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From their perspective the optimal tapping process would be when slag and metal are drained from the furnace at the same rate as being produced and separated in the post tap-hole process. Tangstad et al I . i discussed the optimal tapping process for manganese ferroalloy production in submerged arc furnaces (SAFs) in their paper "Conceptual tapping model of Mn-ferroalloy furnaces". J. D. Steenkamp and Q. G. Reynolds are the Guest Editors for the Furnace Tapping topic in the November 2022 issue of JOM. [Extracted from the article]

Among all methods for investigating the complex phenomenon of the coal and gas outburst, numerical modelling is the most comprehensive one that can consider all involved parameters and simulate the complex multi-physical phenomenon. The main aim of this paper is to review recent numerical modelling studies concerning this disastrous phenomenon observed in coal mining. The paper aims to analyse these studies comprehensively and identify any existing research gaps that could be addressed in future research endeavours. To this end, the concepts and equations that have been used in previous studies to simulate the solid and fluid behaviour during outburst initiation and how these equations are coupled to consider multiphysical interactions were reviewed. Both strengths and deficiencies in past outburst modelling work were highlighted. Finally, potential research topics for future studies were discussed in three categories; looking into the outburst phenomenon in the scale of the particles which is mostly focused on the discrete element method, conservation of the energy as a method to quantitively assess outburst initiation, and the application of statistics in both applying the heterogeneity in the models and assessing the possibility of the outburst occurrence. [ABSTRACT FROM AUTHOR]

In recent years, coal and gas outburst disasters are still occurring and difficult to prevent, seriously endangering the safety of coal mine production. It is well known that the transporting and crushing of outburst coal is the main pathway of energy dissipation during the coal and gas outburst process. However, a consensus regarding how much gas involves in outburst and affects energy dissipation is still lacking. Quantitative study on the gas effect on migration and fragmentation characteristics of outburst coal in restricted roadway space can improve the energy model and guide the prevention and control of gas outburst. In this paper, an improved visual coal and gas outburst dynamic effect simulation experiment system was used to conduct outburst simulation experiments at different gas pressure conditions. The results showed that the movement of outburst coal in the roadway has experienced various flow patterns. In the initial stage of the outburst, under low gas pressure condition, the motion of the outburst coal was dominated by stratified flow. However, as the gas pressure increases, the initial acceleration increases, and the outburst coal mainly move forward rapidly in the form of plug flow. The average velocity at 0.3, 0.5, and 0.8 MPa gas pressure condition were 6.75, 22.22 and 35.81 m/s, respectively. Gas also has a crushing effect on outburst coal. With increasing gas pressure, the number of coal powder particles of the same mass increased significantly, and the range of the particle size distribution of the particles decreaed, and the median particle size decreased. As the gas pressure increases, the outburst intensity gradually increases, and the total energy involved in the outburst work also increases. However, the energy dissipation pathways are different. At 0.3 MPa, the energy dissipation is dominated by crushing energy, which is about six times the ejection energy. As the gas pressure increased to 0.8 MPa, the proportion of the ejection energy gradually increases to about twice that of the crushing energy. Under the experimental conditions, 2.71–13.43% of the adsorbed gas involves in the outburst (AGIO) through rapid desorption, and the proportion increases with increasing gas pressure. This paper improves the energy model of coal and gas outburst, which is applicable to risk assessment and prevention of outburst disasters. [ABSTRACT FROM AUTHOR]

Hydraulic fracturing is extensively utilized for the prevention and control of gas outbursts and rockbursts in the deep sections of coal mines. The determination of fracturing construction parameters based on the coal seam conditions and stress environments merits further investigation. This paper constructs a damage analysis model for coal under hydraulic loads, factoring in the influence of the intermediate principal stress, grounded in the octahedron strength theory analysis approach. It deduces the theoretical analytical equation for the damage distribution of a coal medium subjected to small-flow-rate hydraulic fracturing in underground coal mines. Laboratory experiments yielded the mechanical parameters of coal in the study area and facilitated the fitting of the intermediate principal stress coefficient. Leveraging these datasets, the study probes into the interaction between hydraulic loads and damage radius under assorted influence ranges, porosity, far-field crustal stresses, and brittle damage coefficients. The findings underscore that hydraulic load escalates exponentially with the damage radius. Within the variable range of geological conditions in the test area, the effects of varying influence range, porosity level, far-field stress, and brittle damage coefficient on the outcomes intensify one by one; a larger hydraulic load diminishes the impact of far-field stress variations on the damage radius, inversely to the influence range, porosity, and brittle damage. The damage radius derived through the gas pressure reduction method in field applications corroborates the theoretical calculations, affirming the precision of the theoretical model. These findings render pivotal guidance for the design and efficacy assessment of small-scale hydraulic fracturing in underground coal mines. [ABSTRACT FROM AUTHOR]

Saturation characteristics of water and capillary pressure are important for hydrofracturing or water flooding, which is widely adopted in dust suppression, methane displacement, and gas and coal outburst elimination. In this paper, we have studied the water saturation characteristics of coal samples with different coal ranks and their effect on capillary pressure. It was found that the isothermal adsorption of water vapor from coal samples can be divided into three processes: monolayer adsorption, multilayer adsorption, and capillary condensation. The dent isothermal adsorption model can well describe water vapor adsorption of coal samples, indicating water molecules were first adsorbed on the first‐order adsorption site of pore surfaces at low relative humidity and then on the second‐order adsorption site with increasing relative humidity. An obvious hysteresis occurred in the process of water imbibition and drainage. A capillary pressure of ~325 MPa or even larger was required to displace the water from the coal. Besides, micro‐ and mesopores play a more important role in capillary pressure. The capillary pressure of coal samples was positively correlated with wettability at lower water saturation, but it is not significant at higher capillary pressures. Therefore, the article's results provide a new direction for solving the water‐locking effect in coal seams. [ABSTRACT FROM AUTHOR]

To study the effects of gas hydrates on the prevention and control of coal and gas protrusions, this paper reports the results of acoustic emission experiments on coal bodies containing gas hydrates with different saturation levels. The results showed that few acoustic emission events were generated in the elasticity stages of coal bodies containing gas hydrates, and the first sudden increase in the number of ringing counts generally occurred before and after the yielding point. Additionally, the acoustic emission events in the yielding stage were more active, and the cumulative number of ringing counts increased faster. The peak ringing counts appeared around the damage point, and a small number of acoustic emission events were still generated after destruction of the coal samples. The cumulative ringing counts decreased linearly with increasing saturation. The effect of saturation on the cumulative ringing counts in the elasticity stage of the gas hydrate-containing coal samples was small, but the difference between the cumulative ringing counts in the yielding stage and those in the destruction stage was larger. The total cumulative ringing counts and the cumulative ringing counts during each stage for the gas hydrate-containing coal samples decreased with increasing enclosure pressure. The energy and amplitude of the loading process were consistent with the trend for the ringing counts. The acoustic emission ringing counts of gas-containing coals were greater than those of gas hydrate-containing coals in the yielding and destructing stages. [ABSTRACT FROM AUTHOR]

