降雨诱发松散堆积体边坡失稳的渗流-潜蚀-应力耦合机制研究

Loose landslide deposits are widely distributed in the western mountainous areas of China. When subjected to rainfall, the slopes composed of these deposits fail easily, which may frequently trigger geologic hazards and hence pose long-term serious threats to post-earthquake restoration and reconstruction activities in these mountainous areas. The project proposed here is intended to study the rainfall-induced instability of slopes composed of loose deposits. By combining approaches such as experimental investigation, theoretical analysis and numerical simulation, and from the “seepage-erosion-stress coupling” perspective, this project will: investigate the migration rule of fine soil particles within unsaturated deposits and its effects on the deposits’ mechanical and hydraulic properties; build a seepage-erosion-stress coupled model for unsaturated deposits and develop the corresponding numerical platform; analyze quantitatively the evolution process of multi-field coupled phenomena within these slopes under rainfall infiltration and the corresponding slope failure mechanisms. This project will provide a reliable theoretical basis for the disaster prediction and risk assessment of slopes composed of loose deposits, and therefore improves the scientific level of disaster prevention and mitigation in western mountainous areas of China.

西部震后山区广泛分布的松散堆积体边坡在降雨作用下极易失稳引发次生地质灾害，其影响范围广、持续时间长，对震后山区的恢复和重建工作造成严重威胁。本项目拟以松散堆积体边坡降雨失稳为研究对象，综合试验分析、理论研究和数值模拟等多种手段，从“渗流-潜蚀-应力耦合”的角度，系统研究雨水入渗作用下非饱和堆积土中细颗粒运移规律及其对土体水力性质的影响，构建非饱和堆积土渗流-潜蚀-应力耦合物理模型及数值计算平台，量化分析降雨条件下堆积体边坡内多场耦合演进特征及其耦合失稳机制。项目将为松散堆积体边坡灾害预测和风险评估提供可靠的理论依据，提高我国西部山区防灾减灾科技水平。

西部山区的松散堆积土是一种宽级配弱固结土，其内部细小颗粒易随降雨入渗在粗颗粒土骨架间孔隙发生迁移，改变土体水力特性，诱发堆积土斜坡降雨失稳。松散堆积体斜坡中发生的这类降雨-渗流潜蚀失稳破坏，是引发西部山区滑坡、泥石流最普遍的形式之一。本项目综合理论分析及数值模拟等手段从“渗流-潜蚀-应力耦合”的角度对西部震后山区松散堆积土在后续降雨条件下的滑坡、泥石流起动机制进行了系统研究，取得如下主要成果:（1）基于混合物理论构建了可考虑细颗粒迁移对非饱和堆积土斜坡土体水力特性影响的渗流-潜蚀-应力耦合模型，并开发了非饱和渗流-潜蚀-应力耦合有限元计算程序；（2）提出了考虑细颗粒侵蚀-运移-沉积过程的无限边坡安全性评价方法，量化分析了细颗粒迁移诱发斜坡失稳的破坏机制；（3）推导了一种数值稳定的显式三相单点渗流-潜蚀-应力耦合物质点法模型，并编制了非饱和渗流-潜蚀-应力耦合显式物质点法程序，实现了对非饱和堆积土斜坡从降雨-渗流潜蚀失稳到大变形滑移堆积全过程的模拟。该项目定量分析了降雨-渗流潜蚀诱发堆积体边坡失稳的内在机制，为降雨条件下堆积体斜坡稳定性定量评判及监测预警提供了理论依据，并为堆积土斜坡潜蚀致灾过程定量分析及由细颗粒迁移诱发的滑坡、泥石流起动机制及危险性评价研究提供了其于有限元法及物质点法的数值平台工具。