隧道爆破炮孔堵塞结构运动规律与长度优化研究

Movement Law and Length Optimization of Stemming Structure in Tunnel Blasting

合理确定炮孔堵塞长度对提升爆破破碎效果及控制爆破有害效应具有十分重要的意义。针对隧道爆破堵塞结构的运动规律与长度优化,基于一维轴向运动模型,对炮孔堵塞结构进行了受力分析,考虑了炮孔扩腔膨胀、岩体裂隙扩展及堵塞结构运动对爆生气体压力的影响,优化了爆炸荷载的计算方法,同时还考虑了堵塞结构冲击压缩对滑动摩擦阻力的影响,揭示了附加滑动摩擦阻力的产生机制,建立了用于计算堵塞结构宏观运动过程的“分时分段”计算模型,揭示了堵塞结构滑动摩擦阻力自底部至顶部递减的分布规律,分析了岩体类型、装药结构及堵塞长度对堵塞结构运动规律的影响,提出了允许堵塞结构部分冲出炮孔的“运移式”优化原则,并基于此计算了隧道爆破不同岩体工况下掏槽孔、崩落孔及周边孔的最优堵塞长度。结果表明:堵塞结构运动过程并不是固定不变的,岩体类型、装药结构及堵塞长度均会对其产生显著影响;隧道爆破常见工况下炮孔最优堵塞长度范围为0.3~0.6 m,对于等级为Ⅰ或Ⅱ类的较好岩体,取0.5~0.6 m,对于等级为Ⅲ类的中等岩体,取0.4~0.5 m,对于等级为Ⅳ或Ⅴ类的较差岩体,取0.3~0.4 m;对于较好岩体,掏槽孔与崩落孔的最优堵塞长度相等,且均大于周边孔;对于中等岩体和较差岩体,掏槽孔和周边孔的最优堵塞长度相等,且均小于崩落孔。最后通过工程案例分析验证了结果的可靠性。

To determine the stemming length of a borehole,it is important to improve the blasting fragmentation effects and control the adverse effects of blasting.In this study,a stress analysis based on a one-dimensional axial motion model was first performed to investigate the movement law and length optimization of the stemming structure in tunnel blasting.The calculation method for blast loading was optimized by considering the effects of blasting cavity expansion,crack propagation,and stemming structure movement on gas pressure.The mechanism of additional sliding friction resistance was revealed by considering the influence of shock compression of the stemming structure on the sliding friction resistance.Subsequently,a new time-sharing piecewise calculation method for calculating the macro movement process of the stemming structure was established,and the distribution law of the sliding friction resistance decreasing from the bottom to the top was revealed.Moreover,the influences of rock mass type,charge structure,and stemming length on the movement law of the stemming structure were analyzed.Furthermore,the optimal stemming lengths of the cut,breast,and trim holes that allowed part of the stemming structure to rush out of the borehole under different rock mass conditions were calculated using the optimization principle.The results show that the movement process of the stemming structure is not constant and is significantly affected by the rock mass type,charge structure,and stemming length.Under common tunnel blasting conditions,the optimal stemming lengths range from 0.3 to 0.6 m.Specifically,for good rock mass classified asⅠorⅡ,the range is 0.5-0.6 m;for medium rock mass classified asⅢ,it is 0.4-0.5 m;for poor rock mass classified asⅣorⅤ,it is 0.3-0.4 m.In addition,for a good rock mass,the optimal stemming lengths of the easer and breaking holes are equal,and both are larger than those of the perimeter hole.For medium and poor rock masses,the optimal stemming lengths of the easer and perimeter holes are equal,and both are smaller than those of the breaking hole.The reliability of the results was verified using engineering cases.The findings provide a basis for calculating the stemming length in tunnel blasting.