Research On Paste Filling Replacement Mining Technology In Shallow Coal Seams In Guizho

With the large amount of coal resources mining,the problem of"three under"coal mining is increasingly prominent,which seriously affects the resource recovery rate of many coal mining enterprises.The traditional"three-down"mining method has some disadvantages,such as the traditional strip mining has the problems of low recovery rate,poor adaptability to geological conditions and high excavation rate.Coordinated mining has some problems,such as increasing subsidence rate,increasing management difficulty and limited application range.As a compound"three-down"mining method,strip filling and replacement mining has the advantages of high recovery rate,effective absorption of gangue,effective control of surface settlement and low cost.It has certain economic and social benefits,and is an important development direction of"three-down"coal mining in the future.Taking Miluo Coal Mine in Guizhou Province as the research object,this paper comprehensively explores the mining parameters,filling material ratio,roof subsidence,overburden migration,surface settlement and other conditions required by strip filling replacement mining by field investigation,theoretical analysis,laboratory test and numerical simulation,so as to verify the feasibility of using strip filling replacement mining in"three down"mining.The main achievements and conclusions are as follows:（1）Based on the key layer theory,the unified strength theory and wilson’s coal pillar bearing theory,the unified solution formula of limiting strength,plastic zone width and width of coal pillar is obtained.Based on the effective area theory,the required backfill strength under different mining widths and reserved widths is obtained.According to the strength,local coal gangue,fly ash and other materials are selected as raw materials for paste backfill preparation.After comprehensive analysis,the paste backfill system is prepared with the ratio of fly ash cement material ratio of2.5,fine gangue rate of 45%and mass concentration of 80%.As the filling body parameter of numerical simulation.（2）Using FLAC^3D numerical simulation software,the excavation is divided into two stages,one is strip filling stage,the other is displacement mining stage.The numerical simulation results of the first stage show that the composite bearing structure of coal pillar and filling body formed in underground working face can effectively support the overlying strata.The maximum load borne by coal pillar is5.5MPa,the maximum load borne by paste filling body is 4.7MPa,and the minimum load is 4.2MPa.The numerical simulation results of the second stage show that the single backfill bearing structure can effectively support the overlying strata on the working surface after the coal pillar is recovered,and the maximum surface subsidence is 28mm.（3）Navier--probability integral method was used to calculate the surface subsidence of strip filling and replacement mining,and the calculated result was 22.5mm.Compared with the results of numerical simulation,the relative error of surface subsidence is 19.6%,which is lower than the maximum error of 20%.The improved BP neural network based on Sparrow search algorithm was used to predict the surface settlement caused by strip filling and replacement mining,and the surface subsidence caused by strip filling and replacement mining was 26.4mm.Compared with the results of numerical simulation,the relative error of the two is 5.7%,which is smaller than the surface subsidence value obtained by Navier--probability integral method.The surface subsidence values obtained by the three methods are all less than 30mm,and the mining damage to the surface meets the requirements of national building protection classification and engineering needs.