Assessment on Rock Failure in Underground Caverns Based on Unified Strength Theory

Stability analysis and design of rock support system of underground caverns depend on the failure criterion of rock. The linear Mohr-Coulomb failure criterion and the nonlinear Hoek-Brown failure criterion are two of the most widely used strength criteria in rock engineering. However, the disadvantage of the two criteria is that the effect of the intermediate principal stress is not considered. In underground engineering, the rock is often loaded under true triaxial stress state, and the intermediate principal stress certainly has an influence on the strength and failure of rock. In the present study, according to the principle of non-associated flow rule in Mohr-Coulomb model in FLAC(3D), the constitutive model based on the Unified Strength Theory considering the intermediate principal stress is established in numerical simulation. True triaixal compression numerical tests are performed to investigate the influence of the intermediate principal stress on the rock strength and the results are found to be in good agreement with theoretical analysis. The rock failure near a pumped-storage powerhouse excavation boundary is studied using the Unified Strength Theory. It is observed that consideration of the intermediate principle stress in the Unified Strength Theory is important to estimate and determinate the failure behavior in underground engineering.