双层结构边坡降雨入渗与坡面径流耦合分析

天然土质边坡在地质和人为因素的作用下，通常呈现一定层状结构，在强降雨作用下会产生入渗和坡面径流。研究降雨条件下坡面径流与地表入渗相互影响过程，对山地洪水和滑坡灾害防治具有重要意义，然而，目前为止对层状土边坡地表与地下渗流的相互作用机制的研究理解还极为有限。本文针对上粗下细型层状土边坡降雨入渗研究中忽略坡面径流影响导致入渗分析不符合实际这一问题，基于Moore双层入渗和坡面径流控制方程建立耦合模型，并通过Python编制相应的计算程序分析耦合条件下双层结构边坡降雨产流及停雨后雨水重分布全过程。数值分析结果表明边坡土体降雨入渗过程与坡面径流深度有关；降雨初期降雨强度<坡面入渗能力，入渗速率等于降雨强度，坡面产流后入渗速率随降雨持时逐渐减小趋于稳定；当湿润锋跨过土层交界面时入渗速率急剧减小，最终等于次层土的渗透率，意味着上粗下细型层状土入渗速率主要由次层土控制同时降雨停止后径流快速衰退，已入渗的雨水在重力和湿润锋下方土体基质吸力的作用下继续向下推移，湿润锋入渗深度随雨水重分布历时趋于平缓。算例表明，该计算模型与计算方法可行，能够较好地反映实际层状土边坡的降雨入渗过程，为类似的层状土边坡研究提供计算依据。

Coupling Analysis of Rainfall Infiltration and Slope Runoff in Two-layered Slope

Natural soil slopes often consist in two or more soil layers due to the geological and human factors. Under heavy rainfall, rainwater infiltrates into the slope, and when the rainfall intensity is greater than the infiltration rate of the soil, the runoff occurs very shortly on the slope surface. Understanding the interaction process of slope runoff and surface infiltration under rainfall conditions is critical for flash flood and landslide risk management. However, the mechanism of the interaction between surface and underground seepage of layered soil slopes has so far remained poorly understood. The study of rainfall infiltration into the two-layered slope with coarse-over-fine stratification usually ignores the influence of slope runoff, and leads to an infiltration analysis that is not realistic. A coupled model was established to analyze the rainfall runoff and the rainwater redistribution process after rainfall, and the corresponding calculation program was compiled by Python to solve this problem based on the Moore two-layer infiltration and slope runoff governing equations. The numerical analysis results show that the rainfall infiltration process of the slope soil is related to the runoff depth on the slope surface. When rainfall intensity is smaller than hydraulic conductivity of surface soil, initial infiltration rate is equal to rainfall intensity, and gradually decreases with the rainfall duration after the runoff on the slope, and finally tends to be stable. The infiltration rate dramatically drops and eventually equals the permeability of the subsoil when the wetting front crosses the interface of the soil layers. It indicates that the infiltration rate of the slope with coarse-over-fine stratification is mainly controlled by the lower fine soil layer. The runoff is rapidly degraded after the rainfall stops, and the infiltrated rainwater continues to move downward under the combined action of gravity and the matrix suction of the soil under the wetting front. The runoff is rapidly degraded after the rainfall stops, and the infiltrated rainwater continues to move downward under the combined action of gravity and the matrix suction of the soil under the wetting front. The depth of wetting front tends to be gentle with rainwater redistribution. The example shows that the calculation model and calculation method are feasible, which can better reflect the rainfall infiltration process of the actual layered soil slope, and provide calculation basis for similar layered soil slope.