With the continuous increase of mining depth, coal and gas outburst poses a significant threat to mining safety. Conducting research on the mechanisms of coal and gas outbursts contributes to understanding the evolutionary process of such incidents, thus enabling accurate prediction and prevention of coal and gas outbursts during mining operations. This paper has developed a comprehensive visual experimental system that is specifically tailored to simulate diverse coal body conditions, ground stress and gas pressures. By monitoring and analyzing the real-time progression of coal fissures during the outburst process, we can obtain valuable insights into the evolution and mechanisms of coal and gas outbursts. Additionally, this study introduces a method to determine the critical threshold for predicting coal and gas outbursts, and the critical gas pressure threshold for Jiulishan Coal Mine (Jiaozuo City, Henan Province, China) is established at 0.6 MPa. [ABSTRACT FROM AUTHOR]

Mining-induced disturbance to stress fields can lead to many engineering disasters such as rock bursts, roadway collapses, and coal and gas outbursts. The evolution characteristic of abutment pressure during the mining process is of great significance for prevention of engineering disasters. Based on a case study of No.12526E Panel in Xieqiao coalmine of Huainan mining area in China, this paper investigated the evolution characteristic of abutment pressure during the retreat mining process. A field measurement was performed using three-dimensional (3D) pressure sensor, and the abutment pressure was continuously monitored during the mining process. The monitoring results indicate that the abutment pressure curve can be divided into strong interference area and weak interference area. Further, the evolution characteristics of abutment pressure during the retreat mining process were simulated using a 3D discrete-element program. Periodic caving characteristics of rock strata were obtained, and the major causes of stress concentration and the bearing stress inflection point were analyzed. With the periodic caving of the overlying strata, the stress inflection point appears, and fracture cracks are generated and hinder stress recovery. Finally, the detailed dynamic evolution process of the abutment pressure as well as the deformation and caving characteristics of the overlying strata of the No.12526E Panel were analyzed. The coal and rock near the mined-out area undergo a sharp stress concentration and reduction, which would lead to damage to the rock mass near the mined-out area. [ABSTRACT FROM AUTHOR]

The shock wave of a coal and gas outburst is a high-pressure and high-speed impact airflow formed rapidly after the outburst. The propagation destroys the ventilation facilities and causes the destruction of the ventilation system. The theoretical research on the outburst shock wave is of great significance. In order to deeply understand the formation mechanism of the outburst shock wave, this paper draws on the shock wave theory to theoretically analyze the microscopic formation process of the outburst shock wave. The main difference between the formation process of a coal and gas outburst shock wave and the formation process of a general shock wave is that the outburst shock wave has a solid–gas flow zone in the high-pressure zone. The calculation formulas of pressure, density, temperature and other parameters before and after the outburst shock wave are derived. After the outburst shock wave passes through, the pressure, temperature and density of the roadway air will change suddenly. The relationship expression between outburst gas pressure and outburst shock wave intensity is derived, which can reflect the role of pulverized coal in the formation process of a shock wave. In order to facilitate the understanding and calculation, the concept of equivalent sound velocity of coal-gas flow is proposed, and the direct calculation of the impact strength of a coal and gas outburst is attempted. This paper is helpful to improve the understanding of the essence of a coal and gas outburst shock wave. It is also of great significance to outburst disaster relief. [ABSTRACT FROM AUTHOR]

Highlights: What are the main findings? The 3D stress distributions around the gob after mining are numerically calculated. What is the implication of the main finding? The propagations of hydraulic fractures in different disturbed areas caused by mining-induced stress are compared. The influence of the geological conditions that often appear in situ in hydraulic fracturing patterns in a hard roof is examined. A hard roof can cause serious issues corelated with the stability of the panel including large deformation of the roadway in the gob, rock burst, coal and gas outbursts, etc. Currently, hydraulic fracturing has ever-increasingly been used to help control these above-mentioned issues in many engineering cases. This paper presents a series of numerical simulations for hydraulic fracturing with a recently developed model to examine the weakening effect of this pre-conditioning measure on a hard roof. The results show that large deflections in the principal stress direction occur above the coal seam after mining, which can be progressively enhanced as the working face continuously advances. This further could significantly affect the hydraulic fracturing pattern and result in arc-shaped fracture propagation, especially for the hydraulic fracture in stress-descending areas. The obtained results suggest that the hydraulic fracturing operation in a hard roof is preferable in the areas close to the middle of the gob where the created fractures would be deflected more. At last, sensitivity analysis shows that geological conditions have great influence on the hydraulic fracturing pattern. Among the factors analyzed in this paper, the difference between the maximum and minimum stress has the largest influence and should be fully considered. This study could provide a theoretical basis for the practical hydraulic fracturing operation in a hard roof. [ABSTRACT FROM AUTHOR]

Coal and gas outburst is one of the main dynamic disasters in coal mine production. In order to deeply understand the overall research progress in the field of coal and gas outburst, the Web of Science (WOS) database is used as the sample source, and the bibliometric analysis of the literature in the field of coal and gas outburst from 2000 to 2021 is carried out by CiteSpace software. The knowledge maps of the publication quantity, country, institution, and keyword cluster are drawn. The results show that the time distribution has gone through three stages of germination period, development period, and growth period. In terms of the cooperation network, China, Australia, and the USA are the main core research countries, while China University of Mining and Technology, Chongqing University, and Henan Polytechnic University are the main core research institutions, and the main core journals are IGCG, IGRMM, and Fuel. By drawing the knowledge map of keywords timeline, the evolution law of keywords in the field of coal and gas outburst with time is obtained. Taking keywords as the object, cluster labels with gas outburst, gas extraction, gas control, and pore structure as the core are presented. On this basis, from a new perspective, this paper outlines the "scientific research landscape map" in the field of coal and gas outburst, in order to provide a scientific reference for coal and gas outburst research. [ABSTRACT FROM AUTHOR]

