Outburst Accidents Research Articles

Post-outburst coal pulverization: Experimental insights with representative accident samples

ABSTRACT Coal and gas outburst accidents pose a serious threat to safe coal mining. Coal pulverization and transportation are integral to outbursts, aiding in understanding outbursts process and holding great potential for elucidating outburst mechanisms. However, the lack of on-site coal sample makes it challenging to assess coal pulverization characteristics during outbursts. We collected coal samples from the forefront of five outburst sites in typical tectonic areas over the past decade. Three coal powders and coal blocks underwent particle size, low-pressure N2/CO2 adsorption and adsorption/desorption experiments to characterize their coal-gas properties. The impact of coal pulverization on coal transportation and outburst initiation was evaluated based on energy conservation principles. The results indicate that the particle size range of coal blocks is 0.27 μm to 2.6 mm, with over 50% consisting of particles smaller than 50 μm. The formation of micron-sized outburst coal powder is associated with tectonic movements. Pulverization increases micropore and some mesopore pore volume, and specific surface area initially increases and then decreases with decreasing particle size. The ultimate adsorption capacity of outburst coal at three particle sizes ranges from 16.8 to 36.0 m3/t. Pulverization affects gas adsorption capacity by influencing micropore volume. The methane desorption velocity within the first 60 s ranged from 0.0091 to 0.0998 ml/g/s, with the minimum particle size being 1.6 to 4.4 times the maximum particle size. Coal pulverization leads to an increase in pore quantity, a reduction in pore length, and the disappearance of high adsorption potential pores, resulting in rapid methane desorption. In the five outbursts, 246 to 25,580 m3 (30°C, 0.1 MPa) of desorbed gas is involved in coal transport. This requires gas desorption velocities ranging from 0.014 to 0.171 ml/g/s, with coal particle sizes reaching 5–875 μm. The abundant presence of micron-sized coal powder is essential for outburst initiation and sustained coal ejection, considerably increasing the risk of outbursts in tectonic coal seams.

Dynamic response characteristics of coal/rock during water injection and freezing process under gas atmosphere and its control effect on gas outburst

The freezing method compensates for the defect of sacrificing coal integrity to reduce gas content, which is the case with traditional methods, achieving the improvement of coal body strength while reducing coal seam gas energy storage, improving the safety of coal and gas outburst accidents in deep coal seams during the process of rock cross-cut coal uncovering. This study conducted water injection and low-temperature freezing experiments on coal/rock samples under the gas atmosphere, analyzing the effects of water and temperature on sample temperature, deformation, and gas adsorption and desorption characteristics. The results indicate that water can displace adsorbed gas in coal/rock samples, and the relationship between the gas displacement and the water content of the sample satisfies an improved exponential function. The center temperature Tm of low water content coal/rock samples decreases with time and gradually tends to stabilize, while the Tm of high water content samples experiences a short-term deceleration or stagnation due to the phase transition heat release of water when it drops to around 0 °C. The cooling rate of samples with low water content and no gas is higher and that of rocks is higher than that of coal samples. Coal/rock samples with high water content experience frost heave during the freezing process, but the overall deformation is still dominated by cold shrinkage, and the amount of deformation is negatively correlated with temperature and water. The gas adsorption capacity of coal decreases linearly with the temperature. At the same time, an increase in water content and a decrease in freezing temperature will significantly reduce the gas desorption capacity of coal samples, effectively reducing the gas expansion energy of coal samples, especially the desorption gas expansion energy. In engineering implementation of this method, the ice phase network can fill the coal pores and cracks and improve the mechanical properties of the coal/rock mass, and the gas pressure in the coal seam and stress concentration near the coal rock interface can be reduced by low temperature and cold shrinkage, thereby achieving safe exposure of the coal seam and preventing accidents from occurring.

