Abstract: Based on the Hoek-Brown strength criterion, this study develops a semi analytical approach for calculating the stress and displacement of surrounding rock throughout the excavation and high-pressure operation stages of a compressed gas energy storage cavern, thereby elucidating the evolution patterns of the stress path and failure mode in the surrounding rock. The findings reveal that the geological parameters exert minimal influence on the distribution of radial stresses within the surrounding rock, and significantly affect the distribution of circumferential stresses. Poorer geological conditions lead to a larger circumferential stress and a wider plastic zone. For medium-soft rock formations (e.g. geological strength index GSI = 35), the Mohr-Coulomb strength criterion may overestimate the bearing capacity of surrounding rock during high-pressure air storage stage. Should the surrounding rock transition into a plastic state during cavern excavation, it will be subjected to both radial and circumferential compression under conditions of high internal gas pressure. As the internal gas pressure escalates, the stress state of the surrounding rock sequentially progresses through plastic unloading, plastic loading, and plastic expansion stages. Notably, the critical internal pressure threshold during the plastic expansion stage is roughly twice the initial in-situ stress. Once the internal gas pressure reaches this critical pressure, the radius of the plastic zone in the surrounding rock expands almost linearly with the internal pressure, resulting in a swift enlargement of the plastic zone and a nonlinear surge in the displacement of the surrounding rock. Consequently, under unfavorable geological conditions, it is inadvisable to indiscriminately elevate the maximum gas storage pressure within the cavern.

Key words: compressed air energy storage, underground caverns, surrounding rock, stress path, Hoek-Brown strength criterion, analytical solution