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Aiming at the shortcomings of the “three-rate method” in determining the sensitive indicators for coal roadway outburst prediction and the threat of outburst to personnel during detection, in this paper, a laboratory method for determining the sensitive index and critical value of coal roadway outburst prediction is presented. According to the principle that the apparent density and moisture of simulated soft stratification are consistent with the original coal seam in the field, the forming pressure and pressing steps of simulated soft stratification were determined. Then filling the simulated soft layer with low pressure and high pressure gas, drilling and measuring various coal roadway outburst prediction indexes respectively, the relative sensitivity of each predictor is known and one of the highest predictors of sensitivity can be obtained. Through outburst simulation or measuring the initial release gas expansion energy, the critical value of the index can be determined. Through the application in the coal mine site, it is proved that the prediction index and critical value obtained by this method are effective, and can be directly used in the field coal roadway prediction.

Coal and gas outburst is a dynamic phenomenon with violent eruptions of coal and gas from the working coal seam, resulting in economic loss and casualties. It has been proved that rapid desorption within a short period is necessary for occurrence of an outburst. Due to limitation of the present test condition, gas desorption characterization for the first several seconds (0–10 s) hasn’t been researched sufficiently. In this study, initial desorption characterization of gas in coal is studied by experiments with methane and carbon dioxide. The most remarkable characteristic of the experimental setup is application of a self-developed real-time data acquisition system with time interval of about 1.6 ms, which achieves the goal of collecting enough pressure and temperature data for analysis and calculation. The data is used to study gas pressure variation and calculate initial amount of desorbed gas and initial expansion energy of released gas. From the experimental results, new proof has been found to verify that coal and carbon dioxide outburst is more dangerous than coal and methane outburst. [ABSTRACT FROM AUTHOR]

The gas pressure of a coal seam is one of the important parameters for studying gas reserves, law of gas flows, gas emissions, predicting coal and gas outburst risks and developing gas-control measures. In this study, the effects of the depth of the borehole drilled in a coal seam on the time required to determine the gas pressure and its value were discussed. Accordingly, elastic-plastic mechanics were applied to analyze the variation in the stress around the borehole, and the effective flow radii expressions of the spherical and radial flow boreholes were derived. The COMSOL Multiphysics numerical simulation software, was used to simulate the gas-flow range of the boreholes drilled at different depths in a coal seam, which were exposed for approximately 2 h. Finally, the boreholes of different depths was used to determine the gas pressure of No. 二 2 coal seam in the Xuehu coal mine (Henan Province, China). The results show that the time required in measuring the gas pressure is longer for boreholes drilled to a greater depth in a coal seam. For the same exposure times, the determined gas-pressure value will be smaller. Furthermore, the confined water and fractures in the roof and floor of the coal seam can be sealed by injecting high-pressure slurry into the borehole, which provides a reference for determining the gas pressure of the coal seam quickly under different geological conditions in future studies. [ABSTRACT FROM AUTHOR]

The law of gas initial desorption from coals is greatly important for understanding the occurrence mechanism and predicting coal and gas outburst (hereinafter referred to as 'outburst'). However, dynamic characterization of gas initial desorption remains to be investigated. In this study, by monitoring the gas pressure and temperature of tectonically deformed (TD) coal and primary-undeformed (PU) coal, we established the evolution laws of gas key parameters during the initial desorption. The results indicate that the gas pressure drop rate, mass flow rate, initial desorption rate, and gas velocity increase with increasing gas pressure, with stronger gas dynamic effect, generating a high pressure gradient on the coal surface. Under the same gas pressure, the pressure gradient formed on the TD coal surface is greater than that formed on the surface of the PU coal, resulting in easily initiating an outburst in the TD coal. Moreover, the increased gas pressure increases temperature change rates (falling rate and rising rate) of coal mass. The minimum and final stable temperatures in the TD coal are generally lower compared to the PU coal. The releasing process of gas expansion energy can be divided into two stages exhibiting two peaks which increase as gas pressure increases. The two peak values for the TD coal both are about 2–3 times of those of the PU coal. In addition, the total gas expansion energy released by TD coal is far greater than that released by PU coal. The two peaks and the total values of gas expansion energy also prove that the damage of gas pressure to coal mass increases with the increased pressure, more likely producing pulverized coals and more prone to initiate an outburst. [ABSTRACT FROM AUTHOR]

Highlights • Gas pressure drop rate is lower with tectonically-deformed coal. • The time to release 90% of gas expansion energy is shorter compared to gas energy. • The total gas expansion energy accounts for about 14%–16% of the total gas energy. Abstract Coal and gas outbursts (hereinafter, collectively referred to as 'outbursts') often last for just a few tens of seconds and occur mostly in gas-bearing tectonically-deformed (TD) coal. It has been proved that, in comparison to primary-undeformed (PU) coal, TD coal is more susceptible to outbursts due to its lower mechanical strength, stronger gas-adsorption capability, and faster gas-desorption rate. At the same time, the energy required for the outburst process is mainly provided by the gas. However, the characteristics of the gas-desorption behavior and gas-release energy in TD and PU coal during the first dozen seconds or so have rarely been studied. In this study, gas desorption experiments were carried out on TD and PU coal at different gas pressures using self-assembled desorption equipment. The experiments focus on roughly the first 13 s. The results show that the drop rate of gas pressure is lower with TD coal compared to PU coal, while the gas desorption rate is higher for TD coal compared to PU coal. Most of the gas is released from the two types of coal in the first few seconds. For both TD and PU coal, the time taken to release 90% of the total gas expansion energy (TGEE) is shorter than that to release 90% of the total gas energy (TGE). At the different gas pressures used, the TGEE of the two types of coal accounts for about 14–16% of the TGE. The higher the gas pressure is, the greater the TGEE released by the coal samples gets, and thus the larger the TGEE: TGE ratio becomes. Although the TGEE released from the TD coal is about 3 times that released from the PU coal, it accounts for a slightly smaller proportion of the TGE compared to that in the PU coal samples. [ABSTRACT FROM AUTHOR]

Coal and gas outburst accidents occurring in underground coal mines generally cause great casualties and economic losses, especially in construction areas of coal seams where the outburst risks are not accurately evaluated. Therefore, accurately identifying the outburst risks of coal seams is necessary and critical to prevent and control outbursts. In order to improve the prediction accuracy for outbursts in working faces of coal roadways, a self-designed drilling device that can simulate the in-situ outburst prediction of coal roadways was used in this study. We used the coal samples with different coal ranks to adsorb CO 2 and N 2 with different pressures in the laboratory, so as to simulate the coal seams with different outburst risks. Finally, boreholes for predicting the outburst risk were drilled in the simulated coal seams to study the correlation between common dynamic phenomena (e.g. gas and coal being ejected from the borehole (GCEB) and drill pipe being stuck by coal mass in the borehole (DPSC)) and outburst risks. The results show that the greater the outburst risks of coal seams, the more frequent the occurrence of GCEB and DPSC is. The GCEB phenomenon for outburst prediction is attributed to small-sized coal and gas outbursts in boreholes, while the occurrence of DPSC phenomenon does not affirm that there definitely are outburst risks on working faces. The DPSC phenomenon indicating outburst risks is generally accompanied with GCEB, which form a linkage system and are triggered successively. [ABSTRACT FROM AUTHOR]