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The feature selection of influencing factors of coal and gas outbursts is of great significance for presenting the most discriminative features and improving prediction performance of a classifier, the paper presents an effective hybrid feature selection and modified outbursts classifier framework which aims at solving exiting coal and gas outbursts prediction problems. First, a measurement standard based on maximum information coefficient(MIC) is employed to identify the wide correlations between two variables; Second, based on a ranking procedure using non-dominated sorting genetic algorithm(NSGAII), maximum relevance minimum redundancy(MRMR) algorithm is subsequently performed to find out candidate feature set highly related to the class label and uncorrelated with each other; Third, random forest(RF) is employed to search the optimal feature subset from the candidate feature set, then the optimal feature subset that influences the classification performance of coal and gas outbursts is obtained; Finally, an improved classifier model has been proposed that combines gradient boosting decision tree(GBDT) and k-nearest neighbor(KNN) for outbursts prediction. In the modified classifier model, the GBDT is utilized to assign different weights to features, then the weighted features are input into the KNN to verify the effectiveness of proposed method on coal and gas outbursts dataset. The experimental results conclude that our proposed scheme is effective in the number of feature and prediction accuracy when compared with other related state-of-the-art prediction models based on feature selection for coal and gas outbursts. [ABSTRACT FROM AUTHOR]

The objective of this paper is to identify the outburst danger of coal from the perspective of adsorption capacity, nitrogen adsorption experiments had been performed on six different coal samples. With cubic spline interpolation method, the amount of nitrogen adsorbed in the coal at p/p0 = 0.001, 0.01, 0.50, and 0.99 were obtained. The results show that the outburst coal has more micropores than that of non-outburst coal. When the relative pressure p/p0 is 0.001 and 0.50, six coal samples have significant differences in adsorption capacity. Using the adsorption amount of these two points as the quantitative indexes, six coal samples were classified into two types by iterative self-organizing analysis technique (ISODATA). Compared with the results of traditional classification, the results obtained by the new classification method in this paper are consistent with that. The iterative self-organizing analysis technique can be as a method to identify the risk of coal and gas outburst. The cluster center in the classification process can be dynamically optimized. The data obtained in the experiment are limited, and some experiments were needed to continuously optimize the cluster center to make it keep within a little range. This method has a deep understanding of the structure and the quantity of coal pores. It not only has an important significance for studying the mechanism of coal and gas outburst, but also makes the identification of coal and gas outburst easier. [ABSTRACT FROM AUTHOR]

The aim of this study was to explore the evolution and release rule of internal energy storage in the process of coal and gas outburst and to further reveal the mechanism of coal and gas outburst from the perspective of energy. In this paper, the experiment of gas expansion energy release of coal samples under different adsorption pressures and with different moisture contents was carried out with the self-developed experimental device for release of gas-bearing coal expansion energy under load, and the energy of the whole outburst process was divided into three parts: the total expansion energy of gas, the energy consumed by destroying and throwing out coal body and the energy released inefficiently. On the basis of reasonable assumption, the energy evolution calculation model of each part was constructed with mathematical method. By analyzing the changes and distribution rules of three parts of energy under different experimental conditions, this paper explored the controlling effects of gas pressure, water content, and other variables on the energy evolution rules in the process of coal and gas outburst. Experimental and theoretical studies showed that in the gas-dominated coal and gas outburst process, the destruction of coal body was in the form of stratification; under each experimental condition, there existed a critical gas pressure value for the occurrence of coal and gas outburst, and there was a sudden change of energy evolution near this value; the existence of water made the critical pressure and the minimum energy consumption of coal and gas outburst increase obviously; under the experimental conditions, there was a linear relationship between the critical gas pressure and water content and a positive exponential relationship between the minimum energy consumption and water content. [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]

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]

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]

