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Vibrations caused by downhole operations often induce coal and gas outburst accidents in tectonic zone coal seams. To clarify how vibration affects the pore structure, gas desorption, and diffusion capacity of tectonic coal, isothermal adsorption-desorption experiments under different vibration frequencies were carried out. In this study, high-pressure mercury intrusion experiments and low-pressure liquid nitrogen adsorption experiments were conducted to determine the pore structures of tectonic coal before and after vibration. The pore distribution of vibration-affected tectonic coal, including local concentration, heterogeneity, and connectivity, was analyzed using multifractal theory. Further, a correlation analysis was performed between the desorption diffusion characteristic parameters and the pore fractal characteristic parameters to derive the intrinsic relationship between the pore fractal evolution characteristics and the desorption diffusion characteristics. The results showed that the vibration increased the pore volume of the tectonic coal, and the pore volume increased as the vibration frequency increased in the 50 Hz range. The pore structure of the vibration-affected tectonic coal showed multifractal characteristics, and the multifractal parameters affected the gas desorption and diffusion capacity by reflecting the density, uniformity, and connectivity of the pore distribution in the coal. The increases in the desorption amount (Q), initial desorption velocity (V0), initial diffusion coefficient (D0), and initial effective diffusion coefficient (De) of the tectonic coal due to vibration indicated that the gas desorption and diffusion capacity of the tectonic coal were improved at the initial desorption stage. Q, V0, D0, and De had significant positive correlations with pore volume and the Hurst index, and V0, D0, and De had negative correlations with the Hausdorff dimension. To a certain extent, vibration reduced the local density regarding the pore distribution in the coal. As a result, the pore size distribution was more uniform, and the pore connectivity was improved, thereby enhancing the gas desorption and diffusion capacity of the coal. [ABSTRACT FROM AUTHOR]

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Coal and gas outburst is a common coal-rock dynamic disaster. Such accidents frequently occur, and the mechanism underlying the occurrence of these outbursts is complex. As a typical failure mode of a gas-filled and pressure-relieved coal body, the spallation mechanism should be investigated to reveal the mechanism of coal and gas outburst and guide outburst-prevention strategies. In this paper, a fluid-solid coupling model for coal seam gas flow is established. This model considers the adsorption characteristics of coal. Numerical calculations are used to simulate the stress field distribution and evolution of gas-filled coal bodies under different boundary conditions. The mechanical mechanism of the spallation occurrence after the pressure relief of coal is explained from the perspective of seepage breaking coal. The control of the flow and stress state of the gas to the spallation failure is analyzed. The mechanical-quantitative conditions for the initial failure of the coal body under seepage and the mechanical-qualitative conditions for the continuous advancement and termination of spallation are studied based on numerical solution results. The numerical calculation results show that the formation of a flow field after pressure relief will apply a drag force (tensile stress) on the porous media of coal. The presence of this force plays a crucial role in promoting the spallation and cracking of coal and, thus, the promotion of spallation. The tensile strength, initial adsorption pressure, and pressure relief rate of the coal body jointly control whether the initial failure can occur and the thickness of the fracture layer cracks. Spallation propulsion is mainly determined by the pressure relief conditions of the undestroyed coal body and pressure changes in the spallation space; the former can be quantitatively obtained by numerical calculations, whereas the latter is related to the thickness of the spalled layer and the degree of the layer-crack structure. [ABSTRACT FROM AUTHOR]

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

In order to improve the monitoring and prediction of coal and gas outburst, this paper proposes a new method for dynamic regional prediction of coal and gas outburst using microseismic (MS) monitoring. The theoretical basis of this method is presented. An index evaluation system was established and applied, based on which field tests were carried out in a coal mine. The results show that seismic monitoring with frequency and energy indexes can obtain good results for mining disturbance intensity monitoring and geological structure detection; the regional stress distribution detected by seismic wave tomography is consistent with the theoretical stress field, making its use of great significance for optimizing coal and gas outburst drilling parameters and improving overall tunneling efficiency. This approach overcomes the limitations of traditional methods in the temporal and spatial dimensions and realizes dynamic and continuous monitoring of coal and gas outburst-prone areas. [ABSTRACT FROM AUTHOR]

In recent years, with the increase in mining depth and strength, coal‐rock gas dynamic disasters, such as coal and gas outburst, have shown an increasing trend. Acoustic emission (AE) technology has been viewed as a promising method that can effectively forecast coal and gas dynamic disasters. This paper first tests the AE characteristics of coal and rock samples during loading. Then, self‐developed AE continuous monitoring and early warning equipment is used to monitor and predict the coal and gas outburst dynamic disasters on the working face. And it is found that the coal samples primarily show ductile failure, and the AE exhibits the evolutionary characteristics of "rise‐peak‐fall". The rock samples primarily exhibit brittle failure, and the AE evolution mode is almost no falling stage. Coal and gas outbursts occur after the stress peak. Before coal and gas outbursts occur, there is a clear increasing trend in the AE ahead of the gas concentration variation. When the gas‐bearing coal is damaged by the load, the coal body first breaks due to the stress, and the AE value increases. Then, due to the fracture of the coal body, the crack penetrates, gas rushes out, and the gas concentration increases. The research results can provide an advanced technical method for the monitoring and early warning of coal–rock gas dynamic disasters, and improve the prediction accuracy for dynamic disasters. The AE exhibits the evolutionary characteristics of "rise‐peak‐fall"; the rock sample exhibits brittle failure, and the AE evolution mode lacks the "decline" stage. There is a clear increasing trend in the AE before the gas concentration variation and accidents. When the coal‐containing gas is damaged by the load, the coal body first breaks due to stress, and the AE value increases. [ABSTRACT FROM AUTHOR]

