Deformation of the Rock Mass

Abstract

Settlement of the immediate roof over the workings, as described in the previous section, continues in higher strata if the mine excavation is so wide that it can no longer be bridged by the overlying rock and the pressure arch in the roof beds collapses (Figs. 12 and 49). In settling, the lower roof beds, if they become detached in sections from the rock bond along horizontal slip planes and loosened bedding planes, withdraw their support from higher beds. Being no longer fully supported, these immediately give under their own dead weight and the extraneous load bearing on them and lay themselves on the beds that have already gone down. The downward movement spreads in this way very rapidly until it reaches the upper earth surface (see Fig. 118).