BMT1 was defined as a generic far-field model of fractured crystalline rock (with three alternative spacing (100 m, 50 m and 25 m) of two orthogonal sets of parallel fractures following the cubic law), and with a repository located at 500 m depth in a 2D space, as shown in Fig. 2a. The main objectives were: 1) to evaluate the performances of the computational methods and computer codes; and 2) to simulate coupled THM processes and understand their impact on a repository’s performance. Four research teams conducted the modeling (cf. Table 1 and Table 2), using different numerical modeling codes and methods: VIPLEF/CHEF/HYDREF (FEM code by ENSMP), UDEC (DEM code by INERIS), CASTEM 2000 (FEM code by CEA) and THAMES (FEM code by KPH/PNC). Figures 2b and 2c show two examples of the calculated vertical displacements and horizontal water flow velocity at one of a number of monitoring points.
The main scientific/technical findings were that the numerical methods based on equivalent continuum and discrete block systems of fractured rocks generate differences in numerical results, especially different mechanical effects of fracture spacing in the DEM and FEM models, which led to future work in DECOVALEX project phases for more comprehensive studies on homogenization and upscaling issues of fractured rocks. The results showed that, in general, the applied computer codes and their mathematical representations of the coupled THM processes are useful and can be developed for more sophisticated tools for modeling coupled THM processes of fractured rocks under more complex initial and boundary conditions and material behavior. The main outstanding issue was that there was no measured data support for more comprehensive validating tests of the models and computer codes, and there was a need for further 3D modeling problems and computational abilities for a more realistic research on the modeling of coupled THM problems.