Abstract
As mines become deeper, the potential for coal and gas outbursts in deep rock cross-cut coal uncovering is enhanced. The outburst precursors are unclear, which restricts the effectiveness and reliability of warning systems. To reveal the evolution characteristics of coal and gas outburst precursor information in deep rock cross-cut coal uncovering, briquette specimens are constructed and experiments are conducted using a self-developed true triaxial outburst test system. Using acoustic emission monitoring technology, the dynamic failure of coal is monitored, and variations in the root mean square (RMS) of the acoustic emissions allow the effective cracking time and effective cracking gas pressure to be defined. These characteristics are obviously different in deep and shallow coal. The characteristic parameters of gas outburst exhibit stepwise variations at different depths. The RMS and cumulative RMS have stepped failure characteristics with respect to changes in gas pressure. The characteristic parameters of coal failure are negatively correlated with the average in-situ stress and effective stress, but positively correlated with the lateral pressure coefficient of in-situ stress and the critical gas pressure. The transition characteristics are highly sensitive in all cases. The critical depth between deep and shallow coal and gas outbursts is 1700 m. The expansion multiple of acoustic emission intensity from the microfracture stage to the sharp-fracture stage of coal is defined as the outburst risk index, N1. For depths of 1100–1700 m, N1 ≥ 7 denotes a higher risk of outburst, whereas at depths of 1700–2500 m, N1 ≥ 3 indicates enhanced risk.
Highlights
Coal and gas outbursts are the most harmful dynamic coal mine disasters in China, seriously threatening the safety of underground workers (Chen et al 2014; Wu et al 2020; Wang and Meng 2018; Cao et al 2019, 2020; Ma et al 2020a)
The above-mentioned research indicates that many scholars have investigated the precursor information and outburst risk indicators of coal and gas outbursts
The variation of influence of the average in-situ stress, lateral pressure coefficient of in-situ stress, critical gas pressure, and effective stress on the coal failure characteristic parameters is explored, and new principles are provided for deep coal and gas outburst
Summary
Coal and gas outbursts are the most harmful dynamic coal mine disasters in China, seriously threatening the safety of underground workers (Chen et al 2014; Wu et al 2020; Wang and Meng 2018; Cao et al 2019, 2020; Ma et al 2020a). The above-mentioned research indicates that many scholars have investigated the precursor information and outburst risk indicators of coal and gas outbursts. Using a self-developed true triaxial coal and gas outburst simulation test device, this study conducted outburst simulation experiments on coal samples from Hongyang No 3 mine, which is an outburst coal seam with a current mining depth of 1100 m. Based on the dual parameters of the acoustic emission signal and the gas pressure, a risk index for deep coal and gas outburst is established. The variation of influence of the average in-situ stress, lateral pressure coefficient of in-situ stress, critical gas pressure, and effective stress on the coal failure characteristic parameters is explored, and new principles are provided for deep coal and gas outburst
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