ABSTRACT
Damage is mainly caused by development of cracks, displacement along existing joints, and disturbance of stresses. The original state of the in situ rock mass, such as stress, strain, rock stability, water flow, etc. are affected to some extent around an excavation. The definition of the affected zone depends on the nature or the purpose of the excavation. For example, a major concern for a road tunnel is the regions in which rock blocks have undergone notable displacement, or where the tangential stress shows a major increase, which controls tunnel stability. For nuclear waste disposal, a region with hydraulic changes is of more concern than the tunnel’s local stability because it changes the water flow, and hence increases the possibility for the migration of radioactive materials. Figure 1 shows a conceptual diagram of the damage zone around a tunnel.
