Effect of unconfined compressive strength of rock on dynamic response of shallow unlined tunnel

Abstract

Tunnels and underground space have been evolved as an integrated part of sustainable transportation infrastructure of both the developed and developing countries. Tunnels also have strategic importance in the defence sector of the nation. In recent decades, tunnels have been subjected to several events of intentional and unintentional blast incidents. The present study investigates the response of shallow unlined rock tunnels subjected to an internal blast. The effect of different unconfined compressive strengths (UCS) of rock on the extent of damage produced due to blast loading has been investigated. UCS representing dolomite, shale, sandstone, granite, basalt and quartzite medium has been investigated through a three-dimensional finite element model having dimensions of 30 m × 30 m in cross section and 35 m in length generated in Abaqus. The diameter of the unlined tunnel has been taken as 5 m having overburden depth of 12.5 m. Coupled-Eulerian–Lagrangian modelling has been adopted to simulate the blast loading. Nonlinear Mohr–Coulomb failure criteria have been adopted for different rock media. Trinitrotoluene (TNT) explosive has been used to simulate the blast loading, and Jones–Wilkins–Lee material model has been adopted to model the characteristics of TNT. Subsequently, a relation has been proposed to understand the damage caused by TNT blast loading in a shallow unlined tunnel. The total induced energy due to internal blast loading has been found to be maximum and minimum in dolomite and quartzite, respectively.