Elastoplastic analysis of deep circular tunnels affected by blasting damage and hydraulic flow

In drill and blast method, due to uncontrolled blasting operations, the blast-induced damaged zone (BIDZ) is formed, whose mechanical and hydraulic properties are altered. This zone affects the behavior of the rock mass such that it reduces the strength of surrounding mass, and stability of the excavation. On the other hand, the groundwater is also effected by damaged zone induced stress and displacement, leading to a change in hydraulic flow around the tunnel which subsequently could produce new stress and displacement fields. In this research, an analytical solution for evaluating the stress and displacement of deep circular tunnels in elastoplastic rock mass is proposed, assuming the presence of BIDZ and hydraulic flow around the tunnel. The tunnel is subjected to in situ hydrostatic stresses, under radial hydraulic flow, and the damaged zone is supposed cylindrical shaped surrounding the cavity. Four different scenarios are predicted for stress evolution around the cavity considering the seepage zone, damage zone and plastic zone spread for elastic brittle-plastic behavior of surrounding mass. The analytical solution is validated using FLAC software, which shows excellent agreement. Examples are given to investigate the effect of BIDZ on the stress and displacement fields around the tunnel in both drained and undrained condition. The results show a significant impact on tunnel wall displacement especially for small magnitude of the ratio of seepage zone to damage zone radii, indicating its great significance in tunnel practice in terms of support and ground control.