Abstract:
The stability of deep circular tunnels excavated in rock materials subjected to gravitational loading is assessed by construction of the ground response curves. The reduction of internal support pressure results in the development of a plastic (broken) zone around the tunnel. Due to the self-weight of the broken material, crown of the tunnel experiences the highest radial convergence. In this study, considering the weight of broken material at the tunnel crown, a new analytical method for determining the ground response curve of tunnels excavated in the generalized Hoek-Brown rock mass is developed. The effects of gravitational loading on the ground response curve are investigated for several tunnel cases. The results show that in poor quality rock masses, gravity has significant effect on the ground response curve of the tunnel and the tunnel stability and higher support pressure is required to limit the convergence at the tunnel crown than the tunnel sidewalls.
Introduction
Determination of the stresses and displacements around circular openings has been one of the most fundamental problems in geotechnical, petroleum, and mining engineering. Design of tunnel liners and the validation of numerical models are among the practical applications of displacement analysis around circular openings. Several analytical and numerical solutions for this axisymmetric opening problem have been developed and various rock mass behaviors including the elastic-perfectly plastic, elastic-brittle-plastic and elastic-strain-softening models with different yield criteria have been assumed for the rock (Brown et al., 1983; Wang, 1996; Carranza-Torres and Fairhurst, 1999; Alonso et al., 2003; Park and Kim, 2006; Sharan, 2008; Lee and Pietruszczak, 2008; Park et al., 2008; González-Caoa et al., 2013). Although Mohr-Coulomb yield criterion has been widely used in analysis of rock mass due to its simplicity, many studies and experimental observations show that the strength envelope for rock is non-linear. Among the non-linear yield criteria, the Hoek-Brown (H-B) failure criterion (Hoek et al., 2002) is widely accepted by the rock mechanics community and has been applied in a great number of projects around the world.
