Experimental study on intensity and energy evolution of deep coal and gas outburst

Abstract

Coal and gas outburst is the most serious dynamic disasters in coal mining. The essence of mechanics is the instability and destruction process of coal and rock caused by energy accumulation and release. With mining depth increase, complex geological and stress conditions make coal and gas outburst present new characteristics, which severely restricts the reliability and effectiveness of disaster warning. For this study, the coal and gas outburst tests at different simulation depths were carried out to explore more effective prediction and prevention measures. The results show that a two-phase flow of coal and gas is ejected from the outburst mouth at high speed for 0.6–1.5 s. As the simulation depth increases, both the critical gas pressure and relative outburst intensity decrease, but the unit outburst intensity increases. The deep coal and gas outburst was characteristic of low threshold of gas pressure, easy to trigger and high intensity. The evolution of acoustic emission (AE) energy has experienced “steady-rise-peak” process. The cumulative AE energy in the early incubation is relatively small which is gradually increases at the later incubation. The cumulative AE increases sharply exposed strong outburst risk at the excitation. The propagation of impact force in the roadway has experienced “rise-peak-decrease” process, showing a “crest effect”. The cumulative AE energy increases exponentially with the peak impact force. According to the range of changes in the outburst indicators N1 and N2, the outburst risk is divided into five levels: no risk, low risk, medium risk, high risk and strong risk. A new prediction method for coal and gas outburst based on acoustic emission parameters is proposed, and its applications are discussed.