Accurate and rapid prediction of the coal and gas outburst is very significant for preventing accident and protecting environment, the paper presents a novel feature selection and outburst classifier framework which can identify effective candidate features and improve the classification accuracy. First, Apriori is applied for preliminarily extracting the association rules from sample data and attribute features in coal and outburst, and it can present the effective sample data and features for outburst prediction. Second, in order to reduce the redundancy of the strong association rules obtained from Apriori, Boruta is applied for selecting all highly relevant optimal features based on the obtained strong association rules. Third, Random Forest(RF) is used to assign different weights to different features in optimal candidate features considering the importance of different features to outburst, based on the above obtained high-quality sample data and optimal features, the parameters of KNN model optimized by Bayesian Optimization(BO) is used to predict the coal and gas outburst. The experimental results show that the proposed feature selection model Apriori-Boruta can obtain significant sample data, and the proposed RF-KNN optimized classifier model can achieve higher performance in terms of the number of optimal features and prediction accuracy compared with traditional prediction models. [ABSTRACT FROM AUTHOR]

Featured Application: The XGBoost–GR–stacking gas outburst early warning model established in this article demonstrates high accuracy and practical performance, making it suitable for gas outburst risk warning in mining safety. To improve the accuracy of gas outburst early warning, this paper proposes a gas outburst risk warning model based on XGBoost–GR–stacking. The statistic is based on gas outburst data from 26 mines and establishes a data generation model based on XGBoost. The obtained virtual datasets are analyzed through visualization analysis and ROC curve analysis with respect to the original data. If the augmented data has an ROC area under the curve of 1, it indicates good predictive performance of the augmented data. Grey correlation analysis is used to calculate the grey correlation degrees between each indicator and the "gas emission". The indicator groups with correlation degrees greater than 0.670 are selected as the main control factor groups based on the sorting of correlation degrees. In this study, SVM, RF, XGBoost, and GBDT are selected as the original models for stacking. The original data and virtual data with correlation degrees greater than 0.670 are used as inputs for SVM, RF, XGBoost, GBDT, and stacking fusion models. The results show that the stacking fusion model has an MAE, MSE, and R2 of 0.031, 0.031, and 0.981. Comparing the actual and predicted values for each model, the stacking fusion model achieves the highest accuracy in gas outburst prediction and the best model fitting effect. [ABSTRACT FROM AUTHOR]

Gas extraction quantity from coal seam is the key index to evaluating the effect of eliminating coal and gas outbursts. The prerequisite for increasing the gas extraction quantity and improving the effect of gas control is to make clear the influencing factors of gas extraction. The main factors affecting gas extraction are permeability, gas pressure, and buried depth of coal seam in this paper. The qualitative and quantitative analyses of gas extraction quantity by three factors are carried out according to the test data. The research results show that: (1) In the areas with high permeability and gas pressure, the gas extraction volume shows random characteristics, indicating clear regional differences. (2) The increase of buried depth of coal seam will reduce the fluctuation of gas extraction quantity, resulting in a lower extreme value of gas extraction quantity. The possibility of gas extraction at a lower level will be significantly increased. (3) The correlation analysis shows the change law of the positive correlation coefficient between gas extraction quantity, gas pressure, and permeability, and shows the opposite trend with the increase of the buried depth of coal seam. The results show an important guiding significance for improving the efficiency of gas control. [ABSTRACT FROM AUTHOR]

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 coal mine in deep mining can easily form a compound dynamic disaster with the characteristics of rock burst and gas outburst. In this paper, the analytic hierarchy process (AHP) and the entropy weight method (EWM) are combined, and the fuzzy comprehensive evaluation (FCE) secondary evaluation model of compound dynamic disaster is proposed to evaluate the risk of compound dynamic disaster, which avoids the problems of the imperfect evaluation index system and strong subjectivity of index weight. Based on the statistical analysis of typical compound dynamic disaster cases in China, three first-level indicators were established, and sixteen second-level indicators were developed. The verification results show that the accuracy and weight are better than the traditional evaluation methods. Combined with geological and mining data, the compound dynamic disaster risk assessment was carried out on the second mining area of mine B, in the Pingdingshan mining area, and the result was grade II (weak risk). Corresponding prevention measures and parameters were implemented, and no compound dynamic disaster occurred during the working face excavation. [ABSTRACT FROM AUTHOR]

The surrounding rock during a coal mine excavation is prone to significant engineering disasters such as considerable deformation and rock bursts. Pressure release can improve the stress field of a deep rock mass and prevent the occurrence of dangers such as roadway collapse and coal and gas outbursts. This paper uses the ANSYS 19.0/LS-DYNA finite element software to simulate the crush area and fracture zone of a detonation charge with different diameters under in situ stress. The stability of the surrounding rock was analyzed based on the impact stress and velocity, and was verified by field tests. The research results show that the blasting load primarily affects the damaged area near the borehole, while the in situ stress affects far-field crack propagation. The crack propagates in the direction of high surrounding rock pressure. When the uncoupling index is 1.5, the impact pressure of a 60 mm diameter cartridge is eight times that of a 20 mm diameter cartridge. The impact speed can reach two times that of the 20 mm diameter cartridge. The high-energy event at the roof is transferred to the front of the working face, the distribution is no longer concentrated, and a better pressure-relief blasting effect is achieved. The research results can help guide the prevention and control measures of rock bursts and other mining disasters. [ABSTRACT FROM AUTHOR]

Coal and gas outbursts are some of the most serious coal mine disasters, and effective prediction of coal and gas outbursts can reduce the likelihood of accidents and fatalities. Previously conducted studies have established that machine learning has achieved results in the prediction of coal and gas outbursts, but there is a problem that the available accident data of coal and gas outbursts are diminished or missing. This paper proposes a prediction model based on multiple filling of chained equations for random forests (miceforest) and the Harris Hawk optimization algorithm with Piecewise chaos mapping (PHHO) to optimize the kernel extreme learning machine (KELM) to solve the problem of missing data in coal and gas outburst prediction and to improve prediction accuracy in the case of missing data. Firstly, the miceforest algorithm was adopted to fill missing values in the salient samples, and then the PHHO algorithm was used to optimize the parameters of KELM. Finally, the datasets before and after filling were input into the PHHO–KELM model for experimentation and comparison with other models. The results show that miceforest filling is effective in improving the salient sample accuracy and overall accuracy of predictions, but the improvement is not significant for non-salient samples. The use of the PHHO–KELM model can effectively avoid falling into a local optimum and further improve the prediction accuracy of the KELM algorithm. The salient sample accuracy and overall accuracy of the miceforest–PHHO–KELM model prediction are 96.77% and 98.50%. And an effective coal and gas outburst model has been proposed, which is the miceforest–PHHO–KELM model. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Mine Automation is the property of Industry & Mine Automation Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Rock and gas outbursts occur most frequently in coal mining. Gas-induced geodynamic events in dolomite are a new and unexplored phenomenon. In the last time, two outbursts of gas and dolomite have occurred in the Legnica-Głogów Copper Region in southwestern Poland, which is one of the world's largest copper ore mining regions. Gas-induced geodynamic events are dependent on the co-occurrence of two factors: rock porosity, and the presence of gas under significant pressure in the pores and crevices of the rock. This paper presents a condensed energy balance for the phenomenon of outbursts of dolomites and gases. The quantity of energy depends on the type of transformation taking place during decompression. The work produced enables first the disintegration of the rock, and then its transportation along the mine working space. This paper has focused on the estimation of the energy required to disintegrate the rock. It has been estimated that 0.38 MJ is needed for the size reduction of 1 m3 of ejected mass. Highlights: In the case of a dolomite outburst, the energy is accumulated primarily in the form of compressed gas present in the porous structure of the rock and causes the rock to disintegrate and its transport along the mine working space. Gas decompression during a gas-induced geodynamic phenomena can be between isothermal and adiabatic. Existing disintegration theories: Rittinger's, Kick's and Bond's are based consists chiefly of crushing, compression or abrasion, caused by the action of external factors. Author's theory of disintegration of research on tensile stress and is based on Brazilian tests. The disintegration of 1 m3 of rock requires the production of energy of approximately 0.38 MJ. [ABSTRACT FROM AUTHOR]

