Research For The Movement Law Of Top Coal And Roof In Fully Mechanized Top Coal Caving In "Three Soft" And Extra-thick Coal Seam

At present,fully-mechanized top-coal caving mining is a kind of safe and high efficiency coal mining method for extra thick seam,but recovery ratio of fully-mechanized top-coal caving mining is low,and there are many floating coal in goaf that hiding dangers of spontaneous combustion,and the movement of top coal and roof is complex,which affect the safe and efficient production of coal mine.Therefore,based on Yima coal mine 13180 fully-mechanized caving face as the paper's background,the numerical models of PFC^3D and UDEC are established;The the breaking process and fracture pattern,the subsidence law of roof strata,the distribution of stress field of surrounding rock and the influence of different drawing technology on the flow state and the release rate of top coal are studied in the paper.Combined whit mine pressure observation data,the paper studies the distances of first weighting and periodic weighting of main roof,as well as the adaptability of the working resistance of the support.At last,according to the theory of ellipsoid of top coal,the maximum caving height is analyzed quantitatively.The degree of coal-drop of main coal seam is studied by fuzzy mathematics,and the location of the key stratum is determined by the criterion of key stratum.These conclusions can be drawn by numerical calculation analysis such as PFC³DD and UDEC,field research methods and theory analysis.The first weighting step of main roof is about 40m,and periodic weighting step is 20m.With the increase of advancing distance,the roof subsidence was firstly increased and basically unchanged after reaching the maximum value,but the subsidence curve extends to the deep.The stress relieving zone and stress concentration zone also appeared in surrounding rock of the mining face.The top coal particles can form a stable velocity field and two loose regions in the initial caving process.One cut one falling,interval top-coal caving coal and full-seam top-coal caving are the best top-coal drawing technology.The rated working resistance of hydraulic supports used by Yima Coal Mine is relatively high,so they can achieve the better supporting effect to the 13180 fully-mechanized caving face,and meet the requirements of strata behavior.The fuzzy mathematics method is used to determine the caving difficulty of the main coal seam,and it is not necessary to adopt the top coal weakening treatment,and it is determined that the quartz sandstone layer is the key layer.The research of this paper has important guiding significance and reference value for the construction of safe and efficient mine.