Understanding the dynamics of mild explosive activity is a fundamental tool for hazard assessment at open conduit volcanoes. This is a particularly critical task for Etna volcano. Etna is in fact characterized by frequent, mild explosive activity, punctuated by lava flows and paroxysmal events ('lava fountains'), which, because of their greater impact, have been the main target for hazard studies, whereas more frequent Strombolian activity has been overlooked. As a result, their impact and associated hazards have been never quantified, despite the extensive monitoring and surveillance activities carried out on this volcano. In this paper, we analyze video recordings of a sequence of Strombolian explosions occurring at the summit craters of Mt. Etna, in Italy, in February 2020. Data were also integrated with a petrographic analysis of collected samples, and drone surveys were performed at the same time as the video recordings. We estimate the frequency of explosions (20–12 per min); particle exit speeds (1–50 m/s), and erupted mass (100–102 kg) of those explosions. A very regular, small-scale activity (marked by a single burst of gas breaking the magma free surface into bombs and lapilli fragments) was occasionally punctuated by larger explosions, (at least one every 5 min), with a longer duration, fed by larger magma volumes, and consisting of two to three distinct pulses followed by a stationary phase. We found that the repose times between explosions follows a log logistic distribution, which is in agreement with the behavior of open vent explosive activity. The four largest explosions of the sequence were analyzed in detail: they emitted particles with median diameters (Mdphi) ranging from −10.1 to −8.8 phi, with bimodal distributions. [ABSTRACT FROM AUTHOR]

The strong disturbance of upward mining of the short-distance multiseam results in frequent fractures in the coal seam to be mined, jeopardizing the operation safety due to the instability of the surrounding rock of the overlying stope and risks of coal and gas outburst. A lucrative alternative is the downward mining of multiseam, which wide implementation is limited by the lack of reliable data on stress evolution characteristics. In this paper, the evolution, nonlinear interaction, and superposition characteristics of mining-induced stress after multiple pressure relief in the short-distance multi-seam were investigated by the numerical simulation and physical simulation, taking the endowment and mining technology characteristics of group B short-distance multiseam in Pan'er Coal Mine in Anhui Province of China as an example. The numerical and physical models of multiple (2—5 times) mining activities in pressure relief multiseam (with five main coal layers) under downward mining are constructed and implemented with the FLAC3D software and 1 : 100 scaling, respectively. The results showed that a pressure relief arch, which bears and transfers stresses, is formed on the coal seam's roof and floor. In downward mining, the local arch expands to the long arch, which bearing capacity within the influence range of multiple mining disturbances is weak, and the arch structure is prone to instability. If a coal pillar is left in the upper coal seam after its mining, the lower coal seam mining will switch from the large-scale low-stress area under the goaf to the small-scale high-stress area of nonlinear interaction of the multiple mining stresses with the stress under the coal pillar. [ABSTRACT FROM AUTHOR]

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Coal deformation caused by gas adsorption is a well‐known phenomenon and has played an important role in many engineering fields. For example, the bulk coal deformation induced by gas is a primary factor in coal and gas outbursts, and the changes in coalbed permeability are primarily determined by the evolution of the coal fracture volumetric strain during gas recovery. However, the current models of coal deformation induced by gas do not fully consider the coal seam field conditions or the deformation factors. To better fit coal seam field conditions and provide a basis for engineering applications, in this work, based on coal's physical structure, coal seam field conditions, the energy balance approach, poroelasticity, mathematical differentiation, and previous scholars' research results, the volumetric strain models of bulk coal, coal fracture, and coal matrix under coal seam field conditions are established. In addition, based on the analysis of the effect of gas pressure on coal deformation, the difference in gas pressure effects on the bulk coal deformation between experimental conditions and coal seam field conditions revealed that when the bulk coal deformation is tested in a laboratory, the gas pressure exerts a compressive effect on the bulk coal. However, under coal seam field conditions, the gas pressure has a swelling effect on the bulk coal. Additionally, gas pressure exerts an compression on the coal matrix and a swelling on the coal fracture under coal seam field conditions. At the end of the paper, the established models were analyzed and discussed from multiple perspectives. It was shown that the coal deformation models established in this paper are all accurate and reliable. [ABSTRACT FROM AUTHOR]

