Numerical Analysis of Himalayan Rock Tunnels under Static and Blast Loading

Abstract

Tunnels have been the necessary element of the modern construction industry. Due to their importance for the infrastructural and economic point of view, several tunneling projects are being carried out. The present numerical study investigates the response of rock tunnel under static and surface blast loading. The response of tunnel have been observed in three different types of rocks predominantly observed in Himalayan mountains, i.e. Phyllitic Quartzite, Quartzitic Phyllite and Migmatic Gneiss. The study has been carried out on a 3D numerical model of dimension 70 x 70 x 80 m. The tunnel has 11 m diameter with concrete liner of 0.45 m initial thickness and the overburden has been applied in the form of pressure initially as a height of 50 m of overburden rock. The overburden pressure and the lining thickness have been varied under static loading conditions. In addition, the shape of the tunnel cross-section has been varied as Arch, Circular, Rectangular and Horseshoe. The surrounding rocks have been modeled as a nonlinear elastoplastic constitutive material model, with concrete liner as Mohr-Coulomb (M-C) and Concrete Damage Plasticity model respectively. Initially, the response of the tunnel has been observed under static loading conditions for different overburden pressure and tunnel cross-section. Later, a surface blast analysis has been carried out using CONWEP method with source at a standoff distance of 10 m from the ground surface. The blast analysis has been carried out for initial conditions of concrete liner and overburden pressure. It has been concluded that under static loading, circular shape is the safest rock tunnel among all four shapes. However, Arch shape of rock tunnel provides maximum resistance under blast loading condition.