Prediction model of coal seam gas content based on kernel principal component analysis and IDBO-DHKELM

Abstract Accurate coal seam gas content assists in the effective prevention of coal and gas outburst accidents. To solve this problem, an IDBO-DHKELM coal seam gas content prediction model is proposed by combining improved Dung Beetle optimization algorithm (IDBO) with a deep hybrid kernel extreme learning machine (DHKELM). First, the index factors of the coupled gas content are determined according to the influence factors of coal seam gas content and the actual situation of mine production. The correlation of index factors is analyzed by SPSS 27 software via Pearson correlation coefficient matrix. Then, the principal components of the original data are extracted using the principal component analysis method (KPCA). Second, sine chaotic mapping, fusion improved sinusoidal algorithm, and fusion adaptive Gauss–Cauchy hybrid mutation perturbation are introduced to improve the Dung Beetle optimization algorithm (DBO) to enhance its global search capability. Third, IDBO is used to optimize the number of hidden layer nodes, regularization coefficient, penalty coefficient, and kernel parameter in DHKELM, which improves the prediction accuracy and further avoid the phenomenon of overfitting. Finally, the principal component extracted by KPCA is taken as the model’s input, and the gas content as the model’s output. The results are compared and analyzed with those of PSO-BPNN, GA-BPNN, PSO-SVM, and DPO-DHKELM models. The results demonstrate that the IDBO-DHKELM model’s performance is the best in each performance index. Compared with other models, the mean absolute error of test samples in the IDBO-DHKELM model is reduced by 0.402, 0.4407, 0.3554, and 0.0646, respectively. The mean absolute percentage error is decreased by 3.67%, 4.07%, 8.27%, and 6.35%, respectively. The root mean square error decreased by 0.7861, 0.7148, 0.3384, and 0.1186, respectively. The coefficient of determination (R 2) is increased by 0.1544, 0.1404, 0.0955, and 0.0396, respectively. Finally, the IDBO-DHKELM model and other models are applied to an experimental mine. The resulting IDBO-DHKELM model is the closest to the actual value, which further verifies the universality and reliability of the model. Therefore, the model is more suitable for the prediction of coal seam gas content.

Study on fissure evolution of overlying rock in lower protective mining

Protective layer mining is the most effective and economical technical measure to prevent coal and gas outburst accidents. At present, in the study of multiple concentrated coal layer stress, plastic damage and mining pressure discharge range, there are problems such as less research on the protection effect of protective layer and less measured measurement points resulting in large experimental error. In view of the above problems, taking the 2305 working face of a Shanxi mine as the test mine, the crack evolution characteristics of downhole drilling were detected by this method, by means of the deep base point technology, and study the plastic damage, pressure relief characteristics and expansion characteristics in the mining process of protective layer, the findings suggest that, the crack development of the protective layer is mainly characterized by small width and quantity, after protective exploitation, the number of width and number of cracks were significantly increased, the injection is three times higher than before the protective mining, the degree of fissure development is greatly improved. The settlement change of each rock layer on the basic top presents periodic and nonlinear changes, divided into the initial deformation, violent deformation, deformation and decline of the three periods; the plastic damage area, pressure relief curve and expansion curve of protective layer are “saddle type”, the overall pressure discharge rate of the protected layer has decreased by 60%, to meet the requirements of the critical value of expansion rate in the detailed rules for preventing coal and gas outburst, the protective layer mining technology applies to other working faces of the coal mine.

The Pore Structure Multifractal Evolution of Vibration-Affected Tectonic Coal and the Gas Diffusion Response Characteristics

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.

Numerical Multifield Coupling Model of Stress Evolution and Gas Migration: Application of Disaster Prediction and Mining Sustainability Development

At present, coal mining is gradually shifting towards deep areas, and coal mines under deep mining conditions are more prone to coal and gas outburst accidents. In this research, we aim to explain the causes and mechanisms of dynamic disasters, which are caused by the combined action of static load, gas, and dynamic load on tectonic regions in complex stress field environments. Through numerical simulation using COMSOL Multiphysics software, based on the geological conditions of a mine in Jilin Province, it was found that faults lead to abnormal stress in tectonic regions. The combined action of dynamic and static loads results in excessive stress, causing the fragmentation and displacement of the coal body, leading to coal mine disasters, thus disrupting sustainability. Additionally, the coal matrix gas entering fractures raises the gas pressure and leads to the accumulation of methane near earthquake sources. Dynamic loads accelerate gas desorption in coal and increase porosity and permeability, facilitating rapid gas migration. This influx of gas into the roadways exceeds safety limits. Then, based on these findings and on-site conditions, a set of sustainable measures for coal mines has been proposed. This research offers theoretical guidance for enhancing safety, stability, and sustainability in coal mining processes.

