Study on normalization of critical values of the prediction indicator initial gas emission from boreholes

Outburst prediction during coal roadway excavation, which is characterized by multiple prediction numbers and rapid cyclic construction, is a key link of outburst prediction in coal mines. This study is aimed at accurately predicting the outburst risk of coal roadway working face by the initial gas emission from boreholes (IGEB) indicator in the field. First, a theoretical calculation model for gas emissions from drill cuttings and borehole wall was established. Based on this model, it is concluded that the drilling speed significantly influences the critical value of IGEB for outburst prediction. Furthermore, the IGEB per meter was experimentally investigated at different drilling speeds and under different gas pressures with the aid of a self-developed IGEB outburst prediction device. The investigation results show that the value of IGEB is linearly correlated with the gas pressure at the same drilling speed, and it is also linearly correlated with the drilling speed. Besides, the values and critical values of IGEB at different drilling speeds were normalized to the values at the standard drilling speed, for the purpose of eliminating the influence of drilling speed on the determination of the critical value of IGEB for outburst prediction. Finally, a field test was carried out on the 3# coal seam of Xinjing Coal Mine, and a good application effect was achieved in the field test.