Discussion on ultra-deep depth problem of slot hole in blasting excavation of rock roadway in coal mine

The cutting technology is the key of affecting the efficiency of drilling and blasting method of rock roadway in coal mine.In order to explore the relationship between the ultra-deep depth of the cutting holes (the difference between the depth of the cutting hole and the non-cutting hole) and the utilization rate of the blast hole, a literature search was used combined with field tests. Taking the actual cases of rock tunnel blasting in the past 40 years as research objects, the relevant literature on the construction of coal mine rock tunnels in China were analyzed from five aspects including time, lithology, section size, blast hole depth, and trenching form. The research results show that since the 1 980 s, the ultra-deep depth of the slotted holes designed for rock blasting has been set to about 200 mm, and the blasthole utilization rate has been maintained at about 90%. Among the five aspects, lithology has the most significant effect on the blasthole utilization rate.On-site blasting tests were carried out on the ultra-deep depths of 200, 300, 400, and 500 mm. The utilization rate of the holes was increased to 93%, 97%, and 97% from 89% when the ultra-deep depth was 200 mm. The maximum increase is 8%. Under test conditions, the optimal depth of the slotted hole is 400 mm; there is a strong correlation between the ultra-deep depth of the slotted hole and the utilization rate of the blast hole. Increasing the ultra-deep depth of the slotted hole can significantly increase the utilization rate of the blasted hole, and the determination of the ultra-deep depth of the slotted hole under different construction conditions needs further study.