Optimizing roadway location and cross section under superposition of residual coal pillars and adjacent goafs in close distance coal seams

The residual coal pillar and adjacent goafs in the upper coal seam have a superposition effect on the stress environment of the lower coal seam in close distance coal seams with downward mining. Therefore, it is essential to determine the appropriate location and cross section of the roadway. Through field measurement, theoretical analysis, and numerical simulation, the stability performance of the roadway was analyzed under the superposition effect of the residual coal pillar and adjacent goaf in the close distance coal seam at Meihuajing Coal Mine. Finally, the appropriate location and cross section of the roadway were determined. The results show that: (1) The 60 m wide residual coal pillar in the upper coal seam can effectively bear the surrounding rock pressure and keep the roof structure stable. (2) The optimum position for the roadway in the lower coal seam should be located in the vertical stress decreasing area, with a horizontal distance of 10 m between the roadway and the edge of the residual coal pillar. (3) The roadways with the straight wall semi-circular arch (SWSCA) cross section and the three-centered arch (TCA) cross section have the highest stability, while the one with the rectangular cross section (R) has the lowest stability of the surrounding rock, combining with the distributions of vertical stress and plastic zone. (4) Considering the superposition effect of the residual coal pillar and adjacent goaf, the roadway with SWSCA cross section is recommended for implementation in the lower coal seam because of its good stability and simple construction.