The front abutment of a longwall face

Abstract

Sieve analyses of samples of the cuttings from drilling a long hole in a coal seam indicate the regions where the seam is subject to load, increasing pressure giving finer cuttings. This effect is so pronounced that other factors affecting cuttings size do not seriously interfere. Trials on a number of longwall faces have shown that a well-defined zone of pressure is always present ahead of the face. The width and distance from the face of this zone appear to be related to seam thickness, not depth. It has a complex form at the face end and continues in the rib-side. On the inner side of the zone there may be a narrow relaxed zone in the seam, providing a passage for the flow of water and presumably firedamp. The information obtained is discussed in the light of existing knowledge. Reasons are given for supposing that the zone described is the abutment of the fractured strata extending above the face, and that the higher beds are carried by a separate abutment zone further in.