Deep mining is the most important way to obtain the resource in China now. Thus, rock is the main objective that the deep mining will encounter. Meanwhile, the frequent catastrophes in deep mining such as rock burst, coal and gas bursts, roof caving, water bursts, is the most serious problem. To have a better understanding of the mechanisms of fracture and the laws of damage evolution of rock and coal under deep environment, in this paper, the micro- and meso-scale method is employed to study the behavior of coal under different temperature, confining pressure and gas pressure. Then, the significance of the effect of temperature, confining pressure, and gas pressure on mechanical parameters is analyzed by using the ANOVA method. The fractal study of coal failure pattern by employing the SEM test and fractal dimension was carried out. The fractal dimension of coal fractures was calculated by using the box-covering method. Then, the effects of all factors on the fractal dimension of coal fractures were analyzed. [ABSTRACT FROM AUTHOR]

As coal mining gradually extends deeper, coal seams in China generally show high stress, high gas pressure and low permeability, bringing more difficulty to coal mining. Therefore, in order to strengthen gas extraction, it is necessary to carry out reservoir reconstruction after deep coal seams reached. In this paper, the distribution and evolution laws of fracture zone overlaying strata of J15 seam in Pingdingshan No. 10 coal mine after excavation were studied by combining similar simulation and numerical simulation, meanwhile, the gas transport law within fracture zone was numerically simulated. The results show that the fracture zone reaches a maximum of 350 mm in the vertical direction and is 75 mm away from W9,10 coal seams in vertical distance. Since W9,10 coal seams are in an area greatly affected by the bending zone of J15 coal seam under the influence of mining, the mining of J15 coal seam will exert a strong permeability enhancement effect on W9,10 coal seams. The J15 coal seam can act as a long-distance protective layer of W9,10 coal seams to eliminate the outburst danger of the long-distance coal seams in bending zone with coal and gas outburst danger, thereby achieving safe, productive and efficient integrated mining of coal and gas resources. The gas flux of mining-induced fractures in the trapezoidal stage of mining-induced fracture field is far greater than that in the overlaying stratum matrix. The horizontal separation fractures and vertical broken fractures within the mining-induced fracture field act as passages for gas-flow. Compared with gas transport in the overlaying stratum matrix, the horizontal separation fractures and vertical broken fractures within the mining-induced fracture field play a role in guiding gas-flow. The research results can provide theoretical support for the arrangement of high-level gas extraction boreholes in roof fracture zones. [ABSTRACT FROM AUTHOR]

The section of appropriate prediction index is of great importance for coal and gas outburst prediction. The quantity of gas emission is a key factor directly relating to the outburst risk of tunneling working face in the coal roadways. Therefore, accurately predicting the quantity of gas emission is necessary and critical to prevent and control outbursts. In this paper, using the sphere diffusion equation of coal particle gas and radial unsteady flow equations of coal seam gas to analysis gas flow of fallen coal and coal wall, and a dynamic prediction model of gas emission is established including key factors, research shows that: (1) in tunneling working face, the change rule of gas emission of the new model, in which mechanical state, physical properties of coal seam, roadway tunneling parameters, and gas adsorption parameters are considered, is the same as that of the conventional index, which indicates the feasibility of the new model; (2) The new model shows that the gas emission is positively correlated with the gas pressure, driving speed and permeability coefficient of coal seam, and negatively correlated with the uniaxial compressive strength of coal mass; (3) By comparing the old prediction model of gas emission, the predicted value of the new model is closer to the measured value, fluctuating within a smaller range, and has a higher accuracy after taking the gas emission of coal particle into account. In addition, the multiple characteristics of the coal body in front of the working face are comprehensively considered. The research results offer practical significance for improving gas prevention and control of tunneling working 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]

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]

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]

Coalbed methane (CBM), which is extremely rich in deep coal reserves in China, is not only the material cause of gas explosion and coal‐gas outburst disasters but also a clean and environmentally friendly energy source. Gas drainage must be carried out during deep coal mining to avoid gas accidents while obtaining clean energy. The low‐level roadway is an effective gas drainage measure for coal seams with high coal‐gas outburst risk and low‐permeability, and it can simultaneously realize the functions of gas drainage before and during mining. Roadway tunneling has a strong influence on the stress and permeability properties of the adjusted coal seams, and further determines the gas drainage efficiency and the layout of the air‐return roadway. Taking the Pingshu Coal Mine as an example, this paper analyzes the influence of the vertical distance between the low‐level roadway and the underlying coal seam, and the influence of the width and height of the low‐level roadway on the stress relief and deformation characteristics. The results indicate that the low‐level roadway tunneling results in a nonuniform stress disturbance of coal seam #15. And a reasonable layout and size parameters of the air‐return roadway in coal seam #15 were proposed based on which gas drainage practices were carried out with good effects in panel #15211. The research can effectively guide the elimination of coal and gas outburst in return air roadway, and achieve the purpose of safe and rapid tunneling coal roadway under the environment of highly‐gassy coal seam. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd. [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]

