，降雨作用是此类反粒序堆积体渐进性失稳的最主要诱发因素。鉴于当前缺乏对降雨诱发反粒序堆积体破坏的冲蚀-潜蚀-渗流耦合作用机理的深入认识，项目选取多个典型高速远程滑坡形成的反粒序堆积体为理论研究基地，在其水文和工程地质特性调研基础上，采用人工降雨物理模型试验，综合三维激光扫描、PIV系统监测、声发射等测试技术，揭示冲蚀-潜蚀耦合作用对其渗流、变形、破坏及颗粒运移的影响规律。建立坡面径流与非饱和-饱和渗流数学模型，开发物质点法（MPM）与非连续变形分析方法（DDA）耦合的数值模拟程序，揭示降雨诱发反粒序堆积体水-力耦合破坏作用机理和颗粒运移机制，建立考虑内部颗粒运移量、孔隙率的孔隙水压力动态演化模型；提出冲蚀-潜蚀-渗流耦合作用下反粒序堆积体降雨期动态稳定性评价方法。预期成果将加深对降雨诱发堆积体滑坡机理的认识，为稳定性评价提供理论支撑。

高速远程滑坡易于形成具有颗粒粒径上大下小特点的反粒序堆积体，而降雨作用是触发其破坏的重要因素。.项目以典型高速远程滑坡（谢家店子滑坡）形成的反粒序堆积体为研究对象，揭示其水力冲蚀-潜蚀-渗流耦合失稳作用机理，采用一维成层土柱渗流实验、三轴渗流实验及人工降雨物理模型试验，结合改进的数学解析模型及LBM-DEM耦合方法，探明冲蚀-潜蚀耦合作用对其渗流、变形、破坏及颗粒运移的影响规律。主要研究内容及重要结果包括：（1）开展反粒序土柱渗流侵蚀试验，发现反粒序砂土体发生管涌颗粒跃层后，细颗粒含量越高，临界水力梯度越大，水力梯度与渗流系数呈二次函数关系，管涌发生后其颗粒呈现剥离-沉淀-剥离-沉淀中下层颗粒交替侵蚀的运移模式；（2）开展含局部强渗区的土样渗流潜蚀实验及数值模拟细观研究，结果表明自出流口处向源发生潜蚀破坏，强渗区材料渗透性对土体的潜蚀破坏影响显著；（3）开展了人工降雨作用下反粒序堆积体渗流侵蚀破坏实验，揭示了细颗粒的运移特征参数（运移方向、速率）是诱发坡体的破坏关键因素，其促使土体结构与雨水的渗流路径发生变化，导致产生多种坡体破坏模式；（4）基于改进的Green-Ampt（G-A）模型对成层边坡的降雨入渗过程及稳定性进行计算，其安全系数随着雨水入渗深度的增加不断降低，并且在层间积水点形成时产生突变现象，边坡中潜在滑动面位置随降雨历时及强度产生变化，前期潜在滑动面位置出现在湿润锋处，后期则出现在饱和层交界面处；（5）开发LBM-DEM耦合程序，解决了宽级配堆积体水力破坏过程中颗粒拖曳力作用难题，实现了对多种粒径颗粒构成的堆积体水力冲蚀-潜蚀的有效模拟。以上成果有助于更深入地认识降雨诱发反粒序堆积体破坏演化模式及降雨冲蚀-潜蚀-渗流耦合作用机理，可为此类堆积体的稳定性分析及灾害预测提供理论支撑。