(GRS 555) Experimental Study of the Mechnical Behaviour of the Sandy Facies of Opalinus Clay at Mont-Terri

The indurated Opalinus Clay formation (OPA) has been proposed as a potential host rock for a deep geological repository for high-level radioactive waste (HLW) in Switzerland /NAG 02/14/. Recently, the part of the OPA formation in Southern Germany has been considered as one of the German generic models for elaborating the methodology of safety demonstration of a HLW repository in clay rock /JOB 17/. The selection of OPA as a potential host rock is due to its favourable attributes, such as appropriate formation size and depth, homogeneous and stable rock mass, extremely low hydraulic conductivity, self-sealing potential of fractures, and high sorption capacity for the retardation of radionuclides. The potential repositories will be constructed in the clay formation with a thickness of about 100 m at a depth of 400-700 m below the ground sur-face.