Influence of drainage system on the stability of underground CAES gas storage under different lateral pressure coefficients

As demand for large-scale physical energy storage increases, lined rock caverns (LRC) have emerged as an ideal solution for compressed air energy storage (CAES). However, drainage systems, a crucial component of LRC, have often been overlooked in prior studies. Drainage pipes behind the lining can be considered as defects since they increase the cracking potential of the concrete lining when subject to high internal circulating pressure. In this study, a comprehensive LRC model is established, consisting of a steel lining sealing layer, C30 concrete lining, C25 concrete spray layer, drainage system, and surrounding rock. Both excavation and operation stages of LRC are simulated considering various drainage system parameters (drainage pipe spacing: 1 m and 2 m, drainage pipe inner diameter: 10 cm and 15 cm) and lateral pressure coefficients (0.8, 1.0, 1.2). Results show that the drainage system has minimal impact during the excavation phase, causing stress concentrations in the C25 concrete spray layer near the drainage pipes but little effect on the surrounding rock displacement or steel lining stress. In contrast, the drainage system affects LRC stability significantly in operational phase, inducing substantial stress concentrations and damage in the C25 concrete spray layer and C30 concrete lining, as well as an increase in steel lining stress and surrounding rock displacement. The stability of LRC is optimal when lateral pressure coefficient is 1.0 or 1.2, and worst when it is 0.8. In the worst scenario, the maximum steel lining stress in the LRC increases by 29.89 MPa and the displacement of the surrounding rock roof increases by 1.46 mm, compared to LRC without a drainage system. Meanwhile, the inner diameter of the drain pipe has a greater effect on the stability of the cavern than the spacing. These findings suggest that while the presence of a drainage system can be neglected in the design of conventional tunnels, its influence must be carefully considered in the calculation, design, and construction of LRC for CAES.