Study on the potential instability patterns of tunnel type underground caverns for compressed air energy storage

With the rapid development of new energy sources, the compressed air energy storage(CAES) underground caverns, which differ from traditional tunnel conditions, face stability issues in the overlying rock mass. The potential instability modes of these shallow-buried tunnel-type CAES caverns urgently need to be studied. Adopting the Mohr-Coulomb strength criterion and based on the ultimate stress field of the rock mass and considering both tensile and shear failure modes, the problem of potential instability modes in shallow buried high internal pressure tunnel-type lined rock caverns is reduced to the initial value problem of a cluster of ordinary differential equations, and the solution method is given. The reliability of the method is verified by comparing and analyzing the results with the physical model test results. In addition, the effects of burial depth, tunnel diameter, in-situ stress ratio and internal friction angle on the instability pattern are investigated, and the results show that the in-situ stress ratio and internal friction angle have a significant influence. The horizontal stress direction is perpendicular to the axis of the tunnel, which is more conducive to the stability of the overlying rock. On the other hand, the influence of the internal friction angle on the instability pattern depends on the in-situ stress ratio. When the in-situ stress ratio is less than 1, the smaller the internal friction angle is, the closer the potential rupture surface is to the horizontal;when the in-situ stress ratio is equal to 1, the internal friction angle has almost no effect;when the in-situ stress ratio is greater than 1, the larger the internal friction angle is, the closer the potential rupture surface is to the horizontal. In view of this, the design of cavern layout, burial depth and diameter should consider both in-situ stress and internal friction angle. Finally, potential failure surface morphology is parameterized in a simple geometric way, and the correspondence between the geometric parameters and the in-situ stress ratio and internal friction angle is given for engineering reference. In terms of failure modes, when the geostress coefficient is small, the potential failure surface exhibits a tensile-shear composite mode, with the tension region located near the cavern wall and the ground surface. When the geostress coefficient is large, the failure mode is primarily shear. © 2024 Academia Sinica. All rights reserved.