The H-mode transport barrier allows confinement of roughly twice as much energy as in an L-mode plasma. Termination of H-mode necessarily requires release of this energy, and the timescale of that release is of critical importance for the lifetimes of plasma facing components in next step tokamaks such as ITER. H-L transition sequences in modern tokamaks often begin with a transient outburst which appears to be superficially similar to and has sometimes been referred to as a type-I edge localized mode (ELM). Type-I ELMs have been shown to be consistent with ideal peeling ballooning instability and are characterized by significant (up to ~50%) reduction of pedestal height on short (~1ms) timescales. Knowing whether or not this type of instability is present during H-L back transitions will be important of planning for plasma ramp-down in ITER. This paper presents tests of pre-transition experimental data against ideal peeling-ballooning stability calculations with the ELITE code and supports those results with secondary experiments that together show that the transient associated with the H-L transition is not triggered by the same physics as are type-I ELMs. [ABSTRACT FROM AUTHOR]

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

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

Analyzing the causes of accidents, excavating accident paths, and applying accident prevention are important tasks in safety management. Focusing on coal and gas outburst accidents, this study examined the primary accident path and conducted applied research on the reasoning of the accident case. First, combined with the obtained accident causes, a coupling analysis of the causes of coal and gas outburst accidents was conducted. Second, using the method of data mining coupled with Apriori algorithm, the coupling relationship between each cause module of the coal and gas outburst accident was obtained, and consequently, a path map of the coal and gas outburst accident was drawn. Third, a Bayesian network model for the causes of coal and gas outburst accidents was established based on the accident path map and the probability of occurrence of each cause. Finally, considering the safety concept element (SC1) as an example, the Bayesian network model was used to conduct a sensitivity analysis of accident causes. Thereafter, considering the coal and gas outburst accident of the Sanjia Coal Mine in Guizhou Province as an example, probabilistic reasoning research on the cause of the accident was conducted. The application results showed that (1) under normal conditions, there are approximately 797,280 accident paths for coal and gas outbursts. Following data mining, 188 main accident paths were found. (2) Sensitivity analysis determined 19 factors that were sensitive to safety concept elements (SC1), of which the three most sensitive factors were (i) resource management system procedures (SM7), (ii) safety policy (SM1), and (iii) safety training system procedure (SM8). 13 paths exhibited a sensitivity ≥0.5%, of which 7 exhibited strong sensitivity. (3) The absolute accuracy rate of accident cause reasoning in the Sanjia Coal Mine in Guizhou Province was 71.43%, while the relative accuracy rate was close to 100%. Thus, it was concluded that: (1) the accident path mining method proposed in this paper is feasible for main accident path mining. (2) The Bayesian network model for the causes of coal and gas outburst accidents established in this study can be practically applied for the sensitivity analysis of accident causes and exhibits high reliability in the probabilistic reasoning of accident causes. The results of this study is expected to aid in the prevention of coal and gas outburst accidents, and provide reference and help for the path mining of other accident causes and the probabilistic reasoning of accident causes. [ABSTRACT FROM AUTHOR]

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

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

The coalbed methane energy resources waste, environmental pollution and miner's health remain challenging problems in worldwide mining operations accompanied by coal-gas outbursts; thus, the safe and efficient yield of these resources plays a vital role in the world's energy market. The tectonic coal development is a significant geological feature of coal and gas outburst sites, and the study of coal and gas outburst mechanism should be based on more precise geological occurrence characteristics. In this paper, the geological characteristics of coal and gas outburst sites were analyzed. The failure law of coal body under the stratified occurrence of tectonic coal and raw coal seam with different thickness was studied. The mechanical equilibrium equation of non-synchronous deformation of tectonic coal and raw coal was constructed, the initiation criterion of coal and gas outburst was established based on the support body model, and a case study was carried out. The results show that with the thickness increase of the tectonic coal seam, the peak displacement of the driving face increases. The outburst start-up and development of coal and gas outburst, coal and gas extrusion outburst and coal and gas collapse outburst were deeply analyzed, as well as the internal reasons of the occurrence of coal-gas outburst portent are explained, based on the support body model. The development process from the start to the end of coal and gas outburst is revealed, and a new perspective is proposed for the prevention and control of coal and gas outburst: improving the strength of support body is also of great significance for the prevention and control of coal and gas outburst. • Asynchronous deformation induced coal-gas outburst mechanism. • The initiation criterion of coal and gas outburst was established. • The start and development process of the three types outburst were revealed. • New theoretical method and direction into dynamic disaster monitoring. [ABSTRACT FROM AUTHOR]

