Mechanical characteristics and permeability evolution of salt rock under thermal-hydro-mechanical (THM) coupling condition

The mechanical characteristics and gas tightness of salt rock play a decisive role in the safety evaluation of salt caverns. Triaxial compression coupled permeability tests were performed on Chinese impure salt rocks under thermal-hydro-mechanical (THM) coupling condition. The results revealed that the peak strength decreased with the decrease of confining pressure and the increase of temperature. The permeability of salt rock decreased with the increase of confining pressure, while the increase of temperature led to an increase in permeability under lower effective confining pressure, and a decrease in permeability under higher effective confining pressure. Moreover, there is a critical effective confining pressure, which controls the evolution trend of salt rock permeability with temperature. The dilatancy boundary and failure strength envelope of impure salt rock at different temperatures were given, which can be expressed by exponential and hyperbolic functions respectively. An empirical formula for the evolution of the final permeability of the salt rock with the effective confining pressure at different temperatures was established. Considering the effects of effective confining pressure and inelastic volume strain, a new model was proposed to predict the permeability evolution of salt rock under THM coupling condition at different temperatures. The results of this paper can help understand the mechanical characteristics and permeability evolution of salt rock under THM coupling condition, and provide the necessary basis for the safety evaluation of salt caverns.