Study On The Development Law Of Water Conducting Fracture Zone In Overburden Of Short-distance Coal Seams In The North Of Yulin

The mining area,located in northern Yulin,Shaanxi Province,is not only a key coal mining area but also an important protection zone of water source.This mining area is rich in coal resources,with a large number of coal seams and close inter-layer distances.For the mining area in northern Yulin,the main problem is how to realize the harmonious development between the reasonable mining of Contiguous coal seam group and effective protection of natural resources,Therefore,taking the near distance coal seam group in northern Yulin as the research object,this paper studies the development law of water conducting fracture in the overlying rock of the near distance coal seam group mining through the research methods of field investigation,numerical simulation,similar simulation experiment and theoretical analysis.The results can be summarized as follows:(1)Based on the field investigation and the measured data of single coal seam mining,the main influencing factors of the development height of overlying water-conducting cracks are determined as follows:Mining height,bedrock thickness and loose layer thickness by theoretical analysis;On the basis of this,the influence of coal seam interval on the development height of overlying water-conducting fractures in the Contiguous coal seam group is considered and this influence is divided into two working conditions:①Coal seam spacing is less than the height of falling zone;② Coal seam spacing is greater than height of falling zone.(2)Simulating the mining of close coal seam group by using 3DEC numerical simulation software,it is found that the main influencing factors are:mining height>coal seam spacing>bedrock thickness>loose layer thickness,and the development height of the overlying water conduction fracture zone are given(3)Taking a mine in the northern Yulin mining area asthe object of research,the probability integral parameters of the Contiguous coal seam group and the development characteristics and failure basic form of overlying water-transmitting cracks under repeated mining conditions are obtained as Collapse-breakthrough-periodic fracture of interbedded Strata-periodic fracture of overlying strata by the simulation tests.(4)According to the probability integral parameters,combined with the characteristics of the Contiguous coal seam group,through the integration of the prediction method of the development height of the single coal seam overburden hydraulic fracture zone with the equivalent mining height and equivalent mining depth theory of the coal seam group,the prediction method of the development height of the overburden hydraulic fracture zone of the Contiguous coal seam group is proposed,and its reliability is verified by the previous research results.The research results of this paper can provide effective solutions for the coordinated development of coal environment and natural resources in mining area in northern Yulin,and also provide reference value for the mining technology of contiguous coal seam group.