Mining protective coal seams is an effective approach for coal and gas outburst control, but a large amount of gangue is usually produced when mining a thin protective seam and dealing with the gangue can be a challenging task. In the paper, a novel integrated mining system by extracting two panels simultaneously was demonstrated in the 12th coal mine of the Pingdingshan coalfield: one panel was mined in the thin protective coal seam, and the other one was mined in the protected coal seam. The thickness of the protective seam was only 0.8 m, but the mining height reached 1.8 m, indicating that there was about 1 m thick roof stone being mined. An underground coal preparation plant was built, and the mixture of coal and gangue from the protective panel was sorted underground. The sorted coal was delivered to the surface stockpile, while the waste rock was directly backfilled into the gob of the panel in the protected coal seam. Thus, waste rock did not need to be lifted up to the surface, which can reduce material handing cost and minimise mining footprint on the surface. In order to prevent the migration of pressure relief gas into the working areas of the protective coal seam, the main reasons causing gas exceedance in the upper corner of U-shaped ventilation system were investigated, and then the Y-shaped ventilation system and various gas extraction boreholes were implemented to effectively control the pressure relief gas. Numerical models were developed to assess the effect of applying gob backfilling during the extraction of two panels in parallel. The results show that the gob backfilling can reduce the surface subsidence and horizontal movement, which is very helpful for the protection of ground water and surface infrastructures. [ABSTRACT FROM AUTHOR]

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

Gas outbursts pose a significant threat in the mining of deep low‐permeability coal seams. As mining depth increases, there is a rise in coal and gas dynamic disasters, rendering the gas outburst prevention technology from shallow mining areas unsuitable for deep coal seam exploitation. Addressing the challenges posed by deep, highly gassy coal seams, this study introduces a gas outburst prevention technology integrating destressing in the close distance underlying roadway with gas drainage. The article investigates the relevant technical parameters and assesses the feasibility of this approach. First, it establishes destressing model for the underlying roadway to derive an analytical solution for stress distribution in the coal seam. Second, appropriate technical parameters are designed considering the seepage characteristics of gas in the coal seam. Finally, the gas drainage technical scheme is implemented at Qujiang coal mine to verify its on‐site effectiveness. Field test results indicate an increase in gas permeability within the coal seam following destressing in the underlying roadway, accompanied by significant improvements in the efficiency of gas drainage and the advancement speed of the coal roadway. Specifically, the driving speed of the coal roadway has escalated from 40 m/month to 150 m/month. These outcomes demonstrate the potential of this technology as a promising approach for preventing gas outbursts in the challenging context of deep, low‐permeability coal seams, facilitating swift coal roadway excavation. [ABSTRACT FROM AUTHOR]

The coal and gas outburst and rockburst coupling disaster is becoming increasingly serious due to deep mining. To clarify the mechanism inducing the outburst–rockburst coupling disaster, a true triaxial single-sided unloading mechanical test was conducted with the aid of a true triaxial solid–thermal–gas coupling test device, an industrial computed tomography (CT) system, and an acoustic emission system. Through this test, the mechanical characteristics, meso crushing characteristics, and acoustic characteristics in the disaster formation process were obtained. Additionally, the outburst–rockburst coupling instability disaster law was verified by numerical simulation. The results demonstrated that the stress unloading degree of the coal body was negatively correlated with the initial gas pressure in the outburst–rockburst coupling disaster. The time domain parameter count and energy of acoustic emission exhibited a "bimodal" distribution pattern in the instability stage. The rockburst would occur when the peak value was in a "low-count and high-energy" state, while coal and gas outburst would occur when the peak value was in a "high-count and low-energy" state. The meso slice revealed that gas degradation promoted the development of microcracks in the coal body, and the penetration of cracks resulted in the main cracks of structural instability during rockburst. The coal and gas outburst was mainly attributed to the "cross" shear failure pattern of the coal body. These research findings may lay a foundation for the effective prevention and control of outburst–rockburst coupling disasters. [ABSTRACT FROM AUTHOR]

Addressing common challenges such as limited indicators, poor adaptability, and imprecise modeling in gas pre-warning systems for driving faces, this study proposes a hybrid predictive and pre-warning model grounded in time-series analysis. The aim is to tackle the effects of broad application across diverse mines and insufficient data on warning accuracy. Firstly, we introduce an adaptive normalization (AN) model for standardizing gas sequence data, prioritizing recent information to better capture the time-series characteristics of gas readings. Coupled with the Gated Recurrent Unit (GRU) model, AN demonstrates superior forecasting performance compared to other standardization techniques. Next, Ensemble Empirical Mode Decomposition (EEMD) is used for feature extraction, guiding the selection of the Variational Mode Decomposition (VMD) order. Minimal decomposition errors validate the efficacy of this approach. Furthermore, enhancements to the transformer framework are made to manage non-linearities, overcome gradient vanishing, and effectively analyze long time-series sequences. To boost versatility across different mining scenarios, the Optuna framework facilitates multiparameter optimization, with xgbRegressor employed for accurate error assessment. Predictive outputs are benchmarked against Recurrent Neural Networks (RNN), GRU, Long Short-Term Memory (LSTM), and Bidirectional LSTM (BiLSTM), where the hybrid model achieves an R-squared value of 0.980975 and a Mean Absolute Error (MAE) of 0.000149, highlighting its top performance. To cope with data scarcity, bootstrapping is applied to estimate the confidence intervals of the hybrid model. Dimensional analysis aids in creating real-time, relative gas emission metrics, while persistent anomaly detection monitors sudden time-series spikes, enabling unsupervised early alerts for gas bursts. This model demonstrates strong predictive prowess and effective pre-warning capabilities, offering technological reinforcement for advancing intelligent coal mine operations. [ABSTRACT FROM AUTHOR]

