Method for mining ultra-thick coal seam by utilizing goaf solid backfilling technique

A method for mining an ultra-thick coal seam by utilizing a goaf solid backfilling technique, comprising:

• a. slicing the ultra-thick coal seam into three mining slices from top to bottom, wherein the three slices are an upper slice, a middle slice, and a lower slice respectively;
• b. first, mining the middle slice, wherein mining the middle slice comprises:
• arranging a solid dense backfilling coal mining working face in the middle slice for stoping, paving metal meshes along a floor in a process of moving a hydraulic support through a step distance, connecting adjacent metal meshes by iron wires at an interval corresponding to the step distance, backfilling a goaf with solids, and tamping the solids until a backfilling and a mining of the middle slice are completed to form a backfilling layer, wherein the backfilling layer serves as an artificial floor of the upper slice and an artificial roof of the lower slice in the mining;
• c. next, mining the upper slice, wherein mining the upper slice comprises:
• arranging a top coal caving working face of the upper slice for stoping, based on the artificial floor formed by backfilling the goaf in the middle slice, wherein top coals break and fall down as the top coal caving working face of the upper slice moves forward, and the top coals exit from a coal caving port of a fully mechanized top coal caving hydraulic support and are delivered out from the top coal caving working face of the upper slice by a conveyor located at a rear part of the fully mechanized top coal caving hydraulic support, and the backfilling layer is further tamped by fallen waste rocks and an overlying rock strata;
• d. subsequently, mining the lower slice, wherein mining the lower slice comprises:
• arranging a top coal caving working face of the lower slice along a floor of the ultra-thick coal seam for stoping, under a shield of the artificial roof formed by backfilling the goaf in the middle slice, wherein top coals break and fall down as the top coal caving working face of the lower slice moves forward, and the top coals exit from the coal caving port of the fully mechanized top coal caving hydraulic support and are delivered out from the top coal caving working face of the lower slice by the conveyor located at the rear part of the fully mechanized top coal caving hydraulic support,
• wherein clay is added into a solid backfilling material of the middle slice.