The Elasto-Plastic Response of Deep Tunnels with Damaged Zone and Gravity Effects

Analysis of stresses and deformations around circular tunnels and shafts are is critical for evaluation of the interaction between the support system and the ground and, hence, the tunnel support design and stability. The damage induced in the material by the excavation method (i.e., blasting or mechanical excavation) can significantly influence the ground response as the excavation alters the rock mass properties over the damaged zone. When the provided support pressure inside the tunnel falls below a critical value, a zone of plastic (broken) material develops around the tunnel. The self-weight of the broken material is significant at the roof (crown) of the tunnel and may exert higher pressures to the support system at the roof than the sidewalls. This study presents a new analytical–numerical solution for the determination of stresses, strains, and deformations around a circular deep tunnel with the consideration of the gravity effect and the damaged zone. A modified equilibrium equation for the ground is used and the elastic and plastic zones of the tunnel are analyzed. The results indicate that gravity and the damaged zone have significant effects on the tunnel convergence and the distribution of stresses in the rock mass. The presented method in this paper is novel and allows tunnel designers to assess the combined effect of damage induced by excavation and the gravity on tunnel convergence.