This work discussed the results from tests conducted to study the desorption and outburst characteristics of soft and hard coal under different gas conditions. The research found that gas type has a greater influence on the outburst and desorption characteristics of soft coal. Triaxial compression failure can improve the desorption rate of coal specimens, and the gas desorption rate of hard coal is more affected by triaxial compression failure. In the outburst experiments, the greater the test gas pressure, the greater the crush degree of the coal specimen, and the proportion of small-sized coal powder (<0.1 mm) increases but gradually stabilizes. Moreover, the acoustic emission (AE) signals during the outburst process were recorded, and the evolution law of gas pressure in the outburst carven was also analyzed. Finally, the changes in AE signals and gas pressure could be used to predict the damage and destruction characteristics of coal specimens well. [ABSTRACT FROM AUTHOR]

For the characteristics of high frequency and strong suddenness of dynamic disasters in deep coal mines, the traditional detection and evaluation techniques applied to shallow coal mine failed to accurately judge the risk degree of disasters. Therefore, it is of great significance to use advanced detection technologies and appropriate evaluation methods to improve the accuracy and efficiency of risk assessment in the process of coal mining. The present paper applies the rapid detection and multi-source dynamic detection technologies used in the field of mining with the purpose of improving the reliability of detection technologies for typical dynamic disaster. In this study, the data fusion technology was used to analyze data obtained from laboratory experiments, engineering survey, detection and historical data, so as to form the final dynamic and static indicators. Then, the new combined evaluation models with time series of coal and gas outburst as well as rock burst were established respectively to carry out the comprehensive risk evaluation using the least-squares method and the time-varying weight method. After the comprehensive analysis on the results of the above two evaluation models, the risk areas of the typical dynamic disasters were judged and classified. Finally, the evaluation models were coded to build an early-warning software platform that could achieve automatic evaluation and the actual 3D visualization of coal mining areas. The early-warning software platform was applied to risk assessment of dynamic disasters in Gengcun Coal Mine in Yima City, Henan Province, China. The results of the 6-month experiment showed that the risk assessment accuracy and reliability of the proposed evaluation models was 100% and 90% respectively, which indicates that the newly developed approach is reliable and can be recommended for applying in more coal mines to improve the process safety risk control. [ABSTRACT FROM AUTHOR]

A thin coal seam mined as a protective coal seam above a gas outburst coal seam plays a central role in decreasing the degree of stress placed on a protected seam, thus increasing gas permeability levels and desorption capacities to dramatically eliminate gas outburst risk for the protected seam. However, when multiple layers of coal seams are present, stress-relieved gas from adjacent coal seams can cause a gas explosion. Thus, the post-drainage of gas from fractured and de-stressed strata should be applied. Comprehensive studies of gas permeability evolution mechanisms and gas seepage rules of protected seams close to protective seams that occur during protective seam mining must be carried out. Based on the case of the LongWall (LW) 23209 working face in the Hancheng coal mine, Shaanxi Province, this paper presents a seepage model developed through the FLAC3D software program (version 5.0, Itasca Consulting Group, Inc., Minneapolis, MI, USA) from which gas flow characteristics can be reflected by changes in rock mass permeability. A method involving theoretical analysis and numerical simulation was used to analyze stress relief and gas permeability evolution mechanisms present during broken rock mass compaction in a goaf. This process occurs over a reasonable amount of extraction time and in appropriate locations for comprehensive gas extraction technologies. In using this comprehensive gas drainage technological tool, the safe and efficient co-extraction of thin coal seams and gas resources can be realized, thus creating a favorable environment for the safe mining of coal and gas outburst seams. [ABSTRACT FROM AUTHOR]

Owing to the gas content is an important indicator in coal and gas outburst prevention, we set up a gas adsorption and desorption experimental system with temperature controlling, and draw out a method combining with experimental analysis, theoretical calculation and project inspection to determine the critical value of gas content in coal and gas outburst prediction. This paper takes D6 coal seam in Pingdingshan No.1 coal mine as an example, sets up the powder function equations among the gas content, gas pressure and gas desorption of drill-cuttings (Δh2). The gas content minimum is calculated as 5.04m3/t as the gas pressure and Δh2 reach their critical values respectively, which is lower than the critical value of gas content (5.19m³/t) determined by Langmuir formula, considering a deformed coal with a thickness of 0.6m exists in D6 coal seam, the critical value of gas content is determined as 5.0 m3/t finally, and its accuracy is proved well in engineering application. [ABSTRACT FROM AUTHOR]