Pore structure characterization plays key role in efficient development of petroleum, natural gas and shale gas, and it also holds important place in the evaluation of gas outburst and rock weathering damage. In this paper, a high-precision, nondestructive, and repeatable method for characterizing pore size distribution of rock is proposed. By taking sandstone, marble, granite, and rock-like samples as object, capillary pressure curves derived from the transverse relaxation time and centrifugal results are acquired based on the nuclear magnetic resonance test and centrifugation test. The pore size conversion coefficients are obtained through capillary pressure curves fitting, and they are compared with the value gained by the other two methods. Results show that the pore size conversion coefficients of sandstone, marble, granite, and rock-like specimens calculated by the proposed method are 0.483 μm/ms, 0.583 μm/ms, 0.253 μm/ms, and 0.077 μm/ms, respectively. These pore size distribution curves obtained by the proposed method are quite close to curves obtained by the other two methods. One defect of this method is that it cannot obtain complete capillary pressure curves. Overall, it provides a new idea and path for characterizing pore structure accurately and repeatedly. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Tectonically deformed coal (TDC) is closely related to gas outbursts. Since TDC exploration is an essential objective for coalfield exploration, it is of great significance to study the petrophysical properties of TDCs and explore their differences. This study collected 17 TDCs and undeformed coal samples from the Huaibei coalfield and ultrasonically tested their petrophysical parameters, including densities, P- and S-wave velocities, and their derived petrophysical parameters (VP/VS ratio, P- and S-wave impedances). Undeformed coal and TDCs with different deformation types (brittle, shear, and plastic deformations) show significant differences in their petrophysical parameters, and cross-plot analysis can directly differentiate them. As with traditional geological methods, acoustically measured petrophysical parameters are good indicators to determine the type of coal deformation. However, the TDCs with the same deformation type have similar petrophysical parameters; it is not easy to distinguish them directly. Instead, the proposed method incorporating principal component analysis and clustering can accurately distinguish up to five classes of TDCs. Different types of tectonic deformation environments and their intensities are highly correlated with the clustering results. This paper also provides essential petrophysical parameters for undeformed coal and TDCs in the Huaibei coalfield, and these parameters can help interpret undeformed coal and TDCs using wireline logs and seismic data. [ABSTRACT FROM AUTHOR]

Copyright of Coal Geology & Exploration is the property of Xian Research Institute of China Coal Research Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The overburden rock mining fissures are the main cause of coal spontaneous combustion, gas pooling, and mine water inrush caused by goaf air leakage. Rapid and accurate determination of the development and evolution law of mining fissures have great significance for the application of coal spontaneous combustion prevention and control, gas disaster prevention and control, and water damage prevention and control measures. In this paper, a preliminary judgment of the development height of the water-conducting fracture zone is made based on the theoretical analysis, and the physical model size of the numerical simulation is determined according to its judgment result. It is judged that the development height of its water-conducting fracture zone is between 49 and 64.2 m, which is in line with the actual results. Based on this, a three-dimensional solid model was established in PFC (Particle Flow Code) software to analyze the fissure development pattern of the overburden rock and the development height of the water-conducting fracture zone when the main key stratum of the rock seam is in different positions by simulating the excavation process of the coal seam. The results show that when the main key stratum is located in the "original crack belt boundary," the development of water-conducting fracture zone is significantly inhibited; when the main key stratum is located in the "original caving zone," the water-conducting fracture zone is fully developed, and the crack belt finally develops to the top of the model. In order to verify the accuracy of the numerical simulation, similar material simulation experiments were performed under the same scheme. The results are consistent with the numerical simulation conclusions, effectively verifying the accuracy of the numerical simulation. Finally, the extraction of porosity of the goaf was carried out based on numerical simulation, and the permeability zoning of the goaf was performed; the results show that the development of the water-conducting fracture zone has a significant influence on the permeability of the mining area, and the more fully developed the fissure is, the greater is its permeability. In this paper, the fissure development law in the goaf under different key stratums is explored by various research stratums, and the results show a good consistency, which provides a scientific basis for the prevention and control of disasters such as water inrush and coal and gas outburst in mines, and provides theoretical guidance for safe mining. [ABSTRACT FROM AUTHOR]

Outburst of coal and gas is a major hazard in underground coal mining where coal seam gas content/pressure is high. A cone‐shaped cavity is often observed in the coal seam after bursting, implying the likely mechanical structure being formed during outburst propagation. Although the mechanism for outburst initiation and propagation is very complex, mining‐induced fracturing and damage of the coal material is an essential component. This paper investigates the mechanical conditions that are essential to initiate fractures around a spherical cavity, a simplified form of the cone‐shaped outburst cavity. The cavity is assumed to be situated in an infinite isotropic homogeneous elastic body under internal gas pressure and far‐field hydrostatic compressive stresses as a further simplification for analytical investigation. The analytical conditions under which circumferential and radial fractures can initiate around the cavity are formulated, based on extensional strain criterion for fracture initiation. Low internal pressure on the cavity surface and high far‐field compression lead to circumferential fractures. In contrast, high internal pressure and low far‐field compression lead to radial fractures. Subsequent numerical simulations with FRACOD3D and FRACOD, the 3D and 2D in‐house fracture simulation codes, were carried out to investigate fracture patterns around a cavity and inclusion. The simulation results confirmed the analytical results, including fracture shapes and the size of fractured zone. These results provide a new angle to understand the complex mechanism of outbursts. [ABSTRACT FROM AUTHOR]

