Outburst characteristics of CO₂ gas-coal mixture with tunnel outburst simulator in deep mining

This study designs a tunnel outburst simulator to quantify the outburst characteristics in a deep tunnel. During the outbursts, shock waves, generated by the rapid gas-coal flow, are recorded using three high-frequency gas pressure sensors at three different locations along the tunnel pipe. The amplitudes of the shock waves induced by the outbursts (688.7, 1225.8, and 1207.2 kPa) are tens of times larger than those induced by the pure gas eruptions (38.8, 51.2, and 61.4 kPa) at the initial pressure values of 200, 400, and 600 kPa. The shock waves caused by compressed air occur before the shock waves caused by the gas-coal mixtures. Trajectory segregation of coal deposition along the tunnel pipe is found after the outbursts. Larger coal particles flow easily and move further than the smaller ones during the outbursts. Furthermore, the major energy contributing to the outbursts is derived from the expansion energy of high-pressure CO₂ gas. The free gas in the coal voids contributes toward more expansion energy than the desorbed gas from the coal. An index denoting the quantitative intensity of the outbursts is developed, by considering energy dissipation, to describe the consequence of the outbursts. The findings of this study can be useful for the early warnings of outbursts in tunnels.