WITHDRAWN: Effect of geo-material on dynamic response of tunnel subjected to surface explosion

Abstract

Prime materials involved in a problem such as underground structures are concrete, reinforcement steel and geo-material surrounding the tunnel. Among these three materials, concrete and steel are manufactured materials and their properties can be controlled up to a certain extent. However, geomaterial is a naturally occurring material whose constitutive properties vary from region to region making it highly unpredictable. Findings from one study cannot be applied to other geotechnical problems directly, especially, in the case of tunnels subjected to surface explosion. The blast wave generated has to travel through the geo-material before it interacts with the tunnel. As the shock wave propagates radially its characteristics are most likely to get altered by the geo-material. Limited study has been carried out considering this problem. In the present study, the effect of various types of geo-material on the blast response of tunnels subjected to surface explosion is investigated. Finite element analysis has been carried out using LS-DYNA® wherein the problem has been modelled using multi-material arbitrary Lagrangian Eulerian (MM-ALE) method. Materials with fluid behavior such as air, explosive and soil are modelled using ALE formulation. Other materials including tunnel lining, reinforcing steel and rock are modelled using Lagrangian formulation. Blast loading is simulated using Jones-Wilkins-Lee (JWL) equation of state. Geo-materials considered for the comparative study are sandy loam, sandstone, and granite. Vertical displacement measured at the crown of the tunnel is used to determine the response of tunnel. Sandy loam soil being a highly compressible soil, exhibits non-linear and fluid-like behavior under high strain loading such as explosion. Tunnel undergoes extreme deformation in the case of sandy loam soil as compared rock cases. Additionally, the effect of weathering of rock on the tunnel response is investigated in the case of sandstone and granite. It was observed that weathering rock led to more displacement of tunnel crown as compared to intact rock.