Abstract
Clear understanding of coupled interactions between coal-rock and gas subjected to static and dynamic loading will be crucial to convince that coal-gas dynamic events can be effectively monitored. Here, we attempt to fill this gap by gathering microseism (MS) and acoustic emission (AE) information on the interactions of gas with coals and the effects of coal-rock fracture on abnormal gas emission. Field investigations disclose two phenomena observed for interactions of coal-rock fracture and gas emission: (1) overpressuring gas in coal can induce fast crack initiation and growth ultimately producing a gas outburst with relatively low energy; and (2) under the influence of a shock wave generated by dynamic loading such as a rockburst, the coal-gas medium may be destroyed. For smaller pressure and lower desorption energy, only abnormal gas emission is generated. The abovementioned phenomena occurred in a gas-containing coal seam, MS&AE activities prior to, during, and after two unusual gas emissions and the spectrum evolutions were analyzed, and the corresponding mechanisms were revealed.
1. INTRODUCTION
Since the first reported coal and gas outburst in the Issac Colliery, Loire coal field, in 1843[1], more than 14,000 outbursts have occurred in China [2]. Many researchers have studied relationships between coal outbursts and geological factors for different coal fields, and have come to different conclusions because of the complexity of the mechanisms. Coal and gas outbursts in mines are engineering geological hazards. The dynamic stress on coal and rock material closest to the outburst source results from additional impact load produced by roof fracture or blasting, will result in sudden rupture of coal material in the critical stress condition, produce fissures forming outburst channels, and accelerate the escape velocity of gas resulting in coal and gas outbursts [3]. For coal seams containing gas, an abnormal emission due to higher pressure of gas and higher stress may be an effective precursor for a rockburst. Simultaneously, recorded MS signals from roof strata may also be a precursor of coal and gas outbursts. Many abnormal gas emission phenomena following rockbursts have been reported and recorded in Chinese coal mines in the Fuxin and Beipiao coal fields in Liaoning province and Hegang coal mines in Heilongjiang province [4-6]. In addition, in the Rhine-Westphal coal field, Hawusike coal field, and Ruhr coal field in Germany, many rockbursts events have been accompanied by abnormal gas emissions [7, 8]. The correlation between rockburst and gas outburst was confirmed by MS observation, gas monitoring, and accident investigations by some scholars [9, 10-12].
