Abstract: For the geological disposal of high-level radioactive waste, the geological barrier system, as an important defense, is the last barrier for hazardous substances to enter the environment. Clayey rock, in virtue of its properties, such as low permeability, self-healing, and strong adsorption capacity, is considered a reasonable geological barrier for the disposal of high-level radioactive waste. In this study, the hydro-mechanical coupling mechanism and long-term rheological properties of a clayey rock were studied through a series of laboratory experiments. Triaxial tests show that the compression strength and excess pore water pressure have a positive relation with confining pressure. Permeability tests show the anisotropic hydraulic properties of the clayey rock and the permeability notably decreases under high confining pressure. Creep tests show that creep deformation and creep deformation rate are closely related to the load level. That is to say the larger the load is, the more significant the creep deformation is, the longer it takes for the creep deformation rate to reach stability, and the larger the corresponding steady-state creep rate is. According to the stress threshold and isochronal curve method, the long-term strength of the clayey rock is preliminarily determined to be 1.0-1.2 MPa. The results of this study will be of great significance to the geological disposal and safety assessment of high-level radioactive waste in clayey rock in China.

Key words: geological disposal of high-level radioactive nuclear waste, clayey rock, hydro-mechanical coupling, tests