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Studying the evolution of characteristics associated with the energy of gas-bearing coal is essential for exploring the mechanism of coal and gas outbursts and disaster prevention. In this paper, uniaxial compression and acoustic emission (AE) localization experiments were conducted using coal under different gas pressures. The mechanical characteristics, AE parameters and energy evolution of coal were analyzed and compared. The mechanism of the influence of gas on the mechanical characteristics of coal was studied. The connection between the destruction and the energy evolution of coal was revealed. The research showed that gas pressure can induce considerable initial damage inside coal. The compressive strength of coal decreased by 65.82% as the gas pressure increased from 0 to 4 MPa. The energy evolution and the failure characteristics of coal were closely related to the gas pressure. At low pressure, coal underwent elastic deformation before failure, elastic strain energy dominated during the loading process, and slight damage was observed after failure. Based on these observations, the ratio of dissipated energy to elastic energy ( U d / U e ) was used to characterize the severity of the damage. The ratio increased from 0.161 to 2.189 as the gas pressure increased from 0 to 4 MPa. Mild, weak and strong failure occurred when U d / U e < 0.5 , 0.5 ≤ U d / U e < 1 , and U d / U e ≥ 1 , respectively. The results of this study will contribute to future studies of the mechanism of coal and gas outbursts and will provide guidance for the prediction and prevention of outbursts. [ABSTRACT FROM AUTHOR]

The hazard of coal and gas outburst underground is extremely high, with complex influencing factors and uncertain risk categorization. In this case, the traditional regional outburst prediction methods fail to fulfill the demands of spatial risk quantitative distribution, complicating the implementation of targeted regional outburst prevention measures. By combining the matter–element cloud model (MECM) with improved Dempester–Shafer evidence theory, this work proposes a novel regional outburst prediction approach based on the spatial distribution of risk index. First, a 14-indicator risk system (denoted as GCCG in this paper) is constructed using the 50 percent coverage cross-unit division approach from four categories, including gas occurrence, characteristics of coal body, coal seam occurrence structure, and ground stress and concentration, and each indicator, as an independent evidence source, generates basic probability assignments by MECM, which takes into account the contribution of the internal attribute of evidence sources to fusion results through subjective and objective weights. Then, high conflict evidence is filtered using the coefficient K. The Jousselme distance and Euclidean distance (ED) were employed to increase the reliability of evidence sources, thus obtaining comprehensive risk fusion results. The improved Centre of Distribution criterion, which is more suitable for outburst prediction, is developed based on the Centre of Distribution criterion to achieve scientific quantification of outburst risk distribution. Finally, the validity and feasibility of such a prediction method are confirmed by collecting parameters of 294 units divided by field examples, concluding that the improved evidence source of the ED method better satisfies the demand for outburst prediction. [ABSTRACT FROM AUTHOR]

The primary purpose of this paper is to research the law of gas seepage considering gas desorption in heterogeneous coal theoretically. A mechanical model on gas seepage considering gas desorption in heterogeneous coal is established, and the governing equation of gas seepage is discretized by the finite volume method with a new meshing strategy. Moreover, the gas state distribution and change in coal with different heterogeneity are calculated. The numerical results show that the effects of coal heterogeneity on gas seepage and desorption are significant. The coal with high heterogeneity is not accessible for gas to seep in it, resulting in a great gas pressure gradient, which is necessary for an outburst initiation. Additionally, the gas pressure gradient in the coal with high heterogeneity decreases more slowly than that with low heterogeneity. Hence, the possibility of outburst initiation is greater, and the outburst duration may be longer if the coal has high heterogeneity. Due to the strong randomness of the distribution and change of gas velocity in heterogeneous coal, the coal and gas outbursts in the field may be far more complex than that induced in the laboratory by using briquette, which is close to a homogeneous porous medium. [ABSTRACT FROM AUTHOR]

