Abstract: The cracking of conventional concrete linings in underground compressed air energy storage (CAES) caverns fractures the flexible sealing layer. To address this challenge, a composite lining structure composed of high-toughness engineered cementitious composite (ECC) and fiber-reinforced polymer (FRP)-filled concrete is proposed. Experimental investigations were conducted on the mechanical properties of Chinese-produced polyvinyl alcohol fiber-reinforced ECC suitable for underground CAES caverns. Digital image correlation technology was used to analyze the strain distribution and failure characteristics of ECC, yielding stress-strain curves that were used to establish corresponding parameters for a plastic damage constitutive model of ECC. Subsequently, a finite element model of a CAES cavern with a composite lining was developed. A comparative analysis was performed on the stress distribution within the lining, the distribution of cracking damage, and the deformation of the surrounding rock between the CAES cavern with the composite lining and that with a conventional concrete lining. Furthermore, a parametric sensitivity analysis was conducted on the ECC layer thickness and the FRP reinforcement ratio. The results indicate that ECC exhibits excellent deformation capacity and multiple microcracking capability, with a maximum crack width of 0.12－0.15 mm at ultimate strain, effectively mitigating the fracture risk of the flexible sealing layer. Furthermore, under poor surrounding rock conditions, the ECC-FRP-reinforced concrete composite lining demonstrates superior deformation performance compared to the conventional concrete lining. The composite reduces stress concentration in the lining and minimizes the plastic deformation zone in the surrounding rock while more effectively transferring the internal cavern pressure to mobilize the bearing capacity of the surrounding rock. In addition, the maximum stress in the FRP bars decreases with increasing ECC layer thickness and FRP reinforcement ratio in the composite lining. The maximum deformation of the surrounding rock increases with increasing ECC layer thickness. The maximum stress in the ECC layer initially decreases and then increases with increasing thickness, and gradually decreases with increasing FRP reinforcement ratio.

Key words: compressed air energy storage, underground cavern, engineered cementitious composite/fiber-reinforced polymer-filled concrete composite lining, deformation performance