Effect of Explosion and Fire on Underground Structures

Abstract

It appears that explosion in a closed space of underground works together with extreme increase of temperature influences the bearing capacity of underground structures, particularly road and rail tunnels, underground power stations, underground parkings, etc. The explosion is caused by various resources (terrorist attack, explosion of inflammable material positioned on freight cars, and such). This paper is focused on the effect of a fast change of load in tunnels and especially on the tunnel linings from fiber reinforced concrete. Shock wave caused by both the explosion and increased temperature leads to a spalling of concrete, i.e. to a reduction of thickness of the bearing structure and decrease of feasibility of the support. Relatively complicated system, describing an interaction between the air (shock wave described by gas dynamics), and the solid part (tunnel lining and the rock surrounding the tunnel obeying the equations of elasto-plasticity) is to be simplified in this paper. First, laminated cylinder describing the solid structure of the tunnel and the non-linear Winkler subsoil simulates the rock. The cylinder is loaded by the influence of explosion and change of temperature. It is to be shown that the superheated vapor together with interacting waves of the open charge inside of the underground space may cause an extensive occurrence of fissures on the surface exposed to the external loading envisaged. On the other hand the rock surrounding the underground structure interacts with the underground structure as a dumper. The simplified model starts with axisymmetric geometry and axisymmetric load by the shock wave and change of temperature, and moreover, generalized plain strain assumption is considered with a constant change of pressure in the axial direction of the tunnel. The governing equations adopt this assumption and the solution is then easier. The generalization to more complicated non-symmetric problems is straightforward. Couple of examples is to verify the theoretical considerations.