Experimental investigation on the characteristics of transient electromagnetic radiation during the dynamic fracturing progress of gas-bearing coal

There are extensive studies on electromagnetic radiation (EMR) effects during coal and rock deformation and fracturing processes, but few systematic studies on the EMR features of gas-bearing coal under impact failure circumstances. In order to investigate whether the EMR is affected by the gas (CO2,CH4/N-2) sorption, coal type and impact energy, we performed a series of impact loading tests on both briquette coal specimens (BCSs) and raw coal specimens (RCSs) at various pore pressures (0-1.5 MPa). We developed a drop hammer test apparatus to allow impact loading tests on gas-bearing coal, and recorded the EMR signal of the damage of coal simultaneously. The result showed that (i) the amplitude range of the EMR signal generated by the impact damage of the gas-bearing coal is approximately 10-600 mV, with an effective duration time of 3-1500 ms and accumulated energy of 0.1-1000 mu j; (ii) when pore pressure is increased, the maximum amplitude, duration and pulse counts of the EMR decrease accordingly; (iii) the coal powder size and impact energy affect damage features and EMR characteristics, where a higher impact impulse causes more severe damage to coal specimens and (iv) the influence of the presence of adsorptive gas on the EMR signal caused by the destruction of coal bodies has both enhancement and reduction effects. During the early warning assessment of coal and gas outbursts using EMR parameters, not all the waveform parameters are sensitive to coal mine methane, but the significant effect of methane on signal volatility should be considered.