Coupled model of fluid-saturated porous materials based on a combination of discrete and continuum approaches

The numerical model of fluid-saturated porous brittle materials is proposed. The model is based on a hybrid approach combining the particle-based numerical method with finite difference method. In the framework of the model an enclosing porous solid is described with the discrete element method. An ensemble of discrete elements is used to model the processes of deformation of a porous solid and filtration of single-phase fluid in interconnected network of “micropores” (which are the pores, channels and other discontinuities enclosed in the volume of discrete elements). Relations between stress and strain of a discrete element, the change in volume of its pore space and fluid pore pressure in the “micropores” are proposed. Fluid mass transfer between the “micropores” and “macropores” (which are considered as the areas between spatially separated and non-interacting discrete elements) is calculated on the finer grid freezed in the laboratory system of coordinates. The developed coupled model was applied to study the mechanical response of samples of elastic-brittle material with water-saturated pore space under uniaxial compression. It is shown that the strength of fluid-saturated samples is determined by not only the strength properties of “dry” (unfilled) material and the fluid pore pressure, but largely by sample aspect ratio, rate of deformation and the characteristics of porosity of the material. Analysis of simulation results allowed authors to suggest a generalizing dependence of the uniaxial compressive strength of water-saturated permeable brittle material on the reduced diameter of filtration channels, which is the ratio of the characteristic diameter of the filtration channels to the square root of the sample strain rate. Presented results demonstrate the ability of the developed model to study nonstationary processes of deformation and fracture of fluid-saturated materials under dynamic loading.