Evaluation of Changing Effects of Density and Thickness of Polyurethane as a Protective Coating on Underground Tunnels under Surface Blast

The use of polyurethane as a sacrificial coating is an important factor in reducing risks and improving the safety of structures against explosions caused by war and terrorist attacks. The parameters of polyurethane can have a positive effect on reducing damage to tunnels under the impact of surface explosions. In this paper, the effect of density and thickness of the protective cover of polyurethane (as an energy absorber) in reducing the damage caused by surface explosions on underground tunnels was studied by computer simulation with AUTODYN software. Six different foam modules with thicknesses between 60 and 150 cm, and five different types of foams with densities between 90 and 250 kg / m 3 and their ability to reduce the maximum pressure caused by an explosion were compared. The results of this study illustrated that by increasing the thickness of the protective cover of polyurethane, a significant decrease occurred in the amount of pressure and vertical displacement in the tunnel crown. Moreover, the findings on the effect of polyurethane density indicated that at a density of 140 kg/m3, the optimum reduction in pressure in the tunnel crown occurred.