Microscopic numerical model of fluid flow in granular material

A microscopic numerical model of fluid flow through granular materials using the discrete-element method is developed to take account of the effect of particle movement. The scheme solves for fluid pressure in void spaces surrounded by the particle elements used in the discrete-element method to consider the compressibility of fluid during particle movement and diffusion, that is flow across void spaces in a one-dimensional form of Darcy's law. The calculated fluid pressure is applied to particles involved in the void space as a body force proportional to the occupied area in the space. This microscopic two-way coupling method enables the analysis of the microscopic mechanical characteristics of granular materials associated with fluid, as many problems in geotechnics involve such interactions between particles and a pore fluid. The approach can be applied in situations with undrained dynamic loading inducing excess pore water pressure and subsequent liquefaction. The paper first describes the formulation and the numerical scheme, then two-dimensional simulations are conducted to validate the scheme.