三相耦合渗流侵蚀管涌机制研究及有限元模拟

管涌的发生、发展过程是土骨架相在渗流作用下侵蚀为可动细颗粒相，并随水相在孔隙通道中运移流失的过程。在该过程中，渗流与侵蚀相互耦合，相互促进，水相、土相、可动细颗粒相互作用，因此，管涌过程是一个多场、多相耦合的高度非线性的动态过程。现有的管涌试验结果表明，只有当水力梯度大于起始水力梯度时，细颗粒相才会随水相从土体中运移流失，土体才会发生管涌侵蚀，且管涌稳定后土体的孔隙率（稳定孔隙率）和水力梯度之间存在对应关系，根据该结果，提出管涌稳定孔隙率的概念，修正传统的渗流侵蚀本构方程，建立多孔介质中三相耦合的修正的渗流侵蚀管涌控制方程。最后，针对特定应力状态下的土体建立稳定孔隙率和水力梯度之间的对应关系。基于Galerkin有限元法编制有限元程序，在轴对称情况下对该土体的管涌过程进行数值模拟。结果表明，修正后的管涌控制方程能更全面地描述管涌发生、发展直至稳定状态的特性。

Mechanism study and finite element simulation of three-phase coupling seepage erosion piping

The occurrence and development of piping is the process that skeleton solids translate into fluidized-solids under the action of seepage; then flow with fluid in the pore channel and outflow the soil; Finally, during the process, seepage and erosion coupled and promoted each other, water and soil mutual effected as well; this means that the piping process is a highly nonlinear dynamic process during which multifield coupling and multiphase coupling. The experimental result of piping shows that only when the hydraulic gradient is bigger than the starting hydraulic gradient will the fluidized-solids outflow the soil with the fluid; then piping occurrence ，and there exists a corresponding relation between the porosity (stable porosity) and the hydraulic gradient in the stable phase of piping. This paper proposes the concept of stable porosity, revises the traditional constitutive law of seepage and erosion, establishes a modified governing equation for the three-phase coupling piping in porous media considering the experiment result. Finally, a soil sample in specific stress state is chosen to build the relation between the porosity (stable porosity) and the hydraulic gradient, a finite element program is designed to simulate the process of piping for this sample in axisymmetric cases based on the Galerkin finite element scheme. The results show that, the modified governing equations can describe the occurrence and development untill stable phases of piping than before.