3D thermo-hydro-mechanical-migratory coupling model and FEM analyses for dual-porosity medium

Abstract

One kind of 3D coupled thermo-hydro-mechanical-migratory model for saturated-unsaturated dual-porosity medium was established, in which the stress field and the temperature field are single, but the seepage field and the concentration field are double, and the influences of sets, spaces, angles, continuity ratios, stiffness of fractures on the constitutive relationship of the medium can be considered. The relative three-dimensional program of finite element method was also developed. By comparing with the existing computation example, reliability of the model and the program were verified. Taking a hypothetical nuclear waste repository as a calculation example, the radioactive nuclide leak was simulated numerically with both the rock mass and the buffer being unsaturated media, and the temperatures, negative pore pressures, flow velocities, nuclide concentrations and normal stresses in the rock mass were investigated. The results showed that the temperatures, negative pore pressures and nuclide concentrations in the buffer all present nonlinear changes and distributions that even though the saturation degree in porosity is only about 1/9 of that in fracture, the flow velocity of underground water in fracture is about 6 times of that in porosity because the permeability coefficient of fracture is almost four orders higher than that of porosity, and that the regions of stress concentration occur at the vicinity of two sides of the boundary between buffer and disposal pit wall.