Rainfall infiltration process of multi-layer slope based on improved Green-Ampt model stability analysis
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摘要:
降雨作用下，边坡土体的饱和度及含水率升高，基质吸力减小。随着降雨历时的增长，雨水入渗深度对坡体的稳定性产生影响。然而传统多层结构边坡的入渗计算方法并未考虑随入渗深度不断变化的基质吸力与层间积水点的形成，且忽略饱和层内沿坡体层面流动的部分雨水对入渗过程的影响，亦未考虑潜在滑动面位置随降雨历时的变化。将入渗过程分解为若干个子过程，并基于Green-Ampt（G-A）入渗模型对传统多层结构边坡的入渗计算方法进行改进，以对每个子过程进行求解，最后将其合并为整体入渗过程的解。在此基础上对层间积水点的形成时刻进行计算，进而分析雨水入渗深度与时间的关系，并研究降雨强度与雨水入渗深度对边坡不同位置处（湿润锋、饱和层）稳定系数和滑动面位置的影响。研究表明：（1）基于G-A模型的改进计算方法所得结果比传统多层结构边坡入渗计算方法所得结果更接近于数值模拟结果。（2）对于多层结构土质边坡，其安全系数随着雨水入渗深度的增加不断降低，并且在层间积水点形成时产生突变现象。（3）随着降雨历时和降雨强度的增大，边坡中潜在滑动面位置会产生变化，前期潜在滑动面位置出现在湿润锋处，后期则出现在饱和层交界面处。该方法提高了多层结构边坡传统降雨入渗计算方法的精度，更加全面的对多层结构边坡的稳定性进行评价，其工程应用范围亦得到进一步扩大
Abstract:Under the effect of rainfall, the saturation and water content of slope soil increase, while the matric suction decreases. With the increasing rainfall duration, rainwater infiltration depth has an effect on slope stability. However, the traditional infiltration calculation method of slope with the multi-layer structure does not consider the matric suction and the formation of inter layer water points that change with the infiltration depth, and ignores the influence of part of rainwater flowing along the slope layer in saturated layer on the infiltration process. The variation of the location of potential sliding surface with the rainfall duration is also not considered. Therefore, in this paper, the infiltration process is decomposed into several sub-processes, and the infiltration calculation method of traditional multi-layer slope is improved based on the Green-Ampt (G-A) infiltration model to solve each sub-process. The solutions of sub-precesses are finally merged into the solution of the whole infiltration process. The formation time of interlayer water point is calculated, the relationship between rain water infiltration depth and time is analyzed, and the influence of rainfall intensity and rain water infiltration depth on stability coefficient and sliding surface position at different positions of slope (wet front, saturated layer) is also studied. The results show that (1) the results obtained by the improved calculation method based on the G-A model are closer to the numerical simulation results than those obtained by the traditional multi-layer structure slope infiltration calculation method. (2) For the soil slope with multi-layer structure, its safety factor decreases with the increasing rainwater infiltration depth, and the phenomenon of mutation occurs when the interlayer water point is formed. (3) With the increasing rainfall duration and rainfall intensity, the position of the potential sliding surface in the slope change. The potential sliding surface appears at the humid front in the early stage, and at the interface of the saturated layer in the later stage. This method improves the accuracy of the traditional rainfall infiltration calculation method of the multi-storey structure slope, makes a more comprehensive evaluation of the stability of the multi-storey structure slope, and further expands its engineering application scope.
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表 1 土体力学参数
Table 1. Mechanical parameters of soil
土体力学参数 坡积土 风化土 基岩 饱和重度/（kN·m−3） 20.0 21.0 25.0 孔隙率/% 47.3 40.2 37.6 初始黏聚力/kPa 27.0 32.8 150.0 初始内摩擦角/（°） 20.0 21.0 25.0 饱和度/% 64.4 86.9 77.8 饱和度差/% 13.0 10.0 16.5 基质吸力/m 0.200 0.098 0.800 饱和黏聚力/kPa 17 26 8 拟合参数a −0.270 −0.095 −0.040 拟合参数b 0.75 0.40 0.20 
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