砂土管涌-滤层防治的离散元数值模拟

Numerical simulation of piping-filter prevention in sandy soil by discrete element method

结合小比尺细观模型试验,利用并开发基于离散元理论的颗粒流程序(PFC3D),充分考虑流固耦合作用,建立渗流理论模型,对不同层间系数下砂土管涌的基料-滤层系统进行离散元数值模拟,跟踪记录渗流过程中砂样运动、流失量、孔隙率、渗透系数、颗粒间接触力、水力梯度等参数的动态变化过程,从细观角度揭示管涌发展过程中颗粒的运动特性和滤层防治机理。数值模拟结果表明,层间系数D15/d85s大小是滤层是否有效的关键因素;在有效的层间系数下,随着水力梯度的加大,基料的细颗粒运动并进入滤层,在滤层-基料交界处存在的自滤现象。模拟结果与有关的模型试验结果吻合较好,一定程度上验证了该数值方法的可行性和合理性。本文所揭示的结果有益于对砂土管涌和滤层防治机理的更深入研究。

Combining with the small-scale model tests and using Particle Flow Code based on discrete element method, the seepage erosion model established with the coupling of solid and fluid taken into account. The numerical model of base soil-filter system during seepage in sandy soils is simulated under various coefficients between layers. The variations of the path of moving particles, loss fraction of gains, porosity, permeability, contact force, hydraulic gradient of particles, and etc are traced and recorded. The movement Characteristics of particles and the filter prevention mechanism arc studied from the viewpoint of meso-mechanics. The results show that the coefficient between layers （D15/d85a）is important to the effectiveness of filter layer. Following the accretion of hydraulic gradient, under the effective coefficient between layers, the self-filter phenomenon exists in the base soil-filter interface when the movable particles of base soils entering into the filter layers. The rationality of the proposed numerical method is validated by comparing the numerical solutions with the relative experimental results. The results are valuable to probe into the piping and filter mechanism in sandy soils further.