Protective layer mining, as a dominating method for preventing coal and gas outburst, is generally adopted in highly gassy coal mines. In the absence of a suitable thickness coal seam to serve as the protective layer, the rock-coal composite protective layer was proposed in this paper. We conducted a series of simulations and engineering measurements to investigate the protective effect under the mining of the rock-coal composite protective layer of the Zhongtai coal mine located in the Hebi area of Henan, China. The numerical simulation analysis showed that, after the completion of protective layer mining, the minimum vertical stress of the No. 2-1 coal seam had been reduced to 3.46 MPa. The maximum vertical displacement of the No. 2-1 coal seam is 455.01 mm. The maximum expansion deformation of the No. 2-1 coal seam is 9.77‰; the effective pressure relief range is as long as 160 m. The similarity simulation experiment revealed that, after the completion of protective layer mining, the minimum vertical stress of the No. 2-1 coal seam is 4.0 MPa. The maximum vertical displacement of the No. 2-1 coal seam is 640 mm. The maximum expansion deformation of the No. 2-1 coal seam is 26.37‰; the effective protection range reaches 130 m. The engineering measurements demonstrated that the variation law of gas drainage parameters in the protected layer corresponds to the protected layer's vertical stress distribution law in numerical simulation and similarity simulation. With the exploitation of the composite protective layer, the protective layer's pressure begins to release. The average gas drainage concentration is 2-3 times of that before the composite protective layer mining. [ABSTRACT FROM AUTHOR]

Coal and gas burst is one of the significant and catastrophic hazards in underground longwall operations. To date, the protective coal seam mining has been recognized as the most effective mining method for minimizing or even avoiding the effect of the coal and gas burst. In this paper, numerical modelling and field test were carried out for the longwall operation in Qidong Coal Mine in order to investigate the induced stress and coal seam gas drainage performance in the protected coal seam after the complete extraction of the protective coal seam. It was found that four stress zones can be classified in the protected coal seam being the original stress zone, stress concentration zone, stress relief zone, and recompaction zone. In addition, the monitoring data of gas concentration and volume change in the field agree well with the numerical modelling results. [ABSTRACT FROM AUTHOR]

The thick and hard rock strata (THRS) exist widely in coal measure strata, which control the movements of overlying rock strata in stopes. When THRS break, great energy is released, which could aggravate the risks of coal and gas outburst, rock burst, and other dynamic disasters. Therefore, the foundation and key of preventing dynamic disasters are to distinguish the THRS that could induce coal-rock dynamic disasters and to analyze the laws of rock stratum breaking and energy releasing. The paper proposed the theoretical calculation methods of the energy accumulation and attenuation of rock breaking which is greatly affected by the hanging length of rock strata and the spreading distance. One or more roof strata that play a leading role in inducing dynamic disasters of the underlying coal mass are defined as the key disaster-inducing strata (KDIS). The disaster-inducing coefficient (DIC) is defined and used as the criterion of KDIS. The greater the source energy, the shorter the spreading distance, and the smaller the attenuation coefficient are, the easier the roof strata are to become KDIS. The disaster-inducing ability of the main THRS was analyzed, and the igneous sill was judged as KDIS, taking the Yangliu Coal Mine as project background. The breaking laws of the igneous sill were obtained by the methods of UDEC numerical simulation and microseismic monitoring, which verified the criterion of KDIS. [ABSTRACT FROM AUTHOR]

