Dynamic performance and damage assessment of a shallow buried tunnel under internal explosion

Abstract

The tunnel entrance is usually made of arch members buried at shallow depths. These contribute to the greater performance of the tunnel under static or seismic loading. If an explosion occurs in the shallow buried tunnel, the tunnel arch at the entrance might be destroyed by the intense blast loading, thereby causing the collapse of the tunnel entrance or the surrounding ground. Hence, it is extremely important to investigate the dynamic behavior of a shallow buried tunnel arch under the conditions of an internal explosion and to evaluate its damage after the blast. In this paper, four scaled tunnel arch structures were fabricated and tested for their anti-blast performance under internal explosion. The following laboratory static load test was conducted on the undamaged and blast-damaged specimens to obtain their maximum and residual bearing capacities, respectively. The field blast test results showed that the tunnel arch experienced local punching failure under the internal contact explosion, and the dimensions of the failure zone increased as the explosive equivalent increased. In addition, for the same explosive equivalent, the residual bearing capacity of the specimen after the contact explosion at the arch crown was the lowest among other blast-damaged specimens, indicating that the damage on the arch crown significantly deteriorated the bearing capacity and stiffness of the tunnel arch. The finite element (FE) model of the shallow buried tunnel arch under the internal explosion was developed by adopting the arbitrary Lagrangian–Eulerian (ALE) algorithm in LS-DYNA and validated on the actual measurements from the field blast test. It is shown that the results from the FE model and field blast test measurements compared well in terms of damage pattern, crater diameter, acceleration and reflected overpressure readings. The full restart method in LS-DYNA was further employed to calculate the bearing capacity of the specimens. Finally, the damage levels of the blast-damaged specimens were assessed by taking the residual bearing capacity of the tunnel arch as an indicator. The damage assessment charts for the shallow buried tunnel arch under the conditions of an internal explosion were further established. From the chart, the blast resistance of the shallow buried tunnel arch can be quickly assessed under different internal blast loading conditions. This research is of direct significance for the design of the shallow buried structures with increased blast resistance.