Stress and Deformation Analysis of Circular Tunnels With Consideration of Blast-Induced Damage and Gravity

Analysis of stresses and deformations around circular tunnels and shafts are critical for evaluation of the interaction between the support system and the ground and therefore the tunnel support design and stability. The damage induced in the material by the excavation method (i.e., blasting) 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 crown of the tunnel and may subject the support to larger stresses. This study presents a new analytical-numerical solution for the determination of stresses, strains, and deformations around a tunnel with the consideration of the gravity effect and the blast induced 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 effect on the tunnel convergence. The presented method in this paper is novel and allows the tunnel designers to assess the combined effect of blasting quality and gravity in the tunnel convergence.