The Effect of Weight of Plastic Zone on Distribution of Stresses and Radial Displacement around a Tunnel

With starting plastic deformation around the tunnel, the pressure on the tunnel roof increases due to the weight of the plastic area, which influences on the tunnel stability. In this paper, with considering strain-softening rock mass around the tunnel and plastic region weight and using the generalized Hook-Brown failure criterion, the stress and displacement equations around the tunnel were rewritten and solved by the semi-analytical method. The results show that considering the weight of the plastic region caused the distribution of stress around the tunnel are changed and the amount of displacement and radius of the plastic region increases. This becomes more importance in conditions with larger plastic radius. Also, by investigation of the effect of Hook-Brown criterion parameters on the displacement around the tunnel, the importance of each of the parameters is shown. The results show that Hook-Brown parameters in plastic condition have a greater effect on the displacement around the tunnel than in peak conditions.