Evolution characteristics of precursor information of coal and gas outburst in deep rock cross-cut coal uncovering

Abstract

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, N 1. For depths of 1100–1700 m, N 1 ≥ 7 denotes a higher risk of outburst, whereas at depths of 1700–2500 m, N 1 ≥ 3 indicates enhanced risk.

Keywords

• Deep coal and gas outburst
• Rock cross-cut coal uncovering
• Acoustic emission
• Critical gas pressure
• Risk index