Coal and gas delayed outburst is a special type of outburst. At present, it is in the exploratory stage to research on coal and gas delayed outburst, so the research work is of great significance. In this paper, the cause of coal and gas delayed outburst is discussed from the viewpoint of coal body structure characteristics. Some understandings are concluded as follows: the coal and gas outburst may occur when the energy conducive to outburst is greater than the energy not conducive to outburst, which is the mechanics criterion of coal and gas outburst. Among the numerous mining coal seams, some coal seams are consisted of soft-andbroken coal and hard-and-lump coal, and these two coals are may alternately arrayed. For these soft coal and lump coal alternated coal seams, the soft-and-broken coal is with the positive effect of outburst while the hard-and-lump coal is with the negative effect of outburst. At the beginning of unloading, the outburst may not occur when negative effect is greater than positive effect. Along with the time, the deformation of the hard-and-lump coal will increase after unloading, so the negative effect of outburst will decrease gradually. To a certain point of time, the instability and failure of hard-and-lump coal will occur, and this causes the result that the positive effect is greater than the negative effect, which may lead to the outburst of coal and gas. This outburst is a delayed coal and gas outburst, which is the mechanism of coal and gas delayed outburst. [ABSTRACT FROM AUTHOR]

For deep coal mines, geological disturbances or mining activities can cause damage to coal and rock masses, easily inducing dynamic disasters such as rock bursts or coal and gas outbursts, which seriously threaten the safety production of coal mine. In this paper, first, the Liyazhuang Coal Mine introduced the SOS MS (Sensor Observation Service Microseismic) monitoring system from the Polish Research Institute and verified the accuracy of its positioning. Then, to study the characteristics of MS signals induced by different mining activities, based on the field monitoring results, the waveform and frequency spectrum characteristics of MS signals at different energy levels induced by different mining activities are analyzed, and the energy levels of MS signals caused by different mining activities are classified. Studies have shown that there are large differences in the waveform and spectral characteristics of MS signals at different energy levels. High-level energy seismic signals are characterized by large amplitudes, low frequencies, relatively concentrated distribution, long vibration duration, and slow attenuation. In addition, the relationship between mining activities and MS events is also statistically analyzed based on the spatial and temporal distribution of MS events with the advancement of working face, and the results show that the increase of vibration frequency and energy can be precursor information for roof pressure. With the advance of the working face, the MS energy has the characteristic of periodic distribution, which is consistent with the periodic weighting revealed by the working resistance of the support. This study provides a reference for further revealing the energy release mechanism of rock burst. [ABSTRACT FROM AUTHOR]

The influencing factors of coal and gas outburst are complex, and now the accuracy and efficiency of outburst prediction are not high. In order to obtain the effective features from influencing factors and realize the accurate and fast dynamic prediction of coal and gas outburst, this article proposes an outburst prediction model based on the coupling of feature selection and intelligent optimization classifier. Firstly, in view of the redundancy and irrelevance of the influencing factors of coal and gas outburst, we use Boruta feature selection method to obtain the optimal feature subset from influencing factors of coal and gas outburst. Secondly, based on Apriori association rules mining method, the internal association relationship between coal and gas outburst influencing factors is mined, and the strong association rules existing in the influencing factors and samples that affect the classification of coal and gas outburst are extracted. Finally, svm is used to classify coal and gas outburst based on the above obtained optimal feature subset and sample data, and Bayesian optimization algorithm is used to optimize the kernel parameters of svm, and the coal and gas outburst pattern recognition prediction model is established, which is compared with the existing coal and gas outburst prediction model in literatures. Compared with the method of feature selection and association rules mining alone, the proposed model achieves the highest prediction accuracy of 93% when the feature dimension is 3, which is higher than that of Apriori association rules and Boruta feature selection, and the classification accuracy is significantly improved. However, the feature dimension decreased significantly, the results show that the proposed model is better than other prediction models, which further verifies the accuracy and applicability of the coupling prediction model. [ABSTRACT FROM AUTHOR]

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

Determining the influence scope of the airflow disorder is an important problem after coal and gas outburst accidents in ventilation systems. This paper puts forward the indexes of airflow disorder, including the length of the excavation roadway, the outburst pressure, the pressure difference of the air door, and the air quantity of the auxiliary fan. Using the orthogonal table of L9 (34) and numerical simulation method, the characteristics of airflow reversal are studied, and the outburst airflow reversal degree is calculated should the ventilation facility fail. Furthermore, on the basis of fuzzy comprehensive optimization theory, the comprehensive evaluation model of the airflow disorder is established. The results show that the length of the excavation roadway is the most important factor affecting the stability of the ventilation system, followed by the outburst pressure, pressure difference of the air door, and air quantity of the auxiliary fan. The influence of a gas outburst accident on the return air system is greater than that on the inlet air system, and a larger air velocity has a greater impact on the ventilation system, especially the air inlet part. Moreover, the airflow reversal degree of the ventilation system increases with the increase of the outburst pressure or decreases with the length of the excavation roadway. This paper provides a basis for the prevention of gas outburst accidents. [ABSTRACT FROM AUTHOR]

