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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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

China's current energy consumption is primarily fueled by coal, increasing coal mining with growing energy demand. Coal and gas outburst accidents are common problems in coal mining, and prediction methods are fundamental for preventing such accidents. The gas emission characteristics of boreholes are a combination of comprehensive coal properties and coal seam gas occurrence status; thus, the accurate prediction of gas emissions from boreholes is crucial for preventing such hazards. This paper presents a method for measuring the gas flow rate in continuous boreholes, which is used to predict outburst danger in front of the working face. The model was compared with field measurement data and found suitable for research. The effects of different initial gas pressures, different borehole radius, and different burial depths on gas emissions from boreholes were studied. The results showed that (1) initial gas pressure is the main influencing factor of gas gushing. The amount of gas emission during drilling and the attenuation of gas pressure are more sensitive to pressure. An increase in gas pressure considerably increases the amount of gas gushing out of drilling holes. (2) The increase in the drilling radius increases the generation of coal cuttings, the area of the drilling hole wall, and the degree of damage to the drilling hole wall. Consequently, the amount of gas gushing out of the drilling hole increases. (3) In situ stress occurs mainly because of the increase in gas pressure with an increase in burial depth and the increase in gas desorption caused by the increase in damage to the borehole wall. This study provides a new outburst prediction method, which involves identifying outburst hazards through the gas gushing out of the borehole. The results are expected to aid the control of underground coal and gas outbursts and ensure the safe production of coal mines. [ABSTRACT FROM AUTHOR]

Coal and gas outburst (CGO) is a devastating disaster in the coal mining industry at the cost of human life. Considerable efforts have been done to eliminate this hazard, but CGO still occurs frequently. The geological structure is a critical factor influencing CGO, and it has recently been found that sudden change in coal property plays an important role in CGO. In this paper, the stress transmission, coal deformation, energy accumulation, and plastic damage when the roadway is excavated to the geological structure with the sudden change in coal property are analyzed by numerical method, based on Shoushan No.1 coal mine. It is found that the geological interface between soft coal and hard coal transfers the stress from soft coal to hard coal within a certain range, causing the occurrence of tectonic stress. The tectonic stress increases gradually with roadway excavation and finally superimposes with the peak stress. The coal deformation and elastic energy increase, leading to a high probability of CGO. When the heading face is closed to the geological structure, the coal damaged area is obviously increased no matter the roadway is excavated from hard coal to soft coal or from the opposite direction. Engineering trial shows that controlling the tunneling speed and pre-grouting to reinforce the geological anomaly area are effective methods to improve the safety of roadway excavation. [ABSTRACT FROM AUTHOR]

Coal and gas outburst is one of the main disasters that seriously threaten workers' safety during coal production. Timely identification and evaluation of the potential outburst before tunneling helps to implement the targeted control measures. Nevertheless, the influencing factors of outburst are so complex that there is no suitable index system and evaluation method available yet. In this paper, a more reasonable and complete index system (three categories of factors and 16 indicators) for outburst risk is established, in which, the risk level is divided into three levels. Then, the triangular fuzzy numbers are adopted to quantify the indicators and the logarithmic fuzzy preference programming method to calculate the weight. The cloud distribution under finite interval processing is generated based on cloud numerical characters of each indicator. In addition, the risk level is determined according to the calculation results of multi-index comprehensive membership degree. Finally, the entire evaluation system is applied to two excavated coal roadways for experiments, which show that the finite interval cloud model delivers a more objective and reasonable risk assessment. Five potential outburst threat areas of 58 excavation cycles evaluated show different degrees of outburst dynamic appearance, indicating a good relationship between the evaluation results and the actual risk. This method effectively considers the fuzziness and randomness between indexes, and it is able to classify outburst risk effectively, providing insights for the scientific and accurate assessment of such risks in front of the driving face. [ABSTRACT FROM AUTHOR]

