Comparative Study of Single Tunnel and T- Intersection Subjected to Impact Load

Intersection is the region where two or more openings share common points. These are constructed in several subsurface structures including road tunnels, railway tunnels, mines and hydel projects. In road tunnels, cross passages are constructed at regular intervals to facilitate access to the egress tunnel. The junction of cross passage with the main tunnel is the critical part of the tunnel. Tunnels are subjected to impact load when projectile hits the surface. The purpose of this study is to understand the influence of intersection of tunnels by comparing it with single tunnel constructed in rockmass. This is accomplished by comparing the displacements observed at the tunnel crown in both configurations, that is, single and T-section, when subjected to different low-velocity and high-velocity impacts at the ground surface. Tunnel intersections fall in the ambit of three-dimensional problem owing to the geometrical aspect and hence, the problem is attempted in this study through numerical simulation using FEM-based explicit module of ABAQUS. The tunnels are circular in shape of diameter 5 m and intersect each other at the same level from the ground surface at cover depth / diameter ratio of 1. The location of impact is above the centre of the tunnel crown. The study focusses on solving the combination of non-linear problem of impact and criticality of the geometry. The results provide an idea about the magnitude and extent of damage incurred by the roof in single and T-section. The displacements at the crown in the single tunnel are found to be less as compared to that in the T-section but the deformed area is more in the former. This eventually develops an insight on ways to improve the roof support system.