Optimization and Effectiveness Analysis of Hydraulic Fracturing Technology for Large Height Coal Seams in Extra-thick Coal Seams

In the process of formulating the mining strategy for large-height top coal mining in extra-thick coal seams, the interaction between the hardness of the top coal and the air-mining zone at the top of the working face has caused a variety of technical problems. The hydraulic fracturing technology of alternating deep and shallow drilling was adopted to optimize the mining operation, and an industrial test was carried out in the 5105 working face of Pulongwan Coal Mine, and the effect of hydraulic fracturing was evaluated by using the numerical simulation of FLAC^3D and on-site monitoring technology. The results show that, after applying the hydraulic fracturing technology of alternating deep and shallow drill holes in the mining operation of extra-thick and high-hardness coal seams, a fine network of microfractures and penetrating main cracks appeared in the edge area of the drill holes, which effectively weakened the overall mechanical strength of the top coal seam, facilitated the natural collapse of the top coal and its efficient extraction, shortened the cycle length of the fluctuation of the mining pressure, and reduced the load-bearing pressure of the stent in the fractured area. After hydraulic fracturing, the size of coal lumps in the top coal was reduced from 800 mm to 300 mm, and the recovery rate of the top coal was increased by 11.3%, which promotes the recycling and utilization efficiency of coal resources.