Process Description and Initiation Criteria of Coal and Gas Outbursts Based on Energy Principles

An energy criterion model of coal and gas outbursts was established to study the energy conversion mechanism. Ideal gas law was utilized to establish a correlation between dissipated energy (i.e., energy dissipated during outbursts) and accumulated energy (potential energy leading to outbursts) in gas-containing briquettes. This relationship, along with the expression for the energy criterion, was derived from the deformation of briquettes under load, which led to instability and eventual failure expulsion. Hence, physical simulation experiments on coal and gas outbursts were conducted to analyze the energy conversion mechanism and to determine the change law of the initiation energy criterion index for outbursts. Besides, energy conditions were verified for the initiation of coal and gas outbursts. Potential energy includes the expansive deformation energy of adsorbed gas desorption, the expansive deformation energy of free gas, the elastic potential energy of gas-bearing briquettes under the stored load, and the gravitational potential energy work of unstable coal. Besides, the dissipation energy of outbursts included coal-crushing energy and coal-throwing power. The potential energy-to-dissipation energy ratios of outbursts were 1.07 and 1.04 in two groups of experiments. These values greater than 1 surpassed the threshold of the activation energy criterion, resulting in coal and gas outbursts. The firmness coefficient and Poisson's ratio of coal were negatively correlated with the energy criterion index, while the elasticity modulus, density, and initial velocity of gas emissions were positively correlated with the energy criterion index. The five experimental parameters (i.e., initial gas pressure, coal amount, maximum principal stress, average velocity of coal outbursts, and falling height of unstable coal) were positively correlated with the energy criterion index. The findings provide further insight into the mechanism of coal and gas outbursts, establishing a basis for their control, prevention, and dynamic warning systems.