Gas Outburst Hazard Research Articles

Prediction of coal and gas outburst hazard using kernel principal component analysis and an enhanced extreme learning machine approach

In order to enhance the accuracy and efficiency of coal and gas outburst disaster risk prediction, a novel approach combining kernel principal component analysis (KPCA) with an improved whale optimization algorithm (IWOA) optimized extreme learning machine (ELM) is proposed for precise forecasting of coal and gas outburst disasters in mines. Firstly, based on the influencing factors of coal and gas outburst disasters, nine coupling indexes are selected, including gas pressure, geological structure, initial velocity of gas emission, and coal structure type. The correlation between each index was analyzed using the Pearson correlation coefficient matrix in SPSS 27 software, followed by extraction of the principal components of the original data through kernel principal component analysis (KPCA). The whale optimization algorithm (WOA) was enhanced by incorporating adaptive weight, variable helix position update, and optimal neighborhood disturbance to augment its performance. The improved Whale Optimization Algorithm (IWOA) is subsequently employed to optimize the weight ф of the Extreme Learning Machine (ELM) input layer and the threshold g of the hidden layer, thereby enhancing its predictive accuracy and mitigating to some extent the issue of "over-fitting" associated with ELM. The principal components extracted by KPCA were utilized as input, while the outburst risk grade served as output. Subsequently, a comparative analysis was conducted between these results and those obtained from WOA-SVC, PSO-BPNN, and SSA-RF models. The IWOA-ELM model accurately predicts the risk grade of coal and gas outburst disasters, with results consistent with actual situations. Compared to other models tested, the model's performance showed an increase in Ac by 0.2, 0.3, and 0.2 respectively; P increased by 0.15, 0.2167, and 0.1333 respectively; R increased by 0.25, 0.3, and 0.2333 respectively; F1-Score increased by 0.2031, 0.2607, and 0.1864 respectively; Kappa coefficient k increased by 0.3226, 0.4762 and 0.3175, respectively. The practicality and stability of the IWOA-ELM model were verified through its application in a Shanxi Province coal mine where predicted values matched actual values exactly. This indicates that this model is more suitable for predicting coal and gas outburst disaster risks.

Acoustic emission spectrum characteristics of structural coal destruction in negative pressure environment

Abstract The uniaxial compression experiments under a low-pressure environment were performed by using structural coal samples. The frequency domain response characteristics of coal mass failure under loading in a low-pressure environment were acquired by FFT transformation and wavelet packet decomposition. The results show: As the loading stress of coal increases, the AE spectrum becomes more abundant, and the whole AE spectrum shows a left-shift trend. When the gas pressure increases, the acoustic emission signals change from low-frequency high-energy to high-frequency low-energy, the frequency band gradually narrates, and the spectrum changes from complex multi-peak shape to single-peak shape. As stress increases, the proportion of energy in the band 0-4.38 kHz gradually increases, while that in other bands gradually decreases. The energy response to stress changes in the two frequency bands of 2.92-4.38 kHz and 4.38-5.84 kHz is the most obvious. When the pressure changes, the energy in three frequency bands of 2.92-4.38 kHz, 4.38-5.84 kHz, and 7.3-8.76 kHz present an evident response trend with the pressure change, and the response trend (increase) of the latter two is exactly opposite (decrease) to that of the former. This phenomenon indicates that 2.92-4.38 kHz and 4.38-5.84 kHz are the characteristic frequency bands of the coal fracture process. The findings of this research offer crucial foundational data to support the monitoring and early warning of coal and gas outburst hazards.

Study on the water transport characteristics during spontaneous imbibition and its impact on gas desorption