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

This paper investigates the problem of gas outburst prediction in the working face of coal mine. Firstly, based on a comprehensive analysis of influence factors of gas outburst, an improved entropy weight algorithm is introduced into a grey correlation analysis algorithm; thus, the reasonable weights and correlation order of the influencing factors are obtained to improve the objectivity of the evaluation. The main controlling factors obtained are used as the input of the prediction model. Secondly, by utilizing the improved particle swarm optimization (IPSO), the penalty factor and kernel parameter of least square support vector machine (LSSVM) are optimized to enhance the global search ability and avoid the occurrence of the local optimal solutions, and a new prediction model of gas outburst based on IPSO-LSSVM is established. At last, the prediction model is applied in the tunneling heading face 14141 of Jiuli Hill mine in Jiaozuo City, China. The case study demonstrates that the prediction accuracy of the proposed model is 92%, which is improved compared with that of the SVM model and GA-LSSVM 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]

To analyze the effect of small faults in the working face on coal and gas outbursts, the coal and gas outburst accident in the 21431 working face was studied with the 3DEC numerical simulation method, and the main research contents were the change laws of both stresses at the small fault and the overburden strata movement rate in the small fault zone of which the drop height and the strike were designed into different groups. The results show that the risk of small fault slip increases with the advancing working face. In addition, there is a positive correlation between the risk and the small fault throw. The movement rate of overburden strata in the small fault zone increases along with the rising of the small fault throw, which increases the energy transferred to the coal seam from the surrounding rock under the effect of the small fault. Hence, the effect of small faults on the working face on coal and gas outbursts was positively correlated with the small fault throw. Under the influence of a small fault strike, the closer it is to the small fault along the dip distance at the same working face, the greater the risk will be of a coal and gas outburst. And the bigger the small fault strike is, the greater is the stress concentration degree in front of the working face and the more the elastic energy is stored and the greater is the possibility of an outburst. The paper analyzes the influence of small faults on coal and gas outbursts in the working face, which has reference significance for the prediction and prevention of coal and gas outburst disaster in the working face. [ABSTRACT FROM AUTHOR]

The study of the energy accumulation and rate of release in hard coal under dynamic, static, and coupled dynamic-static loading and its failure mode is of significance when studying the mechanism underpinning coal mine dynamic disasters such as rock burst, coal, and gas outburst. In this paper, four experimental methods (uniaxial compression, Brazilian splitting, and coupled dynamic-static tensile and coupled dynamic-static compression) were used to analyze the energy accumulation, energy rate of release, and failure modes of this type of hard coal under different loading conditions. It was concluded that (1) the energy accumulation and rate of releases of this type of hard coal under static compression are 17.63–179.90 times and 18.57–13157.89 times those under static tension; the energy accumulation and rate of releases in dynamic compression are 2.11–248.53 and 0.23–48 times those under dynamic tension, respectively. (2) During dynamic loading, the ratio of compressive energy accumulation to tensile energy accumulation is reduced by 1.6 times compared with static loading, and the ratio of compressive energy release to tensile energy rate of release is decreased by 363.84 times compared with static loading. (3) The energy accumulation and rate of releases of this type of hard coal for dynamic tensile are, respectively, 2.64–17.42 and 1.07–5.26 times those under static tensile load; the energy accumulation under dynamic compression is greater than that under static compression, being 0.24–15.04 times that under static compressive, but the energy rate of release under dynamic compression is 0.0003–0.56 times that under static compression. (4) The greater the prepeak energy accumulation, the greater the degree of damage of the coal sample at each stage, and also the higher the degree of fragmentation after the failure. The research results play an important guiding role in further understanding the mechanism of coal mine dynamic disasters. [ABSTRACT FROM AUTHOR]

Methane is a companion of coal formations, and it has a complex interaction with the coal seam and its surrounding rock. Methane not only has characteristics of weakening coal strength but also influences the characteristics of electromagnetic radiation (EMR) during coal damage. In this paper, a drop hammer impact test method was introduced to conduct dynamic loading on gas-containing coal samples with different pore pressure treatments. Then, a typical high gas and outburst coal mining workface was selected to carry out a long-term field site experiment. The EMR signal features collected during both the experimental tests and field site tests were analyzed to investigate the influence of methane. The results show that: i) there is a clear correlation between the pore pressure and the transient EMR signal characteristics during the failure of the gascontaining coal sample; with the increase in the pore pressure, the overall intensity, duration and total energy of the EMR signal decreases accordingly; ii) the EMR signals measured in the two directions at the site have great consistency; these signals are cluster pulses with energy in the range of 0.1 mJ-2 mJ; iii) the energy, pulse counts, and duration of the EMR signal have good positive correlation with the blasting charges; and iv) with the increase in the gas content in the coal seam, the amplitude and energy of the EMR signal induced by the blasting vibrations are significantly decreased; however, the main frequency of the signal is not substantially affected. This study provides a basic demonstration to prove the effect of methane on the dynamic rupture of coal and the features of the produced EMR, which are of great significance to the application of EMR to conducting early warning of outbursts. [ABSTRACT FROM AUTHOR]

