降雨入渗诱发黄土斜坡变形破坏过程的水分时空动态研究

Homogeneous infiltration and preferential flow are coexist in the rainfall infiltration of loess slope, the distribution and migration of soil moisture within the slope are heterogeneous. A small amount of traditional point moisture monitoring such as time-domain reflectometry (TDR) is difficult to accurately represent the soil moisture dynamics and distribution within the slope, which limits the comprehensive and deep understanding of the hydrological process of loess slope, and furtherly may lead to the failure of landslide warning. Therefore, this project intends to set the typical loess slope as the research object, execute the time-lapse electrical resistivity tomography as the main technology mean, in combination with point moisture monitoring, ground penetrating radar, three-dimensional terrestrial laser scanning. Laboratory and field test, field monitoring, in-situ artificial rainfall experiment and numerical simulation were carried out. Firstly, determine the internal structure of loess slope, analyze the correlation between water content and electrical resistivity of loess, and establish their quantitative relationship. Secondly, realize the two-dimensional imaging of water content, quantify the spatiotemporal soil moisture dynamics within the loess slope, and reveal the hydrological response process of loess slope under rainfall condition. Finally, analyze the rule of resistivity and moisture variation in loess slope at different deformation stages, illuminate the statistical characteristic of wetting index evolution preceding the loess slope failure, and reveal the pattern of soil wetting evolution during critical sliding stage. Anticipated outcomes of this research have scientific significance on improving the theory of hydrological process and forecasting of loess landslide, and could also provide practical reference for executing hydrological monitoring and early warning of loess landslide comprehensively.

黄土斜坡降雨入渗均匀渗流和优势流同时存在，水分在土体中的运移与分布呈非均匀性特点，少量点式水分监测很难准确代表斜坡内部水分的动态变化和空间分布，限制了对黄土斜坡水文过程的深入认识，可能进一步影响黄土滑坡预警预报。为此，本项目拟以典型黄土斜坡为研究对象，以时移电阻率层析成像法为主要技术，结合点式水分监测、地质雷达、三维激光地形扫描等手段，开展室内外测试、野外监测、现场人工降雨试验和数值模拟，确定黄土斜坡坡体结构，分析黄土电阻率与含水量相关性，建立其电阻率-含水量定量关系；实现斜坡内部水分二维成像，定量分析水分时空动态变化，揭示降雨条件下斜坡内部水文响应过程；分析斜坡在不同变形阶段电阻率和水分变化规律，阐明斜坡失稳破坏前增湿指数时空变化统计学特征，揭示黄土滑坡临滑增湿时空演化模式。预期成果对黄土滑坡水文过程和预警预报理论完善有科学意义，为全面合理的进行黄土滑坡水文监测和早期预警提供参考和借鉴。

黄土斜坡降雨、灌溉入渗均匀渗流和优势流同时存在，水分在土体中的运移与分布呈非均匀性特点，少量点式水分监测很难准确代表斜坡内部水分的动态变化和空间分布，限制了对黄土斜坡水文过程的深入认识，可能进一步影响黄土滑坡预警预报。本项目选择典型黄土斜坡为研究对象，以新近发展的时移电阻层析成像法为主要技术手段，结合时序InSAR、室内测试、现场人工降雨试验和野外监测等，开展了黄土斜坡变形破坏过程的水分时空动态研究。取得了以下主要成果：（1）分析了黄土电阻率与不同物理化学参数相关性，结果表明含水率是地层电阻率发生变化的主导因素，基于Archie公式建立了黄土电阻率-含水量岩土物性关系：θ=0.49(ρ/4.20)^(-1/1.62)，实现了黄土斜坡内部水分二维成像。（2）通过人工降雨模拟试验，分析了黄土斜坡对降雨的动态响应规律，重现了黄土滑坡降雨优势入渗过程；揭示了黄土滑坡孔隙水压力与位移变化的不同模式主要是受对应位置的前期含水状态以及水分补给和排泄关系决定的，同时存在三个阶段的变化模式：孔隙水压力增加诱发变形阶段、加速变形导致孔隙水压力快速消散阶段和相对平衡稳定状态阶段，推断出滑带土体剪胀是导致黄土滑坡间歇性运动的力学机制。（3）灌溉条件下，黄土滑坡滑后地下水排泄路径改变对黄土斜坡水文响应规律具有显著影响，地下水位短期内表现出对灌溉快速的响应过程，长期则呈现先下降后上升的特征。滑坡台塬区地下水位强烈波动使斜坡变形表现出明显的空间差异性。（4）探索分析了黄土滑坡启动水分增湿模式，发现增湿导致饱和度持续升高是黄土斜坡失稳的先决条件，饱和度的离散程度决定黄土斜坡变形特征，不同变形阶段饱和度表现出明显差异。斜坡内部饱和度增加到一定程度可诱发変形，而增湿范围由局部向滑带整体扩散可诱发大的变形，饱和度表现出较小离散性。研究成果在一定程度上完善了黄土滑坡水文过程和预警预报理论，为全面合理的进行黄土滑坡水文监测、早期预警和应急勘查提供了参考和借鉴。