Due to the severity and great harm of coal and gas outbursts accidents, outbursts prediction becomes very necessary; the paper presents a hybrid prediction model of feature extraction and pattern classification for coal and gas outbursts. First, discrete wavelet transform (DWT) is utilized as a preprocessing technique to decompose subseries and extract the features with different frequencies and the optimal feature components are retained; second, in order to eliminate the redundancy between the features and uncorrelation between features and outbursts, we use the fast independent component analysis (FICA) to obtain each independent component, obtaining the global information in the feature; then, the obtained features are input into linear discriminant analysis (LDA), under the guidance of class labels, then the local information in features is obtained; finally, the projected features are input into the deep extreme learning machine (DELM) classifier based on the optimal parameters by quantum particle swarm optimization (QPSO) for training and classification. The experimental results on the dataset of coal and gas outbursts show that compared with other models in the current prediction of coal and gas outbursts, this method has significant effect on various indicators. [ABSTRACT FROM AUTHOR]

Tectonic coal in coal seams not only seriously restricts the development of coalbed methane (CBM), but also easily forms coal and gas outburst risk areas. Therefore, it is of great significance to effectively predict the tectonic coal in coal seams under the development scale. Currently, the prediction methods of tectonic coal include geological prediction and geophysical prediction. Due to the large scale of geological analysis and the low identifiability of geophysical response of thin coal seam, these two methods are difficult to meet the prediction requirements of tectonic coal in the development process. Therefore, this paper proposes a new method for predicting tectonic coal based on seismic–geological integrated analysis of main controlling factors. Firstly, the control factors of tectonic coal and their quantitative characterization are determined by geological analysis. Then, the characterization parameters of control factors are obtained by various seismic technologies. Finally, the main control factors are screened by grey correlation analysis, and the prediction model of tectonic coal distribution is established by using the main control factors, and applied in the Qinshui Basin. The results show that the structure, surrounding rock lithology and coal thickness are three kinds of geological factors controlling the development of tectonic coal and the control weight of each factor is different. Structure plays the most important role in controlling the development of tectonic coal, followed by coal thickness and surrounding rock lithology. The prediction error of two verification wells is less than 2%, which indicates that the method can provide effective guidance for coal structure evaluation in the process of CBM development and coal mining. [ABSTRACT FROM AUTHOR]

The serious situation of China coal mine safety has caused great concern in China. Gas accidents have been the subject of statistical analysis studies in some of the literature, and little research has focused on societal risk and tolerability criteria. This paper reports the results of a preliminary study of societal risk and tolerability criteria of gas accidents in China. This analysis is based on a study of 10 years of gas accidents statistical data from 2004 to 2013. After applying hierarchical cluster analysis, eight sets of data are available. Subsequently, regression analysis is used to establish F-N curves for gas accidents; these F-N curves are then revised to reflect the practical situation in China. Moreover, gas accidents' risk tolerability criteria are decided according to the ALARP principle. This study reveals that tolerability criteria in developed countries are stricter than those in China. The findings of the paper give an in-depth look at the severity of gas accidents and may contribute to the improvement of the safety conditions of China's coal industry. [ABSTRACT FROM AUTHOR]

This paper proposed a coupled model of effective feature extraction and optimized classifier, which can overcome the existing problems of coal and gas outbursts classification in the literatures. Firstly, we support the use of kernel principal component analysis and linear discriminant analysis methods to extract linear and nonlinear feature information from coal and gas outbursts influencing factors. Secondly, in order to realize the complementarity and correlation between coal and gas outbursts influencing factors, we perform parallel feature fusion to combine the extracted linear and nonlinear feature information. Thirdly, an improved classifier called BO–MKRVM has been proposed that combines mixed kernel relevance vector machine (MKRVM) and Bayesian optimization (BO) algorithm to predict coal and gas outbursts according to the extracted features. In BO–MKRVM model, an effective mixed kernel function which combines Gaussian kernel function and Sigmoid kernel function is proposed to improve the learning and generalization ability of the MKRVM classifier, then the BO and tenfold cross-validation are utilized to optimize kernel parameters and weight coefficients of MKRVM with strong global and local search capability, the proposed BO–MKRVM classifier is performed on coal and gas outbursts dataset. Compared with the single feature extraction method, the combination of linear and non-linear feature extraction methods can obtain complete feature information and contribute to the classification performance of outbursts. The mixed kernel function considers the characteristics of coal and gas outbursts sample data, which can also effectively improve the outbursts accuracy. After the MKRVM classifier is optimized by BO algorithm, the BO–MKRVM classifier has better fitting effect and generalization ability, and obtains higher accuracy with a lower time. The experimental results are obviously better than those of other classification models, which further verifies the applicability of the proposed coupled model. [ABSTRACT FROM AUTHOR]

