Identification Model and Indicator of Outburst-Prone Coal Seams

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Coal and gas outburst with a sudden and violent ejection of a large amount of coal and gas from the working face is the most harmful dynamic phenomenon during coal mining (Aguado and Nicieza 2007; Lama and Bodziony 1998; Torano et al. 2012). Outbursts have occurred in all the major coal-producing countries around the world; however, nearly one-third of the total outbursts have occurred in China (Guan et al. 2009; Skoczylas 2012; Xu et al. 2006). The process of judging the possible occurrence of coal and gas outburst in the near future is defined as the identification of outburst-prone coal seams, which is of great significance for underground mining safety. The identification of outburst-prone coal seams can be conducted before or after the occurrence of dynamic phenomenon. Since the vast majority of coal seams do not show dynamic phenomenon, it is necessary to identify outburst-prone coal seams before the occurrence of dynamic phenomenon. To this end, many dynamic characteristic indicators have been used. For example, gas content thresholds of 9 m/t for CH4 and 6 m /t for CO2 were used in the Sydney Basin to indicate outburst-prone conditions, but they were based on empirical experience from operations and may vary from one coal seam to another. The DP indicator, based on the initial rate of gas desorption from coal, has been widely adopted in Europe. However, in Australia, outbursts occurred in coal seams showing low DP values (Beamish and Crosdale 1998). Currently in China, the ‘‘Four Indicators [degree of coal fracturing (for more details, see Table 1), Protodyakonov strength index (f), initial rate of gas emission (DP), and gas pressure (P)] Method’’ given in the Chinese standard AQ 1024-2006 (State Administration of Work Safety, SAWS 2006) is used as the standard for the identification of outburst-prone coal seams. If all the measured values of the four indicators exceed their thresholds given in Table 2, the coal seam is identified as an outburst-prone coal seam. This method has been widely used in China for its simplicity. However, the predictions with the ‘‘Four Indicators Method’’ are not always consistent with the occurrence of dynamic phenomenon during underground mining, and outbursts causing large casualties still occur in some nonoutburst seams identified using this method. Thus, the accurate identification of outburst-prone coal seams is an urgent issue. In this paper, a novel identification model under the ideal condition of uncovering coal in crosscut (IUCC) is proposed, in which the initial expansion energy of released gas (IEERG) is used as an indicator to identify outburstprone coal seams. To obtain the threshold of the IEERG indicator, numerous experiments of coal and gas outburst were carried out and the IEERG of coal samples were measured. After that, the ‘‘IEERG Indicator Method’’ was used on the spot to verify its accuracy. C. Jiang (&) L. Xu X. Li J. Tang Y. Chen S. Tian H. Liu School of Safety Engineering, China University of Mining and Technology, Xuzhou 221116, Jiangsu, China e-mail: xlh0612@163.com