短时强降雨下残积土斜坡水分非平衡运移特性与灾害演化机制研究

In recent years, research achievements show that non-equilibrium flow is the main flow manner of moisture immigration in macropore medium. The characteristics of non-equilibrium transport on macropore slope under short-time heavy rainfall condition can be a link to reveal the time order effect of rainfall infiltration, non-equilibrium flow, hydromechanical coupling and landslide. All of these are very useful for improving theory of precipitation-induced landslide. Due to the short history of theroy of non-equilibrium flow, there are some problems such as characteristics of non-equilibrium flow and the hydromechanical coupling model considering the non-equilibrium flow are still unclear..Taking non-equilibrium flow as the main line，this project mainly studies on evolution mechanism of geological hazard on residual slope induced by short-time heavy rainfall. The main content of the project is as follow：Firstly, macropore distribution, multifractal features, three-dimensional restructure and macropore network model are proposed by computed tomography and digital graphic processing technique. Secondly, on the basis of the combination of Lattice Boltzmann Method, stochastic network pore model and tracer infiltration experiments, characteristics of heterogeneous flow of residual soil sample are revealed. Thirdly, spatial-temporal evolution pattern of non-equilibrium flow of residual soil slope is revealed based on macropore model, overland flow model and seepage experiment of unsaturated transparent soil. Finally, the interaction mechanism of moisture field, stress field, deformation field and collapse mode of residual soil slope are analyzed by the hydromechanical coupling model considering the non-equilibrium flow and the field test under short-time heavy rainfall condition. Based on the research work above, the results of this research can enrich the theory of precipitation-induced landslide and provide a theoretical basis for.disaster prevention.

近年研究发现水分非平衡运移是含大孔隙土壤水迁移的主要形式。刻画短时强降雨对含大孔隙斜坡的水分非平衡运移机制，进而揭示“降雨-水分非平衡运移-水力耦合-失稳”时序耦合效应，极具理论价值。但目前存在大孔隙特征刻画不足、水分非平衡运移与水力耦合机制滞后等问题。项目以水分非平衡运移为主线，重点研究短时强降雨条件下斜坡水分非平衡运移特性与灾害演化机制。具体为：综合工业CT断层扫描及数字图像处理技术，揭示残积土样大孔隙空间分布并构建三维重构模型、随机大孔隙网络模型；结合LBM法、随机网络法以及显色示踪试验，刻画土柱水分非均匀细观运动机制；基于大孔隙两域渗流模型、坡面流模型以及非饱和透明土渗流试验，揭示斜坡坡面坡内水分非平衡运移的时空演变规律；构建考虑非平衡流的斜坡水力耦合模型，分析短时强降雨条件下残积土边坡的水分场、应力场、变形场相互作用机制以及垮塌模式。成果可丰富暴雨型滑坡理论基础并支撑灾害防治。

与普通降雨不同，台风暴雨具有降雨时间集中、短时降雨强度极大以及累积降雨量多等特点。课题以水分非均匀迁移为主线，重点研究了强降雨条件下斜坡水分非均匀迁移特性与灾害演化机制。具体为：.（1）综合工业CT扫描及图像处理技术，构建原状残积土大孔隙网络模型，得出了原状土体在不同深度处大孔隙率变化范围介于5.8-22.7%，连通孔隙的等效半径介于2-2.4mm，孔隙配位数主要集中在20以内，超过20的孔隙配位数分布呈离散点状。.（2）采用格子Boltzmann方法进行细观渗流数值模拟，展现了不同时刻下孔隙区域内的渗流速度和流线分布情况，并计算渗流稳定后渗透率k为0.4921μm2，与室内试验所测0.4470μm2相对比，误差仅为9.35%。.（3）基于透明土与图像处理技术，研究了优先流路径连通性与相邻优先流路径旋转角对非饱和土优先流迁移的影响，得出相邻O-C型优先流区域形成新的优先流，土体达到高饱和度，增长速率随旋转角的增加而减小，优先流转角为90°、60°和30°时稳定入渗速率分别为均匀流的1.5倍、1.3倍和1.2倍。.（4）基于大孔隙两域入渗模型，研究得出大孔隙参数ωf增大，两域入渗深度将有所减小，而大孔隙参数μ增大，边坡两域含水率变化规律呈现相反的趋势，基质域土湿润锋深度随着μ的增大而减小，大孔隙域湿润锋深度随着μ的增大而增大。.（5）构建考虑非均匀流的斜坡水力耦合模型，分析了短时强降雨条件下残积土边坡的水分场、应力场、变形场相互作用机制以及垮塌模式，得出边坡失稳破坏面积随降雨时间而增加，水分随着坡度的增大影响较小，但破坏面积区域最高增幅近4倍，同时参数ωf和μ值增大，边坡局部稳定性下降最大幅度分别为44%和6.8%。.本基金以东南沿海常见的花岗岩残积土为例，结合了台风短时强降雨气候条件，从细观、宏观角度分别剖析花岗岩残积土大孔隙空间分布与结构特征，并揭示短时强降雨下坡内水分非均匀宏细观运移机理以及边坡失稳机制，实时满足当前基础建设和防灾减灾工作需要，不仅具有区域特色，同时也具有向全国其他类似气候与土质类型的区域进行推广的应用价值。