Protective coal layer (PCL) mining is a preferred regional method for preventing coal and gas outbursts; stress‐relief of PCL mining is the prerequisite of pressure‐relief gas drainage. In order to study the stress‐relief effect of PCL mining on protected coal seams and determine the protection scope of PCL mining under different inclinations, this paper uses physical simulations to study the stress‐relief law and deformation characteristics of the strata during upper PCL mining with a gentle inclination (25°), an intermediate inclination (45°), and a steep inclination (65°). The results show that as the coal seam dip increases, the degree of deformation and failure of the overburden strata gradually decreases, the severe subsidence and expansion area of the overburden strata tends to gradually develop in the uphill direction of the working face, and the floor strata underlying the protective seam significantly expand toward the goaf. However, the absolute value of the upward movement of the floor strata is much smaller than that of the roof strata; and the greater the dip angle, the greater the ratio of floor displacement to roof subsidence. The stress‐relief curve of the protected layer is approximately U‐shaped. As the inclination of the coal seam increases, the stress‐relief range decreases gradually. The maximum relief‐stress and the stress release coefficient of the protected layer initially increase and then decrease. The stress concentration coefficient of the protected coal seam initially increases first and then decreases in both uphill and downhill of the working face in the PCL. As the inclination increases, the stress‐relief angle of the downhill boundary initially increases and then decreases, while the stress‐relief angle of the uphill boundary decreases gradually. Our research results provide guidance for the delimitation of the protected scope of PCLs with different dip angles. [ABSTRACT FROM AUTHOR]

• A two-phase gas-solid flow model for outburst shock waves is established. • Three parameters of the release of gas pressure potential energy are defined according to the energy transformation during gas expansion process. • The gas dynamic characteristics of two-phase flow in the initiation stage are quantitatively studied under the four factors: initial gas pressure, particle volume fraction, particle size and outburst hole size, which is verified by experiments. The dynamic effect of coal and gas outburst seriously threatens the safety of underground equipment and workers in mines. In this paper, the models for outbursts are established, and according to the energy transformation during gas expansion process, three parameters of the release of gas pressure potential energy are defined and the gas dynamic characteristics of two-phase flow in the initiation stage are quantitatively studied under the four factors: initial gas pressure, particle volume fraction, particle size and outburst hole size. The gas dynamic characteristics in numerical simulations are verified by experiments. The results show that for the influence of the factors on the gas dynamic characteristics of two-phase flow, initial gas pressure >outburst hole size >particle volume fraction ≈particle size. The solid particles block the pressure potential energy release from chamber, so does the caliber. However, the maximum of pressure drop occurs when the caliber is 80% of the chamber, which explains the outbursts in mines are so violent due to the caliber smaller than the internal space. This paper provides a novel quantitative research method of gas dynamic characteristics of coal and gas outburst, which is of guiding significance to the design of outburst prevention facilities and emergency rescue measure. [ABSTRACT FROM AUTHOR]

The revelation of the distribution characteristics of stress and fractures in the floor strata is of great significance to improve the regional gas drainage efficiency and to eliminate or reduce the risk of coal and gas outburst in adjacent coal seams during multi‐seam mining. In this paper, the stress distribution in the floor under mining condition was derived, and the characteristics of stress zones in the floor were elaborated while mining the 22201 working face in Shaqu coal mine in Shanxi province, China. Besides, the propagation laws of fractures in different stress zones were theoretically analyzed, and the distribution law of fracture angles in the floor strata under different mining‐induced stresses was obtained. The research results demonstrate that the compression and transition zones show high vertical stress and less developed fractures and are dominated by fractures with a large angle (>60°), which is unfavorable for gas drainage. The expansion zone in the floor within 2‐40 m in the rear of the working face is characterized by high unloading degree of vertical stress and developed fractures. Moreover, fractures with a small angle (<60°) dominate the spatial distribution of the fractures, which is favorable for gas drainage. The research results can not only be a beneficial supplement to the theory of coal and gas co‐exploitation in multi‐seam mining but also provide theoretical support for optimizing the design parameters of cross‐measure boreholes under similar conditions. [ABSTRACT FROM AUTHOR]

