A safety-critical component for large-scale underground hydrogen storage: The role of concrete sealing plug

Underground hydrogen storage (UHS) is a cornerstone technology for enabling a reliable and large-scale hydrogen economy. However, the high diffusivity and cyclic storage pressure of hydrogen pose significant challenges to the long-term integrity of storage caverns. The concrete sealing plug, as a primary barrier against hydrogen escape at the cavern mouth, is a safety-critical component. This study addresses this energy storage challenge by developing a comprehensive mechanical model to guide the optimized design of a wedge-shaped plug for a UHS project in Daye, China. The model's accuracy was validated through laboratory shear tests on a limestone-concrete interface with joints. Furthermore, a high-fidelity 3D (three-dimensional) numerical model was established to simulate the complex geological conditions. The key findings are: (1) The proposed wedge-shaped design not only ensures stability but also minimizes excavation volume, thereby reducing the construction cost and environmental footprint of UHS facilities—a crucial factor for their economic viability. (2) The plug's key dimensions, determined via limit equilibrium analysis, are governed by the cavern diameter, rock mass strength, joint properties, internal pressure, and manhole diameter. (3) Numerical simulations reveal that internal pressure induces tensile debonding at the rock-concrete interface, with the maximum compressive stress located at the plug base, pinpointing a potential failure initiation zone. The result provides essential theoretical foundations and practical guidelines for designing robust concrete seals, contributing to the safe and efficient deployment of underground hydrogen storage systems.