Analysis Of Circular Tunnel With The Influence Of Axial In Situ Stress Based On The Linear And Nonlinear Failure Criteria

Underground engineering is generally simplified to a circular section tunnel plane strain problem in the infinite homogeneous isotropic medium under hydrostatic pressure, during theoretical analysis of the Stress and strain state. In most of the current study, out of plane stress was assumed to be intermediate principal stress, and the impact of it on the tunnel surrounding rock stress and displacement was ignored, which obviously does not meet the actual engineering requirements under complex stress conditions. In this article, elasto-plastic analysis of stress and displacement during the excavation of a circular tunnel underground was studied on the basis of generalized nonlinear Hoek-Brown strength criterion and plane strain problem. Based on the rock elastic-brittle-plastic model and non-associated flow rule, nonlinear theoretical solutions were presented for stress, displacement and plastic radius of a circular tunnel considering the influence of axial stress. And the elasto-plastic solutions are easily derived by setting the residual strength parameters equal to the peak ones. A new numerical solution for strain softening rock with the influence of axial in situ stress was established based on the linear and nonlinear failure criteria. The main results are as follows.(1) Taken the hydraulic seepage pressure into account as body force, solutions for stress, displacement and plastic radius of cylindrical and spherical cavity based on generalized nonlinear Hoek-Brown strength criterion were obtained respectively. The theoretical results have some practical value.(2) Theoretical solutions were presented for displacement, stress and plastic radius with the different axial in situ stress taken into account. Elastic-brittle-plastic constitutive model with a non-associated flow rule and generalized nonlinear Hoek-Brown strength criterion was used in the analysis. The elasto-plastic solutions were easily derived by setting the residual strength parameters equal to the peak ones. By the method of converting Hoek-Brown parameters to the equivalent Mohr Coulomb parameters, comparative analysis between theoretical solution of this article and Wang’s was made to verify the correctness of this article by programming calculation.(3) Step-by-step method was evolved to solve the stress-strain characteristics of strain softening rock with the influence of axial stress, and based on which the numerical solutions were obtained for the stress and displacement of a circular tunnel in a strain softening rock mass with the influence of axial stress. Both the linear Mohr-Coulomb criterion and generalized nonlinear Hoek-Brown strength criterion were taken into account.