花岗岩残积土降雨滑坡起动过程剪胀效应及其临界灾变机制研究

The southeast of Guangxi province is a typical distribution area of granite residual soil in China. Granite residual soil frequently induces landslide disasters under the fragile geological environment and strong rainfall. These landslides have caused incalculable losses to the lives, property, engineering facilities and economic development in the region. The scholars have carried out extensive research on granite residual soil and achieved fruitful results. However, the catastrophic mechanism of landslides in the southeastern Guangxi province, which considers the dilatancy effect of granite residual soil, has not yet been clarified. It seriously restricts the effective early warning and prevention of landslide hazard. Therefore, this application project will focus on the granite residual soil landslide, and adopt a variety of methods and techniques to carry out the research, such as field investigation, laboratory model experiments, in-situ tests, theoretical analysis and numerical modeling. The purpose of this project is to clarify the spatial and temporal variation characteristics of soil physical property parameters in the process of landslide initiation. Furthermore, the mechanical properties, the influencing factors and the internal mesoscopic mechanism of phase transformation in the process of landslide initiation are discussed. Finally, the catastrophic mechanism of landslide is revealed which is considering the dilatancy effect. The research results are expected to provide the scientific support for the effective early warning and prevention of landslide hazard.

桂东南是花岗岩残积土的典型分布区。花岗岩残积土在脆弱的地质环境条件和强降雨激发作用下，频繁地诱发群发性的滑坡灾害，给人民生命财产、工程设施和经济造成了难以估量的损失。虽然学者们已对其他区域花岗岩残积土滑坡开展了广泛研究并取得了丰富成果，但是考虑剪胀效应的桂东南花岗岩残积土滑坡机理依然尚未被明晰，致使滑坡的监测预警和防治收效甚微。为此，本项目以桂东南花岗岩残积土滑坡为研究对象，以其力学性状为核心脉络，基于现场调查、室内模型试验、原位监测、理论分析、数值模拟等方法与手段开展研究，旨在明晰滑坡起动过程中，土体物理性质参数的时空变化特征；进而探讨滑坡起动过程中残积土的力学性状、影响因素及其相变转化的内在细观机制；最终揭示考虑残积土剪胀效应的滑坡灾变机理。预期研究成果将能指导花岗岩残积土滑坡预警与防治。

基于剪胀效应的桂东南花岗岩残积土滑坡机理尚未被研究，致使滑坡的监测预警和防治收效甚微。本项目以花岗岩残积土的力学性状为核心脉络，采用现场调查、模型试验、数值模拟与理论分析相结合的方法，研究残积土滑坡起动过程中土体物理性质参数的变化特征、力学性状及其转化的影响因素和细观机制，揭示考虑残积土剪胀效应的滑坡灾变机理。结果表明：(1) 体积含水率和孔隙水压力对降雨的响应不同步。初始干密度和降雨强度对响应有显著影响。大密度能抑制雨水入渗速率与孔隙水压力的波动。高降雨强度能导致体积含水量的响应时间缩短；然而，这并不适用于密度较小的土体。孔隙水压力的波动取决于土体的力学特性与孔压扩散的时间尺度。(2)残积土滑坡起动时间和模式是存在差异的。起动时间随着初始干密度和坡度的增加而延迟，但随着降雨强度的增加而缩短。随着初始干密度的增大，破坏模式由突发型转变为渐进型。（3）残积土滑坡起动过程均包含5个类似阶段：雨水入渗、坡脚土体滑动、坡面径流与侵蚀、陡峭临空面形成、坡顶土体滑动。这些过程伴随着细小颗粒的迁移、裂纹和大孔隙的形成。（4）滑坡起动时残积土的力学性状存在剪胀和剪缩两种类型。（5）剪胀对滑坡运动的调节作用与其变化趋势有关。当剪胀角恒定时，超孔隙水压力的增量与静孔隙水压力的增量能相互抵消。这使得基底总孔隙水压力保持在滑块起动时的数值，滑块处于较平缓的渐进滑动状态。剪胀角的衰减会促使加速度的显著增大。当剪胀角增大时，滑块的加速度及其增幅均较小。剪胀角衰减时的速度和位移最大，剪胀角不变时的次之，剪胀角增大时的最小。当剪切带出现剪缩时，坡体内迅速产生正的超孔隙水压力使得基底总孔隙水压力急剧增加，导致滑块完全液化。此时滑块的运动过程具有突然且迅速的特征。研究成果为该地区滑坡的风险评估和防治预警提供科学支撑。