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In view of the problem of limited pressure relief and anti-impact ability of large diameter boreholes in high stress and strong disturbance coal seams. The methods of theoretical analysis, numerical simulation and field test were adopted to study the mechanism of pressure relief and anti-impact of large diameter boreholes, and the control measures of pressure relief and anti-impact of large diameter boreholes were proposed to improve the pressure relief and anti-impact performance of high stress and strong disturbance coal seams. The results show that the pressure relief range of large diameter boreholes is directly proportional to the drilling radius, surrounding rock stress, and disturbance stress increment, and inversely proportional to the constraint force of the fracture zone and plastic zone. Increasing the pressure relief range of large diameter boreholes can increase the attenuation of dynamic stress wave energy, transfer static load energy to the deep surrounding rock, and reduce the risk of coal seam rockburst. As the disturbance coefficient increases, the range of pressure relief for large diameter boreholes and the gathering elastic energy around the boreholes show an increasing trend. The vibration acceleration of borehole increases exponentially with the increase of disturbance coefficient and shock energy. When the disturbance coefficient is greater than 2, the impact dynamic load is superimposed, and the large diameter borehole is blocked to achieve the ultimate anti-impact ability. The use of dense drilling method and repeated drilling method can increase the pressure relief range of large diameter drilling, reduce the risk of coal seam rockburst. After field test, the deformation of surrounding rock of roadway is reduced by 31.5%~67.0%, the stress value of coal body is lower than the critical warning value, and the stability of surrounding rock of roadway is significantly improved.
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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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