Research on three-field evolution and rational coal pillar staggered distance in shallow buried closely spaced multi-seam mining
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Graphical Abstract
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Abstract
In order to explore the rational staggered distance of coal pillars based on the three-field (stress field,dis- placement field and fracture field) evolution and realize the reduction of ground pressure and surface damage in shal- low buried closely spaced multi-seam,the mining at No. 1-2 and No. 2-2 coal seams in the east of northern Ningtiaota coal mine was investigated in this study. Combining with FLAC3D ,UDEC numerical calculation,physical simulation and theoretical analysis,the three-field evolution of overlying strata and ground surface in closely spaced multi-seam mining were revealed. Meanwhile, the relationship between the coal pillar staggered distance and the concentrated stress,displacement and fracture evolution of overlying strata and surface was obtained,the rational coal pillar stag- gered distance based on the three-field was put forward. The results show that the concentrated development of fractures and the concentrated tensile and compressive stress are due to the uneven strata subsidence by coal pillars. After upper single seam mining,high stress area of coal pillar,low stress area and high stress area in the middle of longwall face were formed in the floor. In order to avoid the vertical stress superposition of upper and lower coal pillars,the low- er roadway should be placed in the low stress area. There was a close relationship between tensile stress field,displace- ment field of surface and coal pillar staggered distance. Through rational arrangement of coal pillars,the “ wavy” am- plitude of surface subsidence decreased,and the tensile stress and horizontal deformation were effectively controlled. As the coal pillar staggered distance increased,the fracture field changed from superposition to separation,and the sur- face fractures decreased gradually,consequently,the coal pillar staggered distance had control function on overlying strata fractures and surface fractures. Finally,the coupling control model of stress field-displacement field-fracture field was established,and the calculation method of coal pillar staggered distance was proposed. It can realize the coupling control for reducing the concentration of ground stress and development of ground fractures. It is verified by engineer- ing practice,and will be adopted in the subsequent layout of Ningtiaota coal mine.
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