Coal Burst Research Articles

Mechanism and Energy Evolution Characteristics of Coal Burst in Mining Thick, Deep, and Large Inclined Coal Seams: A Case Study from a Chinese Coal Mine

Coal burst is a severe and dynamic hazard, and understanding its mechanism is crucial in preventing such incidents. Strong tremors during the working face mining in the stress anomaly zone of the pinch-out coal seam are frequent. Theoretical analysis, numerical simulation, and field measurement methods are used to analyze the energy evolution law for mining at the working face and mechanism of coal burst. Mechanical models of the inclined and strike overhang structures are established, and the theoretical analysis of the strike and inclined energy distribution characteristics of the working face roof is carried out. The two key areas with a high overhang bending deformation energy accumulation are identified at the lower end and middle-upper part of the working face. The simulation results show that the energy accumulation area of the roof in the inclined coal seam has prominent asymmetric distribution characteristics. The roof energy accumulates in the lower end and middle-upper area of the working face. The floor energy accumulates in the lower end area of the working face, and the peak position of the overhead energy of the working face in the direction shifts toward the coal-wall side. Influenced by the local absence of the No. 8 coal seam, the vertical stress of the surrounding rock at the working face of the massive, inclined coal seam increased by 12.7%; the peak of roof energy at the working face inclination and strike increased by 46.2% and 32.2%; and the range of roof energy accumulation expanded. A deep directional hole blasting plan to prevent the phenomenon at the working face roof is developed, which effectively reduces the stress and energy level of the inclined hanging roof and avoids the occurrence of coal bursts in the abnormal stress area of the working face.

An Improved Connection Cloud Model of an Updated Database: A Multicriteria Uncertainty Model for Coal Burst Liability Evaluation

An Improved Connection Cloud Model of an Updated Database: A Multicriteria Uncertainty Model for Coal Burst Liability Evaluation

Coal burst and mining-induced stress evolution in a deep isolated main entry area – A case study

Main entries in some underground coal mines are tunneled into coal seams. During coal mining, main entries usually have a one-side gob or two-side gobs. Serious coal bursts have occurred in the isolated main entry area (IMEA). In this study, coal bursts in the IMEA are investigated. A large-scale numerical model is built to depict the static-dynamic stress evolution in the IMEA. Likewise, the study discusses the coal burst mechanism in the IMEA and proposes the measures to decrease the coal burst risk. During tunnelling of the main entry, coal bursts in the IMEA occur in the intersection of roadways. During coal mining, coal bursts mainly arise in the area between the gobs on both sides. Coal bursts in the IMEA are induced by high static and low dynamic stress. When coal is mined, the abutment stress around the gobs on both sides transfers to deeper regions and intersects in the IMEA, leading to higher static stress in coal mass. The seismic-based dynamic stress negatively correlates to the distance between the seismic sources and the IMEA. During coal mining, dynamic stress fluctuates, then the amplitude decreases and finally remains at a low value and exerts slight dynamic disturbance on the IMEA. When static stress is low, only higher dynamic stress can lead to coal bursts. However, when static stress is high, low dynamic stress can induce coal bursts. Coal bursts in the IMEA are caused by the superposition of high static stress in coal seam and low seismic-based dynamic stress disturbance from longwall panels. Roof blasting in the IMEA and roof pre-splitting blasting in longwall panels are proposed and implemented on site. Field monitoring results indicate that the de-stressing measures significantly decrease the coal burst risk in the IMEA.

