强降雨条件下植被发育斜坡非饱和带土体大孔隙流试验研究

Because of the ever-increasing global warming, the frequency of extreme intensive rainfall and regional group slope failure events following the heavy rains in vegetated mountainous areas are getting higher and higher. The study on intensive rainfall infiltration process in the unsaturated soils of well vegetated slopes is important and fundamental for the study on the mechanism of slope failure; however, the current studies focus mainly on matrix flow. The importance of macropore flow has received much less attention. Taking typical well vegetated slopes in warm and humid areas as research objects, this study will concentrate on the rainfall infiltration process of macropore soils in the unsaturated zones of well vegetated slopes and the mechanism of macropore flow under intensive rainfall. Field monitoring, in situ tests, fine surveying, laboratory tests will be combined with indoor chemical analysis, indoor observation in this study. On the basis of test results, the following problems will be in-depth probed into: physical-chemical-hydraulic parameters distribution of unsaturated soils, 3D geometries and distribution pattern of macropore networks, etc; influence of macropore on rainfall infiltration, mechanism of wetting front instability and wetting front migration process, etc; relationship between macropore flow process and subsurface flow, interaction of macropore flow and matrix flow, etc. The results of this project will promote the development of the theoretical research of slope failure induced by intensive rainfall in well vegetated slopes in warm and humid areas and improve the forecast accuracy of regional group landslides in vegetated mountainous areas, and so this study is of theoretical interest and also of great relevance to applications.

受到日益加剧的全球变暖趋势的强力驱动，强降雨及与之相伴的山区流域植被发育斜坡的失稳事件的发生频率越来越高。植被发育斜坡非饱和带土体的强降雨入渗过程研究在斜坡失稳机制研究中处于重要地位，但对该过程的既有研究忽略了大孔隙流。本项目将以温湿气候区植被发育典型母岩斜坡为研究对象，综合采用现场试验、精细调查与室内试验、观察、分析、测试等相结合的方法，通过对非饱和带土体相关参数的空间分布、大孔隙结构及其几何特征；大孔隙对降雨入渗过程的影响，湿润前锋不稳定的约束机理及迁移过程；大孔隙流过程与表土层地下径流的关系、大孔隙流与基质流相互作用等问题的系统研究，查明强降雨条件下植被发育斜坡非饱和带大孔隙发育土体的降雨入渗过程及大孔隙流机理。本项研究对推进强降雨诱发温湿气候区植被发育斜坡失稳理论研究的发展，提高植被发育山区群发性斜坡灾害预报精度具有理论意义和应用价值。

以云南省昆明市呈贡区段家营斜坡、昭通头寨滑坡左翼斜坡、保山市昌宁县共浴滑坡、个旧象冲斜坡、怒江东月各斜坡、文山州麻栗坡县猛硐乡滑坡、昆明白泥山斜坡和贵州八渡滑坡为研究场地，综合采用现场调查、试验、监测及室内试验、观察、分析、测试和数值模拟等研究手段和相关计算技术，对强降雨条件下植被发育斜坡非饱和带土体的大孔隙流过程进行了系统研究。研究结果表明，植被发育斜坡土体的干密度随深度增加而增大，孔隙率、孔隙比、有机质含量和饱和渗透系数总体随深度增加而减小，是富含大孔隙的多孔疏松强~极强透水介质，尤其是表层土体。植被发育斜坡土体的大孔隙有腐烂根系通道、根-土间隙、动物通道、团聚体间大孔隙、土-石间隙、干缩裂隙和成因不明大孔隙，其中前4种是主要类型，不同类型大孔隙的多尺度几何形态和分布特征不同，各种大孔隙往往彼此交织组成大孔隙网络系统。大孔隙数量密度和大孔隙率总体随深度增加而减小。植被发育斜坡土体大孔隙可使全部降雨渗入土体内而不产生地表径流。大孔隙具有优先流功效，推测有87~95%的降雨通过大孔隙补给深度土体。在强降雨过程中，植被发育斜坡土体的水流路径是非均匀的, 湿润前锋不水平，非平面，甚至非连续，表层土体容易形成暴雨径流。大孔隙截留表土层暴雨径流而形成大孔隙流，导致湿润前锋形态不规则。大孔隙的直径、长度、弯曲率、密度和轴向影响大孔隙流流速和湿润前锋形态。在表土层和大孔隙底部，大孔隙流与基质流相互作用显著。研究成果为进一步探究大孔隙流对植被发育斜坡稳定性的影响，即大孔隙流与斜坡土体相互作用奠定了重要基础，对提高降雨诱发型滑坡的预测预报预警具有理论意义和应用价值。