Effective potential energy associated with coal and gas outburst during underground coal mining: case studies for mining safety

Outburst of coal and gas is a major dynamic hazard during coal mining and has to be controlled for reducing mining disaster risk. Despite significant advances made in outburst prediction and control technologies, some fundamental issues remain to be resolved, particularly in understanding the physical mechanism of this phenomenon. Because of the wide variety of conditions under which outbursts occur, there is still no single theory that could explain the phenomenon although a number of hypothesis and theoretical models have been proposed. In this study, energy approach was adopted to explain the process of an outburst. The potential energy in gas-containing coal was analyzed with particular reference to the effective potential energy available and contributing to the process of an outburst. Six real cases of outbursts were investigated of their effective potential energy, and new insights on the outburst mechanism were gained. Results show that the energy of free pore gas in coal and the energy of desorption gas from coal respectively made up 39.7% and 53.7% in the total effective potential energy. In other words, the gas energy played a dominant role in the process of outbursts. This implies that the risk of outbursts could be effectively minimized through reduction in gas energy of gas-containing coal. As gas energy in coal is largely determined by gas content or pressure, the risk of outbursts could therefore be minimized by decreasing gas content or pressure in coal. An energy threshold value of 0.339 MJ/m3 for outburst was also proposed in this study. Outcomes of this study are expected to provide some references on outburst prediction and prevention for improving mining safety level. © 2021, Saudi Society for Geosciences.