Overburden failure and water–sand mixture outburst conditions of weakly consolidated overlying strata in Dananhu No.7 coal mine

This study presents a case of weakly consolidated strata developed in Dananhu No.7 coal mine. Using a combination of numerical simulation, field measurement comparison, and the critical hydraulic gradient criterion, we investigate the overburden failure and the risk possibility of water–sand mixture inrush during excavation. The following are the principal findings: (1) Weakly consolidated rocks have poor physical characteristics, particularly when they are mudded and disintegrated after encountering water, which may become a favorable source of water–sand inrush; (2) The water-conducting zone develops to a height of 160.5 m with a crack-mining ratio of 15.29 times, extending upward to Toutunhe Formation aquifer. The predictions are consistent with measurements in adjacent mines with similar geological conditions; (3) Cracks without larger subsidence are developed at the front edge of the mining direction, and some parallel stepped cracks behind the goaf could be easily observed. Ground subsidence along the goaf center finally displays a symmetrically wide-gentle U shape; (4) The critical hydraulic gradient of Toutunhe Formation aquifer, aquifer above 3# coal seam, and aquifer of 3#–7# coal seam in Xishanyao Formation is 1.314, 1.351, and 1.380, the actual value is 0.692, 2.089, and 7.418 accordingly. It is inferred water–sand mixture outburst will not occur in Toutunhe Formation aquifer, while the potential risk exists in the aquifers of Xishanyao Formation. Through drainage and depressurization projects, a water–sand mixture outburst accident does not occur during excavation. This study reveals the overburden failure characteristics and the initiation mechanism of water–sand inrush in weakly cemented strata, as well as the internal relationship between them, which provides new research ideas for safe operation in other mining areas with similar geological conditions. The research work has certain practical guiding significance.

Study on the gas outburst control effect of goaf on the neighboring working face: Case study of Pingmei No.4 Mine

AbstractAs coal mining depth increases, there is a corresponding increase in both ground stress and gas pressure, leading to a higher incidence of coal and gas outburst accidents. To investigate the stress distribution law and gas release degree of the adjacent coal body within the goaf of the outburst coal seam, and to acquire an understanding of the impact range of the large mining face goaf on the stress of the coal seam, this study employed theoretical analysis and numerical simulation to analyze the impact and scope of the goaf on the adjacent coal body, and measured the gas content of the coal seam. The findings indicated that following the completion of mining on the working face, there was a redistribution of stress in the coal and rock layers within 40 m of the goaf, with the stress concentration phenomenon observed at a distance of 2.6 m from the goaf. Affected by the stress relief effect of mining, the stress, gas content, and other related factors have been studied in detail by researchers. Affected by the stress relief effect of mining, the stress, gas content, and gas pressure of the surrounding rock near the goaf in the coal seam are significantly reduced. The research results verify that tunneling along the goaf is an effective method to prevent coal and gas outbursts and improve stoping efficiency.

Accident case data-accident causation model driven safety training method: Targeted safety training empowered by historical accident data in coal industry

The content and methods of traditional safety training can no longer meet the needs of the industry or accident-targeted safety training. To solve this problem, this study proposes an accidental case data accident causing model-driven safety training method (ACDACM method) based on an analysis of the content and methods of China's safety training. This method is theoretically driven by the accident causation model and data-driven by the accident case information. Through data analysis of historical accident cases, basic information and comprehensive reasons for accidents can be obtained. Using data mining algorithms, the causes and combinations of high-frequency and high-risk accidents can be mined, supported by accident data, and a path map of the accident causes can then be obtained. The developed safety training project is more targeted by comparing accident causes with industry standards and regulations. This study considers coal and gas outburst accidents as an example and uses 24Model to analyze 84 coal and gas outburst accidents in China. The targeted safety training plan had eight parts of training content, and supporting PPTs, handbooks, and videos were produced. The application shows that this method can provide targeted safety training designs for industries or accidents and has industry universality. Finally, the advantages and development of the ACDACM method are elaborated and the future of safety training is discussed. This study provides theoretical and methodological support for targeted safety-training programs.

