Outburst mechanism of tunnelling through coal seams and the safety strategy by using “strong-weak” coupling circle-layers

Outbursts are triggered by the elastic energy near the heading face and developed by the gas expansion energy and elastic energy distant from the heading face. In this study, the method of “strong-weak” coupling circle-layers was proposed to reduce the outburst hazard when roadways excavated through gassy coal seams. This method was proven to be valid by the comparative experiment. The weak circle can be realized by boreholes and hydraulic cutting. It could not only reduce the elastic energy near the heading face but also prevent the distant energy from contributing to the outburst accident. In addition, the strong circle can be made by injecting water slurry and applying anchors. It could help to reduce the strength difference between coal and rock, thereby decreasing the local stress concentration, resisting the residual outburst energy near the heading face, and preventing the outburst from being triggered. The “strong-weak” coupling structure was successfully applied in Bailongshan coal mine when uncovering the #7,8 coal seam. This structure can effectively promote gas drainage, reduce the coal and gas outburst risk. As a result, the mining efficiency improves a lot, and the uncovering time greatly decreases from the expected 2 years to 5 months.