The effect of applied stresses on the permeability of a middle rank coal to water

Abstract The flow of water through 2-in. cubes of Cwmtillery Garw coal has been measured. The specimens were visually similar but gave widely differing rates of water flow from 0·001 to 0·11 cm 3 /min at a water pressure of 100 lb/in 2 and from 0·20 to 1·85 cm 3 /min at 600 lb/in 2 flow rate suddenly rose. Reduction of the water pressure brought the flow rate down again water pressure. There tended to be a critical water pressure for each specimen at which the to roughly the original value. The behaviour of the flow rate when the specmen was clamped between steel plates under pressure is explained by assuming that disk-shaped cracks in the coal open or close according to the direction of the confining forces.