A Fiber-Reinforced Cement-Based Composite Sealing Material for Compressed Air Energy Storage Caverns: Optimization via Orthogonal Experiments and Performance Validation Under Coupled Thermal–Hydraulic–Mechanical Processes

The sealing performance of compressed air energy storage (CAES) caverns represents a multi-physics challenge involving coupled thermal–hydraulic–mechanical processes, characterized by complex interacting factors. As a critical determinant of the long-term operational efficiency of CAES facilities, this study developed a fiber-reinforced cement-based composite sealing material through systematic orthogonal experiments investigating four key parameters: water–cement ratio, sand ratio, fly ash–silica fume content, and basalt fiber content. An optimized mixture was formulated with a water–cement ratio (0.36), sand ratio (42%), fly ash–silica fume content (22%), and basalt fiber content (1.0%). Under this optimal mix proportion, the measured permeability coefficient of the sealing layer is 1.92 × 10 −13 cm/s, and the uniaxial compressive strength and tensile strength are 37 MPa and 3.9 MPa, respectively, with a corresponding elastic modulus of 18 GPa. Meanwhile, the P-wave velocity is approximately 2823 m/s, and the porosity is 0.15, achieving balanced performance in permeability, strength, and porosity. The material was validated in a CAES physical model through gas charge–discharge tests under various operational scenarios for the composite sealing layer-lining-surrounding rock system.