Research on Double Effect Weakening Technology in the Whole Area of Coal and Rock Mining under the Condition of "Two Hard" Coal Seam

In order to solve the problem of low top coal recovery rate caused by the hard top plate in the thick coal seam fully mechanized mining of Pulongwan Mine, theoretical analysis, numerical simulation, and underground measurement were carried out using the 5108 working face as the background. Analyze the coupling relationship between roof and roof coal mechanics, reveal the dynamic response characteristics of overlying strata and the evolution law of roof coal fracture. The focus is on the dual effect weakening effect of ground fracturing technology on the roof, and its mechanism of action is manifested as follows: based on the stress distribution characteristics of the roof coal, the overlying rock bearing system is divided into three typical modes: "short cantilever beam hinged rock beam" mixed bearing, short cantilever beam independent bearing, and hinged rock beam independent bearing. Weakening treatment significantly reduces the stability of overlying rock by changing the mechanical properties of rock layers, promotes the extension of fracture fissures to deeper depths, and eliminates the overhanging effect. The measured data shows that the end resistance of the stent cycle decreases by 25.4% under non cyclic pressure and 15.3% under cyclic pressure. The rock layers exhibit obvious layering characteristics, and the hard and thick rock layers show a trend of thin layer fracturing. Engineering practice has shown that the top coal recovery rate has increased by 6.1%.