Airtightness of a flexible sealed compressed air storage energy (CAES) tunnel considering the permeation accumulation of high-pressure air

Determining the airtightness of compressed air energy storage (CAES) tunnels is crucial for the selection and the design of the flexible sealing layer (FSL). However, the current airtightness calculations for flexible sealed CAES tunnels often ignore the process of high-pressure air penetration and accumulation in the lining and surrounding rock after passing through FSL. Consequently, the tunnel airtightness cannot be accurately assessed. In this study, we examined the continuous permeation of high-pressure air in materials with various properties, where the FSL represents a dense material, whereas the lining and surrounding rock are porous media materials. Furthermore, we developed an airtightness calculation model according to the operating characteristics of the CAES system. The model considers the permeation accumulation of high-pressure air in the lining and surrounding rock after passing through FSL. Finally, the rationality of the model is confirmed by two engineering cases, and the influence of high-pressure air permeation accumulation is analyzed based on the CAES project of Yungang Mine. The permeation accumulation of high-pressure air is conducive to the sealing of the tunnel. When the sliding pressure range is 4.5-10 MPa and the permeability of the lining and surrounding rock is 1 x 10-16 m2, the cumulative pore pressure outside the FSL increases from 0.1 MPa to 1.28 MPa after 100 cycles. Moreover, the 24hour gas loss rate of the tunnel decreases from the initial 0.66 % to 0.57 %, presenting a decrease of 13.6 %. When the lining and surrounding rock permeability is greater than 6.92 x 10-16 m2, the air permeating through the FSL rapidly dissipates, and the impact of air permeation accumulation can be ignored. By contrast, the effect of air permeation accumulation should be considered.