The sudden outburst of coal and gas is a complex and dynamic incident in the underground coal mines, resulting in the release of thousands of tons of coal and large amounts of gas into the working face within a short time. Due to a rise in the number of exploitations and the depth of extractions, the intensity, and frequency of explosions have increased in recent years. Consequently, these explosions have endangered miners' health and safety, brought about equipment loss and seriously affected coal production. To overcome these obstacles, the first step is to predict the occurrence of such incidents in the coal mines. There are a lot of factors playing a part in the sudden outburst of coal and gas, which can be categorized into natural and operational parameters, each of which has a different role. In this paper, a novel method is proposed to predict the possibility of gas outburst in coal seams. For this purpose, ten parameters are considered as the main variables influencing the outburst of coal and gas. To study the interrelation between these determining parameters as well as the uncertainty of the effect of one parameter on another, a fuzzy interaction matrix based on Fuzzy Rock Engineering System (FRES) has been employed. To evaluate the capability and efficiency of the proposed classification system, the C1 coal seam of Tabas coal mine is selected, and the proposed index is used to investigate the potential risk of the outburst in this mine. Index as mentioned earlier could be utilized as a basis through which one can decide on the possibility of the outburst of coal and gas in coal mines to reduce the risks of this incident. [ABSTRACT FROM AUTHOR]

The deformation of coal during the injection of sorptive gases can be classified into two types: deformation due to the pore pressure and the swelling deformation of the coal matrix induced by adsorption. These types of deformation have not been investigated separately in the previous researches. The main reason is that measuring the radial strain of the coal core directly and accurately is extremely difficult under triaxial stress. This paper demonstrates that by injecting both sorptive and non-sorptive gases into a coal sample with different pore pressures, while measuring the radial deformation of the coal sample with a high precision instrument (± 0.227 mm3), deformations due to the pore pressure and deformations induced by adsorption were separated from each other. The adsorption-induced deformations have an important influence on the effective stress. We studied the relationship between Biot coefficient and the swelling deformation due to the adsorption based on the Biot effective stress theory. The experimental results show that the Biot coefficient is the bilinear function in terms of the volumetric stress and pore pressure, shown as α = a + b Θ + c p + d Θ p . The data and results obtained in this experiment played a fundamental role in the applications of gas extraction, coal and gas outburst prevention and control, displacement of coalbed methane with CO2, and the establishment of the solid–fluid coupling model. [ABSTRACT FROM AUTHOR]

The gas outburst, resulting in substantial economic losses and even casualties, is the biggest obstacle in coal mines, mostly caused by an imbalance of gas-geological structure. For accurately measuring this proneness, in this paper, a novel evaluation method was proposed based on the gas-geology theory. In this method, a standardization model of statistical units was presented first, which was used to standardize and quantify the 12 chosen gas-geological factors; and then, an associated function was established for computing the gas-geological complexity index (GCI). With increasing GCI values, the evaluated area was divided into four grades: simple, medium, complex, and extremely complex region, in which the associated proneness of outbursts was SAFE, POTENTIAL, HIGH, STRONG, respectively. Taking the XueHu Coal Mine as an example, site verification was carried out with a good result. Research and application indicate that (1) gas outburst is unbalanced and closely related to the complex of the gas geological structure, showing a greater GCI leads to a higher outburst possibility; (2) the most likely area for the gas outburst is the extremely complex region and the transition zone between adjacent areas with different GCI grades; (3) upgrading-targeted control measures are the best way for preventing and controlling disasters caused by the gas and outburst unbalanced distribution. This novel method provided a reliable quantity approach for predicting and zonally managing gas outbursts and improving the effectiveness of outbursts prevention. [ABSTRACT FROM AUTHOR]

