Stability control and support optimization for large-span underground caverns in fractured rock masses under low in-situ stress

Abstract The rapid expansion of pumped storage power stations in China highlights a critical engineering challenge: ensuring the stability of large-span underground caverns excavated in intensely fractured, mosaic-fragmented rock masses under low in-situ stress. Taking the Liyang Pumped Storage Power Station as a case study, this research systematically investigates cavern instability mechanisms and corresponding support control technologies. Field investigations and theoretical analysis identify three predominant failure modes: block fall, crown collapse, and sidewall sliding. Cavern geometry and construction sequences were optimized via coupled Discrete Fracture Network (DFN) and Discrete Element Method (DEM) simulations, indicating a project-specific recommended rise-span ratio of 0.235–0.314 for a 25.5 m span and a recommended spacing of 40–50 m between the main and auxiliary caverns. Mechanistic evaluations further clarify the differentiated reinforcement effects of support elements using block beam thrust line and compressed arch theories; specifically, inclined bolts stabilize the arch by enhancing horizontal thrust, while vertical bolts improve load-bearing capacity through layer-integration effects. Guided by these insights, a collaborative support system—integrating mortar bolts, prestressed anchor cables, and steel arch ribs—was developed and implemented. Both field monitoring and numerical validation confirm that this system effectively constrains surrounding rock deformation and ensures construction safety. This work establishes a systematic, practical design framework for similar large-span underground projects in complex geological environments.