Numerical study on the effect of sudden change in coal property on coal and gas outburst during roadway excavation

Coal and gas outburst (CGO) is a devastating disaster in the coal mining industry at the cost of human life. Considerable efforts have been done to eliminate this hazard, but CGO still occurs frequently. The geological structure is a critical factor influencing CGO, and it has recently been found that sudden change in coal property plays an important role in CGO. In this paper, the stress transmission, coal deformation, energy accumulation, and plastic damage when the roadway is excavated to the geological structure with the sudden change in coal property are analyzed by numerical method, based on Shoushan No.1 coal mine. It is found that the geological interface between soft coal and hard coal transfers the stress from soft coal to hard coal within a certain range, causing the occurrence of tectonic stress. The tectonic stress increases gradually with roadway excavation and finally superimposes with the peak stress. The coal deformation and elastic energy increase, leading to a high probability of CGO. When the heading face is closed to the geological structure, the coal damaged area is obviously increased no matter the roadway is excavated from hard coal to soft coal or from the opposite direction. Engineering trial shows that controlling the tunneling speed and pre-grouting to reinforce the geological anomaly area are effective methods to improve the safety of roadway excavation.