Damage of Cast-Iron Subway Tunnels under Internal Explosions

The threat of terrorist attack on subway system using explosives intensifies considerably in recent years. Explosion inside subway tunnels may damage the subway structures and result in further socioeconomic losses. Specifically, the century-old single-track cast-iron subway tunnels in New York City and London are very vulnerable to this type of attack. In this study, a 3D Finite Element procedure was developed to investigate the damage of cast-iron tunnels in saturated soils subject to internal explosions using medium amount of explosive (75 kg TNT) that might be perpetrated by terrorists. The stress path and damage mode of these tunnels subject to internal blast loading were firstly investigated, based on which the damage of cast-iron tunnel lining was simulated using hardening elasto-plastic model considering shear damage. The study then focused on the influences of soil-structure interaction and the compression of saturated soil under large compressive loading. It was found in the study that compressibility of saturated soil influenced significantly the damage of cast-iron lining while the effect of soil-structure interface was much smaller.