Influence of blasting at tunnel face on an existing adjacent tunnel with oblique cross angle and small clear spacing

Abstract

The influence of blasting at a new tunnel face can directly influence the existing adjacent tunnel, especially for cross tunnels with a small clear spacing. To analyze the blasting vibration on the cross tunnels, this study took the cross tunnels in Lanzhou City, Gansu Province as the research background. These cross tunnels have an oblique cross angle and a small clear spacing of 1.365 m. First, blasting vibration on the existing tunnel was recorded in field tests. Second, the blast pattern and the resulting vibrations were simulated by software FLAC3d, and the simulation was verified by the recorded data in field tests. Finally, based on the peak particle velocity (PPV) on the lining area, the existing tunnel was divided into three sections, namely, the serious influence zone, slight influence zone, and no influence zone. Results demonstrate that the PPV induced by upper bench blasting is greater than that induced by the lower. The serious influence zone and slight influence zone of the existing tunnel are 9 m, 9–16 m from the intersection point, respectively. Meanwhile, the no influence zone is beyond 16 m from the intersection. When the blasting at the new tunnel face is 12 m in front of the cross-section and 10 m behind it, the PPV is relatively large, thus indicating that the blasting should be strictly controlled in that place. This study can effectively ensure the safety of existing structures and provide a reference for similar cross tunnels.