The Dengfeng coalfield belongs to the typical "three soft" coal seam and has a high gas content ranging from 10 to 13 m3/t, and the coal seam gas content reaches a maximum 13.69 m3/t. Because of its coal seam occurrence, no protective layer can be mined. The conventional regional pre-pumping measures have several problems. For example, the construction of a pre-pumping borehole is difficult, and it easily causes a coal and gas outburst. The low permeability and rheological characteristics of the coal seam lead to the collapse of the borehole and seriously affects the drainage effect. The influence radius of the drainage borehole is small, which results in a larger quantity of new drilling boreholes and significantly increases the operational cost. Compared to the conventional regional pre-pumping measures, floor roadway hydraulic flushing rapid outburst technology can effectively overcomes these issues. Hydraulic flushing uses water to flush the borehole, and the newly formed fractures and the release of free gas greatly reduce the elastic potential and gas expansion energy of coal and rock, which thus significantly improve the permeability of the coal and improve the coal seam degasification efficiency for outburst risk control. In this paper, a hydraulic punching method is utilized for coal seam stimulation in the Machi mine. Reasonable technical parameters of hydraulic punching were obtained: the water pressure of punching and breaking coal is 8–15 MPa, and the equivalent diameter of the hydraulic punching nozzle should be < 7.47 mm. After the implementation of the hydraulic punching measures, the gas extraction capacity of the coal around the borehole is greatly improved. For 90 days gas extraction after stimulation, the gas content of the 11,061 lane decreased from 8.42–12.12 m3/t to 3.09–5.75 m3/t, relieving pressure and increasing permeability of "three soft" coal and simultaneously eliminating the outburst danger of the coal seam. [ABSTRACT FROM AUTHOR]

Coal is China's dominant energy at present,but gas outburst occurs frequently in gassy coal mines, and it causes significant losses to people's lives and properties. Hydraulic fracturing is a valuable technology for gas permeability improvement in gassy coal mines. In this paper, the field experiment of hydraulic fracturing was conducted in a coal mine located in Yibin City, Sichuan Province. The transient electromagnetic instrument was applied before and after hydraulic fracturing respectively, combined with numerical simulation analysis of FLAC3D, aimed to estimate the influence scope of hydraulic fracturing. The numerical simulation results denote that the plastic zone principally distributes along the interface of the coal seam and roof due to the existence of stratification. Transient electromagnetic method analysis demonstrates that the coal-rock mass firstly cracks at 35 m and 41 m of borehole depth, the dominant fissure distribution range is in the interval of 33–50 m. And the influence area covers the range of 28–64 m, which means the influence scope is up to 36 m. It also reveals that it is feasible to determine the influence scope of hydraulic fracturing through transient electromagnetic method. [ABSTRACT FROM AUTHOR]

