Study and application of the o-shaped circle theory for relieved methane drainage

Experiments and discrete simulation results have revealed that as the excavated area is large enough, mining-induced fractures are repressed and closed in the middle zone of goaf, but the fractures can still exist around the goaf for a long time, so that an O-shaped circle with developed fracture is formed around the goaf with the width about 30m. The experiment results have shown that the O-shaped circle is the main flowing passage of relieved methane, and the relieved methane drainage holes should be laid in the O-shaped circle. Guided by the O-shaped circle theory about relieved methane drainage, the industrial experiment to drain methane from long away overlying coal seam through surface well has been completed successfully. The plan to drain the relieved methane in the goaf of LuLin colliery has been put forward and applied.