During the exploitation of deep coal resources, the gas hazard becomes increasingly significant, severely threatening the high-quality development of the coal industry and the occupational safety and health of miners. Coal seam water injection is underground coal mines' most commonly used dust control measure. Additionally, it is an effective method for preventing localized coal and gas outburst hazards. After injecting water into the coal seam, spontaneous imbibition causes the retained water in the fractures to migrate under capillary action and widely distribute the water within the coal seam, which enhances the wetting degree of the coal by water and the effectiveness of gas prevention. To reveal the migration characteristics of water in the coal during spontaneous imbibition and its impact on gas control, a self-developed gas-bearing coal spontaneous imbibition system was used to conduct isobaric water injection imbibition and gas desorption experiments on gas-bearing coal samples. The results showed that after the water was injected into the coal sample, it migrated from bottom to top under capillary action, resulting in three stages of abrupt, rapid, and gradual changes in the electrical resistivity of different layers of the coal sample over time. The migration distance of water increased with the imbibition time, but the rate of increase gradually decreased. The compaction load increase reduced the coal sample's average pore size, resulting in faster water migration speed. After imbibition, the water content decreased gradually from bottom to top along the axial direction and showed a non-uniform distribution in the radial direction. During imbibition, the water displaced gas within the coal sample, and the amount of gas displaced increased with the imbibition time. Increasing the amount of water injected and the coal sample compacted load can promote water migration within the coal, expanding the wetted area and displacing more gas. After imbibition, due to the displaced gas being released and the water-lock effect, the atmospheric gas desorption amount of the coal sample decreased with an increase in the amount of water injected, following a modified power function relationship. When the amount of water injected into the coal sample was low, increasing the water-injected amount could significantly reduce the gas desorption expansion energy of the coal sample. However, this trend became less apparent as the amount of water injected continued to increase. To improve the effectiveness of coal seam water injection in preventing gas outburst hazards, it is recommended to carry out water injection operations as early as possible to expand the wetted area of the coal seam and to add gas drainage holes to prevent increased coal body outburst tendencies due to local gas pressure rise in the coal seam.

Water Injection Into Coal Seams for Outburst Prevention: The Coupling Effect of Gas Displacement and Desorption Inhibition.

Gassy coal seams generally have low permeability and dry coal bodies, which are susceptible to coal and gas outburst hazards in the process of mining. Water injection into coal seams can significantly alter the gas release rate and flow behavior. However, water has dual effects on coal seams: gas displacement and water-locking, and the coupling mechanism of these two effects is not clear in the whole process of coal seam water injection. By measuring high-pressure gas adsorption isotherms and gas diffusion initial velocity, it was found that both the Langmuir adsorption constant a and gas diffusion initial velocity ΔP decrease with the increase of water content, which would reduce outburst risks. Through the self-developed integrated experimental device of "gas adsorption + water injection displacement + gas desorption″, the changing rules of gas displacement amount, desorption amount, and water lock amount under different water injection conditions were studied. The results show that when the water injection ratio increases from 6 to 25%, the gas displacement would increase from 0.62 to 1.16 mL/g, with an increase of 87.09%. Also, at the same time, the gas desorption capacity would decrease from 4.86 to 4.05 mL/g after pressure relief, with a decrease of 16.67%. The amount of water-locking increased from 0.11 to 0.38 mL/g. The effect of water injection to control coal and gas outburst occurs in two different water injection stages. In the process of water injection, water plays a major role in gas displacement, which is conducive to reducing the gas content of the coal seam. After the completion of water injection, the static water pressure remaining in the coal seam can reduce the gas emission rate. The combination of these two effects can effectively reduce the risk of outbursts.

Re-thinking methane storage mechanism in highly metamorphic coalbed reservoirs — A molecular simulation considering organic components

Highly metamorphic coal plays a significant role in China's energy development plan owing to its high calorific value. Its complex organic composition provides outstanding storage capabilities for methane (clean and efficient unconventional natural gas), which leads to terrible gas outburst hazards. Minimizing the main storage sites of CH4 (micropores) through organic solvent extraction provides an efficient and safe route for exploiting coal and natural gas energy sources. This phenomenon can be elucidated by the removal of the chemical components that have an adverse impact on the micropore filling theory. In this study, we constructed macromolecular models of highly metamorphic coal, and relative dynamic simulations under experiment and field conditions are performed. The corresponding CH4 storage capacity and spatial coordination distribution of the coal after five treatments were derived. Combined with the results of the micropore filling theory, it was shown that the equilibrium distance of CH4 filling in the micropore increased with the degree of extraction (from 0.351 nm for XT to 0.572 nm for XT-DMF). Also, the trend of CH4 adsorption position in the representative samples (the number of monolayer affixations decreased from 10 to 9) provides crucial support for the conclusions, and the low-potential region with a high potential difference contributes to CH4 stability. The breakthrough of this study will provide strong support and a solid theoretical basis for the efficient and safe exploitation of CBM (Coalbed methane) energy resources.