Coal and gas outbursts are anthropogenic hazards that can be divided into four stages: preparation, occurrence, development, and termination. Studying the influence of gas on coal damage and energy changes during the formation of outbursts is highly important for investigating the entire hazard. In this paper, laboratory experiments were performed on samples. The energy changes and failure mechanism of coal under different gas pressures were revealed, and a seepage model was established based on compressibility and adsorption to investigate gas-induced coal damage. The results demonstrated that gas pressure caused initial damage within the coal, resulting in nonlinear deformation and strength deterioration of the coal. Gas-induced damage affected the energy evolution mechanism of coal under loading, as pressure caused the premature release of energy at the tips of internal microcracks and reduced the ability to accumulate energy. These changes increased the proportion of dissipative energy under unstable conditions. The combined acoustic emission (AE) parameters—rising angle (RA) and average frequency (AF)—were used to study the fracture mode of gas-containing coal. As the gas pressure increased from 0 to 4 MPa, the RA–AF distribution pattern changed from tensile failure to tensile–shear composite failure, with the proportion of shear cracks increasing from 0.30% to 25.44%. As the complexity of the crack network increased, the randomness of crack propagation increased, and the fracture surface roughness parameters, arithmetic mean height S a , root mean square height S q , and maximum height S z increased by 90.33%, 94.02%, and 81.70%, respectively. These findings could contribute to a comprehensive understanding of the underlying mechanism of coal and gas outbursts and guide for predicting and preventing these hazards. [ABSTRACT FROM AUTHOR]

The global coal industry, as an important basic industry, has strongly supported the stable and rapid development of the international economy and society. Although the level of automation in the context of coal mining has reached a very high degree, coal mine accidents such as roof collapse, side falling accidents, gas outburst potential, etc. continue to take place. Therefore, lots of intelligent systems are installed into collieries. For example, intelligent safety analysis technology represented by deep learning has been widely implemented in coal mine safety. The intelligent coal mining applications are always computing resource sensitive. They are usually deployed in the cloud centres that are located on the ground. As we all know, coal mining applications such as coal mine safety requires a comprehensive consideration of the mining, transportation, ventilation, hydrology, geology and other integrated factors. The transmission of all detecting data about these factors especially for multimedia from the underground face to the cloud computing centre is time-consuming. However, coal mine accidents always happen in a short span of time. This long transmission time is unacceptable for coal mine safety. In this paper, we propose a novel edge computing based intelligent processing architecture that integrates Internet of Things (IoT), fifth generation (5G), and Edge computing technologies for the coal mining intelligent system. Experiments are conducted on a deep learning based video fire prediction algorithm to prove the effectiveness of the architecture [ABSTRACT FROM AUTHOR]

In this study, coal and gas outbursts are the "biggest killer" of mine safety production. With the deepening of mining, the mine gas disaster is becoming more and more serious. From the perspective of big data, the establishment of a dynamic visualization system of gas geology integrating gas geology, gas drainage, dynamic outburst prevention, and other information can effectively improving the defects of gas disaster prevention and control in the coal industry, such as insufficient advance, lack of systematic identification methods and backward information collection methods, which is of great significance to improve the ability of gas hazard identification. Based on the precise detection of geology, structure, and gas, this paper proposes to use information technology, the Internet of things, big data analysis, and other technologies to comprehensively analyze the changes in gas occurrence and coal seam occurrence on the basis of the causes of mine gas geological outburst, fully consider the logical relationship between different factors and outburst and adopt the disciplinary advantages of grey theory, fault tree theory, BP neural network, and so on. The tree of coal and gas outburst accidents with general significance is constructed by 24 relatively independent factors. The input vector is determined as the matrix composed of eight main factors affecting and controlling outburst, including gas pressure, coal mechanical strength, comprehensive characteristic coefficient of coal fragmentation, the permeability coefficient of coal, comprehensive characteristic coefficient of coal seam bifurcation and combination, comprehensive characteristic coefficient of coal thickness and coal thickness change, fault complexity coefficients and interlayer sliding comprehensive characteristic coefficient. The geological data affecting coal and gas outbursts are analyzed and calculated scientifically so that the gas geological data can be updated in time, and the change of gas geological laws is presented dynamically, so as to guide the mine to predict the gas disaster more scientifically and reliably. [ABSTRACT FROM AUTHOR]

Coal mines may change from non-outburst mines into coal and gas outburst mines with increasing mining depth. Therefore, scientific and rapid prediction of the coal seam outburst risk and effective prevention and control measures could ensure coal mine safety and production. This study aimed to propose a solid–gas–stress coupling model and assessed its applicability in predicting the coal seam outburst risk. Based on a large amount of outburst case data and the research results of previous scholars, coal and coal seam gas constitute the material basis of outbursts, and gas pressure is the energy source of coal seam outbursts. A solid–gas–stress coupling model was proposed, and a solid–gas–stress coupling equation was established via regression. Among the three major outburst factors, the sensitivity to the gas content during outbursts was the lowest. The causes of coal seam outbursts with a low gas content and the effect of the structure on outbursts were explained. It was theoretically revealed that the coupling of the coal firmness coefficient, gas content and gas pressure determined whether coal seams could experience outbursts. This paper provided a basis for assessing coal seam outbursts and classifying outburst mine types and listed application examples of solid–gas–stress theory. [ABSTRACT FROM AUTHOR]

Coal-gas outburst is a violent phenomenon of energy release and strong dynamics is generated in underground coal mining. Coal-gas outbursts are accompanied by strong coal pulverization, and the gas desorbed by pulverized coal will in turn promote the development and spread of outbursts. Quantitative study on the role desorption gas played can improve the disaster-causing mechanism of coal-gas outburst and guide the work of outburst prevention and disaster reduction. Based on established gas emission model, the gas desorption is combined with the outburst process and its dynamic characteristics in this paper. The energy contribution and outburst dynamics with desorption gas are quantitatively studied under various desorption conditions, verified by outburst experiments. The results indicate that the energy contribution of desorption gas is 15.49–58.59% for JG71 coal, 4.49–57.26% for JG82 coal. The coal pulverization in the JG82 coal seam has a great influence on the energy contribution of desorption gas. After correction of gas desorption, the energy contribution increases by ∼20%. The maximum energy release rate (MERR) of the outburst with 0.075–0.15 mm JG71 coal sample reaches is 2.87 times that of the 1–2.36 mm coal sample at 3 MPa, and even 5.72 times that of the JG82 coal sample. For the outburst experiments, the energy contribution of desorption gas is 31.97–40.06% with 1–2.36 mm coal, 50.29–52.76% with < 0.25 mm coal. This paper presents a novel quantitative study defining the role of gas desorption in outburst energy and dynamics, applicable to disaster risk assessment and an accurate method to derive the energy contribution of desorption gas in experiments is proposed. [ABSTRACT FROM AUTHOR]

