Fatigue Behavior of Salt Rock and Mudstone Interlayers Under Cyclic Loading in Bedded Salt Caverns and Simulation of Surrounding Rock

Salt rock is an ideal host for compressed air energy storage (CAES) due to its low permeability, creep self-healing, and stable properties. Chinese bedded salt deposits have thin salt layers and frequent mudstone interlayers. The response law of surrounding rock under cyclic injection–production-induced temperature fluctuations and creep-fatigue loading remains unclear. This study combines experiments and simulations to investigate the mechanical behavior and damage evolution of salt rock and mudstone interlayers under temperature and cyclic loading. Uniaxial tests at 20 °C, 50 °C, and 80 °C reveal thermal softening of salt rock and thermal hardening of mudstone. Creep-fatigue tests under loading rates of 0.25, 1, and 2 kN/s show salt rock has residual strain of 0.9–1.375% after 30 cycles, dominated by viscoplastic creep, while mudstone has a residual strain of less than 0.1% and is dominated by elastic deformation. A thermo-mechanical model based on the Jintan cavern simulates 150 cycles. The temperature field reaches a dynamic equilibrium after 500 h with spatial non-uniformity. Displacements concentrate at cavern waist and interlayer interfaces. The simulated volumetric contraction is 6.28% after 150 operational days, providing a baseline for short-term stability assessment. This study reveals the contrasting mechanical responses of salt rock and mudstone and the resulting interface deformation incompatibility. These findings support the stability assessment and operational optimization of bedded salt cavern CAES.