Blast resistance of a folded arch cross-section immersed tunnel subjected to internal explosion

Abstract

With the completion of the subsea immersed tunnel of the Hong Kong–Zhuhai–Macao Bridge (HZMB), the tunnel structure in a closed environment for a long time will inevitably be threatened by sudden extreme accidents such as car accidents and car bombs. However, intensive research efforts have been devoted to understanding their performance under service and seismic loads, and the vulnerability of the tunnels against accidental blast loads is seldom discussed. The present study performs an immersed tunnel model of HZMB was constructed at a scale of 1:5 to carry out the explosion test. The results showed that after an internal explosion of a van-type bomb, the roof subsidence of the tunnel model doubled under the same water pressure. The test also revealed that the peak overpressure load on the roof was up to 50 MPa, which showed the multi-peak characteristics, and evident cracks appeared on the top slab and at the junction of the roof and middle wall. In addition, based on the fully verified constitutive model of high strain rate materials, a refined finite element model was established. The propagation characteristics of the blast wave in the tunnel, dynamic response characteristics, and failure process and modes of the tunnel structure were discussed in the developed FE model. The results showed that the ultimate blast resistance of the tunnel model was 41.8 kg TNT (scaled distance is 0.363 m/kg1/3). Furthermore, a resonance effect was observed between the middle wall and roof. The deformation and damage of the roof could be significantly reduced for the explosion height of 1.06–1.25 m. This height range could be very useful for developing traffic standards guiding the safe transportation of hazardous chemicals in tunnels. Based on the numerical and test data, four blast damage levels were finally identified and categorized according to the scaled distance to the tunnel roof.