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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]

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]

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]

Taking coal mine dynamic disaster as research background in this paper, five samples of coal–rock composite bodies (CRCBs) with different coal thicknesses were designed, and the uniaxial loading tests were carried out on them by using the MTS uniaxial loading instrument and the DS5 acoustic emission instrument, and the damage process of the samples were analyzed from the perspective of energy conversion. The results were as follows. With increase in coal thickness of CRCBs, the uniaxial compressive strength and elastic modulus of CRCBs decreased while the peak strain increased, and the overall bearing capacity of the samples decreased, resulting in a decreasing trend of AE peak ringing count and peak energy. According to the theory of conservation of energy, it was found that the dissipated energy of the samples in the compaction stage accounted for a large proportion, and the elastic stage was dominated by the accumulation of elastic energy. After the plastic stage, the energy conversion rate in the samples accelerated, and the dissipated energy increased rapidly, leading to the gradual failure of the samples. The energy storage limit of samples decreased logarithmically together with increase in coal thickness. Finally, it was found that coal was the main energy storage structure of the whole coal and rock composite system by analyzing the energy accumulation mechanism of coal and rock composite structure in practical engineering. Therefore, to prevent and control underground dynamic disaster in practical engineering, the internal energy storage of a coal seam should be released and the clamping effect of roof and floor on coal body should be weakened. The achievements of this study will be a theoretical guidance for preventing and controlling dynamics. [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]

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]

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]

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]

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]

Understanding the combined effect of stress, pore pressure and temperature on methane permeability is crucial to hazards detection and mitigation in deep coal mining. It is well known that mine temperature increases with mining depth and methane permeability decreases correspondingly. Methane extraction before coal mining lowers mine temperature and thus enhances permeability near working faces. On the other hand, coal seams can reach yield deformation more easily and even induce stress sharp drop or failure in higher temperature environments. The combined effect of stress, pore pressure and temperature might easily trigger a rapid enhancement of permeability near working faces or even coal and gas outbursts. Therefore, understanding this combined effect on methane permeability is a key issue to hazard detection and mitigation. So far, this combined effect has not been well understood in either experimental measurements or numerical simulations. This paper investigated the methane permeability of six gas-containing coal samples in a complete stress-strain process through our thermal-hydro-mechanical (THM) coupled test apparatus. In these tests, coal specimens were taken from the anthracite coals of Sihe colliery and Zhaozhuang colliery within the southeast Qinshui Basin in Shanxi province of China. A self-made 'THM coupled with triaxial servo-controlled seepage apparatus for containing-gas coal' was developed for these tests. The evolution of methane permeability in a complete stress-strain process was continuously measured under constant differential gas pressure, constant confining pressure and three constant temperatures of 30, 50 and $$70\,^{\circ }\hbox {C}$$ . These experimental results revealed that: (1) Higher temperature had lower compressive strength and lower limit strain, thus coal seams more easily failed. (2) The evolution of methane permeability of coal heavily depended on stress-strain stages. The permeability decreased with the increase of deviatoric stress at the initial compaction and elastic deformation stages, while it increased with the increase of deviatoric stress at the stages of yield deformation, stress sharp drop and residual stress. (3) Temperature effect on the permeability of coal varied with deformation stages, too. This effect was significant before yield deformation, where higher temperature caused lower permeability, but not important after yield deformation, at which the development of coal cracks became dominant. These observations and measurements are helpful for the design of hazards detection and mitigation measures during coal mining process. [ABSTRACT FROM AUTHOR]

It is very important and effective to characterize the failure mechanism of coal and rock materials from the perspective of energy. Energy dissipation and release are important causes of rock mass failure. To qualitatively and quantitatively characterize the energy evolution process of gas-bearing coal and the energy evolution mechanisms of coal and gas outburst, experimental studies were conducted on gas-bearing coal under different stress paths. The research results demonstrate that the energy evolution of gas-bearing coal has nonlinear characteristics and that the energy density is a quadratic function of stress. The total energy density is mainly stored as elastic energy density and is unrelated to loading paths. According to the distribution characteristics of abutment pressures in a stope, the energy distribution can be divided into an energy dissipation and release zone, an increasing-energy zone, and a stable energy storage zone. During coal mining, abutment pressure in front of the coal wall is an important factor causing energy accumulation, and the stress concentration area is a key area to prevent and control dynamic disasters of coal and rock masses. Furthermore, based on the principle of energy conservation, this study established an energy balance model for coal and gas outburst and derived energy criteria for coal and gas outburst. When Υ > 1 , there is a risk of coal seams have outburst. If Υ = 1 , the system is in a state of limit equilibrium, and mining disturbances could trigger outburst. [ABSTRACT FROM AUTHOR]

