A new semi-numerical method for elastoplastic analysis of a circular tunnel excavated in a Hoek–Brown strain-softening rock mass considering the blast-induced damaged zone

Abstract

Drill and blast method is mostly used method for excavation of tunnels throughout the world. This tunneling method involves the use of explosives. Compared with bored tunneling by Tunnel Boring Machine, blasting generally results in the development of a blast-induced damaged zone around the tunnel boundary. Theoretically, the presence of this zone, with its reduced strength and stiffness, will affect the overall performance of the tunnel, as well as its construction and maintenance. In fact, the extent of the damaged zone is finite. However, the effect of this zone is traditionally considered by a damage factor D applied to the entire rock mass surrounding the tunnel. This is a common modeling method which can greatly underestimate the strength and stability of the overall rock mass. In this paper, a semi-analytical solution is proposed for analysis of tunnels considering the damaged zone. The solution is presented for circular tunnels excavated in rock masses obeying a new proposed non-linear strain-softening behavior and the non- linear Hoek–Brown failure criterion. The damaged zone is assumed to have a cylindrical shape with reduced strength and deformability parameters.