黄土陡坡降雨冲刷试验及其三维颗粒流流-固耦合模拟

针对坡角为70°的黄土边坡,进行2.7 mm/min降雨强度下的室内坡面冲刷试验。根据边坡冲刷破坏的过程特征,将边坡侵蚀方式演变过程归纳为试验初期的片蚀、中期的细沟侵蚀、到后期的切沟侵蚀和坍塌。试验中坡顶处侵蚀强度大于其他部位,当坡面形成上下贯通的切沟之后,水流开始掏蚀沟槽底部土体,随着冲刷的持续,切沟两侧土体强度降低,坡顶土体发生坍塌。以此为基础利用三维颗粒流软件PFC3D对边坡降雨冲刷过程进行流-固耦合模拟,在模拟颗粒大变形的同时得到颗粒运动轨迹、孔隙率、流体单元内流速等重要参数,这些参数的定量变化过程反映了降雨过程中边坡遭受侵蚀程度及水流侵蚀能力的分布规律:坡顶处侵蚀最为强烈、水流侵蚀能力最强,且两者随高度降低呈减小趋势,与室内试验结果一致。

Rainfall erosion experiment for steep loess slope and fluid-soil coupling simulation with PFC3D

A series of experiments of slope rainfall erosion were done in laboratory for steep loess slope with slope angle of 70° under a rainfall intensity of 2.7 mm/min. According to the characteristics of slope erosion, the evolution of rainfall erosion process is generally concluded as splash and sheet erosion in earlier phase, rill erosion in middle phase, and finally evolved into gully erosion and collapse in later phase. It was found that the degree of erosion at the slope top is stronger than other positions during the experiment; after a through gully formed on the slope surface, the water flow then began to scour soil inside the gully; with rainfall lasting, the strength of the soil around the gully obviously decreased; consequently collapse took place at the slope top and eventually caused wholly demolition of the slope. Based on the experiment, simulating the slope erosion process with PFC3D with fluid-soil coupling method, observing the large deformation of particles, simultaneously the microcosmic parameters such as particle motion trace, porosity and water flow rate in fluid cells are obtained; from their quantitative change process, the distribution of degree of erosion and erosion intensity of water flow in slope is got; it indicated that the degree of erosion and the erosion intensity of water flow at slope top are strongest and both reduced as the height decrease, which is consistent with the indoor model experiment.