To the challenge of selecting reasonable blasting parameters, a calculation method for smooth blasting parameters based on the radial decoupling coefficient was proposed according to the mechanism of rock fracture between holes under explosive load. Then, the optimal blasting parameters were obtained through numerical analysis and comparison. Finally, these parameters were successfully applied to actual engineering projects. The results show that, under the condition of ensuring the cracking and interconnection of rock between holes while avoiding excessive crushing of the rock wall, the reasonable range of the radial decoupling coefficient Kd at the DK96+152 section of the Tongchuan Tunnel is calculated to be 1.60~2.92. Four blasting schemes with Kd values of 1.6 to 1.94 were proposed. Through numerical analysis of the four blasting schemes, considering both the damage to the surrounding rock and the construction cost, it was found that when Kd is 1.7 and L is 0.5 m, the damage to the surrounding rock is lower and the construction cost is optimal. The optimized smooth blasting parameters were applied to the construction site of the Tongchuan Tunnel, where the actual measured maximum overbreak distance was reduced by 0.27 m (64%), the overbreak area was reduced by 2.82 m² (57%), and the investment was saved by about 3 902 yuan per cycle. An ideal smooth blasting effect was achieved, which can provide a reference for the reasonable selection of smooth blasting parameters in related engineering projects.
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