Study On The Temporal And Spatial Evolution Law Of Stress Distribution During Upward Long-wall Mining In The Residual Pillar Mining Area

The stress distribution of the coal pillars determines whether the safe upward longwall mining can be realized directly.Taking the upward longwall mining of residual pillar mining area in Datong mining area as the engineering background,the methods of physical simulation,numerical simulation and theoretical analysis are used to investigate the temporal and spatial evolution law of stress distribution during upward longwall mining in the residual pillar mining area.The innovation points of this thesis are mainly embodied in the following.(1)The physical simulation experiment is used to study the dynamic evolution law of the abutment pressure of the coal pillars during the formation of the residual pillar mining area and the process of the upward longwall mining.Based on this,the concept of ahead induced-mining pillar is defined.The ahead induced-mining pillar refers to the residual coal pillar in the residual pillar mining area which is affected by the leading abutment pressure of the upward working face and the stress peak value is obviously higher than that before the upward mining.The decisive role of the main key stratum motion on the stress distribution of the stope is revealed.During the upward mining process,the peak value of the abutment pressure of the upward working face and the ahead mining-induced pillar in the lower coal seam reaches the maximum at the initial break of the main key stratum,so as the influence range of the lead abutment pressure,which is decreasing obviously after the breaking of the main key stratum.(2)Using UDEC numerical simulation test,the effects of seven factors including mining width,width of coal pillar,mining height,buried depth of lower coal seam,thickness of interlayer strata,distance between main key stratum and upper coal seam and primary fracture step distance of main key stratum on stress distribution and plastic zone distribution in stope as soon as the initial break of the main key stratum during upward longwall mining in residual pillar mining area are studied.The peak value of the abutment pressure and the plastic zone range of the ahead mining-induced pillar decrease with the decrease of the mining width,so as the plastic zone range of the interlayer strata.It decreases with the increase of coal pillar width.It decreases with the decrease of buried depth.It increases with the decrease of the thickness of interlayer strata.It decreases with the increase of the height of upper coal seam between main key stratum.It decreases synchronously with the decrease of primary fracture step distance of the main key stratum.Although the change of mining height has little effect on the peak value of abutment pressure of the ahead mining-induced pillar,it affects the plastic zone distribution.(3)According to the results of physical simulation and numerical simulation experiments,the mechanical model of ahead induced-mining pillar-overburden spatial structure for the upward longwall mining of the residual pillar mining area is established.The formula for calculating the load of ahead induced-mining pillar is given,and the formula for safe upward mining in residual pillar mining area is determined.(4)It’s estimated that the average abutment pressure of the ahead mining-induced pillar is 40.5~47.2MPa when the main key stratum is firstly broken during upward long-wall mining of No.9 coal seam of 402 Panel in Jinhuagong coal mine.The change trend of the floor subsidence displacement during the upward mining process is in accordance with the dynamic evolution law of the abutment pressure of the coal pillars during upward mining obtained in this paper.