Research on the damage evolution process of support structure in underground CAES cavern support structures: a thermo-gas-mechanical-damage coupled numerical model

To analyze the damage evolution of the underground compressed air energy storage (CAES) cavern support structure (lining and surrounding rock), a thermodynamic gas module was developed using COMSOL Multiphysics based on mass conservation, energy conservation, Darcy's law, and Berthelot's gas state equation. Modules for porous media mechanics, seepage, and temperature fields were added. A real-time, iteratively updated damage variable module was embedded, incorporating maximum tensile stress theory and Mohr-Coulomb criterion. A thermo-gas-mechanical-damage coupled model was established for damage evolution of the CAES cavern support structure, enabling refined simulations of tensile and shear damage. Results obtained from engineering case calculations indicate that the computational results in this paper are relatively close to the theoretical values, and the simulation outcomes comparatively align with the actual evolutionary characteristics of disordered and random expansion and development. Multiple case studies simulated the damage evolution of the lining-surrounding rock system, considering the effects of lateral pressure coefficient and internal pressure. Results showed that during the first operational cycle, damage concentrated before gas injection ended but worsened due to unloading, stabilizing before the second gas storage. The lateral pressure coefficient has a significant impact on the propagation depth of the damage zone. Specifically, under a lateral pressure coefficient of K h = 0.75 (<1.00), the surrounding rock exhibits more severe damage compared to cases with K h = 1.00 and 1.25 (>1.00). The influence depth of the damage zone in the surrounding rock increases at a rate of approximately 1.3 to 1.9 times as the initial internal pressure rises. Within the lining, damage is predominantly characterized by a combination of tensile and shear modes, while tensile damage is the main type observed in the surrounding rock. The findings of this study provide a fundamental basis for research on the stability of underground CAES caverns. • A thermo-gas-mechanical-damage coupled model for underground CAES caverns was developed enables dynamic coupling of damage variables & multiphysics fields, and high-fidelity simulation of support structure damage evolution. • A dual strength criterion (tension-shear damage criterion) was first introduced for CAES support structure analysis, successfully simulating co-evolution of tensile-shear composite damage. • Differential impacts of lateral pressure coefficients and internal pressure levels on support damage mechanisms were revealed. • Initial damage concentration was observed before first gas storage completion, exacerbated by unloading effects during the inaugural operational cycle.