Cross-borehole hydraulic slotting technique for preventing and controlling coal and gas outbursts during coal roadway excavation

• Cross-borehole hydraulic slotting technique is proposed.
• The slots increase the permeability of the coal seam.
• The gas-extraction efficiency of the borehole is significantly improved.
• The coal and gas outburst disasters during excavations is eliminated.

Coal and gas outbursts comprise the predominant hazards in Chinese coal mines. A large number of accidents have occurred during coal roadway excavation. In this study, we propose the application of a cross-borehole hydraulic slotting technique for preventing and controlling coal and gas outburst disasters during coal roadway excavations. In this technique, a high-pressure water jet is applied in a coal body to cut a slot. This helps to increase the permeability of the coal seam, improve the gas-extraction efficiency of the borehole, and prevent and control coal and gas outburst disasters during excavations. In the field test in which hydraulic slotting was employed, the average mass of coal that was discharged from a slotted borehole is 8.2 t; the weight of the largest discharged mass is 16 t. The diameter of the slotted borehole is 12.87 times the diameter of a conventional borehole, which effectively improves the borehole's influence range. After half a month of gas extraction, the average gas-extraction concentration for the slotted borehole is 26%, whereas the average gas-extraction concentration of the conventional borehole is 7%, that is, the gas-extraction concentration for the slotted borehole is approximately 3.7 times the gas-extraction concentration of the conventional borehole. After four months of gas extraction, the residual gas content and gas pressure for the 11091 transportation roadway satisfy the requirement of the State Administration of Work Safety. A conventional borehole requires a minimum period of six months to prevent and control outbursts, whereas a slotted borehole requires a minimum period of four months. These results suggest that the technology can improve the efficiency of gas drainage, reduce the gas drainage time, and is a potential application for preventing and controlling future gas disasters.