Underground » Ventilation, Gas Drainage and Monitoring
During part of 1996, a microseismic monitoring program was carried out at Appin Colliery to investigate the geomechanical behaviour associated with longwall mining. The data obtained in that study also provided the opportunity to investigate any seismic signatures associated with gas emissions from the floor of the Bulli Seam. A signature had been observed previously at Cynheidre Colliery in the UK where a special type of seismicity occurred. This gave a warning of the development of outburst conditions.
No equivalent events were observed at Appin, presumably because of the effectiveness of the predrainage of the Bulli Seam. However, the seismic activity associated with the longwalling showed significant periodic fracturing within the floor and to the tailgate side of the panel. Periods of high gas make from the underlying seams occurred in the vicinity of these fractured zones. The gas make was not within the zones themselves but further behind the face and closer to the maingate. It was captured by cross measure drainage holes. It is speculated that in the vicinity of the floor fractures, there is more intense floor heave and bedding plane separation and the low of gas is from these. Regardless, the present evidence is that periods of high cross measure gas make at Appin Colliery are associated with increases in seismic activity.