A numerical approach is developed to solve the fully coupled hydrological, thermal, and mechanical system in rocks. The uniqueness of this approach is that we solve the coupled system in an interactive environment. In this approach, we extend conventional models for the coupled mechanics of solid deformation, fluid flow, and heat transfer into a single multi-physics model that solves the coupled multiphysics. A series of 2D FEM analyses on rock matrix is conducted to explain the effects of temperature and fluid flow on pore pressure. The high and low permeability values are applied in the case study. It is shown that the temperature gradient and the hydraulic gradient have an important influence on the state of fluid flow in the near field. For different permeability the action of temperature gradient maybe higher or lower than the action of the hydraulic gradient, so that the direction of the flow velocity maybe reverse and the water transporting direction is not unchangeable; the flow velocity fields have an obvious difference according to different permeability values so that the diffusion of radioactive nuclide with underground water flow is also complex. The research can provide guidance for the design of radioactive waste disposal engineering and optimizing a fluid injection operation.
The internal scientific community is now paying increasing attention to the storage of heatproducing radioactive wastes in rock formations deep underground, and this has led us to investigate phenomena involving combined thermal, hydraulic and mechanical effects. Coupled THM processes are potentially important both in the near field and in the far field of a repository. Various coupled THM phenomena can be envisaged in the vicinity of the waste packages or the storage rooms that may impact the waste isolation performance of a nuclear fuel waste repository constructed in lowpermeability rock. These include the opening or closure of fractures with accompanying changes in permeability, thermally driven fluid flow, glacial loading induced hydraulic gradient, thermally and thermo-mechanically induced pore pressure build up which may increase the potential for cracking due to the concomitant changes in the effective stress and failure criteria [l,2,3,4]. A number of experimental studies has been carried out and, in parallel, computer codes have been developed using sophisticated numerical methods to study the coupled THM action [5,6,7,8]. A motivation of this study is to demonstrate our latest success in simulating multiphysics simultaneously by using COMSOL software, a numerical tool that performs equation-based multiphysics modeling in an interactive environment. With COMSOL we extend conventional models for one type of physics into multiphysics models that solve coupled physics phenomena. The crosscouplings among multiple processes are defined by the coupled relations between material properties and independent variables. And a numerical approach for solving the fully coupled hydrological, thermal, and mechanical system in rocks is developed.
