Study On Surface Movement And Deformation Law And Loss Reduction Control Of Near-shallow Coal Seam Group Mining

With the large-scale development of coal resources,coal seam mining is gradually shifting from single coal seam mining to multi-coal seam mining,compared with single coal seam mining,the surface movement deformation caused by multi-coal seam mining is quite different,which has a significant impact on the construction of green ecological environment in mining areas.Therefore,this paper takes the near-shallow buried coal seam group as the research object,and integrates the methods of theoretical analysis,numerical simulation,and similar material simulation,and with the help of mining damage prediction and evaluation software,the research on the surface movement deformation law and damage reduction control of near-shallow buried coal seam group mining is carried out,The research results are of great significance for improving the surface ecological environment and water resources protection in mining areas.The main conclusions are as follows:(1)Through field investigation and theoretical analysis and according to the causes of the formation of surface fractures,it is determined that the characteristics of surface movement and deformation of coal seam mining are tensile fractures,compression fractures and collapse fractures.Based on the analysis of the measured data,it is obtained that the surface subsidence coefficient of the double coal seam mining decreases with the increase of the base mining ratio(thickness of bedrock/mining height of upper seam),the base loading ratio(bedrock thickness/loose layer thickness)and the intermediate mining ratio(coal seam spacing/mining height of lower coal seam).(2)Using Flac3D numerical software to simulate and analyze the influence of different factors on surface subsidence of near-shallow coal seam group:when the mining height increases from 2m to 6m,the subsidence coefficient increases by 21.6%,when the bedrock thickness increases from 30m to 70m,the subsidence coefficient decreases by 18.3%,When the thickness of the loose layer increases from 40m to 80m,the subsidence coefficient increases by 40%,when the coal seam spacing increases from 10m to 60m,the subsidence coefficient decreases by 22.3%;The influence degree of each factor on surface subsidence of near-shallow coal seam group is given by grey relational analysis:Bedrock thickness>Mining height>Loose layer thickness>Coal seam spacing.(3)Taking a mine in northern Shaanxi as an example,the simulation experiment of similar materials is used to obtain the law of surface movement and deformation in the mining of near-shallow coal seam groups:after 2-2 coal mining,the subsidence coefficient is 0.68,after 3-1 coal mining,the subsidence coefficient is 0.77,the repeated mining coefficient is 1.13,after 4-2 coal mining,the subsidence coefficient is 0.84,repeated mining coefficient is 1.1;When the coal seam working face adopts the staggered arrangement,the surface movement deformation value of each coal seam after mining can cancel each other,effectively reducing the superposition of deformation,thereby reducing the damage to the surface;The development process of surface fractures on the side of the incision hole is "generation→expansion→generation of step sinking",and the development process of surface fractures on the side of the mining stop is "generation→expansion→expansion".(4)Based on the numerical simulation results,the relational expressions between the base mining ratio,base loading ratio and inter-mining ratio and the surface subsidence coefficient are given by the method of function fitting.Using the mining damage prediction and evaluation system,the law of surface movement and deformation of the mining near-shallow coal seam group was studied,and it was confirmed with the similar simulation results.Combined with the superimposability of surface movement and deformation,the control effect of staggered mining on surface damage is analyzed:Compared with the overlapping arrangement of the coal seam group working face,the staggered arrangement can offset part of the surface deformation,the extreme value of horizontal movement is reduced by 57.1%,the extreme value of horizontal deformation is reduced by 62.6%,the extreme value of tilt is reduced by 59.4%,and the extreme value of curvature is reduced by 52.5%,although the maximum surface subsidence value does not change much,the surface subsidence basin of the staggered layout is relatively gentle.The research results provide a certain theoretical basis for the detrimental mining of near-shallow buried coal seam groups.