Coal and gas outbursts have occurred in the Zhaozhuang coal mine (a high gas coal mine) since its construction, and these outbursts pose a great threat to lives and property. Therefore, the combination of methane desorption experiments and molecular simulations was adopted to investigate the effects of moisture on the methane desorption characteristics of the Zhaozhuang coal, and the microscopic mechanism was analyzed in this paper. The aim of this work is to provide a method for predicting the effect of moisture on coal seam methane desorption, and quantitatively evaluating the control effect of hydraulic measures on coal and gas outbursts from a molecular perspective. The experimental data (methane desorption amount) were measured under various adsorption equilibrium pressures (0.3 MPa, 0.4 MPa, and 0.5 MPa) and moisture contents (0%, 5%, and 9.8%). Based on the Zhaozhuang coal molecular model, the molecular simulation process was conducted using Materials studio software, which can better match the experimental conditions by setting various pressure parameters (0.3 MPa, 0.4 MPa, and 0.5 MPa) and calculating various numbers of H2O molecules (0, 8, and 16) on the coal molecule. The results show that methane desorption decreases with the increasing moisture content in the experiment. The number of CH4 molecules adsorbed on the coal molecule decreases with the increasing number of H2O molecules in the simulation. This phenomenon can be explained by the competitive adsorption between CH4 and H2O molecule: the interaction between coal molecule and H2O molecules is stronger. The affinity between CH4 molecules and the coal molecule is reduced, and CH4 molecules are less aggregated around the coal molecule because of the presence of H2O molecules. [ABSTRACT FROM AUTHOR]

Rock and gas outburst is one of the most significant natural hazards faced by the mining industry. In the last decade, this issue has appeared in firm rock mining (including copper ore mines) in addition to coal mining. A number of methods have been developed for coal mining to assess the hazard posed by gasogeodynamic phenomena, but in the case of copper ore mines, no studies have led to forecasts of this risk. To face the challenge, the authors decided to propose their own concept of risk assessment principles based on a threshold analysis of the phenomenon and a continuous analysis using fuzzy logic. A series of tests were performed to support the paper, investigating selected parameters which directly affect the risk. The evaluation principles for gasogeodynamic phenomena presented herein were the result of experimental investigations carried out by the authors. [ABSTRACT FROM AUTHOR]

Using a self-researched micro-structure shear testing device for gas-containing coal, this paper studies the characteristics of micro-cracks forming, expanding, and ultimately destroying the sample at different shear rates and then discusses the macro-failure characteristics and the evolution law of micro-cracks in the gas-containing coal at different shear rates. The results show that the shear strength decreases with an increasing shear rate, and the relation between them is a logarithmic relation; the cracking tips are in the upper and lower parts of the coal, and a fine crack appears in the sample when the shear stress is 10% of the maximum shearing stress, while the cracks fully penetrate when the shear stress is 70% of the max; finally, macroscopic damage forms when the shear stress equals the maximum amount. The angle between the direction of the lower cracks and the shear increases with an increasing shear rate; the main fracture of the gas-containing coal is around the coal particles, the fracture surface of the coal is injustice, and the fracture surface roughness becomes worse with an increase in the shear rate. With an increasing shear rate, the gas-containing coal's cranny ratio and crack fractal dimension increases, the degree of damage increases, and the carrying capacity decreases, which leads to a lower stability and a higher tendency for coal and gas outbursts. [ABSTRACT FROM AUTHOR]

In order to precisely measure the dilatation energy of the released gas from underground coal seam, this paper initiated a study on the dilatation energy of gas released from underground coal seam by drilling boreholes. Firstly, an in-depth analysis is made on the two major factors causing outburst, which are crustal stress and gas. By establishing mathematical models of unit coal potential energy and gas dilatation energy, authors make a detailed calculation and results comparison. It verifies that the gas dilatation energy is the important and main energy source of a coal seam outburst. Then, the characteristics of dilatation energy of coal seam gas are further stated. Secondly, based on the analysis on the types and features of gas discharge from coal seam and according to the flow field type, this paper divided gas dilatation energy into unidirectional gas dilatation energy, radial gas dilatation energy, and spherical gas dilatation energy. Then, with the assistant of establishing the mathematical model, the software of MATLAB is used to make numerical calculation on gas dilatation energy release. The results show that dilatation energy of gas released from underground in-seam by drilling boreholes could reflect that coal gas's ability of expansion work under normal occurrence conditions. Finally, according to the theory of coal seam gas dilatation energy and the features of gas flowing in reducing pipe, on-site measuring method and testing equipment are worked out to measure underground gas dilatation energy. The results of field measurements in a coal mine show that the gas dilatation energy could completely reflect the physical and mechanical properties of crustal stress, gas, and coal. It could be used as a most effective indicator in judging whether coal and gas outburst might occur. Thus, it presents good scientific and practical significances for predicting coal seam outburst. [ABSTRACT FROM AUTHOR]

