Numerical and physical modeling of geofoam barriers as protection against effects of surface blast on underground tunnels

Abstract

An explosion on the ground surface may cause significant damage to an underground structure, such as a tunnel or a pipeline. The extent of damage would depend on the intensity of blast, the material and configuration of the structure, as well as the nature and geometry of the intervening material.An underground structure may be protected by means of a protective barrier, installed directly above the structure. The effectiveness of using a compressible barrier, made of polyurethane geofoam, to mitigate the effects of surface explosion was investigated.The effects of a surface explosion were studied through a combination of physical model tests and numerical modeling. Reduced-scale (1:70 scale) physical model tests were conducted using a geotechnical centrifuge, where the scaling law for explosions was utilized to model the effects of a large explosion using a relatively small mass of explosives under a high gravitational field (70 g, in this case). The results of the physical model tests were used to calibrate a three-dimensional numerical model in which a fully-coupled Euler–Lagrange solver was utilized to model the explosions.Tunnel configurations with and without protective barriers were studied to assess the mitigation provided by protective barriers. Material properties for polyurethane geofoam barriers were evaluated from laboratory tests. The influence of barrier thickness in reducing the strains, stresses, and pressures on the tunnel induced by an explosion was studied. The beneficial effects of a protective geofoam barrier were found to increase with increasing barrier thickness only up to a certain thickness, beyond which, further increase in thickness did not result in additional reductions. The results will help in design optimization, while planning protection systems for new tunnels, as well as for retrofitting existing tunnels.