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

Coal and gas outburst is a kind of complex dynamic disaster with short duration and strong explosiveness, and the modes and strength of the outburst are determined by the in situ stress, gas pressure, and physical and mechanical properties of the coal mass. In this paper, the status quo of research on the mechanism of coal and gas outburst in China is described from three aspects: the controlling effect of single factor, the controlling effect of multi-factor, and new understandings of the outburst mechanism in recent years. Firstly, controlling factors of coal and gas outburst are classified for an in-depth analysis of the main factors of the same type of disasters, and the research progress and new understandings of the mechanism of coal and gas outburst are systematically sorted out. Secondly, the influencing factors of the strength coal mass are analyzed, and the related issues of coal mass strength on coal and gas outburst disaster mechanism are discussed. The results show that the stages of incubation, occurrence, development, and stop on coal and gas outburst are affected by the coupling effects of in situ stress field, gas pressure field, and seepage field, and the coal strength becomes an important factor affecting outburst strength under the same in situ stress and gas pressure. Therefore, the scientific and reasonable improvement methods of such similar simulation experiment devices are proposed according to the existing experimental methods and devices, which is of great significance to provide ideas for the continuous transferring to deep mining and preventing coal and gas outburst in China in the future. [ABSTRACT FROM AUTHOR]

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

• 1 Stress distribution was recalculated by stress-softening and prominent dilatancy. • 2 Gas-bearing coal under impact loading was a compaction followed by ruin process. • 3 Measures principles were mainly aimed at fracture and stress-concentration areas. • 4 Preliminary goal-reaching parameter based on principles was proposed and applied. As the increasing demand for coal and the depletion of shallow coal resources, the tendency of coal mining in China is progressively shifting to deeper areas, which brings about a circumstance where the frequency and intensity of coal and gas outburst accidents have further deteriorated. Nowadays, there are many outburst prevention measures being applied on site, while this disaster still occurs from time to time. Therefore, to better improve the preventing outcome of them, this paper came forward with some principles, based on the mechanical theory of deep mining and damage evolution procedure concerning coal containing gas underneath the impact load. The primary conclusions were as follows: the stresses, strains, and associated widths in the three areas, namely fracture area, plastic area, and elastic area, in front of the working face were recalculated by considering stress-softening and dilatancy of coal mass. The damage evolution of gas-bearing coal mass under impact loading was displayed in the LS-DYNA numerical simulation as a process of compaction followed by destruction. The proposed principles could be split into two perspectives, one for the fracture area, specifically, to minimize the descending of the coal mass's strength in this area; another for the stress-concentration zone, namely, to abate the thrust due to extrusion and deformation, on the coal body which was located in the front area. According to those principles, a preliminary goal-reaching parameter was proposed and it was implemented for the evaluation of advanced drilling. The results will cooperate to rationalize the design and layout of local outburst prevention measures, thereby enhancing the efficiency of control and ameliorating the deteriorating scenario of outburst disasters. [ABSTRACT FROM AUTHOR]

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

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

China's coal mines have to extend to greater depths for the exploitation of more mineral resources, and they have suffered catastrophic mining-induced disasters, such as rockbursts, water inrushes, coal and gas outbursts, and roof fall accidents. The microseismic monitoring technique is a practical tool for mine safety management, which is extensively utilized in many Chinese coal mines. Microcracks of coal/rock masses are recorded as microseismicities in the field, and the potential mining-induced instabilities can be assessed by in-depth analysis of the microseismic parameters. This study provides a state-of-the-art review of the achievements and developments of the microseismic monitoring technique in coal mines. It also presents some prospects for improving the location accuracy of microseismicity, efficient and intelligent processing of the microseismic data, comprehensive assessment of coal/rock instabilities, and development of new microseismic monitoring equipment. This study is valuable for mine safety management and may contribute to improving the deep mining production. [ABSTRACT FROM AUTHOR]

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

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

The gas contained in coal plays a crucial role in triggering coal and gas outbursts. During an outburst, a large quantity of gas originally absorbed by coal is released from pulverized coal. The role this part of the gas plays in the process of coal and gas outbursts has not been clearly elucidated yet. Therefore, investigating the changes in gas desorption rate from coal particles of different sizes could provide some meaningful insights into the outburst process and improve our understanding of the outburst mechanism. First, combining the diffusivity of coal of different particle sizes and the distribution function of broken coal, we present a gas desorption model for fragmented gas-bearing coal that can quantify gas desorption from coal particles within a certain range of size. Second, the gas desorption rate ratio is defined as the ratio of the gas desorption rate from coal being crushed to that from coal before breaking. The desorption rate ratio is mainly determined by the desorption index (γ) and the granularity distribution index (α). Within the limit range of coal particle sizes, the ratio of effective diffusion coefficient for coal particles with different sizes is directly proportional to the reciprocal of the ratio of particle sizes. Under uniform particle size conditions before and after fragmentation, the gas desorption rate ratio is the square root of the reciprocal of the effective diffusion coefficient. The gas desorption model quantitatively elucidates the accelerated desorption of adsorbed gas in coal during the continuous fragmentation process of coal during an outburst. [ABSTRACT FROM AUTHOR]

