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Abstract The purposes of the DECOVALEX project(development of coupled models and their validation against experiments) are focused on the various coupled thermo-hydro-mechanical(THM) and geochemical processes occurring in the near field of a high activity radioactive waste disposal facility，of a demonstration for the feasibility of the construction of engineered barriers，and of how they affect the role of performance assessment for radioactive waste disposal. Task_D of the DECOVALEX_IV project includes predictive analysis of the long-term coupled processes(up to 1×104 years) in two generic repositories——FEBEX type and Yucca Mountain Project type for comparison. To better understand the coupling THM processes and their influences on the system behaviours，this paper presents a rigorous treatment of the theory of non-isothermal flow and deformation in unsaturated porous media. The governing equations based on the conservation equations of mass and energy and the equations of equilibrium，Darcy¢s law，Fourier¢s law are derived by using a systematic macroscopic approach. Each of the three phases(solid，liquid and gas) is viewed as an independent continuum，endowed with its own kinematics. Four constituents(solid，water，vapour and dry air) are identified. Four separate but overlapping models are developed as follows：(1) deformation model for solid considering the fluid effective stress，thermal stress，and bentonite saturation swelling pressure；(2) flow model for water and gas considering the mass exchange between water and vapour in evaporation or condensation processes；(3) vapour molecular diffusion and advection model considering the relative movement of vapour to dry air in presumed homogenous pore gas phase；and (4) heat transfer model considering the non-equilibrium local thermal processes that three phases are not at a same temperature. Based on above equations，practical models are developed according to the given Task_D BMT(bench mark test) request，and the codes are programmed to simulate coupled THM processes in 1×106 years with Task_D BMT set-up. Simulation results are shown and verified in Task_D force meeting and the third workshop of DECOVALEX_IV in Kunming(2005)，China. There is a good agreement with results of participant teams from other countries.
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Received: 30 August 2005
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