INTERNATIONAL COMPARISON OF COUPLED THERMO-HYDRO-MECHANICAL MODELS OFA MULTIPLE-FRACTURE BENCH-MARK PROBLEM - DECOVALEX PHASE-I, BENCH-MARK TEST-2

An international inter-code bench mark comparison has been carried out under the auspices of DECOVALEX, an international cooperative project for the development of; coupled (thermo-hydro-mechanical) models and their validation against experiments in nuclear waste isolation, The s ubject bench mark problem, designated BMT2, involves a system of nine blocks of intact hard rock separated by two pairs of relatively soft f ractures. The coupled processes of conductive, convective and dispersi ve heat transport; nonisothermal fluid flow; and thermo-mechanical str esses and displacements in both the intact rock and the fractures were simulated, Five research teams representing four European and North A merican countries participated in this bench-marking exercise using tw o fundamentally different types of numerical models, i.e. finite-eleme nt models and distinct-element models. All teams simulated the fractur es as discrete features, For the coupled hydro-mechanical behaviour of the fractures the modelling teams have used either the empirical, non linear Barton-Bandis-Bakhtar constitutive relation or a simpler Coulom b friction like stress-deformation relation in conjunction with Snow's parallel-plate fracture flow model. For this bench mark problem it wa s found that (1) heat convection significantly affects the distributio n of temperature, thermal stresses and displacements; and (2) the pred ominant coupled effect is fracture closure caused by thermal expansion of the rock blocks, Comparison of the modelling results obtained by t he various teams have indicated very good overall agreement, In partic ular, the results calculated using finite-element and distinct-element codes are quite similar, Practically all the discrepancies among simu lation results can be ascribed to different idealization, constitutive relations, or parameter values adopted by the participating research teams, In-depth discussions among participants have enhanced our under standing of the simulated processes and provided guidance for model im provements.