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Coal and gas outbursts are complex dynamic disasters closely associated with gas pressure dynamics and coal damage. An experimental system was established to investigate the effects of water injection on coal particles. The experiments utilized helium (He) and carbon dioxide (CO2) gases, at initial pressures ranging from 0.25 to 1.0 MPa and water injection periods ranging from 0 to 12 days, to measure gas pressure variation, particle size distribution, equivalent diameter, and newly generated surface area. The results indicated that outburst gas pressure follows a power-law decay, with He decaying more rapidly than CO2. Elevated gas pressure and adsorptivity intensified coal particle damage: each 0.25 MPa rise in pressure increased the new surface area by 1.02 times for He and 1.28 times for CO2, with the CO2's surface area being 5.03–5.20 times larger than that of He. Water injection mitigated the damage caused by adsorptive gases; as the injection time increased, the new surface area initially decreased and then increased, with the least damage at 6 days. For every 3 day increase in the water injection time, the average surface area of He-fractured coal increases by 0.69 times. A gas pressure decay model and a coal damage model considering pressure differential tension, gas adsorption expansion, and adsorption-induced strain were developed and validated against experimental results. These findings provide theoretical insights into coal and gas outbursts. [ABSTRACT FROM AUTHOR]

Coalbed methane (CBM) content is a crucial parameter for CBM exploitation and disaster prevention, with accurate gas loss calculation being essential for improving measurement precision. To investigate the physical response to gas loss and quantify the impact and interrelation of various factors, this study developed a comprehensive model incorporating the effects of gas diffusion, temperature, and pressure effects on porosity and coal deformation. By utilizing the OpenFOAM platform and C++ for numerical solution development and establishing an experimental system for gas loss measurement, the model's reliability was confirmed. The new model demonstrates an 8.56% average error, representing a significant improvement over traditional methods, with error reductions of 26.59% and 18.31% compared to the square root of time and power function methods, respectively. The hierarchy of gas loss is determined to be gas flow > gas-coal deformation coupling > gas-temperature coupling > gas-coal deformation-temperature coupling. Average diffusion contributions are identified as 41.43% from surface diffusion, 30.71% from Knudsen diffusion, and 27.86% from viscous flow. The factors affecting gas loss, in decreasing order of impact, are adsorption equilibrium pressure, temperature, porosity, moisture, and adsorption constants. These findings provide theoretical support for enhancing gas content measurement accuracy and techniques, significantly benefiting CBM extraction and mine safety. [ABSTRACT FROM AUTHOR]

The characteristics of coal desorption strain play a crucial role in coal permeability, coalbed methane (CBM) recovery, and the prevention of outbursts. This study developed an improved thermomechanical diffusion–seepage (TMDS) coupling model to investigate the strain evolution during the gas desorption process in coal. The model considers the time-varying diffusion coefficient, the Klinkenberg permeability effect, and the impact of moisture on adsorption, amending the traditional coal deformation equation and coal permeability model. Utilizing this model, the study explored the mechanism, contribution, and spatiotemporal evolution of desorption strain, while analyzing quantitatively the effects of gas types and TMDS parameters on the dynamics of desorption strain. The results demonstrate that desorption strain consists of fracture pressure, matrix pressure, desorption action, and temperature effects, with desorption action being the predominant factor. The impact of gas type, especially CO2, on desorption strain is significant, with CO2 enhancing CH4 desorption strain more than N2. Additionally, the study explored the sensitivity of desorption strain to TMDS parameters, revealing that gas pressure, permeability, and Langmuir pressure significantly impact desorption strain. Desorption strain can serve as an indicator for predicting and evaluating the risk of outbursts, and the injection of low-temperature liquid nitrogen could help reduce this risk. This research provides insights for further understanding the desorption mechanism in gas-bearing coal, improving CBM recovery, and preventing disasters. [ABSTRACT FROM AUTHOR]

Coalbed gas pressure and content are fundamental parameters for mine gas recovery and disaster prevention. In response to the lengthy measurement cycles and low accuracy of existing models, this research proposes a new model for determining coalbed gas pressure and content based on image analysis. Utilizing dual-threshold edge detection and dynamic cycle extraction algorithms, a desorption image database was developed, enabling rapid inversion of gas pressure/content through an enhanced image similarity calculation method and cycle comparison algorithm. Field experiments demonstrate the high accuracy of the image analysis model in determining gas pressure/content, controlling the absolute error of gas pressure below 0.08 MPa and maintaining relative errors of 2.27–8.05%; for gas content, the absolute errors range 0.105–0.674 ml/g, with relative errors of 1.32–8.21%. Compared to previous desorption models, the image analysis model improves accuracy by 6.30% and reduces the measurement time to within 1.5 h, thus facilitating rapid and precise determination of coalbed gas pressure/content. Furthermore, by applying image recognition principles, this study delves into the critical points and significant change areas of the desorption rate curve, providing new insights into gas desorption behavior and expanding the application potential of image analysis technology in coalbed methane recovery. [ABSTRACT FROM AUTHOR]

