METHANE RELEASE FROM ACTIVELY YIELDING COAL AND ITS IMPLICATIONS FOR YIELD ZONE DETERMINATION

One measure of the capacity of coal pillars to support load is the proportion of material in them which can be classified as "yielded". As a means of determining the extent of yielded material in a pillar, the relation between methane emission and yielding has been investigated through laboratory testing at the Denver Research Center, U.S. Bureau of Mines. Sample yielding, as defined by drops in axial load during uniaxial compression, was monitored coincident with methane concentration, axial deformation, acoustic emission, temperature and gas pressure. While acoustic emission gave an ambiguous measure of yielding, methane release correlated with significant drops in load. No increases in methane concentration were observed before yielding, so increases in methane emission may be correlated with structural yielding of the sample. A large permanent increase in concentration observed at final yielding indicates that a major proportion of gas is in the micropore and unconnected crack system of the coal. Thus, the release of this bound-up portion of gas provides a proportional measure of the degree of structural damage experienced by the coal. © 1990.