RESPONSES OF UNDERGROUND STRUCTURES SUBJECTED TO BLAST LOADING

Terrorism against American citizens and assets is real and growing. The number and intensity of domestic and international terrorist events, along with the September 11, 2001, attacks, change the way Americans think and live. According to the Blue Ribbon Panel (BRP) on Bridge and Tunnel Security assigned by AASHTO, the US transportation system consists of 337 highway tunnels and 211 transit tunnels in 2003. The number is expected to grow in the near future. These tunnels are subjected to the threats of internal explosion, either accidental or maliciously intentional. Explosions inside transportation tunnels would result in direct casualties; and the subsequent damages of tunnel structures could further lead to large socioeconomic losses. Specifically the century-old cast-iron subway tunnels in cities such as New York and London are very vulnerable to this type of attack. This study aims to reveal the fundamental knowledge on the interaction between transportation tunnels and saturated soils subject to internal explosions using medium amounts of explosives (\u3c 100Kg TNT). Centrifuge modeling made it possible to create small scale models using a relatively small quantity of explosives under a high g-level. Two tests conducted at 50g, one under dry sand and the other under saturated one, using 1.2 g of TNT equivalent of explosives, resulted in explosions equivalent to 150 Kg or 1.47 KN (0.15 tons) of explosives under normal gravity (1 g). Strains induced at different location of the model as a result of the explosions were captured using TML strain gauges. Results showed that the stresses in the lining depend on its thickness and the nature of the debris that project due to the explosion which most likely caused the rupture of the tunnel lining