Attenuation characteristics analysis of seismic energy and its application to risk assessment in underground coal mines

Seismic energy analysis is the basis of coal burst risk assessment. The prerequisite for utilizing seismic energy to quantify coal burst hazards is the accurate understanding of seismic energy attenuation. Thereby the characteristics of seismic energy attenuation were first systematically investigated in this paper. Based on the seismic data and 24 coal burst records during the period of sixteen months, a risk assessment method including three indexes (Static Intensity Index (SII), Dynamic Intensity Index (DII), and Risk Assessment Index (RAI)) was derived from seismic energy attenuation. In consideration of the static and dynamic response, the superposition effects of seismic energy were proposed to improve the performance of risk assessment. Results show that residual seismic energy (RSE) is relatively correlated with seismic energy, source radius, and energy attenuation coefficient; the higher seismic energy, source radius, and lower energy attenuation coefficient would result in higher coal burst risk. The case study demonstrated that SII could effectively predict the damaged area, but its prediction efficiency of high-magnitude events (HMEs) is relatively low; DII could predict damaged areas and HMEs, but may lead to risk overestimation; and RAI could efficiently predict the damaged area and HMEs. The sensitivity of the monitoring system and seismicity activeness could be the two main restrictions of the proposed method, leading to low efficiency or even false risk assessment. This paper sheds light on seismic energy utilization to risk prediction in underground coal mines. Highlights The attenuation response characteristics of seismic energy to different factors including seismic energy, source radius, and attenuation coefficient were investigated. A new assessment method based on seismic energy attenuation calculation was proposed to assess coal burst risks. Three seismic-based indexes considering static and dynamic response and their superposition effects were proposed to assess coal burst risk. Sensitivity of monitoring system and seismicity activeness could be the two main restrictions leading to low accuracy or even false in risk assessing, which implies that the proposed method could also have false judgements in the place where rare seismicity is monitored.

A coal seam‐roof‐floor coupling destressing control method of fault coal bursts induced by deep coal seam mining

AbstractFault coal bursts is a common type of coal bursts in coal mining. With increases in mining depths and mining intensities, the occurrence frequency and disaster degree of coal bursts in fault‐controlled areas are increasing in severity. Therefore, in this article, the mechanism and control method of deep mining‐induced fault coal bursts are analysed on the No. 3402 longwall panel controlled by two faults in the Shandong Mine, China. Based on the microseismic monitoring data of the longwall panel, the fault activation process induced by mining can be divided into four stages. The second energy release and fault activation stages are risk stages of fault coal bursts. Using numerical simulation, the evolution laws of vertical stress, elastic strain energy in front of the longwall panel, and the ratio of shear stress to normal stress on fault plane are investigated. The phenomenon of a ‘high elastic energy section‐low elastic energy section’ coal pillar between faults is revealed, and the mechanism of coal pillar coal bursts induced by high elastic energy is discussed. Third, based on the above research results, coal burts risk areas of the longwall panel in the fault‐controlled area are determined. The method of ‘coal seam‐roof‐floor coupling destressing with the reduction in mining speed’ to control fault coal bursts is introduced. Field test results show that the method effectively destroys the integrity and bearing capacity of the coal seam, significantly reduces the energy storage capacity of the superposition area of mining stress and fault tectonic stress, so that the coal bursts risk of the coal seam in the fault control area is relieved, ensuring safe and efficient mining of the longwall panel. The method can provide a reference for other coal mines with similar geological conditions.

Characteristics and contributing factors of major coal bursts in longwall mines

AbstractCoal burst has become one of the most serious hazards in longwall coal mines of many countries, and extensive studies have been conducted on the mechanism, prediction, and prevention of coal bursts. However, most of these studies focus on qualitative descriptions of burst environments and specific case analyses. Few studies have been carried out to explore knowledge through a number of past coal bursts in longwall mines. The main objective is to quantitatively analyze the current burst‐prone conditions in longwall coal mines of China and to summarize corresponding lessons. A database consisting of 54 major coal bursts was established. The characteristics and contributing factors of involved coal bursts were analyzed quantitatively, and high‐risk areas that are common in coal mines were then identified. Finally, some suggestions and lessons were proposed. This study may help for identifying controlling factors and high‐risk areas at a specific mine, and it might provide insights into the control of coal bursts in longwall coal mines.