Experimental investigation of gas diffusion kinetics and pore-structure characteristics during coalbed methane desorption within a coal seam

The desorption-diffusion properties of coalbed methane (CBM) are not only the theoretical basis for investigating gas outburst hazards in a coal mine, but also impose a non-negligible impact on CBM recovery performance. In this paper, the pore structure of coal with five different metamorphism degrees was qualitatively and quantitatively characterized with the scanning electron microscopy (SEM) and low-temperature nitrogen gas adsorption (LTNGA) measurements. The isothermal methane ad/desorption experiments were performed with four initial gas desorption pressure scales. Subsequently, the matching degree between eight empirical correlations (ECs) and the measured methane desorption data was determined, and the methane diffusion coefficient (Dfg) was numerically calculated combining with an FGDG (free gas density gradient) diffusion model. Importantly, we evaluated and discussed the sensitivity of pore structure parameters, initial gas desorption pressure, and volatile fraction to Dfg. The results show that pore density distribution differs among coal samples and the pore structure, especially the micropores, is developed better in high-rank coals than in low- and medium-rank ones. Initial gas release velocity increases with an increase in coal rank and decreases negatively with the increasing particle size in an exponential manner. Among the eight ECs, EC-VIII can be applied to more accurately describe gas desorption process during the whole time scale, and its correlation coefficient with the measured data is larger than 0.9900. Dfg increases with an increase in pore volume and specific surface area (SSA), and it is negatively correlated with the average pore diameter. Additionally, Dfg exhibits an asymmetric U-shaped pattern with an increase in the volatile fraction, which is mainly related to the switch between the dominant roles of mesopores and micropores during coal metamorphism. At a lower volatile fraction, the diffusion coefficient is more sensitive to micropores, while, at a higher volatile fraction, mesopores contribute more to the diffusion coefficient.

Study on the characteristics of coal and gas outburst hazard under the influence of high formation temperature in deep mines

Coal and gas outburst is a type of disaster whose hazard intensifies increase with the formation temperature. In this study, the impact of temperature (10–50 °C) on gas “energy-mass” characteristics was investigated, and the indexes for outburst hazard prediction were improved. Results shown that, temperature has varying influences on gas release parameters, and the influence laws are obviously different under the conditions of the same pressure and the same gas content. Taken the initial expansion energy of released gas (IEERG) as the criterion of outburst hazard, under the same gas content, IEERG changes exponentially with temperature (R2 = 0.9924); under the same gas pressure, IEERG changes as a power function with temperature (R2 = 0.7). The variation coefficients of the influence of temperature change on IEERG under the same gas content and the same pressure are 0.1612 and 0.01489 respectively, indicating the gas content index is more sensitive to temperature. This study also proposed a method to re-evaluate the critical value of the prediction index of coal seam outburst hazard in deep high-temperature mines. This method is expected to provide a solution for the safe mining of deep coal resources.

Coal and Gas Outburst Risk Prediction and Management Based on WOA-ELM

A gas outburst risk level prediction method, based on the Whale Optimization Algorithm (WOA) Improved Extreme Learning Machine (ELM), is proposed to predict the coal and gas outburst hazard level more accurately. Based on this method, recommendations are given according to the gas outburst risk level with the help of the Case-Based Reasoning (CBR) method. Firstly, we analyze the accident reports of gas outburst accidents, select the gas outburst risk prediction index, and construct the gas outburst risk prediction index system by combining the gas outburst prevention and control process. The WOA-ELM model was used to predict the gas outburst risk level by selecting data from 150 accident reports from 2008 to 2021. Again, based on the coal and gas outburst risk level, CBR is used to match the cases and give corresponding suggestions for different levels of gas outburst risk conditions to help reduce the gas outburst risk. The results show that the WOA-ELM algorithm has better performance and faster convergence than the ELM algorithm, when compared in terms of accuracy and the error of gas outburst hazard prediction. The use of CBR to manage prediction results can be helpful for decision-makers.

