Stress state in the face region of a steep coal bed

The stress state of the face region of a coal deposit is characterized predominantly by the supporting pressure, which depends on the depth of the mine working, the displacement parameters of the worked deposit, and its spatial configuration. Qualitative and quantitative estimates of the variation in supporting pressure are based on experiments in mine conditions and on models made from equivalent materials. The general laws of supporting-pressure variation over the depth in working steep beds with narrow and broad columns and the distinguishing features for other typical configurations are considered. The dependence of the supporting pressure on the mine depth is most apparent in broad-column removal of the worked material. In this case, the development of the supporting pressure is a maximum. Since the roof suspension and its conditions of collapse exert an influence on the supporting pressure, constant conditions are considered, with maximum roof span, i.e., only the maximum supporting pressure is taken into account over the depth. Increase in depth of the mine working has a particularly strong influence on the increase in supporting pressure in the first 200-250 m below the surface, when increase in thickness of the worked bed is associated with distribution of its weight over the face region of the bed. At a greater depth, the load on the upper (more remote from the bed) layers of the rod is scattered over a larger area, with a smaller concentration, on account of the smaller flexure of the more remote layers.