Underground coal seam gas drainage is an effective method to lower the risk of coal and gas outburst disaster. However, it is difficult to drainage gas in the low-permeability coal seam, especially low-permeability thick coal seam with a tectonic coal sub-layer. Due to the special structure of this coal seam, many conventional technologies are inefficient. In this paper, to stimulate the coal seam gas drainage, we proposed a hydraulic flushing cavitation technology. Theory analysis, numerical simulation and field tests ware carried out to study the stress relief and permeability increase after adopting this technology. The results indicated that a large hole was formed in the coal seam, which enlarged the scope of stress relief and plastic damaged, and the coal seam permeability and gas drainage efficiency increased significantly. [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 an important energy resource internationally. However, accidents have severely restricted the clean and safe production of coal resources. Among such accidents, coal and gas outburst accidents are a kind of coalmine disaster with high destructive power. Previous research on coal and gas outburst accidents mainly focused on gas factors but ignored the role of human factors. This paper analyses the coal and gas outburst accidents in China from 2008 to 2018 and studies its macroscopic laws. To better understand the causes of coal and gas outbursts, this paper uses the 24modelel to analyse coal and gas accidents and suggest measures for accident prevention from the two aspects 'gas' (risk control) and 'humans' (behavioural safety). Macroscopic law research found the following: (1) March, May, July, and August are the predominant months for accidents. (2) The second to fourth hours of the working hours and the first hour before the end of work are the peak periods for accidents. (3) Guizhou, Hunan, Henan, Sichuan, Yunnan, and Chongqing are the provinces with the most coal and gas outburst accidents. (4) An overall 75.82 % of accidents occurred in the driving face, and 81.08 % of accidents occurred in coal and gas outburst mines. (5) Blasting, drilling, driving, and coal falling are the main inducing factors. Case analysis of accidents found the following: (1) Human error is the leading cause of accidents. Among the errors, the lack of strict enforcement of outburst prevention measures, illegal command, and the illegal operation of miners are the main unsafe acts. (2) Safety knowledge and awareness of miners is not generally high, and serious habitual violations and unsafe psychologies exist. (3) The gas comprehensive prevention system and supervision system in the coal mine safety management system (SMS) can be easily operated improperly, and the safety training system and emergency management system can be absent. (4) Coalmine enterprises seriously lack safety culture. [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 outburst is a potentially fatal risk during the mining of gassy coal seams, which seriously threatens the safe mining of collieries. To understand the outburst mechanism and evolution rules, a new apparatus (LSTT) was developed to conduct simulated experiment. In the context of an outburst accident in Dingji coal mine, the authors launched an authentic outburst experiment to replay the outburst accident. Experimental apparatus, similar criterion, coal‐like materials and gas sources, and experimental design were discussed systematically in this paper. Experimentally, the study analyzed the geo‐stress has significant influence on the outburst evolution. At the driving face, the stress concentration possibly caused gas outburst, under the influence of mining‐induced stress. After the outburst occurred, the stress balance of the coal changed, resulting in the instability of the coal. Furthermore, the elastic energy, gas enthalpy, and gravitational potential energy were released rapidly. The experimental result stated that outburst coal has the sorting characteristics, in line with the field outburst law. The intensity prediction model has been built based on the energy model. Moreover, the factors that impact outburst intensity were analyzed. In the process of coal and gas outburst, the gas enthalpy of gas and the elastic potential of coal are the main energy sources. This study provides guidance for the development of the outburst mechanism and outburst mine management. [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]

