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To accurately predict the risk of coal and gas outbursts under different conditions, an outburst risk prediction system and risk level indices value system were constructed based on extension theory. The prediction system includes 6 indices and 4 risk levels. The subjective and objective weights of the prediction indices were determined according to a fuzzy analytic hierarchy process and simple correlation function, respectively. Finally, a prediction model for the quantitative characterization of the outburst risk through the degree of correlation of the risk level was established. The outburst risk of 12 high-gas mines was predicted by using the prediction model. The prediction result of the outburst risk level was consistent with actual outburst disaster occurrences, and the variation of the actual outburst coal and rock mass quality was consistent with the degree of correlation of the maximum risk level. Based on typical outbursts of coal seam, the values of gas pressure and coal seam gas content were reduced step by step, and then the adjusted values were substituted into the prediction model. When the coal seam gas pressure was reduced to 0.75 MPa, the outburst risk level was reduced to low risk. This value is consistent with the empirical value (0.74 MPa) that is used to define an outburst of coal seam at a coal mine site. The prediction model has practical significance to prevent coal and gas outbursts, optimize gas drainage outburst prevention technology, and improve process safety risk control in coal mine. [ABSTRACT FROM AUTHOR]

• The whole process of outburst was completely reproduced by a simulation test. • The abnormal characteristics of key contact indicators before outburst were detected. • The sensitivity priorities of outburst precursor information in the process of uncovering coal was obtained. • The variation parameters of the key contact indicators had more advantages than the signal itself. The diversity of precursor information is significant for providing accurate early warnings of outbursts. However, the existing research mainly focuses on noncontact indicators, which cannot fully and accurately reflect the outburst risk. To capture the precursor information of the key contact indicators, a simulation test for the whole process of outbursts was carried out. In the test, the newly developed similar materials of gassy coal and ultralow permeability rock and a simulation system were used to simulate the occurrence environment and disturbance conditions of the coal mass. The results show that the outburst phenomenon and gas concentration evolution are similar to the real phenomenon on site, which proved the accuracy of the test results. The abnormal characteristics of a number of physical aspects before outburst were detected: an obvious relief stress zone appeared in the in situ stress curve for coal seam; the gas concentration in the roadway exceeded the safety standard (0.3%) and continued to increase to 3%; the pressure of coal seam and roadway surrounding rock changed from stable to declining, with a total amplitude of 10 kPa; the temperature in coal seam and roadway changed from steady to fluctuating up and down, with fluctuations reaching 3.4 °C and 4.7 °C, respectively. According to the abnormal occurrence time and identification level, the sensitivity priorities of the above information were temperature, gas concentration, in situ stress, and gas pressure. In addition, the moving average, deviation rate, and dispersion rate of the gas concentration, gas pressure, and temperature versus time curve had more advantages than the signal itself. This study provides guidance for the realization of accurate and effective real-time warnings. [ABSTRACT FROM AUTHOR]

The impact mechanism of in situ stress on outbursts plays a key role in the prevention of outbursts during deep coal mining. The in situ stress may influence the outburst by affecting the gas release intensity according to theoretical analysis, but none of the existing studies have taken into consideration this perspective. To explore whether the influence of in situ stress on gas release in coal is an important reason for stress-induced outbursts, experiments on gas release in coal under different axial stresses and on exposure-induced outbursts with different gases were conducted to respectively study the influence of in situ stress on gas release and the impact of gas release on outburst. The results show that with the increase of stress, the methane release intensity rises by 1~2.4 times and shows an obvious periodicity due to different degrees of fracture development. A small increase in gas release intensity can lead to huge increase in the outburst intensity based on an energy analysis of the outburst experiments, indicating that the gas release intensity is a sensitive physical quantity that influences outbursts. The differences in gas release in coal with different stresses will result in differences in the outburst results based on data from the two experiments, proving that the change in gas release intensity during variations of in situ stress is an important factor for in situ stress-induced outbursts. The research achievements can enrich the impact mechanism of in situ stress on outbursts. [ABSTRACT FROM AUTHOR]