A systematic analysis on gas occurrence in geological structure zone is crucial to coalbed gas exploitation, gas disaster prevention and outburst risk prediction. To study the geological control of fold structure on gas occurrence and its contribution on coalbed gas outburst, a typical case taken from Qinan coal mine was investigated by laboratory tests, theoretical analysis and on-site exploration. Thereby, a comprehensive understanding was made from the influence of fold structure on tectonic stress, coal structure and gas occurrence based on integrated factors outburst hypothesis. The results indicate that burial depth from 470 to 675 m has a slight influence on the fundamental properties of 72 coal seam, whereas the existence of Wanglou anticline is more relevant to affect vitrinite reflectance, gas adsorption and emission capacity with a positive correlation. By comparing the field data of gas content, pressure and emission quantity, it can be discovered that gas occurrence in 81 mining area appears to be primarily controlled by fold structure. Similar trends can be found in drilling cuttings index, indicating that geological stress increases with the distance approaching Wanglou anticline. In this case, a detailed description of tectonic stress in studying area is conceptually presented. Based on physical, pore structure and surface analyses, further knowledge on structural transformation by fold structure demonstrates adsorption and seepage pores are well developed with complex and disordered surface morphology, providing an evidence on the geological formation mechanism of tectonic coal in Wanglou anticline zone. Moreover, a conceptual description is proposed to explain the generation, migration and preservation mechanism of gas occurrence in the fold zone, which is consistent with roof and floor lithological properties as well as gas content data. Additionally, the locations of six gas outburst accidents were investigated to verify the relationship with fold structure. Based on the above results, theoretical analysis for coal mine outburst is discussed, which highlights the effect of tectonic stress on gas occurrence and coal structure as well as their contributions to gas outburst. [ABSTRACT FROM AUTHOR]

Highlights from the article: 4Structure of the gas flow system (units: mm). a Borehole assembly schematic, b gas extraction boreholes, c gas inlet part, and d gas outlet part. 5a. The gas flow rate is obtained by the gas flow meters using the Digital MFC software, which has 2 eight-channel data acquisition boards. CO SB 2 sb gas instead of CH SB 4 sb was used in the experiment for safety reasons, and the gas inlet was closed after a saturated gas pressure of 1.0 MPa was attained.

In order to obtain the weakening influence of coal seam water injection on coal and gas outburst, taking the 1100 m outburst coal seam in Sunjiawan Coal Mine in Fuxin of China as the research object, coal and gas outburst energy conversion model was established. The influence of water content on coal and gas outburst test was studied by using a self-developed simulation experimental system. The relationships between water content and critical gas pressure, outburst strength and energy conversion rate were analyzed. The results show that gas pressure is the main power source of coal and gas outburst, and the relationship between water content and critical gas pressure increases exponentially. When the water content increases from 0% to 3% and 6%, the relative strength of outburst decreases by 9.6% and 1.2%, respectively. With the increase in water content, the relative outburst strength and absolute outburst strength will gradually decrease. Gas internal energy is the key factor affecting coal and gas outburst energy which is closely related to the outburst-forming and the outburst-triggering process. As the water content increases, the outburst-forming energy and the outburst-triggering energy increase linearly. However, the energy conversion ratio decreases linearly and the less prone to coal and gas outburst. [ABSTRACT FROM AUTHOR]

Coal and gas outburst disaster of the No. B-1 Coalbed, Henan, China, have lasted for nearly 60 years, and the threat will become more and more serious as mining depths continuously increase. However, coal and gas outburst characteristics and factors of the coalbed have not been studied in detail. To effectively prevent and control coal and gas outburst, we analyzed the type, intensity, location and precursors of coal and gas outburst occurring in the No. B-1 Coalbed. Moreover, the effects of geological conditions (burial depth, faults, folds, coalbed thickness and dip) and mining disturbances on coal and gas outburst were studied. The results showed that these outburst accidents were mostly typical, small-sized and medium-sized outburst, which mainly occurred at the coal roadway working faces. There were many precursors such as blasting sound, changes in coal structure, and abnormal gas emission prior to the accidents. Within a burial depth of 500 m, the average outburst intensity had a stronger correlation with the burial depth, which was more obvious at a burial depth of 301∼400 m, and less obvious at a burial depth of 401~500 m. However, the distribution of these outbursts barely changed within the burial depth. Up to 99.15% of coal and gas outburst occurred at faults, folds, and areas with changes in coalbed thickness and dip. Up to 68.25% were induced by blasting and 18.04% occurred during shelving, coal-shoveling and no operation. The No. B-1 Coalbed was characterized by delayed outbursts. Moreover, specific suggestions were recommended for the prevention and control of coal and gas outburst. The study is useful to government regulators and staffs engaged in the prevention and control of coal and gas outburst. [ABSTRACT FROM AUTHOR]

