Application of acoustic emission technique to the evaluation of coal seam hydraulic flushing effect

Abstract

Hydraulic flushing has the advantages of reducing coal stress and improving coal seam permeability, so it is widely used in high gas outburst coal seams in China. However, the effect evaluation of stress relief and permeability enhancement will be necessary before coal mining. In this paper, an acoustic emission (AE) experiment system of coal seam hydraulic flushing was established, and the AE characteristics of coal during hydraulic flushing were studied. The results show that the changes in AE signals are basically consistent with those in load and water pressure. In addition, the quantitative relationship between the signals and the damage of coal around the borehole is revealed by the theory of damage mechanics. The in-situ AE test of hydraulic flushing was performed in the Liangbei Coal Mine, by measuring gas flow and coal stress simultaneously. The variation of AE activities and the effect evaluation of hydraulic flushing were analyzed. The results reveal that the changes in coal seam stress are basically consistent with those of AE signals. After the flushing has been completed for 1-3 h, the coal seam stress decreases rapidly, and the AE counts and intensity reach the peak. Therefore, this study proposes a new method for evaluating the effect of coal seam hydraulic flushing by AE, which has a very important practical significance.