Early Warning Method for Coal and Gas Outburst Prediction Based on Indexes of Deep Learning Model and Statistical Model

The early warning models for coal and gas outburst have become increasingly more important and have gained more attention in the mining industry in an effort to further improve mine safety. In the warning process, however, the theoretical models do not always work in a timely manner largely due to the delayed capture of the real time parameters. Based on the evolving mechanism of gas outburst, the gas emission is considered a dominant factor in this work because its data is attainable in real time and clearly characterizes the entire outburst process. In order to characterize and distinguish the variation of the gas emission during an outburst and normal mining activity, a total of four statistical methods were employed to quantify the variation of gas emission: the moving average, the deviation ratio, the dispersion ratio, and the fluctuation ratio. Also, the Root Mean Square Error (RMSE) and Mean Absolute Percentage Error (MAPE) are also included to demonstrate the accuracy of the deep learning model for predicting the variation of gas emission. Developed from these six indicators, the multi-factor fuzzy comprehensive evaluation model forms the outburst early warning system by calculating the combined index of the difference among the indicators. The accuracy of the early warning system is examined in the case study of the “3.25” gas outburst hazard in Shigang Coal Mine. The results show advantages of the comprehensive evaluation model established from the six characteristic indicators when predicting an outburst.

Study on the Characteristics of Coal and Gas Outburst Hazard Under the Influence of High Formation Temperature in Deep Mines

Study on the Characteristics of Coal and Gas Outburst Hazard Under the Influence of High Formation Temperature in Deep Mines

Analysis on the Shape and Impact Pressure of the High-Pressure Water Jet during the Hydraulic Flushing Cavity Technique

A large proportion of minable coal seams in China belong to low-permeability soft coal seams. Such coal seams suffer serious coal and gas outburst hazards and endure a high incidence of major disasters in coal mines. The adoption of the high-pressure water jet (HPWJ) hydraulic flushing cavity can effectively promote the gas drainage efficiency and volume and eliminate the hidden danger of gas disasters. Nevertheless, the shape and impact pressure of rotating HPWJ are rarely researched. In this study, on the basis of the numerical simulation, the axial and radial stress distributions of HPWJ and the energy-gathering effect of a conical-cylindrical combined nozzle were analyzed. It is concluded that the submerged condition will accelerate the attenuation of jet velocity and reduce the impact strength of the jet. The jet diffusion angle grows with the increases in the nozzle diameter and water pressure, and 24° is the optimal contraction angle. Finally, the influences of factors such as the rotation speed on the shape and impact pressure of HPWJ were explored, and the results show that the rotation speed should be controlled within 90 r/min. The research findings lay the foundation of the study on the mechanism of coal crushing by HPWJ and provide technical support for the research and development of drilling and flushing integrated equipment.

Study on Gas Control Methods Optimization for Mining Safety

Effective gas control is of significance for safe efficient coal mining in Haizi Coal Mine and other mines with similar geological conditions. This study concentrates on gas control theories and techniques in multiple coal seams of Haizi Coal Mine (No. 7, No. 8, No. 9, and No. 10 coal seam from top to bottom). To minimize risk of high gas emission and outburst hazard, No. 10 seam was mined first as a protective seam prior to the mining of its overlying outburst‐prone No. 7, No. 8, and No. 9 seam. Four gas drainage measures were determined for gas control, including cross‐measure boreholes into overlying coal seams, surface goaf wells, roof boreholes, and roof gas drainage roadway. These gas control measures, if implemented through entire coal seam extraction, would be possibly uneconomic. An investigation was undertaken to analyze effects of those four measures on gas emission, methane concentration, and gas drainage quantity in No. 2 1024 mining panel of No. 10 seam. Results indicate that the highly expensive gas drainage measure of a roof roadway has poor drainage performance and could be effectively replaced by roof boreholes. When adopting the optimized combination of gas drainage measures, drainage efficiency of No. 7 seam, No. 8 seam, and No. 9 seam could reach 58.64% and decrease gas pressure to be below 0.74 MPa. Outcomes of this study could provide beneficial guidance not only for gas drainage design optimization in Haizi Coal Mine but also for other multiple‐seam mines with similar mining and geological conditions, for increasing gas drainage efficiency and guaranteeing mining safety.

