Research On Mechanism Of Overburden Breaking And Fracture Evolution In Thick Coal Seam Fully Mechanized Mining Based On Three-Dimensional Large-scale Physical Simulation

With the increasing complexity of coal mining conditions,gas accidents often occur,which has caused a serious impact on the industry and society.This paper aims at the problem of low efficiency of gas drainage in coal mine gas control work.Taking typical thick coal seam fully mechanized mining as the research condition and synthetically adopting the methods of three-dimensional large-scale physical simulation,mechanical experiment,numerical calculation,theoretical analysis,and field test,the mechanism of overburden breaking and fracture evolution in thick coal seam fully mechanized mining were systematically explored.It has guided the practice of gas drainage and provided a reference for gas control under similar conditions.The main contents of this paper are as follows:(1)Based on the characteristic parameters of acoustic emission(AE),the damage evolution model of similar materials during compression failure was established by means of damage mechanics analysis.The damage characteristics and space-time evolution characteristics of similar materials during compression failure were investigated,and the influence of fracture parameters on the damage of similar materials was further discussed.(2)According to the research results of damage and failure characteristics of similar materials,the mechanism of acoustic emission(micro-seismic)in the process of damage(failure)of similar materials were revealed.Based on the self-developed comprehensive experimental system of three-dimensional large-scale physical simulation for coal and gas simultaneous extraction,a high-frequency micro-seismic monitoring system and a high-definition borehole peep-view system were designed and constructed.Then the mechanism of micro-seismic monitoring of fracture in three-dimensional physical simulation were analyzed.(3)Based on the geological conditions of typical thick coal seam fully mechanized mining face,a three-dimensional large-scale physical similarity model was designed,and the scheme of high-frequency micro-seismic monitoring and high-definition drilling prying were designed.The dynamic distribution characteristics of micro-seismic events in overburden and the variation characteristics of micro-seismic parameters during mining process were analyzed,and the results of borehole peeking in mining overburden fractures were discussed,and the law of overburden activity and fractures evolution in thick coal seam fully mechanized mining were obtained.(4)The 3D numerical calculation model of thick coal seam fully mechanized mining was established,and the characteristics of failure distribution,stress distribution and variation,displacement distribution and variation of mining overburden were simulated and analyzed.Furthermore,the distribution characteristics of overburden activity and pressure relief range in three dimensional thick coal seam fully mechanized mining were obtained.(5)Based on the results of mechanical experiment,physical simulation and numerical analysis,the failure mechanism of jointed overburden in thick coal seam fully mechanized mining was revealed,and the distribution characteristics of overburden fracture in thick coal seam fully mechanized mining were analyzed.The coupling model of fracture parameters and micro-seismic characteristic parameters of mining rock mass was established.(6)Based on the mining face of typical thick coal seam,the micro-seismic monitoring system of mining face was established.By analyzing the spatial distribution characteristics of micro-seismic events in goaf overburden,the characteristics of fracture evolution of mining overburden were obtained.The mechanism of overburden instability and fracture distribution in thick coal seam fully mechanized mining was verified.According to the results of micro-seismic monitoring,the design and arrangement of the high hole of gas drainage in the goaf and the high drainage roadway were carried out.(7)The revealed mechanism of overburden breaking and fracture evolution in thick coal seam fully mechanized mining has been verified and applied in the typical working face of the mine gas disaster control work.After the implementation of the gas drainage measures in the working face,a better effect of gas drainage in the goaf was achieved,which ensured the safe and efficient mining of the working face,and provided guidance and reference for coal and gas simultaneous extraction under similar conditions.