Characteristics and precursor information of electromagnetic signals of mining-induced coal and gas outburst

Coal and gas outburst disasters can cause serious casualties and property losses, which can be effectively avoided by means of early warning. In this paper, based on the theoretical analysis of the electromagnetic radiation (EMR) response law of mining -induced coal and gas outburst, this paper studied the variation law and precursory characteristics of EMR signals before and after the outburst. The results show that: (1) Coal and gas outburst is induced under the disturbance of mining and promoted by gas pressure and highly concentrated mining stress. (2) The EMR signal is related to changes in stress state, fracturing activity and gas flow state in the process of mining, and the increase of the outburst danger will change characteristics of EMR signal in time and frequency domains. (3) In the time domain, the EMR intensity is positively correlated with the outburst danger of coal seam. The variable coefficient of EMR intensity is greater than 0.15 during the dynamic appearance. The peak value of variable coefficient of EMR intensity is positively correlated to the local instability of coal. (4) In the frequency domain, the amplitude of EMR grows, and the signal frequency moves toward a high level. The dominant frequency rises from 6.6 kHz to 17.4 kHz, and the EMR signal components become more complicated. In practical application, the evolution process of coal and gas outburst danger can be monitored in real time through a comprehensive use of EMR intensity value and its variable coefficient, waveform and frequency distribution characteristics, so that the occurrence of coal and gas outburst disasters can be eliminated.