A Prediction Method of Coal Burst Based on Analytic Hierarchy Process and Fuzzy Comprehensive Evaluation

Coal burst has become a worldwide problem that needs to be solved urgently for the sake of coal mine safety production due to its complicated triggering mechanisms and numerous influencing factors. The risk assessment of coal burst disasters is particularly critical. In this work, 15 factors affecting coal burst occurrence are selected from the perspectives of geodynamic environment and geological and mining conditions, and the influence mechanism of each factor on coal bursts is analyzed. An evaluation index system of coal burst risk is put forward. A hierarchical model of coal burst prediction is established, and the weight of each influencing factor to coal burst risk is calculated. Based on the fuzzy comprehensive evaluation method, a coal burst prediction model is established, which can scientifically decompose and simplify the complicated problem and make coal burst prediction and prevention more pertinent and effective. The model is applied to assess the coal burst risk level of a coal mine in Shanxi Province, and the evaluation result is consistent with practical situations. This method considers the influencing factors comprehensively and determines the weight of each factor scientifically compared with other forecasting methods.

The development of specialised modular protective structure on continuous miners against coal burst hazards

As mining progresses into deep ore deposits in Australia, geo-hazards such as coal burst and outbursts are becoming a major concern for mine workers. The occurrence of geo-hazards involved the ejection of coal lumps and sometimes large volumes of hazardous gases such as methane and carbon dioxide. Whilst it is extremely important to de-stress and de-gas the seam and adjacent strata before roadway development and install competent support systems such as steel mesh and bolt, the last line of protection will be the installation of a protective canopy on the Continuous Miner (CM), which is typically used for roadway developments, to shield mine workers from these deadly dynamic impacts of coal and rock resulting from a burst or outburst. This paper aims to introduce the design, manufacture and testing of an innovative modular protective structure on the CM in underground coal mines. The developed protective system can be easily assembled in the underground mining environment and provide a high level of protection against flying debris hazards in the event of a coal burst. The extensive experimental program and numerical simulations have confirmed the high performance of the protective system against high-speed impact loading by single and multiple coal rocks and projectiles.

A quantitative pre-warning for coal burst hazardous zones in a deep coal mine based on the spatio-temporal forecast of microseismic events

The quantitative prediction for a coal burst is challenging since the coal burst mechanism is extremely complex with a verity of influencing factors involved. This study proposes a data-driven strategy to dynamically determine the coal burst hazardous zones in a deep coal mine based on quantitative predictions for microseismic events. A deep learning model, MSNet, comprising a convolutional module, a recurrent module, a skip-recurrent module, and an autoregressive module is built to predict the time, location, and energy for imminent microseismic events. More than ten thousand microseismic events from a workface were collected to form the database for the MSNet model training and testing. The results indicated that the MSNet can predict the event location accurately but that it predicts event timing less accurately. The MSNet demonstrated the worst prediction accuracy for event energy. Furthermore, this study analyzed the possible causes of the model’s prediction errors and provided ways for enhancing the model’s performance. Finally, a coal burst intelligent pre-warning platform was developed, which has been successfully used in coal mines at present. This study realized the quantitative forecast for coal burst hazardous areas on a preliminary basis while laying a foundation for coal burst timing risk prediction.

Ground motion characteristics and their cumulative impacts to burst risks in underground coal mines

Ground motions resulting from seismic waves are one of the main factors to trigger coal burst hazards in underground mines. Ground motion induced dynamic impacts may apply to the highly stressed coal/rock mass and initiate dynamic failure. Although ground motion analysis has been widely used in burst-prone hard rock mines for designing support systems, there are only few studies focusing on the understanding ground motion characteristics in coal mines and their relationship with the coal burst damage. Therefore, based on nine-months seismic monitoring in a case study coal mine, this paper conducted a thorough analysis on quantifying ground motions to roadways in both far-field and near-field zones and correlating strong ground motions to actual coal burst damage. The results showed that most far-field ground motions were insignificant, which were less likely to initiate coal burst damage. However, with the same energy levels and hypocentral distances, the seismic events in coal mines can produce higher far-field ground motions than those in hard rock mines. Compared with the far-field ground motions, the near-field ground motions had much higher intensities. The strong dynamic impacts induced by the near-field ground motions may trigger dynamic failure in coal or rock mass when it is already critically stressed. An index called the number of high ground motions (NHGM) was developed to link ground motions with burst risks in roadways. The roadway zone that had experienced a long history of intensive ground motions, indicated by a higher degree of NHGM, were more likely to expect coal bursts in the future.Article highlightsQuantify ground motions to roadways in both far-field and near-field zones in underground coal mines.Demonstrate the relationship between ground motion intensity and coal burst damage.Develop a method to forecast potential burst damage zones in roadways based on historical ground motions.

