The elimination of coal and gas outburst disasters by long distance lower protective seam mining combined with stress-relief gas extraction in the Huaibei coal mine area

• Long-distance lower protective seam mining technology was used to eliminate gas disasters.
• Gas extraction roadway floors, surface boreholes and boreholes were used to drain gas.
• Gas pressure and content largely decreased, and permeability increased by 4373 times the original value.
• Coal and gas outburst dangers were completely eliminated in the No. 8 coal seam.

The No. 8 coal seam in the Huaibei coal mine area is a soft, thick coal seam with low permeability. This area has a high frequency of coal and gas outbursts. Considering the geological conditions of the coal seam group, long-distance lower protective seam mining combined with stress-relief gas extraction has been used to eliminate coal and gas outburst disasters. Simulations and field experimentation were used to study the rules of pressure relief deformation, mining crack development, the pressure relief protection effect, pressure relief gas flow, gas extraction and outburst elimination of the No. 8 coal seam. The geological conditions in terms of mining include a 1.87-m mining height and a 78-m coal seam interval. The results indicate that the No. 8 coal seam is on the border of the fractured and bent zones after mining the protecting seam. The mining fissures are primarily bedding fractures and vertical or oblique fractures. The expansion deformation rate is 37‰. The permeability increased from 0.0011 mD to 4.81 mD (nearly 4373 times). Gas extraction roadway floors, surface boreholes and drilling boreholes are used to drain the pressure relief gas. The gas pressure of the No. 8 coal seam decreased from 4.6 MPa to 0.6 MPa, with the gas content decreasing from 13.39 m3/t to 3.5 m3/t. The gas extraction rate increased to 74%. Coal and gas outburst disasters were successfully eliminated. Thus, mine safety and high efficiency production have been successfully realized.