Principle and method of stability analysis of tunnel surrounding rock based on limit state

To achieve the quantitative analysis and design of underground support systems, the surrounding rock of deep circular tunnel under uniform stress conditions is regarded as an independent load-bearing component. The stability factor index was used to quantitatively describe the degree of stability of surrounding rock components. A quantitative analysis method for tunnel stability was proposed based on the stability factor of surrounding rock. First, combining the uniform strength theory and shear-slip model proposed by RABCEWICZ, the solutions to the ultimate radial convergence and minimum support pressure required for tunnel stabilities were derived with the consideration of the effects of intermediate principal stress, brittle softening and dilation characteristics. On this basis, based on the convergence-confinement method (CCM), the ultimate carrying capacity of surrounding rock as an independent bearing component was solved, and the stability factor index was derived to characterize the stability degree of surrounding rock. The effectiveness of the proposed method was verified through analytical solutions and physical model experiments. In addition, influences of rock mechanical parameters and stress conditions on the ultimate state of surrounding rock were discussed. The results indicate that the minimum support pressure and ultimate radial strain are both negatively correlated with the intermediate principal stress coefficient, and ignoring the effect of intermediate principal stress would underestimate the mechanical potential of surrounding rock; the ultimate radial strain increases linearly with the increasing dilatancy parameter β; the minimum support pressure and ultimate radial strain both increase with increasing initial stress; the shear strength parameters of surrounding rock significantly affect the ultimate state of surrounding rock and should be considered for their variability. Finally, through the analysis of a project case, the tunnel stability assessment based on the stability factor of surrounding rock was carried out, and the practicality of this method was clarified. This study can provide a new insight for the quantitative analysis and design of underground support systems. © 2024, Central South University Press. All rights reserved.