黄土边坡降雨冲刷试验及颗粒流模拟
Test on rainfall erosion of loess slope and its simulation by PFC3D

为了研究公路工程中黄土边坡的冲刷破坏特征及演化机制，以辽宁西部黄土边坡为研究对象，进行边坡冲刷破坏的室内物理模型试验；监测降雨过程中边坡土体的含水率，分析其雨水入渗规律；以试验为基础，基于水-土耦合理论，借助三维颗粒流程序PFC3D对边坡降雨冲刷过程进行模拟，得到冲刷破坏过程中边坡不同部位土体孔隙率、水流流速、颗粒平均运动速度的分布及变化过程。研究结果表明：在降雨过程中坡脚的浸润范围明显大于其他部位，且这种趋势随着降雨的进行愈发明显；坡面冲刷破坏的演变过程可归结为溅蚀、片蚀→细沟冲蚀→切沟冲蚀→坍塌，坍塌过程由坡脚向上发展，呈牵引式破坏特征，直至边坡完全破坏；随着冲刷的进行，颗粒流失从坡顶到坡脚呈增加趋势，从坡顶到坡脚水流速度呈增大趋势，伴随着单元内颗粒的滑动，流速曲线局部出现峰值，各流体单元内颗粒运动速度的变化特征与水流流速的变化特征相似。颗粒流模拟获得的参数反映出降雨过程中水流侵蚀能力及土体侵蚀强度在坡体内的分布特征：从坡顶到坡脚的水流侵蚀能力呈递增趋势，坡脚处侵蚀破坏最为严重，模拟结果与室内模型试验结果基本吻合，可从细观层面对模型试验做出补充。
To study the rainfall erosion characteristics and its evolution mechanism of loess slope in highway engineering. Taking loess slope in western Liaoning as the research object, physical model test was conducted in laboratory. Moisture content of slope soil during rainfall was monitored and migration law of wetting front in slope was analyzed. Based on the test results and water-soil coupling theory, the rainfall erosion process of slope was simulated by PFC3D, and the void ratio in different positions of slope during rainfall erosion, water flow rate and the distribution and changing process of particle average moving rate were obtained. The results show that the infiltration area at slope toe is larger than the other positions, and with the rainfall this trend is more and more obvious. The evolution of erosion process can be generally concluded as splash and sheet erosion, rill erosion, gully erosion and finally evolved into collapse. The collapse was retrogressively developing upwards, until the slope completely destroyed. Loss of particles and the water flow rate both increased from the top of the slope to the slope toe as the erosion progressed. With the particles sliding, there will be local peaks on the water flow rate curve, and particle moving in each fluid unit exhibited similar variation characteristics with the water flow rate. These parameters obtained from PFC3D simulation the distribution of erosion capacity of water flow and soil erosion intensity in slope, the erosion capacity of water flow was increasing from top to toe of the slope, and the soil erosion intensity at toe of the slope was the most serious place, which was consistent to the result of laboratory model test, also was a supplement for model test on meso perspective