The rock masses that occur in nature are damaged and unstable due to the impact of rock burst, coal and gas outbursts, and other human mining activities, posing a major threat to human life and safety. In the light of the early warning of the danger of the loaded rock mass, this paper adopts acoustic emission (AE) device to analyze the AE signal characteristics and damage laws of the loaded rock under different stress levels. Then, based on the AE signal characteristics of the loaded rock, data mining technology is used to construct a model to predict the failure and instability of the loaded rock mass and, finally, verify the reliability of the prediction model based on data mining. The results show that the AE signal characteristics of red sandstone under uniaxial load are related to the magnitude of the bearing stress. Before the plastic deformation stage, the AE energy and the cumulative count per second are both small. After the loaded rock enters the plastic deformation stage, the AE energy and the cumulative count per second both increase sharply. After the AE energy is greater than 500 mV ∗ ms and the cumulative count per second is greater than 150, the loaded rock mass will issue an early warning signal. The research results can provide a reference value for the safe production of the project site and the dangerous early warning of the loaded rock mass. [ABSTRACT FROM AUTHOR]

High moisture content affecting coal bed methane (CBM) occurrence and transport is a typical feature of low-rank coal (LRC). The mechanism of the influence of moisture on methane diffusion properties of LRC is critical to improve CBM production and prevent coal and gas outburst. In this paper, a new method was designed to prepare coal samples with different moisture contents (0–16.80%). The desorption experiment at different moisture contents was conducted to study the time-varying diffusion properties of selected LRC and medium-rank coal samples. Results show that with the moisture content increase, the desorption volume and the initial desorption rate of LRC decrease obviously. Based on the negative linear relationship between the initial diffusion coefficient (D0) and moisture content (M), a mathematical model between them is established, which can be described as D0 = λM + Ddry, where λ and Ddry are the material constant and D0 of the dry coal sample, respectively. Moreover, with the increase in moisture content, the time-varying diffusion coefficient (Dt) and its decay rate decrease obviously. It indicates that moisture can significantly reduce the diffusion capacity of LRC, and the competitive adsorption between moisture and methane molecules is an important factor affecting the diffusion properties of LRC. It is worth noting that there is a critical value of moisture content, beyond which increasing moisture content has no significant effect on reducing desorption and diffusion capacity. Results can provide a theoretical basis for taking hydraulic technology to prevent outburst in LRC mining. Article Highlights: Moisture can significantly reduce methane desorption capacity of low-rank coal. Effect of moisture on the time-varying diffusion properties of methane in low-rank coal was studied. Mathematical model of methane initial diffusion coefficient and moisture was established. [ABSTRACT FROM AUTHOR]

The mechanical properties of coal containing fluid are an important factor affecting the safe mining of soft coal seams. In particular, for class III–V coal, coal and gas outbursts and other dynamic phenomena are prone to occur due to the influences of gas pressure and groundwater, which seriously threaten the safety and lives of field workers. However, briquette samples are usually used in place of raw coal in laboratory tests conducted on class III–V coal samples. Whether the research conclusions for briquette and raw coal are consistent and whether briquette coal can replace raw coal in research on strength characteristics need to be further verified. In this paper, the evolution of the strength characteristics of fluid-bearing briquette coal and raw coal is studied. The strength characteristics, instability failure characteristics, and acoustic emission characteristics of raw coal and briquette coal under uniaxial and triaxial compression are analyzed in detail. In addition, the influence of the water content and pore pressure on the strength characteristics of class III–V raw coal and briquette coal is further studied. The results show that the failure characteristic of raw coal is overall brittle failure, mainly axial splitting failure, whereas that of briquette is overall ductile failure, mainly cone-shaped continuous spalling. The strength parameters of the raw coal and briquette coal improve under confining pressure, but the internal difference in the raw coal is significantly reduced. The cohesion of the raw coal sample initially increases and then decreases with increasing water content, and the internal friction angle increases with increasing water content. In addition, it is verified that the strength, cohesion, elastic modulus, and deformation modulus of the briquette decrease with increasing pore pressure under different pore pressures, but the strength difference of the class III–V coal decreases under increasing pore pressure. Based on the abovementioned results, the strength parameters of a coal body are estimated using the Hoek–Brown (H–B) criterion. Based on a comparison of the strength parameters of the coal sample and coal body, the estimated strength parameters of the coal body are closer to the actual values on site. [ABSTRACT FROM AUTHOR]

The class labels of collected coal and gas outbursts sample data may be wrong, if these collected sample data are directly used for outbursts classification, the accuracy and efficiency are very low. In this paper, a novel hybrid model that integrates fuzzy c-means clustering based on isometric mapping feature extraction and Bayesian optimized mixed kernel relevance vector machine classifier is proposed and applied to improve the classification performance of coal and gas outbursts. First, the isometric mapping is used to extract the non-linear information, then the significant features are selected, in order to improve the classification performance of coal and gas outbursts, the fuzzy c-means is used to perform clustering analysis on the effective features obtained from isometric mapping, mining the structural information and internal regularity of the sample data and estimating classification labels of sample data. Second, A mixed kernel relevance vector machine classifier is proposed to classify coal and gas outbursts, improving the learning and generalization ability of outbursts classification, and the classifier parameters are optimized by Bayesian optimization with global and local search capability remarkably. Finally, the improved fuzzy c-means clustering is integrated into the mixed kernel relevance vector machine classifier model, and Bayesian optimization algorithm is used to help train a better classifier for outbursts classification. The obtained experimental results on the collected actual dataset of coal and gas outbursts show that proposed clustering method can improve the clustering effect and efficiency, decrease the feature vector size up to 50% and achieves the accuracy and running time of 100% and 5.26 s, respectively, which outperforms prior methods with 98% and 5.38 s,the proposed outbursts combined classification model based on classification and clustering model outperforms other methods by 4%-6% with respect to average accuracy. It is believed that the proposed model is very effective for outbursts classification. [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]

