This article presents a theoretical analysis and numerical simulation studies to determine the suitable position for the lower slice roadway in a residual pillar area after top slicing a thick coal seam. We considered the load concentration on the coal pillar, the goaf floor, and the stress distribution characteristics of the coal pillar area before and after the top slice. With a mechanical model built of the residual pillar load propagation in the floor and the failure model of the floor surrounding rock, the analytical formula we deduced for the coal pillar floor stress and the expression of the floor failure depth of the roadway provides a basis for the reasonable determination of the position of the lower slicing roadway. Studies proved that after mining the top slice working face, the floor stress field of the residual pillar area presented characteristics of the non-uniform distribution. The stress concentration occurred below the coal pillar. The stress variation area appeared at the edge of the coal pillar, with a stable stress area appearing far away from the coal pillar area. Therefore, the roadway layout should avoid the areas below the coal pillar and the coal pillar edge with high stress levels and a large stress variation gradient. High stress concentration formed on the coal pillar transferred to the lower layered coal and floor strata, and decreased the stress concentrations layer by layer. However, mining of the top-layered working face affected the coal, and rock mass damaged the coal pillar floor area and weakened the mechanical properties, which was not conducive to the control of the roadway surrounding rock. The research results applied to No. 30117 working face of the lower slice of the Shancheng Coal Industry, and the proper position of the return airway of the working face was determined to be 8 m outside the east side of the residual pillar in the top slice, achieving a good surrounding rock control effect.
Aiming at the wide range of rock strata movement and collapse, poor stability and high damage rate of the working face support and being prone to crushing of the support in large mining height face, analog simulation, theoretical analysis, and field measurements have been carried out to analyze roof breaking structure form and calculation method of support reasonable support resistance of large mining height face. The researches show that, affected by the space of the mined-out area, the roof of the large mining height working face will take on the structural form of “combined suspended beam-nonhinged roof-hinged roof”; the interaction system between the support and the surrounding rock consists of “hinged roof structure,” “nonhingeable roof structure,” “combined suspension beam structure,” and the support. The support resistance should adapt to the change of the overlying rock structure’s instability movement, bearing the weight of the structure itself and the additional load generated by the movement. Combining with the mining conditions of Jinhuagong Coal Mine’s large mining height face in Datong mining area, the reasonable support resistance of the working face support is analyzed. The mine pressure monitoring shows that the ZZ13000/28/60 type support and shield hydraulic support can meet the requirements of roof control; the research results ensure the safe mining of the large mining height face.
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