Abstract: Deep rock mass is mostly in complex stress field and seepage field. Studying the characteristics of clay rock under confining pressure and osmotic pressure is of great significance for the design and excavation of highly radioactive waste repository. In this paper, we examined the strength and permeability of Tamusu clay via permeability evolution test under loading-unloading confining pressure and full stress-strain permeability test under different confining pressures and osmotic pressures. Having compared the applicability of different strength criteria in characterizing the strength characteristics of clay, we proposed a strength criterion for clay rock in consideration of confining pressure and osmotic pressure by introducing a strengthening coefficient of confining pressure and a weakening coefficient of osmotic pressure. Results demonstrate that the permeability of Tamusu deep clay is in the order of 10^-20 m², and the relationship between permeability and confining pressure conforms to exponential function in loading stage while power function in unloading stage. In the whole stress-strain process, the strengthening coefficient of confining pressure is greater than the weakening coefficient of osmotic pressure. When working together, confining pressure has a dominant influence on the strength of Tamusu clay. The strength criterion considering the interaction of confining pressure and osmotic pressure could better reflect the strength characteristics of the Tamusu clay rock and overcome the limits of Mohr-Coulomb and Hoek-Brown strength criterion which only consider the confining pressure variation.

Key words: clay rock, osmotic pressure, permeability, strength criterion, strengthening coefficient of confining pressure, weakening coefficient of osmotic pressure, Tamusu