Research On The Movement And Deformation Law Of Overburden And Surface Under The Conditon Of Coal Seam Group Mining

Shizuishan mining area is an important coal production base in the western Yellow River Basin.Promoting the coordinated development of coal production and environmental protection is an important requirement for realizing ecological environment restoration and sustainable development.In view of the surface ecological environment problems caused by goaf subsidence in coal mines in the western Yellow River Basin,the Shizuishan mining area was taken as the research object.The field investigation,similar material simulation test and numerical simulation were used to study the overlaying rock and surface movement and deformation law and the stress distribution law goaf caused by coal seam mining.Based on the superposition of two-phase DEM data,the surface displacement changes were statistically analyzed,and the results were verified with similar material simulation test and numerical simulation.The main research results are as follows:(1)Through the similar material simulation test,it is concluded that when the upper coal seam group was mined,due to the thin interlayer,the initial weighting interval and the periodic weighting interval of the main roof of No.2 coal seam was larger than No.3 coal seam,and the average periodic weighting interval was 2.27 times of No.3.With the continuous mining of the lower coal seam,the scope of the ground subsidence basin gradually expanded,and the final subsidence section is ’U’ type.The total thickness of coal seam mining was 26.58 m,the maximum surface subsidence was 19.2 m,which was located in the central position of goaf,and the subsidence coefficient was 0.72.(2)According to the monitoring data analysis of No.3 and No.6 coal seam floor stress sensor,the stress of coal seam floor decreases with coal mining.When the coal seam mining was 30m away from the monitoring point,the floor stress begun to sharp increase.When the working face advanced to 10～14 m after the monitoring point,the stress reached the maximum value,and then gradually decreased with the advancing stress of the working face and finally reached stability.(3)Based on the numerical simulation software,the three-dimensional geological model of coal seam group mining was established,and the numerical simulation of the coal seam group mining process was carried out.The results showed that the mining of No.2 coal seam caused the redistribution of surrounding rock stress,and obvious stress concentration occurred at the coal wall behind the working face,the maximum stress reached 8.47 MPa.The scope of the plastic zone gradually expanded with the mining of each coal seam.At the surface above the open-off cut and stop line,the failure mode of the plastic zone was tensile failure.The surrounding rock of the goaf was mainly shear failure along the direction of the coal seam.The surface subsidence was symmetrically distributed in the type of ’U’,and the maximum subsidence was 21.19 m.The scope of the subsidence basin was much larger than that of the goaf.(4)Under the condition of close-distance coal seam mining,the inter-layer mininginduced fractures are broken and penetrated,and the effect of repeated mining is particularly obvious.The repeated mining-induced instability in the goaf of overlying coal seam is significantly aggravated,and the closer the distance between coal layers is,the more obvious the influence of the erosion rock mining-induced fractures is.The mining thickness of the lower coal seam and the interlayer distance of the coal seam are key factors.(5)Taking Shizuishan mining area’s 1970s and 2003 DEM data superposition analysis,showed that the maximum vertical displacement of No.6 collapse pit was-23.96 m.The analysis results were basically consistent with the maximum ground settlement position obtained by similar material simulation test and numerical simulation.