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Shaped charge blasting technology plays an important role in goaf retaining roadway engineering, and the charge structure is always a hot and difficult issue in current discussions. At present, there is no clear indicator of the pre-splitting charge length of goaf-retaining roof. Taking the track groove of No. 2-11031 working face of the Mengjin Coal Mine as the research background, an isometric charge pre-splitting technology is proposed. Firstly, a three-dimensional directional shaped charge blasting model is established by LS-DYNA numerical simulation software to determine the optimal charge structure. By changing the axial cylinder length and taking the crack propagation length and stress decay rate as the analysis indexes, the numerical simulation shows that the radial slit distance is about 40 cm, and the axial slit distance is about 80 cm per meter when the axial uncoupling coefficient is between 1.25 and 1.7. Additionally, the slit distance is respectively increased by 25% and 12.5% compared with the axial uncoupling coefficient between 2 and 3. Furthermore, the energy utilization is the most reasonable as the stress attenuation rates are all less than 1 when the axial uncoupling coefficients are between 1.25 and 3. Finally, a roof directional blasting experiment with an axial uncoupling coefficient α=1.25~2 was carried out on the track groove of No. 2-11031 working face of the Mengjin Coal Mine. After the pre-split blasting, the middle line of the two holes was drilled and peeping. It is found that the cracks along the cutting seam direction between the two holes have been completely connected, the cracks are smooth, and the field application effect is good. Considering economy and safety, the uncoupling coefficient α=1.7 is the best. The results show that the isometric charging structure can replace the traditional three-stage charging structure.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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