عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Convergence-confinement is one of the most popular methods which is used for analysis of stress and strain fields around a circular opening excavated in rock masses. It is assumed that the circular tunnel is excavated in a continuous, homogeneous, isotropic, initially elastic rock masses under hydrostatic loading. Selection of a suitable failure criterion is extremely important in the analysis since it affects the plastic zone and obtained displacement and stress field around the opening. Brown et al (1983) proposed a stepwise procedure based on Hoek-Brown criterion to obtain stress and displacement around a circular opening. A similar stepwise procedure is implemented in this study for Mohr-Coulomb criterion. Then the effect of Mohr-Coulomb and Hoek-Brown criteria on ground response curve is investigated for various models of rock mass behaviors. Finally a sensitive analysis is implemented for Mohr-Coulomb and Hoek-Brown criteria. By a comparison of Hoek-Brown and Mohr-Coulomb criteria, it can be concluded that the relative displacement in Mohr-Coulomb criterion is at least 5 times more sensitive than that in Hoek-Brown criterion to variation of strength parameters. It is obtained that varying rock mass strength parameters develops more relative deformation for medium-quality rock masses. Therefore, it should be carried out to preserve the inherent strength of rock masses by controlled blasting or mechanical excavation, especially for medium quality of rock masses (often with elastic-strain softening behavior).