The haulage roadway of the F15-22080 working face, No.8 mine is situated within a special non-uniform stress zone. In this area, the extraction-boreholes drilling process frequently triggers coal and gas outburst. Against this background, this study systematically conducted high-pressure gas adsorption experiments and high-pressure gas desorption experiments on coal samples collected from different stress zones and obtained their adsorption/desorption characteristics. Subsequently, coal pore structure characteristics at various scales were investigated by employing scanning electron microscopy, low-pressure N2 adsorption and low-pressure CO2 adsorption techniques and fractal analysis to assess the impact of varying stress levels. On this basis, a comprehensive analysis was carried out to explore the connections between stress, pore structure, adsorption/desorption traits, and the risk of outburst. The results indicate that, with increasing stress, the Protodyakonov coefficient f and the Langmuir pressure PL decrease, while the index of diffusion initial velocity of coal gas Δp and the Langmuir volume VL increase. The desorption amount and rate of gas also increase significantly. The total pore volume and specific surface area of micropores increase, while those of mesopores and macropores show an overall decreasing trend. The surface fractal dimension DF1 increases by 9%, the spatial fractal dimension DF2 decreases by 5.2%, and the volume fractal dimension DSIE increases by 1%. The induced stress leads to a decrease in the abundance of macropores and mesopores, with concurrent increase in micropores. The VL exhibits a linear increase with the DSIE, whereas the PL demonstrates a linear decrease with it. The initial desorption rate rises with the reduction of the DF2 and the increase of the DSIE. The influence of superimposed-stress on outburst stems from alterations in pore structure and adsorption–desorption capabilities. Simultaneously, it collectively heightened the outburst risk by increasing the gas pressure gradient and weakening the strength of the coal. [ABSTRACT FROM AUTHOR]

Coal and gas outburst is a dynamic disaster that poses a significant threat to coal mines. Energy analysis is an effective tool for understanding the mechanisms behind such outburst. The energy sources and dissipation during outbursts were explored using a multifunctional test system, and the energy transformation relationship was analyzed based on experimental results. Based on these, the crushing mechanism of outburst coal was further investigated. The results show that the adsorbed gas does not all participate in the work during an outburst. Thus, an effective desorption ratio was introduced to characterize quantitatively the percentage of volume of adsorbed gas involved in an outburst. The effective desorption ratios were calculated and found to be in the range of 5.07–13.36% under the test conditions and were primarily related to gas pressure and exhibited an exponential growth relationship. The energy of outbursts generally comes from gas expansion energy, which is 52.7 times that of the elastic strain energy. The gas expansion energy consists of adsorbed gas energy and free gas energy and accounts for 81.6–91.0% of the gas expansion energy, and it is the main energy source for continuous coal fragmentation and transport. The energy conversion of an outburst mainly occurs among gas expansion energy, coal crushing, and transport energy. The energy dissipation under high gas pressure conditions was found to be dominated by crushing energy, whereas under low gas pressure conditions, it was dominated by transport energy. The involvement of ground stress increased the breakage rate of the coal by 23%, whereas the breakage rate of the coal constantly increased with increase in gas pressure. The spatial distributions of the coal mass and crushing power in the roadway were consistent; however, the energy required in the initial stage of coal crushing was significantly larger than that in the middle and final stages. The release and consumption of energy during an outburst are processes of rapid decay from strong to weak. Finally, the processes of preparation, initiation, development, and termination of outbursts are described completely from the perspective of energy evolution, and the roles of ground stress and gas (free gas and adsorbed gas) during outbursts are clarified. The results provide reference ideas and theoretical basis for the accurate identification, effective prevention, and control of coal and gas outbursts. [ABSTRACT FROM AUTHOR]

Understanding the adsorbability and thermodynamic properties of tectonic coal (TC) is crucial to prevent coal and gas outbursts. Limited research has been conducted on the effects of mass ratios of TC because of its high brittleness and sampling difficulty. By investigating the adsorbability, adsorption heat, entropy, and Gibbs evolution during the adsorption of coal samples, it was revealed that the TC content affected directly the adsorption capacity, which increased at first and then decreased. For virgin coal (VC) and TC of equal quality (50% mass ratio), the adsorption quality, adsorption constant a, specific surface area Gibbs free energy, adsorption heat, and adsorption entropy reached their peaks, except the adsorption constant b, which reached the minimum value. Therefore, when TC accounted for 50%, appropriate measures should be applied to mitigate outbursts. Moreover, a comprehensive control model of several factors under various mass ratios of TC was proposed to describe the adsorption characteristics and corresponding thermodynamic property evolutions of TC and VC before coal–gas outburst. The results of this study provide guidance for preventing coal–gas outburst in high-gas mine working faces. [ABSTRACT FROM AUTHOR]