Coalbed methane (CBM) is a clean energy source, but its utilization is inefficient due to the complexity and low accuracy of its emission prediction model. In this research, we constructed a mathematical model of gas emission from the excavation workface, and combined the experimental results to propose a new model for accurate and concise prediction. The new model was validated in the field workface and compared with the traditional prediction model. Moreover, the sensitivity of gas emission parameters and the participation ratio of gas emission sources were analyzed. The study results show that the new model has higher calculation accuracy than the old model prediction, with an average error reduction of 4.693%. In the excavation workface, the coal fall gas emission conforms to the negative power function equation, and the coal wall gas emission conforms to the negative exponential function equation. In the early stage of excavation, the proportion of coal fall gas emission is higher than that of coal wall gas emission, and the peak proportion reaches 58.5%. In the later stage, the proportion of coal fall gas emission gradually decreases to below 30%. The order of the sensitivity of gas emission parameters is coal wall gas initial velocity > coal fall gas decay coefficient > coal fall gas initial velocity > coal wall gas decay coefficient. The new model is successfully applied in engineering, which helps to improve the efficiency of coal mine gas disaster control and utilization. [ABSTRACT FROM AUTHOR]

Water-based fracturing fluid is a key component in coal bed methane (CBM) extraction, which is a promising way forward for the green extraction of methane. The adsorption by coal is highly affected by tiny particles in the fracturing fluid. Aiming at exploring the effect of mixing non-adsorbent particles into coal on the adsorption, an atmospheric pressure granulated coal adsorption system with a flow meter was designed to perform tests. During the experiments, the effect of coal particle size, coal mass, and addition of tiny granules on adsorption was analyzed. The obtained results show that the addition of iron powder reduces the adsorption capacity and average adsorption rate of granular coal, and makes the adsorption speed peak earlier. It is found that the change in the adsorption amount has a weak positive correlation with the coal particle size, and the change of the average adsorption rate has a weak positive correlation with the size. However, in the absence of iron powder, the average adsorption rate is negatively correlated with the coal size, and the effect of the coal mass on the average adsorption rate and adsorption capacity is very weak. In large granular coal, the adsorption capacity is independent of size. Under the experimental conditions, strong adsorption occurred between 500 and 1750 s, and the adsorption kinetic process showed a slow-fast-slow "S"- curved distribution. [ABSTRACT FROM AUTHOR]

The prediction of dynamic gas emission is of important significance for the prevention of gas accidents. Currently, multifield coupling theory has been applied to gas drainage, but the physical model of gas emission calculation is underused. In our research, a thermo-hydro-mechanical coupled gas emission (THMGE) model was constructed and verified with the results of gas emission in three driven headings. Through calculation, the effects of temperature, time, gas pressure, and tunneling speed on gas emission were analyzed. The research results show that gas emission is controlled by the coupling of the gas migration field, coal stress field, and coal gas temperature field. It is calculated that when the starting temperature is 298–318 K, the average gas emission increases by 3.51–6.13% as the temperature increases by 5 K. For exposure times of 10, 50, and 100 h, the gas emission is 0.47, 0.31, and 0.25 times the starting value, respectively. When the gas pressure is 1.5 and 2.0 MPa, the gas emission is 1.62 and 2.24 times the gas pressure of 1.0 MPa. The correlation coefficient between the model and experimental data is 0.912–0.961 and is successfully applied in the project, which provides a theoretical basis for the control of gas accidents. [ABSTRACT FROM AUTHOR]

The secondary lining failure of deep buried soft rock tunnel often occurs, which is obviously related to the time factor. The formation mechanism of this phenomenon is studied in this paper. Therefore, the combination of in situ stress measurement and neural network inversion is used to analyze the distribution characteristics of in situ stress. At the same time, the creep characteristics of surrounding rock are tested in laboratory, and the key parameters are obtained. Combined with the characteristics of surrounding rock, the calculation model is established by using discrete element simulation technology and considering the joints of surrounding rock. According to the above multiple information, the stress characteristics of the secondary lining in different time periods are analyzed creatively. Finally, the method of setting arch and adding anchor bolt in key parts is proposed, and significant effect results are obtained. [ABSTRACT FROM AUTHOR]

