Damage evolution of rock salt under multilevel amplitude creep-fatigue loading with acoustic emission monitoring

The use of salt caverns to construct the compressed air energy storage (CAES) plants is an important development for the reuse of abandoned mines in response to the Chinese national green mining strategy and is a significant means to accomplish global carbon neutrality. The study of the mechanical behavior of rock salts is the base for ensuring its stability. Power plant operating conditions consist of periodic gas injection and abstraction, resulting in the cyclical mechanical loading of salt cavern walls. To study the mechanical properties of the rock surrounding a salt cavern storage reservoir under representative conditions, uniaxial and triaxial graded creep-fatigue tests on rock salt were designed, and their mechanical and acoustic emission characteristics were analyzed considering the factual operating gas pressure of the CAES plant. The results show that the residual strain produced by the cycle before the high-stress plateau are larger than that produced by the cycle after the high-stress plateau, and this difference may be associated with the hardening effect during creep. The change in acoustic emission parameters can reflect the different fracture patterns of rock salt and can be used to predict the destabilization and failure of the rock salt. Creep and fatigue have different effects on damage. In particular, at higher stress levels, the damage during creep stage predominates. The high-stress plateau drives the propagation of rock fractures at later stages. Therefore, in the design of gas storage reservoirs, the upper gas storage pressure limit must be taken into account. These findings are deemed important for studying and understanding the longterm stability phenomenon in salt caverns of CAES.