Coal and gas outburst is one of the main gas hazards in coal mines. However, due to the risks of the coal and gas outburst, the field test is difficult to complete. Therefore, an effective approach to studying the mechanism and development of outburst is to conduct the similar physical simulation. However, the similarity criteria and similar materials in outburst are the key factors which restrict the development of physical simulation. To solve those problems, this paper has established similarity criteria base on mechanics model, solid-fluid coupling model and energy model, and presented high similar materials. Combining with three groups of similar number, and considering similar mechanical parameters and deformation and failure regularity, the similarity criteria of outburst is determined on the basis of the energy model. According to those criteria, we put forward a similar material consists of pulverized coal, cement, sand, activated carbon, and water. The similar material has high compressive strength and the accordant characteristics with the raw coal, include density, porosity, adsorption, desorption. The new research is promising for preventing and controlling gas hazards in the future. [ABSTRACT FROM AUTHOR]

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

Magma intrusion has an important influence on the physical and mechanical properties of coal and rock. In the area of magma intrusion, disasters such as gas outburst are prone to occur. Revealing its invasion law will be conducive to disaster management and energy development. For this purpose, changes in industrial analysis components of coal, mineral composition, major oxides, trace elements, and rare earth elements of coal under the thermal metamorphism of magma intrusion were analyzed. It is found that the moisture and volatile matter contents of the thermally affected coals in the mining face are generally lower than that of normal coals, while moisture and volatile matter contents are reduced towards to the magma intrusion contact. For example, the moisture and volatile matter of coal sample M01 decreased by 64.6% and 38.6% respectively compared with coal sample M05. During magma intrusion, some minerals remain on the surface of the coal body, resulting in changes in the mineral composition of the coal body. The decrease in carbon atom net spacing, the increase in crystallite aggregation and ductility, and aromaticity in thermally affected coals have a positive impact on the improvement of coal metamorphism. Due to the influences of magmatic intrusion, the variation rules of major oxides in coal are different, and the closer to the magmatic intrusion zone, the easier the major oxides are to be depleted. However, magma intrusion will not lead to the loss of all major oxides in thermally affected coals, such as content of CaO is 54.8%, which is higher than that of coal not affected by magmatic hydrothermal fluid. Most of the trace elements in the thermally affected coals of the No. 9 coal seam are depleted. The contents of rare earth elements are low on the whole coalbasis, with an average of 29.48 μg/g, and the distribution pattern towards to magmatic intrusion shows a wide and gentle "V" curve with left high and right low, showing the characteristics of enrichment of light rare earth elements. [ABSTRACT FROM AUTHOR]

This study numerically examines the evolution of the stress and displacement fields of rock sur-rounding an oblique normal fault in the longwall working face of a mine. The aim is to determine the law of activation of an abnormal geological body containing coal and rock mass and to provide timely warnings of geological hazards, such as coal and gas bursts, rock bursts, and flooding during coal mining. A high-precision microseismic monitoring system was used to monitor the activation of and damage to the rock surrounding the mine. The results of numerical simulations coupled with those of microseismic monitoring showed that the coal and rock mass near the fault and goaf was situated in an area of high stress, with a high frequency and energy of microseismic events, wherein changes in the displacement of the roof were more significant when the working face was pushed to the fault layer. The combined analysis provides information on the activation of rock surrounding the coal mine and can be used to provide early warnings of mining accidents. The results provide a reference for the safe mining of the working face and technical guidance for the design parameters of pressure relief holes. [ABSTRACT FROM AUTHOR]

