## 6 Conclusions  
This study addresses the inability of monolithic reinforced concrete linings to meet the crack control requirements under high internal pressure by improving the lining structure. A new lining structure design was proposed, and its application in engineering was explored through laboratory tests and numerical simulations. The main findings are summarized as follows:  
(1) Based on the calculation formula for the maximum crack width of hydraulic tunnel linings, a design method for segmented linings with retractable seams was proposed. This method takes into account the shear mechanical properties of the sliding layer, which were determined through laboratory tests, as well as the plasticity of the lining damage. Thereliability of the method was verified by comparing it with results from a typical pressure pipeline model test. (2) The increase in the number of preset seams helps to expand the improvement effect. As the number of preset seams increases, the range of improvement in the lining's performance also expands. The opening displacement of individual seams decreases, while the total seam opening displacement increases, allowing the lining to release more radial displacement. This effectively reduces the reinforcement stress and damage factor at the far end of the seams. However, the increase in the number of preset seams also leads to higher construction difficulty and costs, so the minimum number of seams should be used to meet the performance requirements. (3) Within the lateral pressure coefficient range for the specific engineering case studied, an increase in the lateral pressure coefficient has a positive impact on the lining's safety. As the lateral pressure coefficient increases, the maximum tensile stress in the reinforcement and the areas with higher damage in the lining gradually concentrate near the crown. By appropriately reducing the number of preset seams, both the design requirements for the segmented lining and the construction difficulty and cost can be minimized. For the case studied, when the lateral pressure coefficient is less than one, the maximum tensile stress in the reinforcement and the lining damage factor decrease as the number of preset seams increases. Considering construction costs and technical difficulty, the optimal configuration is six preset seams. When the lateral pressure coefficient exceeds one, four preset seams are the most suitable solution. (4) The design of retractable joints and reinforcement ratios was carried out for a typical case. The results showed that the reinforcement stress in segmented linings with retractable joints was slightly higher than in those without them. However, the use of rebar joints led to a more uniform stress distribution in both the inner and outer reinforcement bars. This indicates reduced bending moments and improved structural integrity of the lining. (5) For a typical case with a working internal diameter of 10 m and a reinforcement ratio of 3%, the applicability of the segmented lining design method was determined. When the storage pressure exceeds 12 MPa, nearly no suitable surrounding rock meets the crack control requirements for monolithic linings. However, by using the segmented lining, the lining can meet crack control requirements as long as the surrounding rock's elastic modulus exceeds 4.5 GPa. The maximum crack width and maximum seam opening displacement have the most significant impact on the lining's load-bearing capacity. This research provides important support for the construction of CAES workings with internal pressures exceeding 12 MPa in the surrounding rock of fair to extremely hard quality, thereby expanding the potential scope for CAES working construction. S.W. : writing--original draft, software, methodology, investigation, and validation. M.G. : methodology and writing--review and editing. C.X. : supervision, funding acquisition, and conceptualization. All authors have read and agreed to the published version of the manuscript.