Performance function derivation for failure modes and stability reliability analysis of super-large-span underground caverns

The overall stability of super-large-span underground caverns serves as a prerequisite for ensuring construction safety and normal service during the operation period. To address the challenge of stability analysis for surrounding rock masses for super-large-span underground caverns, a comprehensive evaluation method based on reliability theory is proposed in this paper. Firstly, performance functions corresponding to two failure modes, namely plastic zone failure and displacement failure of the surrounding rock, are established. Combined with numerical simulation and parameter fitting, a reliability analysis method accounting for the uncertainty of surrounding rock parameters is developed. Subsequently, the Low-Tang spreadsheet method is employed to calculate the reliability index and failure probability, and a practical underground cavern project in South China is taken as a case study for verification. The results demonstrate that for Grade III surrounding rock, the reliability index and failure probability of the plastic zone failure mode of cavern surrounding rock are 3.006 and 0.132%, respectively, those of the displacement failure mode are 3.665 and 0.0124%, respectively. The calculation results of both failure modes satisfy the design specification that the target reliability index shall be no less than 3.0.