Abstract: In this study, experiments were conducted on the high-pressure gas permeability characteristics of porous media under different water saturation states to quantitatively analyze the influence of water saturation on the gas permeability of concrete and sandstone, reveal its underlying mechanism, and provide a basis for assessing the sealing performance of compressed air energy storage underground caverns. The vacuum saturation method combined with the water loss method was employed to precisely control the water saturation of C45 concrete, C50 concrete, and medium-grained sandstone specimens at five target levels: 0%, 25%, 50%, 75%, and 100%. The test was carried out in the range of 0.5－8.5 MPa using the highpressure gas permeation test platform, and gas permeability data were obtained under different saturation degrees. A modified Kozeny empirical model was introduced to fit the experimental results, and a comparative analysis was conducted with existing studies on cement-based materials under low gas pressure conditions. The results indicate that the gas permeability exhibits a three-stage nonlinear decay with increasing water saturation: the decay is slow when the saturation is below 25%, accelerates in the 25%－75% interval, and shows a sharp drop after exceeding 75%, the critical saturation threshold. The intrinsic mechanism behind this phenomenon lies in the structural transformation of the liquid-phase occurrence state: at low saturation, the water phase is distributed in isolated rings or films within small pores, while the gas channels remain connected. As saturation increases, the liquid phase gradually fills and blocks the main seepage pores, reducing the effective connected pathways for the gas phase. When the saturation exceeds 75%, the water phase forms a continuous distribution, leading to extensive blockage of the gas-phase connected network and a sharp decline in permeability. The modified Kozeny model fits the experimental data well and can describe the gas permeability behavior of water-bearing porous media.

Key words: compressed air energy storage, lined rock cavern, porous media, water saturation, gas permeability