Dynamic response and safety control of civil air defense tunnel under excavation blasting of subway tunnel

Abstract

The vibration induced by the blasting excavation of a subway tunnel may cause harmful effects on the adjacent buried structures. To ensure the safety and stability of the adjacent buried structures, it is of great importance to investigate their dynamic response. In this paper, the civil air defense tunnel right above the subway tunnel, excavated using the drilling and blasting method, is studied. The in-situ tests are carried out to monitor the strain of the cross-section of the civil air defense tunnel and the vibration along the axis of civil air defense tunnel. The strain distribution characteristic of the cross-section and the propagation law of the vibration in the civil air defense tunnel is analysed based on the field monitoring data. Three-dimensional finite element simulation is also performed using the dynamic finite element program LS-DYNA and its reliability is verified by the field monitoring data. Based on the numerical simulation results, the positions of the civil air defense tunnel where the stress, vibration velocity reach the maximum are determined. The relationship model between the peak particle velocities and effective stresses is established. According to the maximum tensile strength criterion, the blasting vibration safety criterion of the civil air defense tunnel is calculated using the relationship model. For convenient field monitoring during subway construction, the safety threshold of vibration at the floor of the civil air defense tunnel is proposed. To obtain the maximum charge per delay, five blasting processes with different charges are simulated. The maximum charge per delay is calculated to ensure the safety of the civil air defense tunnel.