Comprehensive analysis of acoustic emission evolution characteristics during deformation and failure process of outburst coal

To study the acoustic emission characteristics and differences during the deformation and failure process of different type coal samples, the raw coal samples and briquette samples from 3 outburst coal seam in Xinyuan coal mine, Yangquan Coal Group, are compressed under the load control method. The results show that during the test, the coal samples undergo three stages: the non-crack development stage, the stable development and unstable development stage of the crack.During the stable development and unstable development stages of the crack, the acoustic emission index increases with the volumetric strain rate of the raw coal samples, and the acoustic emission index violently increases with volumetric strain sharp drop.For the raw coal samples, their unstable development stage of the crack oc-curs before the peak stress, which indicates the brittle deformation after the peak, and the peak of acoustic emission index also occurs before the peak stress. Conversely, for the briquette samples, their unstable development stage of the crack occurs after the peak stress, which indicates the ductile deformation of plastic flow after the peak, and the peak of acoustic emission index also occurs after the peak stress.Two kinds of volume strain-time curves are presented during the raw coal samples test.One is smoother curve, the other is with short-time sudden drop in the stable development stage of the crack.But for the briquette samples, there is merely smoother curve. For the raw coal samples, there is a positive correlation between the acoustic emission parameters and the stress, and the acoustic emission parameters have a higher value during the unstable development stage or after the middle stages of the stable development stage of the crack.Nevertheless, for the briquette samples, the evolution of the acoustic emission parameters can be divided into two stages, the quiet period before the peak and the outbreak period after the peak.Acoustic emission parameters rise from a relatively stable low value before the peak to the maximum value of the higher level after the peak, which indicates a sudden increase in the process of the briquette samples failure. Due to the higher strength of the raw coal samples, which can easily accumulate higher elastic potential energy, and the relatively broken internal structure, the acoustic emission strength of the raw coal samples, including the average strength and the peak strength, is far greater than that of the briquette samples.