Study of gas emission law at the heading face in a coal‐mine tunnel based on the Lattice Boltzmann method

AbstractGas distribution ahead of the coal tunnel is the key risk factor controlling coal and gas outburst. Based on an analysis of the influence of the stress state on the porosity of the coal seam, an improved quartet structure generation set (QSGS) random porous media generation tool is used to reconstruct the coal structure. Adopting the reconstructed pore structure of the coal as the boundary of the flow field, the Lattice Boltzmann method (LBM) is used to simulate the gas dynamic distribution law ahead of the coal tunnel. The gas pressure of the coal seam decreases obviously in the fracture zone only, and the change in gas pressure is very small in the stress concentration zone and ahead of the coal seam. This research is of significance for gas drainage and the prevention of coal and gas outburst hazards in the working face during coal tunneling.

The law and mechanism of dynamic methane diffusion from coal particles under different moisture content

As a theoretical basis, methane diffusion from coal particles can be used to determine the coalbed gas content, gas desorption index by drill cuttings of coal, evaluation parameters of coal gas mining, and the gas outburst prediction. Moisture content is one of the significant factors influencing the diffusion law of gas-bearing coal particles. In this paper, three deformed coal samples with diverse metamorphic degrees, taken from three different coal mines with coal and gas outburst hazard, were investigated through the self-made devices. The variation law of diffusion flux, diffusion coefficient, and diffusion speed with moisture content was experimentally studied. The results show that diffusion flux, diffusion speed, and diffusion coefficients of high-, medium-, and low-rank coal samples decrease significantly with the increasing moisture content until they reach equilibrium moisture content. The diffusion coefficient of dry coal particles is 3–5 times larger than that of coal particles with equilibrium moisture at the same metamorphic degree. The diffusion coefficient of coal samples at different ranks decreases with time and ranges from 1.58E-08 to 3.03E-07 cm2/s. Based on gas migration theory in porous media and experimental results, the influence mechanism of moisture on gas diffusion rules was discussed.

Coal and gas outburst risk prediction based on the F-SPA model

ABSTRACT As the depth of coal mining is gradually increased in China, the intensity of related coal and gas outbursts will become ever-greater. Accurate forecasting of coal and gas outburst is the key to preventing and controlling such incidents. This study uses gray relational analysis (GRA) to identify the four main geological and environmental indicators of coal and gas outburst risk based on the characteristics of the factors influencing coal and gas outburst and their relationships with outburst strength. A Fuzzy SPA (F-SPA) model was constructed using set pair analysis and the coupled weighting method, and coal and gas outburst intensity level was predicted for 25 locations in coal mine No. 8 in the Pingdingshan mining area using the F-SPA model and applying a confidence criterion. The forecast results were compared with those derived using three other methods as well as against actual outbursts that have occurred at those locations. The results of this comparison show that the method proposed in this study has a forecast accuracy of up to 96%. The reliability of the prediction model is verified by error analysis. This case study demonstrates the reliability of the proposed method and provides a new tool for the prevention and control of coal and gas outburst hazards.

Intermediate coal pillar instability and permeability evolution in extremely thin protective seam by auger mining

Protective seam mining method is an effective way to eliminate the coal and gas outburst hazard. Auger mining (AM) is adopted to protective seam thinner than 1.0 m. The key of AM is to set intermediate coal pillar (ICP) because they have two functions: on the one hand, ICPs have to support the roof temporarily to avoid coal auger crushing; on the other hand, they have to be broken subsequently to release the pressure of protected layer above. Theoretical analysis and numerical simulation are used to study the instability mechanism of the ICPs. On this basis, the effect of ICPs on the pressure relief and permeability evolution of the protected layer was analyzed. Results show that the reasonable ICP width is related to many factors, such as AM width, AM height, and ICP strength. The single ICP instability mode is compressive failure and the ICPs collapse one by one gradually instead of collapsing wholly and suddenly. The reasonable ICP width of Chiyu Coal Mine is 2.0 m with the conditions of 1.0 m AM height and 10.0 m AM width, namely when 4 AM rooms are mined by the coal auger and three ICPs are set. These ICPs collapse one by one and the sequence is No. 2, No. 1, and then No. 3. With the AM face advancing, the amount of ICPs increase and the pressure relief effect is also gradually improved. When some of ICPs collapse, the stress within the overburden above the goaf is released rapidly which significantly improves the performance of pressure relief.

