Analysis of factors influencing vibration reduction and design optimization of damping holes in adjacent tunnel blasting

Drilling and blasting is still the most widely used method for tunnel excavation in hard rocks. However, this method causes damage to adjacent buildings and structures mainly because of tunnel blast-induced vibrations. Currently, no specific guidelines are available for optimizing the design of damping holes during controlled blasting. Therefore, this study analyzes the vibration reduction mechanism of damping holes. Six key factors, namely, hole radius, hole spacing, coverage length, arrangement type, number of rows, and row spacing, that can affect the blasting vibration reduction were analyzed theoretically. Six groups of 30 numerical models were established using LS-DYNA. The influences of the six factors on the average and maximum velocities and stress vibration reduction were analyzed to quantitatively evaluate their damping effects. Then, optimization design suggestions for damping holes were proposed. The results revealed that it is necessary to increase the hole diameter and reduce the hole and row spacings as much as possible. The reasonable coverage length of damping holes is 1.5 times the coverage length of blasting holes. The blossom-type arrangement is recommended for practical engineering applications and the number of rows of damping holes should not exceed four. Guidelines for reducing vibration in adjacent tunnel blasting were formulated. Finally, the optimized damping hole design was applied to a typical tunnel project, which verified its reasonability and applicability.