Development and validation of TOUGH-3DEC: A three-dimensional discontinuum-based numerical simulator for coupled thermo-hydro-mechanical analysis

The discontinuum-based numerical methods can simulate the coupled thermo-hydro-mechanical (THM) processes in porous media with multiple discontinuities, so it is appropriate to model the mechanical behavior of a fractured host rock under the coupled processes such as a geological repository for high-level radioactive waste. TOUGH-3DEC, a three-dimensional discontinuum-based simulator for the coupled THM analysis, was developed by linking the integral finite difference method TOUGH2 and the distinct element method 3DEC to describe the coupled THM processes in porous media and discontinuous media. TOUGH2 handles the coupled TH analysis through the internal simulation module, while 3DEC performs mechanical analysis based on the constitutive models of porous media and discontinuity, coupling the thermal and hydraulic responses from TOUGH2. The thermal and hydraulic couplings are key processes and should be carefully verified by sufficient cases, so this study performed TM and HM verifications by modelling analytic solutions including the uniaxial consolidation, fracture static opening, and the heating of a hollow cylinder. As comparative validations, two models describing laboratory-scale experiments regarding the HM and TM processes of fractured rock were simulated and compared to the experimental results. The developed TOUGH-3DEC simulator showed sufficient accuracy in reflecting the coupled THM processes of the small-scale discontinuous rock, but still needs to be verified by more complicated and large-scale coupled process problems to be applicable to the demonstration of the field-scale model requiring the coupled THM processes of various geological media, such as a multi-barrier system of a geological repository. • TOUGH-3DEC links the integral finite difference method and the block-based distinct element method. • The discontinuity is transferred as an assembly of volumetric elements with an aperture-size thickness. • The developed simulator is verified by the analytic solutions and compared with the laboratory-scale experiments.