Recovery Technology of Bottom Coal in the Gob-Side Entry of Thick Coal Seam Based on Floor Heave Induced by Narrow Coal Pillar

To improve the resource recovery efficiency of mining face in thick coal seams, the correlation between deformation failure of bottom coal in the gob-side entry and coal pillar width was analyzed by theoretical analysis, numerical calculation, and similar simulation experiments. The results showed that, when the coal pillar was strong, with the decrease of pillar width, the failure depth of the bottom coal in the gob-side entry and floor heave increased. The deformation failure depth of the bottom coal in the entry was inversely related to the width of the coal pillar. The bottom coal was further fractured and dispersed under the action of tension, shear, and extrusion in the process of floor heave. Based on the floor heave induced by the narrow coal pillar, a recovery technique of the bottom coal with thick coal seams in the gob-side entry was developed. The width of the narrow pillar to be reserved was obtained by theoretical calculation and revised by numerical simulation; ultimately, the reasonable width was determined. Under the complex stress of the narrow pillar, the bottom coal in the gob-side entry was fully heaved, cracked, and separated. To realize the comprehensive mechanization and resource recovery of bottom coal, a matching mining excavator loader, transfer conveyor, and retractable belt conveyor were selected to transport the crushed bottom coal in the entry. This method has been successfully applied to the return airway of working face 8407 in the No. 5 Coal Mine of Yangquan Coal Group with remarkable economic and social benefits.