Numerical Simulation on Instability Mechanism of Section Coal Pillar in Shallow Buried Coal Seams

There is abundant coal resource of Jurassic period in Yulin City, and the problem of shallow buried coal seams mining will occur in every mine area. FLAC3D is used to analyze the plastic failure, deformation characteristic, and vertical stress on shallow buried coal seams mining, based on north No. 2 engineering geological conditions of Hongliulin Mining Corporation. In this paper, the results are shown as follows. The plastic failure fields of section coal pillar forming are smaller; the coal seam hosting is shallower. The elastic region of section coal pillar has a relatively large proportion, which is the coal seam first mined. The value of Z-Displacement for the first coal seam is relatively small. However, for the lower coal seam it is relatively big. The value of X-Displacement for each coal seam is relatively small. The coal wall of section coal pillar is in a steady state. The coal seam hosting is deeper; the more distant is from coal wall to peak point abutment pressure. The stress concentration factor for the first coal seam is relatively big. The research conclusion reveals instability mechanism of section coal pillar, while coal seams mining, which provides a theoretical basis for designing width vale and optimizing supporting scheme of section coal pillar, has engineering experience application value to other coalmines in Yulin City

A Study on the Instability Mechanisms of Coal Pillars in Shallow Coal Seams Group Mining

To explore the instability mechanisms of coal pillars in the upper coal during coal seam group mining in the Yulin area and hence to achieve safe and green mining of the lower coal seams, the engineering geological condition for no. 3−1, no. 4−2, and no. 5−2 coal seams in the north-second panel area of Hongliulin Coal Mine was investigated in this article. Using the combination of physical simulation, FLAC3D numerical calculation, and theoretical analysis, the instability mechanisms, the characteristics of the fracture structure, and fracture evolution between the coal pillars and the interval rocks were all studied. The results showed that a layout position existed that induced instability and subsidence of the coal pillars of the upper coal seam. The instability mechanism was such that the concentrated stress of the upper and lower coal pillars caused shear plastic damage in the interval rock along the direction of stress-transfer influence angle. The phenomenon of “inclined step beam” fracture structure, falling fracture zone, and severe mine pressure happened during seam group mining. Furthermore, the minimum center offset formula was put forward to study the instability of the upper coal pillars. This study provides a theoretical basis for a reasonable layout on how to position coal pillars for shallow coal seams group mining