基于散体介质理论的砂土管涌机制研究

RESEARCH ON PIPING MECHANISM IN SANDY SOILS BASED ON DISCRETE ELEMENT THEORY

结合小比尺细观模型试验,利用基于散体介质理论的颗粒流方法,考虑流固耦合作用,对砂土管涌的发生发展过程进行模拟。模拟方案跟踪记录管涌发展过程中砂样的孔隙率、流速、颗粒接触数、移动轨迹和流失量等参量的动态变化过程。分析结果表明:管涌发展过程中,随着水头增加,颗粒逐渐流失,砂样孔隙率增大,透水性能发生变化,进而影响系统的流速和水头的反应,揭示管涌发展过程中系统几何特性和水力特性的非线性动态变化过程和相互影响特性;颗粒流失量沿渗流方向呈逐渐减小趋势,管涌发展过程中颗粒移动轨迹随机,渗漏通道形成也具随机性,是复杂水土相互作用的结果。颗粒间接触数的剧烈波动揭示管涌发展过程中细颗粒运动剧烈,与粗骨架颗粒进行不断碰撞、分开,而颗粒的流失基本上不影响整个土体的应力场。模拟结果与有关的模型试验结果较吻合,一定程度上验证了该数值方法应用于大变形和流固耦合问题研究的可行性和合理性,所揭示的结果有益于砂土管涌机制的更深入研究。

Using particle flow code（PFC） based on discrete element theory and combining with the small-scale model tests, the piping in sandy soils is simulated with fluid-solid coupling. The porosity of sample, fluid velocity, contact number of particles, pathway of movable particles and loss fraction of eroded particles and so on are traced and recorded in the analytical model. The results show that the movable particles are eroded gradually; and the fluid velocity and porosity of sample increase gradually with the increase of water head; the permeability of sample changes, which will be influenced greatly by the response of fluid velocity and water head. The results reveal that the geometric and hydraulic features of system change dynamically and nonlinearly, which disclose their interactive behaviors during piping. The results also show that the loss fraction of eroded particles decreases along the seepage flow path; the small particles remove randomly; and the leak passages of piping are formed randomly when piping, which are the outcome of the complicated interactions between water and soil. The violent fluctuation of contact number of movable particles shows the violent motion of small oarticles during piping; and the stress field of soils is not influenced by particle erosion fundamentally. The availability and rationality of the proposed numerical method is verified by comparing the numerical solutions with the results of relevant physical model tests. The results are valuable to further probing into the piping mechanism in sandy soils.