An overview of long-term HM measurements around HADES URF

The underground research facility HADES was constructed to study the feasibility of HLW disposal. Since its operational start 25 years ago numerous instruments were placed in the lining and the surrounding host rock. Some set-ups are operational for over 20 years measuring pore pressure, total pressure or displacements. Displacement measurements enable to assess the displacement during and after excavation works; construction and lining techniques have an influence on the amount of displacement. The short-term response of the host rock put into evidence a strong HM coupling. An anisotropic response and evolution of pore water pressure was observed; this phenomenon was attributed to anisotropy of stress and hydraulic conductivity. The ground pressure on the gallery lining was recorded during several years; it increases fast during the first months after construction and a more gradual increase occurs afterwards. Hydraulic conductivity (k) was measured using several methods at different locations, times and scales. The results of in-situ and laboratory tests are consistent; k is of the order of 10-12 m/s. A hydraulic conductivity increase is observed up to some 6m into the host rock and is attributed to lower effective stress-levels experienced in this zone due to stress-redistribution following the excavation.