Research on supporting technology of roadway surrounding rock for downward mining in extreme contiguous seams

In order to study the influence of the stress and goaf on the layout and support effect of the mining roadway in the lower coal seam after the mining of the upper coal seam in extreme contiguous seams, using theoretical analysis, numerical simulation and field practice, the maximum failure depth and range of goaf floor were calculated according to the plastic theory. The maximum failure depth was 9.2 m and the failure range was 20.5 m. Through FLAC^3D simulation, the stress distribution law of the floor roadway surrounding rock of the extreme contiguous seams mining was analyzed, the stress concentration degree at different depths from the floor, and the reasonable plane distance between the lower coal seam roadway and the edge of the upper coal pillar were obtained. The field roadway was straight wall at the top of the arc, and the combined support method of U-shaped steel arch support + anchor cable + grouting was adopted. The observation results show that the displacement of the two sides is nearly 250 mm, the roof subsidence is about 80 mm, and the floor heave is about 50 mm during the excavation.