In the process of coal mining, coal and gas outburst is one of the most severe disasters, which is accompanied by the outbursts of CO2, CH4, N2, and other gases. Since the intensity of the outburst is affected by the adsorption characteristics of different gases, the study of the adsorption characteristics of multi-gas in the coal body is of great significance for the prevention and control of coal and gas dynamical outbursts in coal mining. In this paper, the self-developed adsorption-instantaneous pressure relief test system for gas-containing coal was used to study the damage characteristics of multi-gas in briquette adsorption-instantaneous pressure relief and to characterize coal adsorption expansion deformation and instantaneous pressure relief deformation quantitatively. The results showed that under the same temperature and pressure conditions, the adsorption expansion deformation capacities of different gases were in the order of CO2 > CH4 > N2. With the increasing pressure of pressure relief, the damage of the coal body tended to be more significant. Although the briquette exhibited isotropic mechanical properties, the process of adsorption expansion deformation was not completely consistent with the isotropy of deformation, in which the axial strain was slightly larger than the radial strain. Moreover, it was found that the adsorption equilibrium time was positively correlated with gas pressure and gas adsorption characteristics. [ABSTRACT FROM AUTHOR]

Gas outburst can result in great loss of life and property during tunnel construction. Gas outburst in tunnels in non-coal formation is often more harmful than that in coal-bearing formation. In order to take effective countermeasures to prevent the occurrence of gas outburst during tunnel construction, it is essential to assess the risk of gas outburst before tunnel construction. This paper attempts to establish an assessment system for evaluating the risk of gas outburst in tunnels in non-coal formation in the survey phase of tunnelling based on the attribute mathematical theory. Based on the principle of relevance and operability, eight factors that influence the gas outburst in non-coal formation are selected as the attribute evaluation indices. Attribute measure functions are constructed to calculate the single index attribute measures for evaluation indices. The fuzzy Analytic Hierarchy Process is used to determine weights of evaluation indices. A confidence criterion is applied to recognize the risk grade of the evaluation object. The proposed attribute evaluation system is applied to assess the gas outburst risk in a tunnel in the survey phase. The evaluation results show good agreement with the practical situation of gas, verifying the applicability of this attribute assessment system. [ABSTRACT FROM AUTHOR]

Determining the advanced mining influence range of an underground working face is crucial for preventing dynamic disasters, such as coal bursts and gas outbursts. In this study, the occurrence of advanced seismicity before the working face as well as its correlation with the acoustic emission (AE) activity of coal and rocks under axial loading was analyzed. Based on the results, a novel statistical method to determine the advanced mining influence range based on advanced seismicity data was proposed and then validated with a case study. The results show that advanced seismicity is caused by the combined effects of static and dynamic stresses at the working face. This seismicity can be used to assess the mining influence degree of the working face on the advanced coal and rock mass, and determine the advanced mining influence range. Using the novel statistical method, the normalized curves for the total number and total energy of the advanced mining-induced seismicity can be plotted. Then, the advanced mining influence range can be determined using thresholds. The thresholds can be established based on the AE activities observed in coal and rock samples under axial static loading. In the case study in this research, the thresholds for the total seismic number and total seismic energy are 0.076 and 0.052, respectively. The corresponding advanced mining influence ranges are 275 m and 245 m, respectively. Field monitoring confirms an advanced mining influence range of 255 m, which validates the results obtained using the novel statistical method. [ABSTRACT FROM AUTHOR]

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Gas pressure is one of the major factors to characterize the outburst danger of coal seams. Generally, the process of gas pressure determination is complicate and cannot ensure the accuracy of results, which may cause a wrong identification of outburst danger. This paper discussed and revealed a positive correlation between initial gas emission and gas pressure, which provides a new approach to identify the outburst danger by initial gas emission. Through theoretical analysis and numerical simulation, the liner equation of gas pressure and initial gas emission was deduced. Laboratory experiments under adsorption and desorption of CO2 and N2 were performed using coal samples from Weishe coal mine. The data of initial gas emission under different gas pressure were recorded, and the fitting curves were obtained. The results show a positive correlation between initial gas emission and gas pressure, and the curve of N2 was below the CO2. Especially, while the adsorption gas pressure was under 0.663 and 0.675 MPa, the difference of corresponding initial gas emission was only 0.01 L/s, which indicates the high degree of correlation. The results validated the theoretical and practical feasibility to identify the coal and the gas outbursts through initial gas emission. [ABSTRACT FROM AUTHOR]