By analyzing the gas occurrence, it is found that ground stress plays a leading role in coal and gas outburst in eastern coal mines of Nos. 8, 10 and 12 in Pingdingshan Mining Area where show the most serious outburst hazards. According to the isograms of coal seam depth in F Group, the relationship between the distributions of the fold tectonic stress and the coal and gas outburst was simulated using the ANSYS program. The result shows that the stress concentrates near to the fault and the outcrop of the fault enhances the possibility of gas outburst. The shear stress in the north of the anticline is greater than that in the south. The shear stress direction on the north wing of the anticline is dextral and the coal seam in this area exhibits highest possibility for gas outburst. However, on the surrounding rock, the shear stress direction on the north wing of the anticline is sinistral. The regions with fold tectonic stress ranging from 1.44 to 4.47 MPa correspond to the sites with high risk of gas outburst. Ground stress is the main factor controlling the coal and gas outburst in the three mines. Currently, the distribution of coal and gas outburst in the three mines is in agreement with that of coal shear stress. [ABSTRACT FROM AUTHOR]

A coal and gas outburst can lead to a catastrophic failure in a coal mine. These outbursts usually occur where the distribution of coal seam gas is abnormal, commonly in tectonic belts. To study the effects of the abnormal distribution of this gas on outbursts, an experimental apparatus to collect data on simulated coal seam outbursts was constructed. Experiments on specimens containing discrete gas-enriched areas were run to induce artificial gas outbursts and further study of these outbursts using data from the experiment was conducted. The results suggest that more gas and outburst energy are contained in gas-enriched areas and this permits these areas to cause an outburst easily, even though the gas pressure in them is lower. During mining, the disappearance of the sealing effect of a coal pillar establishes the occurrence conditions for an outburst. When the enriched gas and outburst energy in the gas-enriched area is released suddenly, a reverse unloading wave and a high gas pressure gradient are formed, which have tension effects on the coal. Under these effects, the fragmentation degree of the coal intensifies and the intensity of the outburst increases. Because a high gas pressure gradient is maintained near the exposed surface and the enriched energy release reduces the coal strength, the existence of a gas-enriched area in coal leads to a faster outburst and the average thickness of the spall is smaller than where is no gas-enriched area. [ABSTRACT FROM AUTHOR]

Gas outburst disasters are becoming more serious as the underground coal mines become deeper in China, and a thick zone of deformed coal provides conditions favorable to coal and gas outbursts. The Daning coal mine's main mining seam is the No. 3 coal seam with coal and gas outburst hazard, which often contains two normal coal sub-layers and one deformed sub-layer. Considering both the geological conditions of the coal seam and applications of the in-seam directional longhole drilling technology, a new schematic diagram of in-seam directional longholes for gas drainage is developed. The two borehole layout models of longwall panel and main entries for gas outburst disasters control have been successfully applied. The gas drainage rates of both models are >70 %, and the residual gas contents are both <8 m/t, which can be considered that the gas outburst disasters were effectively controlled. To better guide gas drainage, gas drainage normal and failure modes have been obtained. Although in-seam directional longhole technology has been successfully applied for regional gas drainage with benefits to gas outburst control, there are also some problems that are detrimental to greenhouse gas reductions in gas drainage and gas utilization. The three main problems are air leakage failure in gas drainage, decreasing gas concentration and a low gas utilization ratio. To address the problems mentioned above, five improvements are suggested. [ABSTRACT FROM AUTHOR]

Coal and gas outbursts took place about thirty times at one coal mine in China, which not only caused safety problems but also hindered the regular production in different degree. In-situ geo-stresses of two points are successfully measured near coal and gas outburst locations, and the measured maximum principal stress is approximately at the horizontal direction, while the minimum principal stress is at the vertical direction. A three-dimensional model is built with FEM software of ANSYS, the measured geo-stress are taken as boundary pressures to be applied on the FEM model, and the geo-stress fields in the coal seam are calculated. In the end, the qualitative influence of the maximum principal geo-stress on coal and gas outburst is analyzed based on the relationship between geo-stress and number of coal and gas outburst. [ABSTRACT FROM AUTHOR]

Intrusive igneous rock is usually found in the overlying strata above mining stopes, and its occurrence, lithology, and distribution play important roles in coal mining safety. Of the numerous coal mine disasters in China, a large number have been caused by magma intrusion. Magmatic activity is intense and widely distributed in the Haizi Coal Mine which has suffered eleven coal and gas outburst accidents and one water inrush accident under a thick-hard igneous rock with 120-m-thick. Based on theoretical analysis, laboratory testing and field observations, we found that under the effect of thermal evolution and entrapment of the igneous rock, the coal pore structure developed, the gas adsorption capacity was enhanced, and the risk of gas outburst increased. The igneous rock, as the main key stratum, will not subside or break for a long time after mining. The closing time of fractures and separations is also prolonged and provides good conditions for gas drainage. The distant penetration borehole for draining pressure relief gas is proposed which can ensure effective gas drainage and reduce the number of rock laneways. However, with the continuous mining of a large area, the igneous rock could suddenly break, instantly releasing a tremendous amount of elastic strain energy, which will easily induce the occurrence of complex dynamic disasters, such as rock bursts, water inrush, gas outbursts, and surface subsidence. Based on the cause analysis of dynamic disasters, a reasonable goaf filling height is proposed for fully eliminating mine disasters under the special geological condition. [ABSTRACT FROM AUTHOR]