Mechanism of saturated ground-tunnel interaction under medium blast loading.

摘要

A series of numerical simulations were carried out in this research to study the interaction between subway tunnels and saturated soils subjected to medium internal blast loading (< 200 kg of TNT equivalent). Numerical procedure using Finite Element program LS-DYNA, which can model explosion, air-solid interaction, material damage and soil-structure interaction, was used to conduct the simulations. The excess pore-water pressure was studied with an existing soil model (FHWA) that can simulate pore-water pressure and effective soil pressure. A recently developed blast loading scheme that removes the necessity of modeling the explosive in the numerical models but still maintains the advantages of nonlinear fluid-structure interaction was used to study the process of blast wave propagation in the air domain inside the tunnel.;Centrifuge technique, which has been successfully employed in model tests to investigate the blast effects, was used to simulate the effect of medium- to large-scale explosions at small scaled distances. Extensive parametric studies were carried out to understand the failure and damage to cast iron subway tunnels under internal blast loading and to shed light on their protection by structural and geotechnical measures.;The study found that the blast loading technique could significantly reduce the computation effort, and the initial density of air in the numerical model could be artificially increased to partially compensate the error induced by the use of relatively large air elements. As long as the free air blast at a specific scaled distance was properly simulated, the fluid-structure interaction could be properly duplicated using proper Arbitrary Lagrangian Eulerian (ALE) coupling scheme.;Increase of soil stiffness by certain soil reinforcement techniques, increasing overburden stress on the tunnel and its surrounding soil without significantly increasing static lining stress, and enhancing lining damping through structural measures at its joints, may be adopted to reduce the vulnerability of tunnels. Protective measures by geofoam may only be effective for small amounts of explosive. Explosion close to ventilation shafts would reduce the blast pressure on the lining, but might not alleviate lining damage due to the reduction of lining integrity.