中文摘要：

综合考虑水压力梯度力和拖曳力产生的流固耦合效应，建立3维颗粒流（PFC3D）数值模型，从细观角度分析砂土颗粒运动及水压力分布，与理论结果比较以验证数值模型的可行性，并建立实际的饱和砂土渗流模型，模拟超过临界水力梯度后的砂土颗粒运动及赋存状态．结果表明：水流速和颗粒级配对介质颗粒运动的影响较大，颗粒刚度比和摩擦系数的影响相对较小，但较软的颗粒能提高计算效率．该模型可从宏细观角度更准确地反映饱和砂土介质的渗透破坏机理，对实际工程的渗透破坏具有指导作用．

英文摘要：

Critical hydraulic gradient is always an important method to judge the seepage failure of the saturated sand medium, but for complex problems such as sand boiling, piping and soil flowing, the soil will probably fail when the transient seepage force of some point is larger than the soil particle gravity. Considering the fluid-soil coupling effect including the fluid pressure gradient force and drag force, a numerical model based on 3D particle flow code （PFC3D） was put forward to simulate the particle movement and water pressure distribution, and the results that agreed with the theoretical analysis proved the applicability of the above numerical model. Then a practical model was applied to simulate the sand particle movement when the critical hydraulic gradient was exceeded. The results indicate that flow velocity and particle grading distribution had significant influence on the particle movement, the particle stiffness ratio and particle friction coefficient had minor influence, but the soft particles might improve the calculation effect. The model can more correctly reflect the seepage failure mechanism of the saturated sand, and the method is useful to research on the seepage failure of practical projects.