Abstract
In this study the reversible and irreversible changes in gas permeability of coal have been investigated by applying the acoustic emission methods in order to find a clue to the advancement of gas drainage technology. Actually, the hysteresis of gas permeation rate appeared between the processes of an increase and decrease of applied gas pressure as a result of an increase in acoustic emission activity. The hysteresis was negligibly small and the reversibility was approximately applicable to the relations between permeation rate and applied gas pressure when the amplitude-frequency distribution of acoustic emissions consisted of a simple straight line. On the basis of this reversibility, the opening rate of gas permeable cracks was considered from the characteristic curves of gas permeation rate. Consequently, it became clear that gas permeability of coal depended on the opening or closing of permeable cracks caused by gas pressure in these cracks. This functional relation was expressed by a new gas permeation formula of coal.
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