Abstract: The method of solving the safety coefficient of an underground cavern group based on the local strength reduction method is investigated to accurately evaluate the safety state of large underground cavern groups. A danger zone is defined as an area with YAI （yield approach index） of less than 0.1. The danger zone penetration of the surrounding rock between caverns is used herein as the criterion for the overall damage of the cavern group. The discount factor corresponding to the danger zone penetration is defined as the safety factor of the cavern group damage. The overall stability of the cavern group is quantitatively evaluated. Moreover, the differences in the calculation results of the damage criteria of various cavern groups are analyzed. The results show that: (1)The order of the safety coefficient of each criterion from large to small is equivalent to plastic strain penetration, plastic zone penetration, sudden increase in displacement at critical points, and danger zone penetration. (2)According to the sudden increase in displacement at critical points, the errors of the safety coefficients of the other three criteria are 33.7%, 13.9%, and 2.6%, respectively. (3) The calculation result of the safety coefficient based on the danger zone penetration is closer to that of the displacement surge criterion; moreover, the damage zone based on the danger zone penetration is consistent with the actual damage characteristics of the surrounding rock of the project. The calculation volume is less.

Key words: underground cavern group, local strength reduction method, safety coefficient, yield approach index