Stability assessment of abandoned salt caverns for compressed air energy storage – a study based on true triaxial mechanical test

The utilization of abandoned salt rock caverns for energy storage has emerged as a novel and promising approach. Relying on a CAES project in salt rock in Feicheng, Shandong Province, a series of true triaxial mechanical experiments were carried out on overburden, reservoir and interlayer rock, and the mechanical parameters consistent with the actual engineering conditions were obtained. Furthermore, based on stratigraphic characteristics and three-dimensional seismic data, a three-dimensional mechanical model of abandoned salt cavern group considering the effect of intermediate principal stress is established, and the mechanical response of the reservoir group under different operating pressures was studied. The evolution of reservoir displacement, volume shrinkage ratio, safety factor, strength utilization ratio and plastic zone was obtained. The results show that with the increase of the minimum operating pressure, the maximum displacement and pillar displacement of the cavern gradually decrease; The volume shrinkage of the cavern gradually decrease, but the volume shrinkage rate of the cavern is lower than the threshold of 19.82%; The safety factor of surrounding rock of cavern gradually increases, and the strength utilization rate of surrounding rock gradually decreases. The plastic zone inside the cavern is dominated by shear failure, and shear failure and tensile failure occur in the interlayer. The cavern roof, interlayers adjacent to the cavern, and pillars between neighboring caverns are identified as the most critical zones susceptible to instability and therefore require particular attention in the design of CAES systems using abandoned salt cavern groups. These findings provide new scientific insights into the stability behavior of abandoned salt cavern groups for CAES, and an operating pressure range of 14.6–19.6 MPa is recommended for the Feicheng cavern group. Importantly, this study establishes an integrated workflow combining true-triaxial mechanical testing, three-dimensional seismic-data-based modeling, and parameter calibration, enabling quantitative assessment of salt cavern stability under realistic engineering conditions. From an engineering perspective, the proposed approach provides a practical reference for risk assessment and the safe reuse of abandoned salt caverns for CAES.