Failure Mechanism and Numerical Simulation of Splitting Failure for Deep High Sidewall Cavern under High In-suit Stress

High sidewall cavern splitting failure is a critical engineering phenomenon that occurs during excavation and unloading under true three-dimensional high in-situ stress conditions. This issue significantly impacts the safety of underground cavern construction and excavation, yet its formation mechanism remains unclear. This research utilizes the high sidewall cavern of the main powerhouse at the Pubugou Hydropower Station as a case study to establish an elastic-plastic damage-softening model of splitting failure based on strain gradient theory and to develop a corresponding calculation program. The numerical simulation results effectively elucidate the formation conditions and failure mechanisms of high sidewall caverns. Through comprehensive numerical simulations under various working conditions, we systematically investigate the conditions for generation and the influencing factors of splitting failure. Our study successfully uncovers the generation conditions and formation mechanisms of high sidewall cavern splitting failure. A crucial condition for this failure is that the initial maximum principal stress of the underground cavern aligns parallel to the tunnel axis direction, with a magnitude between 0.21 and 0.7 times the compressive strength. The primary mechanical cause of splitting failure during excavation and unloading is the stress oscillation at the cavern’s sidewall.