A Numerical Study of Stress Distribution and Fracture Development above a Protective Coal Seam in Longwall Mining

Coal and gas outbursts are serious safety concerns in the Chinese coal industry. Mining of the upper or lower protective coal seams has been widely used to minimize this problem. This paper presents new findings from longwall mining-induced fractures, stress distribution changes in roof strata, strata movement and gas flow dynamics after the lower protective coal seam is extracted in a deep underground coal mine in Jincheng, China. Two Flac3D models with varying gob loading characteristics as a function of face advance were analyzed to assess the effect of gob behavior on stress relief in the protected coal seam. The gob behavior in the models is incorporated by applying variable force to the floor and roof behind the longwall face to simulate gob loading characteristics in the field. The influence of mining height on the stress-relief in protected coal seam is also incorporated. The stress relief coefficient and relief angle were introduced as two essential parameters to evaluate the stress relief effect in different regions of protected coal seam. The results showed that the rock mass above the protective coal seam can be divided into five zones in the horizontal direction, i.e. pre-mining zone, compression zone, expansion zone, recovery zone and re-compacted zone. The volume expansion or the dilation zone with high gas concentration is the best location to drill boreholes for gas drainage in both the protected coal seam and the protective coal seam. The research results are helpful to understand the gas flow mechanism around the coal seam and guide industry people to optimize borehole layouts in order to eliminate the coal and gas outburst hazard. The gas drainage programs are provided in the final section.

Different bedding loaded coal mechanics properties and acoustic emission

Using TAW-2000KN electro-hydraulic servo rock press machines and the American Physical Acoustics Company’s SH-II acoustic emission systems, experimental studies began to address the mechanical properties in different beddings of loaded coal and the related acoustic emission characteristics, established based on the acoustic emission damage model, and verify the model. The results show that the mechanical properties of different coal sample beddings are distinctive, with maximum uniaxial compressive strength and elastic modulus of vertical stratification of coal samples and the minimum Poisson’s ratio. Thus, the minimum uniaxial compressive strength and elastic modulus of oblique bedding coal samples along with the maximum Poisson’s ratio in the processes of loading result in different bedding coal samples having different stress–strain curves, especially when different bedding coal samples experience the stages of fissure compression, elastic deformation, plastic deformation and instability and destruction. In addition, the displacement proportions of each stage of the loading process have relatively obvious differences: the loading times of vertical, parallel and oblique bedding coal are 495, 382 and 331 s, respectively, and their acoustic emission mutation points of peak stress are approximately 60, 41 and 33%, respectively. Thus, we can use the mutation point as precursor information to estimate the damage intensity in different bedding seams. The theoretical and experimental stress–strain curves obtained by the coal damage model are basically identical, verifying the reliability of the model and reflecting the feasibility of acoustic emission technology in the study of coal damage. The results can effectively forecast coal and gas outburst hazard in coal mines, especially highly gassy and outburst mines. It can also make comprehensive predictions for flooding accidents, roof fall accidents and other disasters, and provide valuable evacuation time for underground coal mine workers. The results are of great scientific significance in safeguarding the safety of coal mines.

Comparative Experiment Study on Nitrogen Injection and Free Desorption of Methane-Rich Bituminous Coal Under Triaxial Loading

Abstract As a kind of associated geological gas, coalbed methane (CBM) is mainly adsorbed in the coal seam. The coal-methane adsorption phenomenon can be described by Langmuir monolayer adsorptio n model, BET multilayer adsorption model and the Theory of Volume Filling of Micropore (TVFM), whereas the binary gas adsorption phenomenon can be described by the extended Langmuir Model. For the CBM in the low permeability coal seam, the amount of gas released by direct drainage is relatively limited, which cannot eliminate the gas explosion and outburst hazards. Gas injection is an effective method to promote methane drainage. In this paper, the free desorption and nitrogen injection displacement experiments are comparatively analyzed, which allows verifying the effectiveness of nitrogen injection’s enhancement to gas drainage. The experiment of injecting nitrogen gas into the coal body shows that the coal fracture can be maintained or expanded by the injected gas pressure so that more methane can be released. The nitrogen injection has a higher time efficiency than that of free desorption as well. The displacement ratio of N2/CH4 is in the range of 1-3. Both the injection pressure and confining pressure affect the displacement ratio. The analysis of the desorbed gas components shows that the relationship between the methane component and gas flooding time is an “inverted S” shape curve, and the appropriate time for the methane collection can be inferred by the time interval of the rapid decline of the curve.

Coal and gas outburst hazards and factors of the No. B-1 Coalbed, Henan, China

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.