Effects of Surface Explosion on Underground Tunnel and Potential Mitigation Measures

摘要

An explosion on the ground surface can cause significant damage to a tunnel located at a shallow depth below ground. The effects of explosion were studied through a combination of physical model tests and numerical analyses. The physical model tests were conducted on a geotechnical centrifuge, where 1:70 scale models were subjected to 70 g acceleration. Due to centrifuge scaling laws related to explosions, the effects of an explosion, such as cratering and damage, scale as the cube of the g level. Using this scaling relation, it was possible to study the effects of a relatively large explosion in a test, utilizing a small amount of actual explosives. Strain gage readings, collected in real time during the centrifuge tests, provide measurements of damage on the tunnel due to the explosion. Numerical modeling using an explicit dynamic hydrocode allows simulation of the explosion in a three-dimensional model. The results of the numerical model appear to indicate a good match with results of physical model tests. The presence of a compressible barrier immediately outside the tunnel may reduce the damage to the tunnel due to a surface explosion. This was investigated in the physical model tests and numerical models, where a polyurethane geofoam barrier was included. The highest hoop strain at the crown of the tunnel immediately below the explosion reduced from 6.0 to 1.6 % when a 0.9-m-thick polyurethane geofoam barrier was added, in conjunction with a 0.9-m-thick soil cover. The corresponding reduction in vertical displacement was from 1.1 to 0.56 m.