Research and application of offset hole for peripheral blasting design and optimization
Based on existing research,the effects of the empty hole effect and the law of crack propagation when empty holes are set were investigated and discussed.It has been found that empty hole is beneficial for crack penetration and the improvement of blasting quality.However,the drawback that the traditional linear arrangement would lead to cracks deflection was also found,which means cracks tend to deviate from the original path near an empty hole.The empty hole effect and guiding effect could be fully utilized to improve excavation quality if offset empty holes are set.For the effect of offset holes in blasting,the numerical simulation was adopted to explore the crack propagation law and the penetration under different hole spacing and offset angles,and the optimal offset angle were discussed.According to the simulating result,the scheme was optimized and applied to on-site blasting.Results show that the offset hole has a more obvious guiding effect on blasting cracks than the straight hole,which can be observed from following features:blasting cracks go towards the empty hole directly or are guided to change the original route,and finally the main cracks connect to the empty hole or communicate with the other outside the empty hole.Compared with the traditional straight hole,the offset hole is more conducive to the expansion and penetration of the main crack;When the hole spacing is 60 cm or less,the optimal offset angle for peripheral blasting design is 15°.In this case,the direction of the blast hole line forms a crack parallel to the line of the hole center,which can significantly improve the penetration;According to the results,the blasting parameters of one tunnel on the Fuzhou-Xiamen Railway were optimized.By comparing the blasting vibration velocity before and after the optimization and the scanning of excavation quality,it was found that the blasting vibration velocity is reduced by more than 50%,and the over excavation value is also reduced from an average of 25 cm to less than 15 cm.The application works well.This study can provide a certain reference for the research of tunnel blasting vibration reduction and over-and-under excavation control.
smooth blastingperipheral holeoffset empty holeblasting vibration velocityover and under excavation control
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