The finite difference model and particle flow model were constructed to reproduce the process of coal and gas outburst in front of the tunnel. The reliability of the particle flow model was verified by studying the internal stress, gas pressure, and related parameters of gas and coal two-phase flow. Then the process of coal and gas outburst is described from a microscopic perspective. The results show that the particle flow numerical model of coal and gas outburst is in line with reality and can intuitively and conveniently monitor relevant parameters; The concentrated stress caused by excavation of tunnels can reach 1.2 times the in-situ stress; High stress causes the adhesion between coal particles to break down, which is the main reason for the initiation of coal and gas outbursts; The intermittent breakthrough of gas on the coal particle collection that blocks the release channel has caused pulsating characteristics of coal and gas outbursts. [ABSTRACT FROM AUTHOR]

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

Coal and gas outbursts have been a major geological hazard to underground coal mining for over 150 years and continue to cause serious problems in all over the world. In order to have a better understanding of the phenomenon, it is worthwhile making a historical review of the occurrences and a combat of the events. Many investigations and researches have been done to characterize and prevent the outburst occurrences in the worldwide, but there has been no detailed investigation about coal and gas outburst occurrences in Turkey. This paper presents the outburst data of coal mines in Turkey since 1969. Based on the observation of outburst occurrence in Turkey in the period from 1969 to 2012 as well as mining and geological conditions, detailed analysis of the possible causes of outburst accidents is conducted. The influences of some geological parameters such as the depth of occurrence, thickness and inclination of coal seams, the amount of ejected material (coal and gas), and tectonic disturbances on coal and gas outburst occurrences have been statistically investigated. The outburst occurrences throughout the world were reviewed and compared with the Turkish outburst experiences. Suggestions are put forward on future studies that could be of interest to government agencies regarding strategic policies, proper technical management practice, identification of outburst-prone coal seams, as well as prevention and control measures. [ABSTRACT FROM AUTHOR]

The gas pressure in front area of heading face is essential to dynamically evaluate coal and gas outburst during coal mining. In this work, a novel inversion model of gas pressure in front area of the heading face was established on premise of the hypothesis that a time-dependent zone of steady flow exists within newly exposed face. The key parameters in the inversion model were obtained based on the gas emission models and field data of gas emission rate in different times, which were used to calculate the volumes of gas emission from different sources. The results show that the percentage of gas emission from the heading face, coal wall and collapsed coal ranges from 7% to 47%, 47% to 82% and 2% to 11%, respectively. Based on the calculated volumes of gas emission and gas pressure inversion model, the gas pressure was obtained and transformed to the gas content. The absolute errors between the gas content tested and transformed in every hour is 0.4%–33%, which proved the rationality of gas pressure inversion model. Furthermore, the daily drifting footage, the radius of gas pressure boundary and the gas permeability coefficient of coal seam were confirmed to have a great effect on the result of gas pressure inversion. The inversion results verify that the speedy excavation can increase the risk of coal and gas outburst. This work produces a useful method for gas disaster prevention and control that converts the gas emission rate to an index of gas pressure within coal seam. [ABSTRACT FROM AUTHOR]

A probabilistic risk assessment framework was developed to mathematically represent the complex engineering phenomena of rock bursts and gas outbursts for a heterogeneous coal seam. An innovative object-based non-conditional simulation approach was used to distribute lithological heterogeneity present in the coal seam to respect their geological origin. The changing mining conditions during longwall top coal caving mining (LTCC) were extracted from a coupled numerical model to provide statistically sufficient data for probabilistic analysis. The complex interdependencies among abutment stress, pore pressure, the volume of total gas emission and incremental energy release rate, their stochastic variations and uncertainty were realistically implemented in the GoldSim software, and 100,000 equally likely scenarios were simulated using the Monte Carlo method to determine the probability of rock bursts and gas outbursts. The results obtained from the analysis incorporate the variability in mechanical, elastic and reservoir properties of coal due to lithological heterogeneity and result in the probability of the occurrence of rock bursts, coal and gas outbursts, and safe mining conditions. The framework realistically represents the complex mining environment, is resilient and results are reliable. The framework is generic and can be suitably modified to be used in different underground mining scenarios, overcoming the limitations of earlier empirical indices used. Highlights: Parameters causing rockbursts and gas outbursts were linked along with their influences and interdependencies into a probabilistic risk assessment framework. Dynamically updated system feedback from the numerical model was fed into the framework to represent the current stress state in retreating mining and estimate the probability of the occurrence of rockbursts and gas outbursts. Statistically significant data were used to quantify the probability of rockbursts and gas outbursts using Monte Carlo simulation. [ABSTRACT FROM AUTHOR]

