大采高回撤通道“高+低位”断顶爆破实践

Practice of“high+low”roof breaking blasting for large mining height withdrawal channel

大采高冲击地压工作面末采期间面临的冲击地压风险极高,为了解决此类工作面的冲击地压防治难题,针对纳林河二号矿大采高工作面末采阶段顶板的处置问题,从覆岩冲击层位应力阻断和正面保护回撤通道的角度出发进行爆破方案的设计、对比及优化,初步证实“高+低位”具有2个方面明显的技术优势。一是爆破对覆岩的致裂破碎方面,串联一次起爆增强了爆破致裂的效果和对爆破区域块体的破碎作用,与此同时该区域的应力变化梯度Δσ显著降低,更好的起到阻断高应力传递的作用;二是爆破覆盖的尺度方面,实现全层位的应力阻断,避免了卸压盲区。在此基础上,末采阶段工作面压力峰值分布范围、集中程度明显减小,同时末采阶段液压支架阻力正态分布中均值、标准差均减小,且10%~37%应力计不同程度出现卸荷状态,证实“高+低位”爆破对末采阶段、回撤通道及孤立煤体形成了正面保护作用。

The risk of rock burst during the final mining period of the high mining height rock burst working face is extremely high.In order to solve the problem of rock burst prevention and control in this type of working face,the design,comparison,and optimization of blasting schemes are carried out from the perspective of stress blocking in the overlying rock burst layer and positive protection of the retreat channel,in response to the disposal of the roof during the final mining stage of the high mining height working face in Nalinhe No.2 Mine,It has been preliminarily confirmed that“high+low”has two obvious technical advantages.Firstly,in terms of the fracturing and fragmentation of the overlying rock caused by blasting,the series initiation enhances the effect of blasting fracturing and the fragmentation of blocks in the blasting area.At the same time,the stress gradient in the area is significantly reduced,which better blocks the transmission of high stress;The second aspect is the scale of blasting coverage,which achieves stress blocking throughout the entire layer and avoids blind spots in pressure relief.On this basis,the distribution range and concentration degree of the peak pressure of the working face in the final mining stage are significantly reduced.At the same time,the mean value and standard deviation in the normal distribution of the resistance of the hydraulic support in the final mining stage are reduced,and 10%~37%of the stress gauges appear unloading states with varying degrees,which confirms that the“high+low”blasting has a positive protective effect on the final mining stage,the withdrawal channel and the isolated coal body.