Characteristics of the distribution of overlying rock fractures associated with the mining of super-thick coal seam in eastern Junggar coalfield

In order to investigate the evolution of the overlying rock fractures associated the mining of super-thick coal seam mining in Dajing mining area of eastern Junggar coalfield, the authors studied the fracturing characteristics of overlying rocks for different mining methods by using numerical method.The results show that the overlying strata in front of the working face were consequently divided into as the original rock fracture zone, the fracture closure zone, the micro-fracture zone, the rapid fracturing zone, the fault zone, the roof-separating zone, the gradually fracture-closing area which was controlled by rock stress.It also show the heights of the overlying fractures were controlled by the main key-strata of the overlying rocks.The fractures mainly exist on both sides of the mined-out area in the overlying strata, and the fractures show a “八” type distribution along the fracture lines of the rock strata.With the advancement of the working face, the fractures show periodical change in the overlying strata.Overlying rock fractures are the key channel for seepage of overburden aquifer to working face.From the perspective of water conservation, roof-coal-caved sublevel mining method causes little disturbances to overlying aquifers than that of sublevel mining method.