Deformation and damage of tight sandstone surrounding rock under CAES operating air pressure environment

The stability of surrounding rock in underground storage caverns is critical to the safe operation of compressed air energy storage (CAES) power stations. Taking the CAES power station in coal mine roadways as the engineering background, this study systematically investigated the mechanical response characteristics of tight sandstone under cyclic air pressure using acoustic emission (AE) monitoring, computer tomography (CT), core non-destructive scanning, and nuclear magnetic resonance (NMR) scanning techniques. The damage evolution and crack propagation laws of the sandstone were revealed. The results show that different stages of the air pressure cycle have distinct effects on the damage of sandstone. The AE signal density during the high-pressure stage is much higher than that during the low-pressure stage, and this difference becomes more pronounced as the load level increases. CT and NMR scanning results show that sandstone failed under cyclic air pressure develops a through-going main shear plane accompanied by pore network, and increasing the air pressure amplitude intensifies sandstone specimen damage. The T₂ spectrum of intact rock samples exhibits a single relaxation peak, which transforms into a long relaxation peak after failure, accompanied by a significant increase in porosity and a more uniform pore size distribution. The degree of pore structure development varies under different air pressure conditions. The amplitude of cyclic air pressure is a key parameter controlling sandstone strength and damage evolution, whereas the platform stabilization time and the pressure ramp rate have relatively minor effects on sandstone deformation.