The finite element method for analyzing the stress distribution of working faces in mine shafts was used during coal excavation in the new auxiliary shaft of the Luling mine. We measured the
stress and permeability prior to the excavation of the No. 8 coal seam [13], as shown in Figs. 1 and 2.
The No. 8 coal seam occurred at a depth of 483 m in the new auxiliary shaft with a coal thickness of 11.8 m and dip angle of 201. The No. 8 coal seam was an outburst-prone coal seam, the measured gas pressure was 3.1 MPa, and a major outburst accident had previously occurred. Based on the measured data shown in Figs. 1 and 2, we determined that the stress at the working face of the shaft was distributed according to the following rules.
1)When the working face approaches a coal seam, the stress distribution was divided into three zones in the front (i.e., complete) part of the pressure relief zone and the original stress zone. The pressure relief zone has a funnel-like shape, and the maximum pressure relief zone was located at the center of the ‘funnel’, which was surrounded by the partial pressure relief zone. In the front of the working face, the pressure relief level of the coal-rock mass was reduced with the distance from the shaft center line. As the distance between the coal seams and the working face decreased, the extent of pressure relief in a certain zone of the coal seams increased.
2) There was a zone of concentrated stress surrounding the shaft. As the working face approached the coal seams, the range and peak values of concentrated stress increased. The area of stress concentration was about 0–12 m surround-ing the shaft, and the outburst breakthrough point occurred at the corner, the intersection of the base and wall of the shaft.
3) At the same depth, the stress distribution was different around the shaft wall. The peak and influential range of concentrated stress at the upper side of the coal seam along the trend were greater than those on the lower side due to effect of gravity stress of rock mass as well as the combined effects of concentrated stress and gas pressure.