Numerical Analysis of a Tunnel Subjected to Blast Loads in a Transversely Isotropic Rock Mass

Abstract

The present study investigates the stability of a tunnel subjected to blast loads. The tunnel is placed in a transversely isotropic rock mass. Numerical simulations are performed using the discrete-element method. The rock material between the bedding planes/joints is discretized as Voronoi polygons. The research focuses on the significance of discretizing the rock material between the bedding planes as Voronoi polygons for studying a tunnel’s stability under blast loads. To this end, the influence of Voronoi polygon size, joint spacing, anisotropy angle, cover depth, and earth pressure coefficient on the tunnel response are examined. The tunnel response is measured in terms of normalized crown displacement. The study provides many novel insights that can be used to improve the design of rock tunnels. It is found that it is vital to discretize rock grains as Voronoi blocks for studying the tunnel response. When Voronoi blocks are considered, the tunnel stability increases for anisotropy angles 30° and 60° but decreases for angles 0° and 90° when no Voronoi blocks are used. The tunnel becomes more vulnerable to damage as the Voronoi block size increases. It is noted that the joint spacing and Voronoi block size are interlinked, and their influence must be considered together for assessing the tunnel stability. When joint spacing is kept twice or more than the Voronoi size, the crown displacement is higher than when joint spacing is equal to or closer to the Voronoi size. It is observed that the crown displacement is maximum when the earth pressure coefficient equals 2. Therefore, the influence of change in the earth pressure coefficient is considered the most severe of all the parameters studied.