Study On The Height Development Of Cracking Zone And The Deformation And Failure Characteristics Of The Overburden During Repeated Mining Of Double Seam

China is the largest producer of coal; it is important that how to safe, reasonable andefficient development of coal resources in coal production. For close distance seams, because ofthe small distance between the layers, working face during excavation is easily affected fromother coal seam mining. Part of the coal seam roof and floor has been destroyed before start ofmining, which makes the coal mine production safety greatly reduced. So it would be greatsignificance that studying on the law of the fracture about close distance seam.This paper, based on the engineering geological conditions, drilling and pumping test data,analyzed the mine geological characteristics and hydrology type. According to the actualsituation of coal mine production, the research of rock fractures was made on4,5coal seammining repeatedly by means of numerical simulation, similar model test and theoretical analysis.By similar simulation test, the caving zone height was completed with a height of26.0m,and the developmental height of water flowing fractured zone was68.5m when the double seam(4,5coal) mining. Through numerical analysis, the problems of coal mining under differentspacing and different mining thickness were simulated. The overburden stress and displacementfields were analyzed in the process of the double seam mining. The caving zone height wascalculated as28.4m, and the developmental height of water flowing fractured zone was64mwhen double seam recovery completed. the floor rock mass produce more cracks due to periodicpressure. When the lower coal seam mining, fissure zone and caving zone is no obvious changebefore the upper coal seam floor is damaged. After the upper coal seam floor is damaged, thescope of the fracture zone expands and caving zone changes slowly. According to the theory ofengineering mechanics and material mechanics, a judgment is put forward about whetherthere is influence between two coal seams. If the distance between the coal seams is less than H2,it will be as a close distance seam, in turn as a single coal seam.