No abstract

The urban social environment is complex and changeable, and there are accidental and non-accidental explosion risks in tunnels. Performance analysis and assessment after tunnel explosions has become important work. In this study, a prefabricated frame structure (single-layer and double-layer) for urban road tunnels was designed. A three-dimensional refined dynamic response numerical model of a frame tunnel considering the joint effect was established, and the reliability of the modeling method was verified by a full-scale explosion test. Considering factors such as the explosion equivalent (100, 200, 300, and 400 kg), explosion distance (3, 6, 9, and 12 m), and central and external explosions, the deformation characteristics and damage evolution law of the prefabricated frame tunnel after the explosions were explored. The deformation failure mode of the prefabricated frame tunnel was analyzed. The study shows that the roof of a single-layer tunnel and the mid-partition of a double-layer tunnel are weak components of a prefabricated frame tunnel with steel column joints under a central explosion load. The deformation and damage at tunnel joints are greater than those at other positions. Under an external explosion load, the closer the explosion point is, the greater the damage and deformation of the prefabricated frame tunnel lining are. Furthermore, showing a high degree of locality. With the equal amplitude increase of the detonation distance (3–6 m, 6–9 m, 9–12 m), the lining displacement is relatively reduced by about 75.7%, 39.9%, and 10.0%, respectively, and the lining deformation is mainly represented by the overall bending deformation.

A low-clearance tunnel portal in the shallow-buried, joint-developed, broken, and loose surrounding rock slope deposit may cause safety issues during construction. In this study, the Guanyin Mountain Tunnel of the Chong-Ai expressway was taken as a case study, and the characteristics of the loose and broken surrounding rocks, their low clearance, and shallow buried bias were comprehensively studied. The three-dimensional numerical model of the Guanyin Mountain tunnel portal section was constructed by the Rhino, AutoCAD, and FLAC 3D software, and the whole construction process of the tunnel portal was simulated. Under the conditions of loose and broken surrounding rocks, the surrounding rock deformation, surface settlement, and slope stability at the portal of the shallow buried tunnel with a small clear distance during the construction of the center diaphragm (CD) method and circular reserved core soil method were studied. The following conclusions are drawn. During the simulated excavation of the tunnel, the maximum surface settlement is 10.74 mm, which meets the requirement of the specification. When the left tunnel is excavated, the surrounding rock deformation of the right arch shoulder should be carefully considered. The maximum deformation value can reach 14.314 mm. After excavation, the deformation rate of the right tunnel is large, and initial support should be installed in time. Since the stratum rock at the portal of the tunnel is strongly weathered, the uplift value of the arch bottom is large and gradually decreases along the axial direction. The tunnel arch bottom and arch foot are plastic areas prone to tensile damage. Therefore, it is imperative to strengthen the inverted arch support of the tunnel in the strongly weathered rock stratum. The excavation sequence of the tunnel portal section adopts the method of excavating the left tunnel first and then excavating the right tunnel, which is more conducive to ensuring the slope stability.