Mine earthquake, as an underground disaster that occurs frequently, has a great impact on coal mine roadway and support. The stability analysis of the bolt support in roadway under different mine earthquake magnitudes is a key issue to be solved urgently in mining fields. This paper attempted to simulate the occurrence state of mine earthquake with explosive blasting process and verified it with actual coal mine microseismic monitoring data. ANSYS/LSDYNA software was used to analyze the impact of magnitude and location of mine earthquake hypocenter on the stability of bolt support and the dynamic stress characteristics of bolt. The results showed that with the increase in source energy of mine earthquake, the damage location of bolt mainly appears in the front of bolt and the loading position has no obvious change, but there is stress wave superposition effect, which deepens the damage of bolt. The bolts in the middle of the lane and the middle of the roof are greatly affected, so the support strength should be strengthened in these places. In addition, this paper compared the safety factor of bolt and the supporting effect of different schemes from three aspects such as roof subsidence, axial stress of bolt, and safety factor of bolt and then put forward a more economical and effective supporting scheme. [ABSTRACT FROM AUTHOR]

Mine disasters, as associated problems in the development of coal resources, always threaten the life safety of miners and the production safety of enterprises. In coal roadway excavation, the coal in front of the excavation face is in a state of concentrated stress and the deformation is serious. The instability of the coal seam under stress is an important cause of the occurrence of coal and gas outburst. Thus, knowing the mechanical characteristics of surrounding rock in front of the working face is of great significance for deep understanding and effective prevention and control of coal-rock dynamic disasters. By analyzing the characteristics of stress evolution and deformation and failure in front of the heading face, the analytical solution of plastic region distribution in front of the heading face is obtained. According to the established mechanical model, MATLAB numerical calculation software is used to analyze different examples. The influence of different mechanical parameters on the stress state of the working face is studied. The influence parameters of the morphological characteristics of the plastic region are determined, and the change law and characteristics of the plastic region in front of the working face are studied. At the same time, through the characteristics of stress field, the working face dynamic risk assessment of coal and rock dynamic disaster can be realized, which can provide a powerful guarantee for the prevention and control of gas dynamic disasters in deep mine. [ABSTRACT FROM AUTHOR]

Coal and gas outburst is a serious disaster in the mining, and crosscut coal is the most prone to cause the coal and gas outburst. In order to study the mechanism of outburst, this paper studied the stress distribution characteristics in front of the working face in the process of rock roadway driving before implementing crosscut coal firstly. On this basis, the hypothesis of stress distribution on the "strong and soft face" of coal-rock mass was proposed. And by using the hypothesis, the mechanical equation for the parameter changes of the plastic zone in front of the working face in crosscut coal was established, and the width and morphological characteristics of the plastic zone in crosscut coal were analyzed. The results show that during the process, as the working face moves forward, the shape distribution of the plastic zone in front of the working face changes from the "semielliptical" to "semibutterfly," And based on the distribution characteristics of plastic zone in working face in crosscut coal, modification proposals for outburst-prevention measures were proposed and provided technical support for the outburst-prevention measures and key parameters setting to prevent the coal outburst in crosscut coal. [ABSTRACT FROM AUTHOR]

In China, safety policies interfere with the occurrence of work accidents in the form of guidance and restrictions. In this study, the impact of types of safety policies on work accident prevention is quantitatively analyzed. Based on a statistical analysis of China's safety policies and work-related accidents from 2000 to 2020, the following four policy indexes that reflect the impact of safety policies are identified: the stringency level of the policy; the scope; its technical content; and its industrial target. A vector autoregressive model (VAR) is used, and a dynamic analysis of the model is conducted with an impulse response function. The model's degree of fit is 92.9%, the number of deaths and the number of safety policies are linearly related, and the relative error between the fitted values and the real values is approximately 5%. The negative correlation between the death rate per 100 million yuan and the stringency level, scope, technical content, and industrial targets of safety policies is first weak, then strengthened, and then weakens again over time. This study finds that the importance of safety policy indicators is different; especially, the strict safety policy has a long-term negative impact on mortality. For developing countries such as China, where the safety policy system is not yet perfect, increasing the number and implementation of safety policies can significantly improve the situation of production safety. [ABSTRACT FROM AUTHOR]