Study On Overlying Strata Migration And Stress Evolution Law Of Haishiwan Extra-thick Coal Seam Mining

The ground stress in deep mining of coal mine is large,and the phenomenon of rock burst in mining face is more and more obvious.In the first mining area of Haishiwan Coal Mine of Yaojie Coal Power Group,the buried depth of the second layer of coal is 700～950m,and the thickness of coal is 9.9～59.28 m.The thickness of coal seam that can be mined varies greatly along the strike direction of the working face,and the phenomenon of coal earthquake even appears in the later mining process.Considering the large difference in the overburden breaking structure form caused by different mining heights,this thesis takes the 6125 working face of the second layer of coal as the research object.By using the methods of theoretical analysis,physical simulation,numerical simulation and field measurement,the overburden migration and stress evolution law of extra-thick seam non-uniform thickness mining in Haishiwan Coal Mine are studied.The main results are as follows:(1)The key strata of the borehole column near the 6125 working face are identified,and the roof is determined to have 7 key strata;According to this,the development height of three belts corresponding to different mining thickness of two layers of coal along the advancing direction of working face is determined.Combined with the current situation of surface subsidence,a composite cantilever plate model of broken roof structure in non-uniform thickness mining of extra-thick coal seam is constructed,and the results of three-dimensional discrete element simulation are verified.(2)The law of overburden migration,fracture development and goaf stress evolution under different mining thickness of coal layer in Haishiwan No.1 mining area is studied by similar simulation.It is found that the length of fault block in the upper key layer increases with the decrease of coal thickness.After the decrease of coal thickness,mining-induced fracture occurs in the upper key layer in the advanced region of solid coal side before that in the lower key layer.In other words,the mininginduced fracture in the overlying rock develops from top to bottom until the whole fracture movement.Based on this,the composite cantilever plate model is optimized.The stress of goaf is greater after coal thickness is reduced than before coal thickness is reduced,and the crushed block is more fully compacted.(3)In the process of non-uniform thickness mining of extra-thick coal seam,the evolution characteristics of coal body advance stress and goaf stress are analyzed by numerical simulation.The mined thickness of coal seam decreases from 40 m to 20 m,and the advance stress peak increases with the increase of mining area.After the coal thickness decreases,the advance stress peak shows the evolution characteristics of "first increase,then decrease".The stress relationship of goaf in different thickness sections is verified.(4)The field measurement found that after the mining of the 6125 working face,a ground borehole 200 m outside the open-off cut appeared the phenomenon of misblocking hole,which could not be extracted normally.Combined with the research results of the numerical simulation on the mis-momentum of the overlying strata after the mining of the working face,it was clear that the mining of the second-layer working face of the coal would cause the mis-momentum of the overlying strata to increase.The thesis consists of 60 figures,4 tables,and 85 references.