Caichu Xia

Compressed air energy storage (CAES) tunnels undergo daily inflation and deflation cycles during operation. It is inevitable that the surrounding rock will undergo fatigue damage when subjected to long-term cyclic loading. This damage leads to cumulative plastic deformation and a reduction in bearing capacity. Based on the Mohr–Coulomb criterion incorporating fatigue damage and stress path theory, this study presents an analytical solution for the mechanical response of surrounding rock during tunnel excavation, initial inflation, initial deflation, and cyclic inflation–deflation. The findings of the study suggest that the minimum air storage pressure, herein referred to as [ ], exerts a significant influence on the mechanical response of the surrounding rock. In circumstances where the [ ] is elevated (7.5[ ]MPa), the surrounding rock transitions into a stable cyclic stage of plastic unloading–reloading, characterized by the formation of closed stress paths. Conversely, when [ ] decreases to 1.5[ ]MPa, the substantial pressure differential engenders a plastic reloading state during the process of deflation. The stress path subsequently becomes non-closed and gradually shifts toward strength degradation with increasing cycle numbers, accelerating cumulative plastic deformation and reducing load-bearing capacity. Damage parameters exert a staged influence on mechanical behavior: during air storage, they intensify circumferential stress concentration and increase displacement; during deflation, they amplify stress fluctuations and rebound deformation. These findings provide a theoretical basis for determining the operational pressure range and assessing the long-term stability of rock tunnels.

The steel lining is a critical structural component in high-pressure tunnels, serving not only as a sealing barrier but also as a load-bearing element that resists a portion of the internal pressure. Its mechanical performance directly influences the operational safety of the tunnel. However, under conditions such as weak surrounding rock, conventional sealing designs based on elastic assumptions often require excessively large lining thicknesses, leading to increased construction costs and an underutilization of the load-bearing capacity of the surrounding rock. To address these limitations, this study introduces a controlled-yielding design of the steel lining. An elastoplastic analytical solution that incorporates the yielding behavior of the steel lining and its interaction with the surrounding rock is developed, enabling a systematic characterization of their mechanical responses during the plastic stage. The results demonstrate that the controlled-yielding design exhibits pronounced advantages under weak surrounding rock conditions, allowing a substantial increase in the ultimate internal pressure capacity of the cavern without increasing the lining thickness. Moreover, under a given internal pressure, the controlled-yielding design can markedly reduce the required thickness of the steel lining. After the steel lining yields, the contact pressure becomes constant as it is governed by the yielding criterion, meaning that the lining’s load-bearing contribution no longer increases even when the surrounding rock becomes weaker. Consequently, the load-sharing ratio of the surrounding rock increases significantly under weak rock conditions, allowing its bearing capacity to be fully mobilized. Overall, the proposed controlled-yielding design of the steel lining provides a new perspective for structural optimization in high-pressure tunnels. It not only enhances the ultimate internal pressure and improves the load-bearing ratio of the surrounding rock, but also reduces the required lining thickness and lowers construction costs, demonstrating substantial engineering applicability.

High internal pressure can readily cause cracking in the underground cavern of compressed air energy storage (CAES), posing a significant threat to its stability and sealing. To effectively transfer internal pressure loads, enhance cavern deformation capacity, and leverage the bearing capacity of surrounding rock, we propose a flexible lining design using low-elastic modulus flexible concrete as the lining layer for CAES underground caverns. The mechanical properties of flexible concrete under various proportions are initially investigated through laboratory tests. Building on these findings, we propose a modified concrete damage-plasticity (CDP) constitutive model for flexible concrete and establish a mechanical calculation model for underground caverns utilizing flexible concrete. To demonstrate the feasibility of using flexible concrete in CAES underground caverns, this study compares the mechanical response of these caverns with different lining forms and varying flexible concrete ratios. This comparison is conducted within the context of an ongoing CAES underground cavern project. The results indicate that low-elastic modulus flexible concrete can effectively reduce tensile stress in the concrete lining of high-pressure CAES underground caverns. This stress reduction minimizes lining cracking, facilitates internal pressure load transfer, enhances cavern deformation capacity, and leverages the bearing capacity of surrounding rock.