Mechanical Analysis of the First Fracture Characteristics of Hard Roof of Extra-thick Coal Seam

In order to investigate the failure mechanisms of the hard roof in the fully mechanized caving face in the extra-thick coal seam, the mechanical analysis model of the first breaking of the hard top roof in the fully mechanized caving mining of the extra-thick coal seam was developed based on the theory of material mechanics and rock mechanics, and the distribution of the bending moment in the hard roof was analyzed. Moreover, the analytical formulas of the position and distance of the first breaking of the hard roof were derived, and the influence of the key factors such as the thickness of the coal seam, the thickness of the roof, the elasticity modulus of the roof and the strength of the roof on the characteristics of the first breaking of the roof were studied systematically. The results show that the first rupture distance of the hard roof is negatively correlated with the thickness of coal seam, but positively correlated with the thickness, elastic modulus and strength of the hard roof. On this basis, the on-line monitoring of the ground pressure law in the 22203 super-thick coal seam fully mechanized top coal caving face of Hanjiawa Coal Mine in Shanxi Province was carried out. The theoretical analysis results were compared with the on-site monitoring data, and the two were basically consistent.