Physical and Hydraulic Properties of Rock Specimens from Grimsel Test Site, Switzerland

The Grimsel Test Site (GTS) is located at an altitude of 1730 meters in the granite rock of Aar Massif in central Switzerland. It lies at a depth of around 450 meters beneath the surface and was established over 20 years ago by the National Cooperative for the Disposal of Radioactive Waste (Nagra) as a center for underground Research and Development (R&D) supporting a wide range of related research projects. Among many of them, an international cooperative project defined as the Long Term Diffusion (LTD) has been performing to obtain quantitative information on matrix diffusion in rock strata under in-situ conditions. A set of laboratory experiments is also planed to determine the physical, hydraulic and diffusive transport properties of rock specimens taken from the same test site. In this poster, we present the preliminary results of both physical and hydraulic properties of the rock specimens being tested, including the bulk density, porosity, specific surface area and pore distribution, microstructure, P and S wave velocities, electrical resistivity, air and water permeabilities. The results obtained in this study indicate that: 1) The porosity and wave velocities of Grimsel granite are relatively low compared to the average values of igneous rocks indicating that micro-cracks can potentially exist within grain minerals. 2) The air and water permeabilities obtained from the air and water permeability tests are consistent that illustrates the accuracy of both experiments. 3) Permeability is not a simple function of effective confining pressure. It is very sensitive to confining pressure especially at low pressure levels. Besides, the permeability is hysteretic depending on confining pressure, pore pressure and stress history. 4) Similar to the hydraulic properties, diffusive transport properties of rock specimens can also be significantly affected by the confining pressure conditions. Laboratory diffusion tests considering the effects of stress conditions are fundamentally necessary for predicting the process of in-situ diffusion test and for comparing the results to be obtained from the in situ tests in the near future. Acknowledgement: This research project has been conducted under the research contract with the Japan Nuclear Energy Safety Organization (JNES).