Exploration and quantitative evaluation of overburden strata “three zones” in deep strip mining

In order to study the height of overburden fractures in deep strip mining, engineering geological drilling, borehole television and coalfield well logging have been applied to detect and analyze the overburden fractures in a coal mine in Jining coalfield. The results indicate that, under the strip mining with gentle dip(6°), deep depth(538 m) and 1:2 mining-retention ratio(mining -50 m and remaining -100 m), the “three zones” develop prominently, presenting “wavy” destruction in space, and the goaf has no obvious cavity. The height of caving zone is 8.45 m which is 3.0 times of the mining height, and the fault zone is 57.55 m, 20.6 times of the mining height. Among the eight quantitative indicators for judging the development height of “three zones”, borehole television is more accurate than the other two methods. The results of detection are more accurate and reliable, which can provide a basis for the selection of management plan in deep strip mining subsidence area.