Coal and gas outburst is a type of coal mine dynamic disaster with complex causes and serious consequences. In China, the number and scale of outburst disasters are among the highest in the world. It is an inevitable stage for outburst that the mechanical instability of the combination of intact coal and tectonic coal (CICTC) in strata. The dip angle of the interface has an important influence on the instability of CICTC-containing gas. To further understand the instability process of CICTC, the uncoordinated deformation of CICTC was defined. According to this, three strain conditions were delimited. The variations of stress under three strain conditions were analyzed, the expressions of additional interfacial stress were established. Then, based on the Mohr–Coulomb criterion, the strength characteristics and failure forms were analyzed. It was found that the dip angle deflects the principal stress in the interface, and the influences of additional stresses on the value of principal stress are opposite. These two reasons make the principal stress state and instability process of the combination complicated. Finally, combined with actual parameters, the instability processes of CICTC under different stress paths and buried depths were studied. It can be found that the failures of CICTC under different stress paths were concentrated appearing in the tectonic coal body, intact coal interface, and tectonic coal interface. With the increase of buried depth, the initial maximum principal stress increases and the reduction from additional stresses to the strength of intact coal interface enhances, which makes the combination damage easily and the failure form change. The research results in this paper can provide a theoretical basis to prevent and control the outburst of the combination containing gas considering the dip angle of the interface. Highlights: The uncoordinated deformation of combination considering the dip angle was first defined. The expressions of additional interfacial stress of combination considering the dip angle were established The influences of different stress paths and buried depths for the instability of combination were discussed quantificationally. [ABSTRACT FROM AUTHOR]

Development and selection of fuzzy variable weight vector and its application on fuzzy comprehensive decision-making (FCDM) are studied in detail in this paper. Firstly, a parameter contained variable weight vector is developed based on the definition of variable weight vector, and then further extended to obtain the fuzzy variable weight vector. Its capability on weights changing can be adjusted by changing the parameter. In order to make the fuzzy variable weight vector for different changes of states to be selected and applied easily, the concept of fuzzy dispersion degree, which can be used to measure the balance of decision factors' states, is proposed; And then the concept of fuzzy average relative adjustment degree, which can be used to measure the capability of fuzzy variable weight vector on weight changing, is also proposed. Based on the concepts of fuzzy dispersion degree and fuzzy average relative adjustment degree, relationship between the weight changing capability of the developed fuzzy variable weight vector and the parameters it contains is analyzed. With consideration of keeping balance among states, steps on selecting fuzzy variable weight vector with its corresponding capability on weight changing are presented. Based on the fuzzy combined weighting method, a FCDM model with fuzzy variable weight is developed. The fuzzy structured element is used to express fuzzy numbers and fuzzy operations in the model. An analytical algorithm of the FCDM model based on the fuzzy structured element is presented. The developed model was then applied on evaluating and predicting for coal and gas outburst of coal mining panels. The research finding provides an alternative way for fuzzy operations and determination of weights in other fuzzy analysis models. [ABSTRACT FROM AUTHOR]

Mine gas drainage is an important work in high gas outburst coal mines. How to improve the gas drainage concentration and drainage volume has always been the direction of exploration by coal mine technicians. In this paper, the experiment and field test of displacing CH4 with liquid CO2 were carried out. In the process of low temperature liquid CO2 phase transformation, a low stress and high permeability pressure relief area is formed in the coal and rock mass, so as to accelerate the free state of primary gas in coal and realize the intensified gas extraction of low-permeability coal seams. The results show that CH4 concentration and displacement efficiency in the displacement flow decrease at a greater rate and then stabilize; the cumulative CH4 displacement volume increases rapidly and stabilizes after reaching the critical time; the average concentration of gas drainage from single hole increases from 27.2% to 53.2%, and the gas drainage purity increases 2.3 times from 0.018 m3/min to 0.041 m3/min. The technology is simple to operate, does not produce high temperature and open flame, has the advantages of economy, safety, high efficiency and so on, it can be popularized and applied in gas mines. [ABSTRACT FROM AUTHOR]

This paper investigated the effects of gas pressure, in-situ stress, and coal strength on coal and gas outbursts (CGO) based on the laboratory CGO experimental data. Based on the hypothesis of the comprehensive of CGO, the single-factor control variable method was used to analyze and evaluate the relative outburst intensity, the characteristics of outburst holes, the distribution of pulverized coal, the drops of outburst gas pressure, and the pulverized coal density under different outbursts experimental condition. The improved CGO energy equation and instability criterion are proposed as a direction to study the occurrence of CGO as an energy evolution direction. Furthermore, the results shows that the initial outburst gas pressure was 0.45 MPa during the experimental conditions of in-situ stress was 5 MPa, and the coal strength was 0.24 MPa. The gas pressure is directly proportional to the relative outburst intensity, while the in-situ stress and coal strength are inversely proportional to the relative outburst intensity. After the CGO occurred, the outburst coal always show spallation and pulverization characteristics. The results highlight that the gas pressure plays a key role in pulverizing and throwing out the pulverized coal, and the in-situ stress mainly plays a role in destroying the coal, and the coal strength plays a resistance role during the CGO occurs. It is also found that pulverized coal particles size less than 0.28 mm can be used to represent the distribution pattern of the total weight of outburst pulverized coal particles in the different outburst interval. These results clearly illustrate that using effective methods to control gas pressure, in-situ stress, and coal strength has an important role in preventing and controlling CGO on coal mining sites. [ABSTRACT FROM AUTHOR]

High intensity near infrared femtosecond laser is a promising tool for three-dimensional processing of biological materials. During the processing of cells and tissues, long lasting gas bubbles randomly appeared around the laser focal point, however physicochemical and mechanical effects of the gas bubbles has not been emphasized. This paper presents characteristic behaviors of the gas bubbles and their contact effects on cell viability. High-speed imaging of the gas bubble formation with various additives in physiological medium confirms that the gas bubble consists of dissolved air, and amphipathic proteins stabilize the bubble surface. This surface protective layer inhibits interactions of gas bubbles and cell membranes. Consequently, the gas bubble contact does not cause critical effects on cell viability. On the other hands, burst of gas bubbles stimulated by an impact of femtosecond laser induced cavitation can lead to liquid jet flow that might cause serious mechanical damages on cells. These results provide insights for the parameter of biological tissue processing with intense fs laser pulses. [ABSTRACT FROM AUTHOR]

The problem of boreholes deflection in coal mines is common, especially in soft and hard composite coal seams. As a result, the distribution of boreholes is uneven and forms a blank zone in the drainage area, which fails to achieve the regional pre-draining, causing gas explosion or coal and gas outburst accidents. Aiming at the above problems, this paper developed the technology of anti-inclination for drilling based on the causes of borehole deflection in detail. The anti-inclination advice integrates straight keeping, slag removal and smooth back drilling with reasonable technical parameters. Full hole drilling was adopted to realize straight drilling. Three spiral grooving, vertical grooving and three-edge short-circuit were adopted for collaborative slag removal. Three alloy pieces were welded at the rear end of anti-inclination device to act as reverse drill bit, realizing smooth drilling withdrawal. For sticking problems, we improved the anti-inclination device. Three 20 mm millimeters wide vertical grooves were milled in each 120° direction around the device. After using the improved anti-inclination device, the average deviation of dip and azimuth was only 4.8 and 4.5 degrees, respectively, which were reduced by 51 and 44%. The borehole offset was reduced from 9.9 m to 2.9 m, a decrease of 71%, which improved the gas drainage effect and ensured the safe production of the mine. [ABSTRACT FROM AUTHOR]

