Preliminary laboratory thermo - hydro - mechanical characterization of Opalinus clay

1 INSTRODUCTION In the concept of geological radioactive waste disposal, argillite is being considered as a possible host rock in various countries such as France and Switzerland. This material is chosen thanks to its extremely low permeability that is required to limit the transfer of radioactive elements from the waste package towards the environment. During the construction and exploitation phase of the radioactive waste disposal, the host rock will be subjected to various thermo-hydro-mechanical loadings. The mechanical loading can be induced by the excavation of the tunnel or the installation of engineered barriers. The hydrological loading can correspond to the drying process on the inner wall of the tunnel during the excavation and the re-saturation process by water coming from the aquifer after the closure of the tunnel. And finally, thermal solicitation comes from the heat emitting from the radioactive waste packages. On one hand, the behavior of the host rock under each solicitation is important for the design of such storage, on the other hand, the behavior under the coupled thermo-hydro-mechanical solicitations is also needed to be well understood. In the present work, some preliminary results on the laboratory thermo-hydro-mechanical characterization of Opalinus clay are presented. The material is one of the argillites being studied in several research projects in Europe in the context of geological radioactive waste disposal. 2 MATERIAL STUDIED The soil cores of Opalinus clay were taken from the Mont Terri rock laboratory in Switzerland (Bossart & Thury, 2007). Several research projects have been and are being performed in the rock laboratory in the context of the Mont Terri Project which is an International Research Project for the Hydro-geological, Geochemical and Geotechnical Characterization of a Clay Formation (Opalinus Clay). The main properties of Opalinus clay can be found in the work of Corkum & Martin (2007). In Table 1, the typical mineral composition of Opalinus clay is presented. It can be seen that this material is composed of 65% clay particles consisting mostly of kaolinite and illite. The non-clay minerals consist mainly of quartz (20%) and calcite (7%). The index properties are presented in Table 2. With a liquid limit of 38% and a plasticity index of 15%, this material can be classified as Clay of Medium plasticity (CI) following the Unified Soil Classification System. The initial water content is relatively low (6%) corresponding to a low value of porosity (12%). ABSTRACT: Argillite is being considered …