Highlights from the article: With the rapid development of global economy, underground projects such as underground transportation, strategic storage, and mineral resource exploitation are increasing in scale and speed. Four characteristic energy parameters, namely, storage energy rock, storage energy limit, energy storage ratio, and energy dissipation ratio, were proposed to describe energy storage and dissipation properties of rock. "Building Deformation Prediction Based on Ground Surface Settlements of Metro-Station Deep Excavation" authored by D. Li and C. Yan studies the influence of tunnel excavation on ground settlement and building deformation.

The paper presents the results of numerical simulations into the distribution of methane concentration at the intersection of two excavations with a fan (turned on) giving the air stream to the area of the crossing. Assumed case represents emergency situation related to the unexpected flow of methane from an excavation and its mixing with fresh air. It is possible when sudden gas outburst takes place, methane leaks from methane drainage system or gas leaks out the pipelines of underground coal gasification devices. Three options were considered - corresponding to three different speeds of the jet fan. They represent three stages of fan work. First - low air speed is forced by a pneumatic fan, when electricity is cut off after high methane concentration detection. Medium speed can be forced by pneumatic-electric device when methane concentration allows to turn on the electricity. Third, the highest speed is for electric fans. Simulations were carried out in the Fire Dynamics Simulator (FDS) belongs to the group of programs Computational Fluid Dynamics (CFD). The governing equations are being solved in a numerical way. It was shown that proposed solution allows partial dilution of methane in every variant of speed what should allow escape of the miners from hazardous area. [ABSTRACT FROM AUTHOR]

In this paper the problem of coal and gas outburst - the coal pit's most complex and dangerous induced geodynamic phenomenon - occurrence and development has been considered in details. Based on the theoretical and experimental researches it has been shown that this phenomenon may occur in full strength only with sufficient quantity of total potential energy available in the massif's face area together with the conditions required for development of each stage of the phenomenon. However,the main condition shall be occurrence and development of the intensive opening and extension of cracks quasiparallel to the seam's exposed surface and saturation of these cracks with pressurised free gas in the face area. Updating of the coal and gas outburst process allows to improve current prediction of the mine opening hazards with respect to the coal and gas outbursts. [ABSTRACT FROM AUTHOR]

Gas drainage for the single and low gas permeability coal seam is the key technical problem hampering efficient coal mine gas drainage and without which mining safely cannot be realised in China. To solve this problem, this paper presents an engineering method for enhanced coalbed methane recovery based on high-pressure hydraulic flush from floor tunnels. The first step is to evaluate when the likelihood of coal and gas outburst reaches dangerous levels according to coal seam parameters (including coal seam gas contents, gas pressure, permeability and geological conditions). With these parameters in place, the second step is to determine and optimise borehole parameters, such as the effective influencing radius of hydraulic flush, hydraulic flush space between drills and borehole number to make sure that the coal seam stress is fully released and permeability is dramatically increased. What is also included in this step is the employment of a high-pressure hydraulic flush of coal from boreholes drilled from tunnels developed in the floor of the coal seam. Parameters of water pressure, water flow rate and the volume of coal flushed out are selected based on on-site testing and numerical modelling. Finally, numerical modelling and onsite testing are employed to validate the effects of enhanced coalbed methane recovery, which is whether or not coal and gas outburst danger is eliminated according to the national standards of China. The results show that the technology could improve the permeability of a coal seam and that the gas seepage coefficient was increased by about 10.50 times, the pre-gas drainage ratio was up to 35.5–70.4% and the borehole gas drainage experienced a process of increase-steady-decrease, which delayed 15–20 days of the attenuation time. [ABSTRACT FROM PUBLISHER]

The low permeability of coal seams is the primary difficulty for gas production. Hydraulic cutting is one of the most effective technologies for increasing permeability and stimulating gas production. This paper investigates the hydraulic cutting styles in boreholes and the optimal equivalent borehole diameter after discharging the pulverized coal particles. This paper introduces the hydraulic cutting equipment and cutting styles and determines that the cutting cylinder is the most suitable style for a soft coal seam that is prone to gas outburst. The numerical simulation suggests that the radius of the stress-relaxed range increases quickly when the equivalent borehole radius is small, and the rate slows when the borehole radius becomes large. Then the result was verified by a field experiment in Pingmei coalfield. The gas drainage flowrate and stress-relaxed range greatly increased after initially outputting 2 tons of coal from the borehole, whereas the second outputting 2 tons of coal did not appreciably increase the stress-relaxed range and the flowrate. Too much or too little coal discharge is not optimal, and the borehole radius is recommend to be between 0.3 m and 0.4 m after the hydraulic cutting considering the pros and cons in Pingmei coalfield. The results are helpful for the engineering application of the hydraulic cutting technology, for increasing coal seam permeability, and for stimulating gas production. The method for finding the optimal coal discharge in this paper is also helpful for other coal mines. [ABSTRACT FROM AUTHOR]