Experimental Study on Coal and Gas Outburst Risk under Different Water Content Rates in Strong Outburst Coal Seams.

To investigate the alleviation potency of coal seam water infusion on coal and gas outburst, this paper focuses on the Qidong coal mine outburst coal seam, where outburst accidents have occurred many times, and obtains the impact of water content on outburst prediction parameters by studying the features of outburst parameters and gas desorption law under different water content rates. How water content affects outburst was also researched through the use of a self-made outburst simulation test system, and the relationship between water content and outburst intensity and critical gas pressure was studied. It can be concluded that with the rise of water content, the initial velocity of gas diffusion, the gas desorption index of drilling cuttings, and the adsorption constant a decrease, but the firmness coefficient (f) increase, and these indicators are exponentially related to the water content. Meanwhile, as the water content raises, the outburst pressure threshold increases, the outburst intensity gradually decreases, and the less likely outburst occurs. Under 0.5 MPa pressure, as the water content arose from 2.02 to 5.14%, the outburst intensity was significantly weakened, while no outburst occurred as the water content reached to 10.25%. Fitting analysis of the influence curve of outburst parameters and comparing the vital values of outburst prediction indexes finally determined that the water content rate of 5.14% could be used as a key index for water injection measures for coal and gas outburst prevention coal seam in Qidong coal mine no. 9. This research offers a guiding significance for the outburst prevention measures of water infusion in outburst coal seams and gives a feasible scheme for the safe mining of outburst coal mines.

Mechanism of gas pressure action during the initial failure of coal containing gas and its application for an outburst inoculation

Faced with the continuous occurrence of coal and gas outburst (hereinafter referred to as “outburst”) disasters, as a main controlling factor in the evolution process of an outburst, for gas pressure, it is still unclear about the phased characteristics of the coupling process with in situ stress, which induce coal damage and instability. Therefore, in the work based on the mining stress paths induced by typical outburst accidents, the gradual and sudden change of three-dimensional stress is taken as the background for the mechanical reconstruction of the disaster process. Then the true triaxial physical experiments are conducted on the damage and instability of coal containing gas under multiple stress paths. Finally, the response characterization between coal damage and gas pressure has been clarified, revealing the mechanism of action of gas pressure during the initial failure of coals. And the main controlling mechanism during the outburst process is elucidated in the coupling process of in situ stress with gas pressure. The results show that during the process of stress loading and unloading, the original gas pressure enters the processes of strengthening and weakening the action ability successively. And the strengthening effect continues to the period of large-scale destruction of coals. The mechanical process of gas pressure during the initial failure of coals can be divided into three stages: the enhancement of strengthening action ability, the decrease of strengthening action ability, and the weakening action ability. The entire process is implemented by changing the dominant action of in situ stress into the dominant action of gas pressure. The failure strength of coals is not only affected by its original mechanical strength, but also by the stress loading and unloading paths, showing a particularly significant effect. Three stages can be divided during outburst inoculation process. That is, firstly, the coals suffer from initial damage through the dominant action of in situ stress with synergy of gas pressure; secondly, the coals with spallation of structural division are generated through the dominant action of gas pressure with synergy of in situ stress, accompanied by further fragmentation; and finally, the fractured coals suffer from fragmentation and pulverization with the gas pressure action. Accordingly, the final broken coals are ejected out with the gas action, initiating an outburst. The research results can provide a new perspective for deepening the understanding of coal and gas outburst mechanism, laying a theoretical foundation for the innovation of outburst prevention and control technologies.

Current Status of Research on the Coal and Gas Outburst Control Technology of Hydration and Anhydrous.