Small fault area in coal mine has great risk of coal and gas outburst. However, the damage effect of small faults on coal pore structure still lacks systematic research. Taking a small reverse fault under Pingmei No. 2 mine as an example, this paper collects the hanging wall coal samples within 5 m from the fault plane and the coal samples 50 m from the fault plane, where there is no fault development. The pore structure characteristics of the two coal samples were analyzed and compared by means of a scanning electron microscope, mercury injection, liquid nitrogen adsorption, and Raman spectroscopy. The test results show that compared with the coal samples without faults, the coal samples at faults form micron-scale fracture zones with constant spacing, stable occurrence, and flat two walls. The pore volume and pore specific surface area of different pore sizes increase, the pore peak of mesopore (100~1000 nm) shifts from 1000 nm to 200~400 nm, and its connectivity is enhanced. The number of micropores (<10 nm) increased significantly, and the ink bottle type pores developed. Faulting also has a certain impact on the macromolecular structure of coal, which shows that the D peak area decreases and the area of G peak increases, indicating that the order degree of macromolecular structure of coal increases. [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]

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Rock burst is one of the most sophisticated and threatening problems in the process of mining activities of underground coal mines, which can evolve into phenomena such as gas outburst, violent ground pressure behavior of surrounding rock of stope roadway, and high dynamic load energy event of roof overburden fracture through the interaction between various influencing factors. This paper deeply studies the causes, consequences, and disaster mechanism of "2–2 rock burst accident" in Xinjulong coal mine, gives the network diagram of the relationship between the main influencing factors of fault type rock burst and high-energy events, establishes a mechanical model on this basis, and explores the influence and evolution law of fault influencing factors on the elastic strain energy field of surrounding rock of stope roadway. [ABSTRACT FROM AUTHOR]

Coal mining has to develop to deeper strata with the increasing demand for coal, which leads to frequent coal and gas outburst disasters. Especially, when there is a deformed coal in the coal seam, the outburst disasters are easier and more intense. Coal and gas outburst disasters can be promoted by the fragmentation. In order to clearly explain the reasons for the impact of fragmentation on deformed coal and gas outburst, mercury intrusion porosimetry, low-temperature liquid N2 adsorption test, and scanning electron microscope were carried out in this paper. The differences in pore characteristics of intact coal and deformed coal under different particle size conditions were analyzed from pore shapes, pore size distributions, and fractal dimensions. The damage paths of fragmentation on various kinds of pores in intact coal are as follows: macropores, mesopores, minipores, and micropores, and those on various kinds of pores in deformed coal are as follows: macropores, micropores, mesopores, and minipores. According to the fractal dimension theory and experimental results, the calculative results of fractal dimensions show that the fragmentation and tectonism reduce the surface roughness and structural complexity of macropores and mesopores and increase those of minipores and micropores in deformed coal. Finally, combined with the coupling effect of fragmentation and tectonism on pores, the reason of deformed coal with high crushing degree in fields of outburst was explained. The research provides the basis for the prevention of coal and gas outburst. [ABSTRACT FROM AUTHOR]

In the water-rich karst regions, high water and mud outbursts are common geological disasters in tunnel construction. To ensure the safe and smooth construction of tunnel projects, it is necessary to consider anti-water pressure, water inrush prevention and geological disasters during the design of tunnels. Based on the Yongfutun Tunnel Project, this paper studies the application and effect of radial grouting and curtain grouting, which involves those in high-water-pressure tunnels under double-layer support conditions. To obtain the effects and parameters of radial grouting and curtain grouting, the influences of different grouting ranges on the tunnel's surrounding rocks and supporting structures were analyzed and the finite difference method was adopted. The results show that the radial grouting of the surrounding rock can notably improve the initial support of the tunnel, but the impact is less obvious when the grouting range exceeds 4 m. The design of radial grouting is recommended to be 4.0 m to 4.5 m. Curtain grouting can effectively reduce the external water pressure of the tunnel lining. The external water pressure of the grouting area is 23% greater than that without curtain grouting. Curtain grouting can slow down the infiltration of external water pressure. This is beneficial to the stress of the tunnel lining structure, but the improvement in initial support force is slight. Moreover, curtain grouting improves the safety reserve of the secondary lining by strengthening the self-stability ability of the surrounding rock. Meanwhile, the double-layer primary support can effectively share the external water pressure and surrounding rock pressure. This study provides a certain reference for the lining design of high-water-pressure tunnels. [ABSTRACT FROM AUTHOR]

Confining pressure is closely related to the deformation and failure characteristics of gas-containing coal and is one of the key factors for gas outburst-rockburst coupled dynamic disaster. Firstly, this paper briefly summarized the triaxial compression test results of gas-containing coal under different confining pressures, including deformation and stiffness and failure and strength. Then, based on the second developed MatDEM gas-solid coupling program, the macro- and microdeformation and failure process of coal samples under different confining pressures and constant gas pressure were simulated, and the distribution of particle stress, pore stress, and crack, as well as energy conversion characteristics, was obtained. Finally, the influence mechanism of confining pressure on deformation and failure of gas-containing coal was discussed, and the occurrence conditions of coal and gas outburst, rockburst, and their coupled dynamic disasters were distinguished. The results show that the peak strength and residual strength after failure of gas-containing coal both increase approximately linearly with the increase of confining pressure, while the elastic modulus does not change much or increases continuously, which is closely related to the number of microdefects in the coal sample. The strengthening effect of confining pressure on rock stiffness and strength mainly comes from external support and compaction. The total number of cracks decreases with the increase of confining pressure, while the number of shear cracks increases, and the inclination angle between the formed macroscopic main crack and the horizontal plane gradually decreases. The maximum cumulative elastic energy and residual elastic energy both increase with the increase of confining pressure, which leads to the increase of the impact tendency index of coal samples. [ABSTRACT FROM AUTHOR]

The analysis of natural hazards, including gas-geodynamic phenomena, requires study of the basic physical processes that take place at each stage of an event. This paper focuses on analysing the transport of fragmented rock material during rock and gas outbursts. Our theoretical considerations and experiments have allowed us to specify and verify the significant forces acting on fragmented rock during its transport, thus determining the speed of grains of each grain class in the stream of expanding gas. The above study may serve as a preface to a wide-ranging quantitative and qualitative energy analysis of the movement of material ejected during Gas-geodynamic phenomena. [ABSTRACT FROM AUTHOR]