Chemo-hydro-mechanical coupled consolidation for a poroelastic clay buffer in a radioactive waste repository

Salt rock or rock with salty ground water are often encountered as host media for the underground disposal of radioactive waste. The nuclear waste, contained in a metallic canister, is usually placed inside a tunnel or a shaft excavated in the rock deposit together with a buffer of compacted bentonite inserted between the host rock and the canister to provide hydro-mechanical sealing. Due to the very low permeability and rich clay content, the bentonite acts as an osmotic semi-permeable membrane under a gradient of concentration of salt dissolved in the ground water. In addition, chemically induced expansion or shrinkage of the bentonite is generated by changes in the concentration of dissolved salt. By including such important chemical aspects, the hydro-mechanical governing equations are derived for this particular boundary value problem within the framework of a linear Biot-like isotropic poroelastic consolidation. The equations are solved analytically and a parametric study is undertaken to highlight the influence of chemical osmosis and chemical deformation on the flow and mechanical response of the bentonite buffer.