China is one of the countries with the most frequent coal and gas outburst accidents in the world. In the early years of the founding of New China, coal and gas outburst accidents occurred frequently, causing serious casualties, equipment damage, and economic losses. In recent years, some scholars have tried to simulate the coal and gas outburst phenomenon using physical models to study the mechanisms of its occurrence. However, due to the complexity and nonreproducibility of coal and gas outburst disasters, the study of coal and gas outburst mechanisms is still in the hypothesis stage. In order to effectively reduce the risk of coal and gas outburst accidents, coal and gas outburst prevention and control technology have emerged and achieved remarkable results, and the probability of coal and gas outburst accidents has been greatly reduced. Among coal and gas protrusion outburst and control technologies, hydraulic and anhydrous prevention and control technologies are widely used. The purpose of this paper is to briefly explain the mainstream hypothesis of coal and gas outburst, analyze the action principle of hydration and anhydrous control technologies, discuss the current status of research on hydration and anhydrous control technologies, and put forward the problems of current technologies and future development trends.

Nano-scale pore distribution characterisation of coal using small angle X-ray scattering

In the process of coal seam fracturing with liquid nitrogen (LN2), the change of coal pore structure has an important influence on the efficiency of coalbed methane (CBM) extraction. The nano-scale pore size distribution (PSD) in coal particles before and after freezing with LN2 are experimentally studied in this work. Coal samples are collected from four coal mines, where coal and gas outburst accidents have occurred. Small angle X-ray scattering technology (SAXS) and scanning electron microscopy (SEM) are used to study the pore structure changes of coal samples quantitatively and qualitatively. It is found that the scattering intensity of coal samples increases after freezing. The PSD of all samples significantly changes in the range of 0.8–7 nm, showing new pore spaces in 0.8–4 nm and fewer pores in the 4–7 nm range. Both the pore fractal dimension and the radius of gyration of coal samples increase after freezing and are mainly affected by the changes in pores and the anisotropy of the coal matrix. Crack expansion and pore connections are observed in the surface structure of the coal sample using SEM. This study provides a better understanding of the nano-scale mechanism of coal seam fracturing with LN2 for the prevention of coal and gas outbursts.

Experimental Study on the Determinant Factors and Energy Criterion of Coal and Gas Outbursts.

A series of coal and gas outburst tests were conducted on coal seams in north China to determine the important order of gas pressure, in situ stress, and coal strength during coal and gas outbursts. And the typical phenomena of coal and gas outbursts were investigated. In addition, improved outburst energy equations were built to study the coal energy evolution process during coal and gas outbursts. The results show that the coal strength has the strongest influence on coal and gas outbursts, followed by the gas pressure and the in situ stress. The weights of pulverized coal with a particle size of less than 0.28 mm are consistent with the changing trend of the total weights of the pulverized coal particles in the corresponding outburst interval. Furthermore, the results suggest that the gas pressure monitored by the sensors close to the outburst hole begins to drop first and lasts for the longest time. The outburst coal presents obvious fracture and pulverization damage characteristics, and the pulverization damage features of the coal near the outburst hole are more obvious. In addition, the improved outburst energy equation was established, and the rationality of the improved outburst energy equation was verified by using the outburst orthogonal simulation experimental data and the on-site outburst accident cases. The results of this experiment have important guiding significance for preventing and controlling the occurrence of coal and gas outbursts and ensuring safe and efficient mining of coal mines.

A dynamic model of coalbed methane emission from boreholes in front of excavation working face: numerical model and its application.

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

Coal Mine Rock Burst and Coal and Gas Outburst Perception Alarm Method Based on Visible Light Imagery

To solve the current reliance of coal mine rock burst and coal and gas outburst detection on mainly manual methods and the problem wherein it is still difficult to ensure disaster warning required to meet the needs of coal mine safety production, a coal mine rock burst and coal and gas outburst perception alarm method based on visible light imagery is proposed. Real-time video images were collected by color cameras in key areas of underground coal mines; the occurrence of disasters was determined by noting when the black area of a video image increases greatly, when the average brightness is less than the set brightness threshold, and when the moving speed of an object resulting in a large increase in the black area is greater than the set speed threshold (V > 13 m/s); methane concentration characteristics were used to distinguish rock burst and coal and gas outburst accidents, and an alarm was created. A set of disaster-characteristic simulation devices was designed. A Φ315 mm white PVC pipe was used to simulate the roadway and background equipment; Φ10 mm rubber balls were used to replace crushed coal rocks; a color camera with a 2.8 mm focal length, 30 FPS, and 110° field angle was used for image acquisition. The results of our study show that the recognition effect is good, which verifies the feasibility and effectiveness of the method.

