Slicing filling principle and repeated mining key technology for extra-thick coal seams in small coal pit destroyed areas

Aiming to solve the problems of the efficiency of repeated mining technique in small coal pit destroyed areas, the principle of slicing filling and repeated mining was applied, and techniques were proposed for slicing grouting filling in small coal pit destroyed areas and reconstruction of cutting layers, spacer layers and support layers. Grouting filling eliminates potential safety hazards in small coal pit destroyed areas. Simultaneously, a complete area which is best for normal mining was built; the thickness and intensity of each layer were determined, and the filling materials and ratio of each layer were also provided. Field application proved that slicing filling and repeated mining achieves good results in safely recycled coal seams in small coal pit destroyed areas with high efficiency. Although the cost of coal is increased by 1.21 CNY (Chinese Yuan) per ton, the approach provides an innovative method for the safe and efficient backfill mining of coal resources in small coal pit destroyed areas and waste utilization in a mining area.