Research And Application Of Top Coal Pre-cracking Technology In Fully Mechanized Top Coal Caving Mining And Hard Coal Seam

In recent years,with the depletion of coal resources in eastern China.Coal resources mining in China has gradually shifted to the central and Western regions.Among them,Xinjiang,Nei Monggol and S hanxi etc will become coal production intensive areas for a long period of time in the future.High mining height and fully mechanized top coal caving technology have become the main mining means.Because of the large thickness of coal seam and the undeveloped joints and fissures,the efficient exploitation and utilization of resources are seriously restricted,which results in a very serious waste of resources.At the same time,it brings serious potential safety hazards to mine safety production.Based on the research background of Yancon Xinjiang Mining Co,Ltd.(9-15)06 fully mechanized top-coal caving face mining,this paper studies the mechanism and technology of pressure appearance and top-coal strength weakening in fully mechanized top-coal caving mining in hard and thick seam under the condition of short-distance goaf mining by means of theoretical analysis,numerical simulation and field test.The main achievements are as follows.Noodles:(1)Starting from the basic principle of fully mechanized top coal caving mining,the mechanical characteristics of top coal in fully mechanized top coal caving mining are analyzed according to rock mechanics and elastic-plastic mechanics,and FLAC3D numerical simulation software is used to analyze the characteristics of roof(coal)movement,abutment pressure distribution and elastic strain of fully mechanized top coal caving face with different propulsive degree,different parts of working face under the mining conditions of goaf in close coal seam.The law of energy distribution is analyzed and studied.The results show that the mine pressure on the roof(coal)of Liuhuanggou Coal Mine(9-15)06 working face is relatively moderate,and the roof coal can not achieve ideal crushing effect depending on the action of rock pressure.(2)The types of crack propagation in hydrofracturing are classified.Taking the hydraulic fracturing borehole as the center,the mechanical model of borehole fracturing is established,the mechanical mechanism of hydraulic fracturing crack initiation and propagation in hard coal is analyzed,the calculation formula of hydraulic fracturing crack initiation pressure is obtained,and the propagation criterion of hydraulic fracturing crack is given.By using RFPA2D-Flow numerical simulation software and combining with the actual situation of No.9-1 5 coal seam in Liuhuanggou Coal Mine,the numerical calculation model of hydraulic fracturing process of hard coal body is established.Through the analysis of AE acoustic emission and head pressure distribution,the crack propagation stage of hydraulic fracturing is divided.The influence of in-situ stress environment and diameter of hydraulic fracturing borehole on the crack propagation law is studied and selected.The optimum pore size of hydrofracturing is obtained.(3)Aiming at the general situation of Sulfur Gou Coal Mine(9-15)06 working face,the top coal weakening technical scheme of hydraulic fracturing technology in hard thick seam is designed and put forward.Through the field test of top coal pre-cracking technology,the macro-morphology and fracture distribution characteristics of crack propagation in boreholes after hydraulic fracturing are observed by using strata detector.The test results show that hydraulic fracturing is of great significance for improving the fracture degree of coal body and reducing the overall strength of coal body.The research results are helpful to solve the difficulties of top coal caving in fully mechanized caving mining in close-range thick and hard seams in China.It provides an effective reference.