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

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

Coal structure could be roughly divided into four types. Among them, the two kinds of tectonic coal face a high risk of heat-induced gas outburst, which arises from the unfavorable temperature conditions in the coal structure. However, there is not yet an efficient way to identify the type of coal structure. The adjacent types of coal structures are often misjudged. The lack of an efficient identification method hinders the prevention of heat-induced gas outburst, making it difficult to realize energy-efficient and safe mining. To solve the problem, this paper first theoretically analyzes the ultrasonic properties of different types of coals, and applies backpropagation neural network (BPNN) to build up an intelligent identification model for the type of coal structure. Specifically, the characteristic parameters of ultrasonic signal were taken as the basis for judging the type of coal structure, the identification algorithm of BPNN was adopted to accurately identify the structure type of coal, and then the heat-induced gas outburst risk of the coal was evaluated preliminarily. Experimental results show that the proposed model could accurately identify the type of coal structure, and even differentiate between adjacent types of coals. The research results provide a reference for effective prevention of heat-induced gas outburst, and realization of energy-efficient and safe mining. [ABSTRACT FROM AUTHOR]

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

Protective layer mining (PLM) is one of the most effective regional measures against gas outburst, and the most preferred technique to prevent and control gas outburst. This paper attempts to disclose the effect of close-range PLM in Hezhuang Coal mine, Western Henan Coalfield. Firstly, coal seam I 7 was selected as the lower protective layer, and coal seam II 1 was taken as the overlying coal seam. Considering the situation of actual production, a simulation model for lower PLM was established on Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D). The established model was adopted to simulate the mining of the working face 11030# of the lower protective layer (I 7) at the mining depth of 50, 100, 200 and 250 m, respectively. Through the simulation, the authors summarized the laws of stress evolution and deformation of the working face 11030# of the overlying coal seam (II 1) in the upper part of the stope. The research results are as follows: After the lower PLM, the stress distribution of 11030# II 1 in the strike direction can be divided into three parts from the open-off cut to the stopping line: original stress zone, pressure relief zone and stress concentration zone; the stress distribution of 11030# II 1 in the dip direction can also be divided into the three parts from the top to the bottom. However, the stress distribution in the dip direction is less uniform than that in the strike direction. Meanwhile, the 11030# II 1 had an unobvious deformation in the original stress zone, compressive deformation in the stress concentration zone, and expansive deformation in the pressure relief zone; the maximum expansive deformation was observed in the middle of the pressure relief zone. The research results lay the theoretical basis for engineering application of lower PLM. [ABSTRACT FROM AUTHOR]

The authors of the present paper designed and constructed a prototype of an instrument which enables fully automated determination of the desorbable methane content and effective diffusion coefficient in underground conditions. Due to microprocessor analysis of the recorded data and the application of the mathematical model of the diffusion process, it is possible to automatically determine the amount of methane whose release from a coal sample occurred before the sample was placed within a measuring instrument. It is also possible to carry out follow-up extrapolation of the recorded data so the time duration needed to determine reliable results can be reduced. The instrument was tested and optimized, and a number of copies sufficient for performing underground tests were constructed. The concept of the instrument represents a totally new approach to the observation of gas release from a coal sample. Instead of short-period measurements, virtually the whole process of methane release from coal is registered and analysed. This is possibly due to the use of a grain fraction lower than one mm which is presently applied for the sake of evaluating the methane- bearing capacity and desorption intensity. [ABSTRACT FROM AUTHOR]

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

Coal mine methane (CMM) drainage is an effective method to curb the occurrence of coal and gas outburst and gas explosion, to reduce the amount of greenhouse gas emission, and to make full use of the clean energy(methane). Sealing in-seam horizontal boreholes plays a vital role in CMM drainage. Reasonable sealing length is an important factor to achieve high extraction efficiency and reduce the cost of construction. To determine the minimum reasonable sealing length of drainage boreholes, the radius of the fracture zone was obtained based on the ideal elastoplastic model, and this radius was taken as the minimum sealing length. The influencing factors of the minimum sealing length were analyzed and engineering verification test was taken in Zhongmacun mine in Henan province, China. The research results show that the minimum reasonable sealing length should be longer for a larger radius of the coal roadway and the coal seam with a deeper buried depth, while the minimum reasonable sealing length can be shortened with the increase of uniaxial compressive strength and the supporting stress of the coal roadway. The 11.07 m of sealing length calculated by theories was basically consistent with the 12 m of sealing length verified by the method of drilling cuttings. The reasonableness of sealing length (12 m) was verified by the test results of methane concentration and flux within 40 days. All those outcomes can provide references for other mines to determine the minimum reasonable sealing length of in-seam boreholes for CMM drainage. [ABSTRACT FROM AUTHOR]