Principles of formulating measures regarding preventing coal and gas outbursts in deep mining: Based on stress distribution and failure characteristics

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.

Research on Directional Hydraulic Coal Cutting and Outburst Prevention Technology in Soft and Hard Composite Coal Seams.

Affected by tectonics, soft and hard composite coal seams are widely distributed in China; the soft stratification in the soft and hard composite coal seam is the key to controlling the occurrence of coal and gas outburst accidents. Based on this, for soft and hard composite coal seams, in order to accurately extract soft layers, a directional hydraulic coal mining equipment has been developed, including a drilling rig pump truck system, a directional coal wireless measurement system, and a cutter drill pipe system. By constructing a mathematical model and conducting numerical simulations, it was found that the vertical stress, horizontal stress, and gas pressure of the coal body around the borehole after coal extraction decreased significantly compared to normal borehole conditions; the on-site test results indicate that the hydraulic coal extraction volume of directional hydraulic coal extraction boreholes reaches 0.25 m3 per meter. The total amount of coal extracted accounts for more than 3‰ of the total amount of coal within the coverage area. The average concentration of gas extraction in the coal extraction area is 80.15%, and the net amount of gas extraction from 100 m boreholes reaches 0.17 m3/(min·hm). After extraction, the measured residual gas content in the coal extraction and non-extraction areas decreased by 59.27 and 40.38%, respectively. Directional hydraulic coal mining technology can effectively solve the problem of coal and gas outburst prevention in soft and hard composite coal seams and has good application prospects.

Data Mining Technology and Its Applications in Coal and Gas Outburst Prediction

Coal and gas outburst accidents seriously threaten mine production safety. To further improve the scientific accuracy of coal and gas outburst risk prediction, a system software (V1.2.0) was developed based on the C/S architecture, Visual Basic development language, and SQL Server 2000 database. The statistical process control (SPC) method and logistic regression analyses were used to assess and develop the critical value of outburst risk for a single index, such as the S value of drill cuttings and the K1 value of the desorption index. A multivariate information coupling analysis was performed to explore the interrelation of the outburst warning, and the prediction equation of the outburst risk was obtained on this basis. Finally, the SPC and logistic regression analysis methods were used for typical mines. The results showed that the SPC method accurately determined the sensitivity value of a single index for each borehole depth, and the accuracy of the logistic regression method was 94.7%. These methods are therefore useful for the timely detection of outburst hazards during the mining process.

Dynamic behavior of outburst two-phase flow in a coal mine T-shaped roadway: The formation of impact airflow and its disaster-causing effect

The study of the dynamic disaster mechanism of coal and gas outburst two-phase flow is crucial for improving disaster reduction and rescue ability of coal mine outburst accidents. An outburst test in a T-shaped roadway was conducted using a self-developed large-scale outburst dynamic disaster test system. We investigated the release characteristics of main energy sources in coal seam, and obtained the dynamic characteristics of outburst two-phase flow in a roadway. Additionally, we established a formation model for outburst impact flow and a model for its flow in a bifurcated structure. The results indicate that the outburst process exhibits pulse characteristics, and the rapid destruction process of coal seam and the blocking state of gas flow are the main causes of the pulse phenomenon. The outburst energy is released in stages, and the elastic potential energy is released in the vertical direction before the horizontal direction. In a straight roadway, the impact force oscillates along the roadway. With an increase in the solid–gas ratio, the two-phase flow impact force gradually increases, and the disaster range extends from the middle of the roadway to the coal seam. In the area near the coal seam, the disaster caused by the two-phase flow impact is characterized by intermittent recovery. In a bifurcated roadway, the effect of impact airflow on impact dynamic disaster is much higher than that of two-phase flow, and the impact force tends to weaken with increasing solid-gas ratio. The impact force is asymmetrically distributed; it is higher on the left of the bifurcated roadway. With an increase in the solid-gas ratio, the static pressure rapidly decreases, and the bifurcated structure accelerates the attenuation of static pressure. Moreover, secondary acceleration is observed when the shock wave moves along the T-shaped roadway, indicating that the bifurcated structure increases the shock wave velocity.