In this paper, it was determined that all of the three-dimensional principal stresses increase with depth and that both the maximum and the minimum stresses tend to be aligned in the horizontal orientation. The numerical simulation model was built using the software FLAC to simulate two times, as in two different states of original rock stress, respectively; this simulation was used to investigate how the original rock stress affects the gas outburst risk. The results suggest that an outburst is most likely to happen when the maximum original rock stress is perpendicular to the roadway, rather than parallel to the roadway. The results were demonstrated to be correct by a field experiment. The results suggest that most of the roadways in gas outburst risk coal mines should be designed to lie parallel to the maximum stress direction to avoid the high stress concentration in front of the heading face, thereby reducing the gas outburst risk. [ABSTRACT FROM AUTHOR]

In response to the severe situation of coal mine gas disaster in China, a new method of reducing the danger of coal and gas outbursts and improving gas drainage and utilization in coal mines was introduced in this paper. The main idea of this method is to mining thin sub-layer as self-protective coal seam to eliminate or reduce the danger of coal and gas outburst. This method can be implemented by drills along seam and hydraulic jet when the mined seam with a relatively weak risk of coal and gas outbursts is soft or has a soft layer. This method was first applied in the Yian mine to verify its effectiveness. The results of application showed that mining thin sub-layer as self-protective coal seam can effectively eliminate the danger of coal and gas outburst and improve gas drainage and utilization. As this method needs less time and lower cost than conventional protective layer mining, it is of great significance for mining coal seam with the danger of coal and gas outburst. [ABSTRACT FROM AUTHOR]

In this paper we suggest that conditional estimator/predictor of rockburst probability (and rockburst hazard, P( t)) can be approximated with the formula P( t) = P( θ)... P( θ)· P( t), where P( t) is a time-dependent probability of rockburst given only the predicted seismic energy parameters, while P( θ) are amplifying coefficients due to local geologic and mining conditions, as defined by the Expert Method of (rockburst) Hazard Evaluation (MRG) known in the Polish mining industry. All the elements of the formula are (approximately) calculable (on-line) and the resulting P value satisfies inequalities 0 ≤ P( t) ≤ 1. As a result, the hazard space (0-1) can be always divided into smaller subspaces ( e.g., 0-10, 10-10, 10-10, 10-1), possibly named with symbols ( e.g., A, B, C, D, ...) called 'hazard states' - which saves the prediction users from worrying of probabilities. The estimator P can be interpreted as a formal statement of (reformulated) Comprehensive Method of Rockburst State of Hazard Evaluation, well known in Polish mining industry. The estimator P is natural, logically consistent and physically interpretable. Due to full formalization, it can be easily generalized, incorporating relevant information from other sources/methods. [ABSTRACT FROM AUTHOR]

The paper deals with the problems on mechanics of material with gas-filled fissure-like discontinuities, considered in terms of coal, rocks and gas outbursts in coal mines. [ABSTRACT FROM AUTHOR]

The paper considers the conditions of methane hydrate existence in coal seams. The authors estimate volumes of gas emission in a fractured coal layer upon a drop in gas pressure. The authors also give the assessment of outburst hazard of coal seam edge zone. [ABSTRACT FROM AUTHOR]

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