Prediction of coal pillar failures by using Acoustic Emission measurements

In this paper, the strength and failure of coal specimens containing bedding planes at various inclinations are considered. Compressive strength of cubic coal specimens containing weakness planes at various inclinations along with acoustic emission measurements were determined. Test results showed that the strength and the mode of failure of cod specimens depend upon the angle of bedding planes and W/H (or D/H) ratio. During the AE measurements, count rate detected through a low pass window (AE(L)) was compared with that through a high pass window (AE(H)) in each test. The results of accumulated AE history are compared with Mogi's and Boyce's AE signatures. It is shown that AE signature of coal depends upon the weakness planes inclination and the AE signatures can be classified into three groups. Each group has different mode of failure and they are: slip on the weakness planes, fracture across weakness planes and fracture extension through weakness planes. The ratio r = AE(L)/[AE(L)+AE(H)] is plotted against the stress for each test. Test results showed that r also depends upon the weakness planes inclination.