Breaking Factors Analysis of Hard Rock in Close Distance Coal Seams

Overburden rock fracture of close distance coal seams is not only influenced by multiple mining, which is closely related with mining height, interlayer spacing and rock mechanics properties. Based on the analysis of effect of mining height, interlayer spacing and rock mass strength on overburden rock fracture, taking the coal occurrence condition of close distance coal seam group in Jinhuagong Coal Mine as the background, using the method of orthogonal experimental design and UDEC, the overburden rock fracture evolution law of close distance coal seam group and the effect of mining height, interlayer spacing and rock mass strength on overburden rock fracture height are obtained. The results show that the biggest mining fracture height is up to 48 m with arched when coal 7 is mined; as coal 8 is mined, overlying rock crack extends and develops upward and is up to 80 m; the cracks on both sides of the pillar extends to transverse at the same time. The range analysis is applied to analyze the three factors to the sensitive degree of the development of highly fractured zone. The principal factors in sequence would be the mining height, the rock mass strength between the seams and the distance between seams.