Dynamic Evolution Characteristics Of The Overlying Strata Within The Lower Protected Seam Of Deep And High Stress Close Distance Coal Seams

In China,many coal mining areas are suffering from the complex and difficult characteristics such as deep mining,density geological structure,soft coal seam,weak permeability,high gas containing,etc.which has brought the fatal threat to the safety production.Protection seam mining technology not only has been one of the effective controlling measure to preventing from the coal and gas outburst,but also has a good effect to the pressure relief of the protected seam.On the basis of the main reasons,the protection seam mining technology has been the emphasis of the research,especially to the deep coal mine with highly gassy and outburst-prone characteristics.In this paper,the Shanxi Fenxi Zhongxing Coal Limited Company was used as an engineering background,and comprehensive methods were adopted,including experimental test,theoretical analysis,similar simulation,numerical simulation and field monitoring.The main research contents are respectively the experimental test on the physical and mechanical properties of the coal and rock samples of the coal seam collecting from the protected seam,the combined mining stress and fractures evolution characteristics in the mining process of the working face of the protection seam and the protected seam,overlying strata stress evolution characteristics in the mining process of the working face with typical mining spacing between the protection seam and the protected seam,the influence factors analysis of the working face mining in the protected seam.The main research results were as follows:(1)The coal seam 2# and rock samples were collected from the Zhongxing Coal Company and the corresponding physical and mechanical properties were tested.(2)A large similar simulation model including the working face 3201,protected layer working face 3203 and working face 3203 was built,and the rock strata displacement,stress and fractures evolution characteristics of the working faces belonging to the protection seam and protected seam with deep and close distance conditions were analyzed.(3)Two large numerical simulation models were built,and included the one of the spacing protection seam and protected seam in the range the mining influence area of the working face belonging to the protected seam and another one out the range of mining influence area.Based on the two conditions,the stress evolution characteristics of the working face rock strata were respectively simulated and analyzed.(4)According to the on-line monitoring and data analysis on the hydraulic support working resistance during the mining of the working face 3203,and the cloud diagram of the working resistance and the variation characteristics were obtained.(5)Combined with 5 numerical simulation models,the rock strata stress evolution characteristics were simulated,with different kind of inclined length of the working face in the protection seam and the spacing between the working faces belonging to the protection seam and protected seam were while the working face in the protection seam was located above the roadway of the material transportation.Besides,the influence factor of the structure was analyzed.