Experimental study of leakage characteristics and microscopic mechanisms in the sealing plug areas of underground compressed air energy storage caverns

To investigate the leakage mechanism of the sealing plug area in compressed air energy storage (CAES) caverns under various conditions, the leakage evolution characteristics of the simulated samples were systematically studied via a self-developed triaxial seepage testing system. Combined with CT scanning, the development and propagation mechanisms of internal defects were elucidated. The results indicate that the leakage index is significantly positively correlated with the peak air pressure and injection rate but negatively correlated with the confining pressure. Leakage behavior during the charging phase is governed primarily by the peak pressure and injection rate, whereas that during the storage phase is predominantly controlled by the pressure magnitude. A distinct time lag, dominated by peak pressure, was identified between the leakage index and pressure characteristic points. The average peak leakage rate exhibited a “decreasing-then-increasing” trend, transitioning from an initial value of 9.3289 to 7.3267 cm 3 /s and then rebounding to 8.8093 cm 3 /s. The cyclic process enhanced the connectivity of the pore-fracture network; fracture coalescence reduced the number of large pores (> 0.9 mm) but increased the total pore count. This research provides valuable insights for evaluating the sealing performance and rock‒concrete interface seepage of artificial CAES caverns.