Induced Changes in Permeability of Coal Measure Strata as an Indicator of the Mechanics of Rock Deformation Above a Longwall Coal Face

Abstract

In the Coal Measures of South Staffordshire below the unconformity at the base of Trias, there is a zone of increased fissure permeability and porosity in which most sandstones and coals give small makes of water. Very occasionally, considerably larger flushes of up to 1000 g.p.m. have occurred on longwall coal faces working in or close to this zone, even though these faces are at levels much further below the Trias unconformity than the minimum 60m. permitted. One such flush at West Cannock Colliery and the resultant investigation boreholes are described. The information gained from these boreholes demonstrated the existence of tensile zones in the form of bed separations which occur in a regular geometric pattern relating to a series of beams of uniform thickness over the edge of a worked panel.