Developing a New Bursting Liability Index Based on Energy Evolution for Coal under Different Loading Rates

The risk of a coal burst rises with the excavation depth and other mining-related activities. These devastating coal burst activities are a major concern during deep coal mining. During such activities, the loading rate is a major cause of damage. Different indexes, including the elastic strain modulus index (Wet), bursting energy index (Ke), dynamic failure time index (DT), and compressive strength index (Rc), are used for coal bursting intensity; however, the loading rate and damage factors are not included in these indexes. In this study, a new coal bursting liability index called the elastic modulus damage index (EMDI) was developed using rock damage variables and the elastic strain modulus index, and is based on energy evolution characteristics under different loading rates. The results of this new index were compared with the existing indexes, and their range was proposed to evaluate coal bursting liability. The EDMI shows a positive polynomial second order degree relationship with Wet and Ke, having a determination factor of 0.99, while DT shows a negative polynomial second order degree relationship with a determination factor of 0.94. The EDMI and Rc show a positive power relationship having a determination factor of 0.99. The relationships with other indexes revealed that the EDMI can be effectively used in evaluating the coal bursting liabilities in different stress environments.

Progressive damage and fracture of biaxially-confined anisotropic coal under repeated impact loads

Coal masses in underground mines are in multiaxial stress states after excavation, and they are frequently subjected to dynamic loads particularly from continuous mining-induced seismic events. The changes of in-situ stress conditions and external dynamic loads may induce coal bursts, which involves the violent breaking of coal masses. Meanwhile, the coal bursting process may be influenced by bedding planes that are considered as unique structures in coal masses, which raises uncertainties of coal bursting mechanisms. This paper aims to reveal the progressive damage and burst proneness of anisotropic coal under coupled static stress and repeated dynamic loads. The tested coal specimens have five bedding plane orientations (β = 0°, 30°, 45°, 60°, and 90°), where β is the angle between the bedding plane and dynamic loading direction. A triaxial Hopkinson bar (Tri-HB) system is utilised to apply the biaxial static stress on the specimen and then followed by dynamic loading, and the stress and strain can be recorded by the system accordingly. After the loading test, ultrasonic wave velocity is measured to examine the degree of attenuation, and the quantification of microcrack characteristics is conducted by using the synchrotron-based X-ray computed tomography (CT). Then, the specimen is loaded again under the same biaxial static stress and dynamic load, and measured by ultrasonic sensors and X-ray CT. This process will be repeated until the final failure of the specimen. We found that both dynamic peak stress and P-wave velocity show a decreasing trend due to damage accumulation with increasing number of dynamic tests. The bearing capacities of anisotropic coal are mainly governed by bedding angles, for example, the specimen with β = 30° undergoes the lowest impact numbers, but the one with β = 90° can undergo the highest numbers. The crack initiation and propagation are progressively revealed by two-dimensional (2D) X-ray slices and 3D fracture network reconstructions. As impact number increases, both 2D and 3D fractal dimensions of cracks increase exponentially, whereas dynamic peak stress and P-wave velocity are negatively correlated with them.

Mechanism and Prevention Practice of Coal Burst in Deep Gradual Residual Coal Pillar Area: A Case Study

Mechanism and Prevention Practice of Coal Burst in Deep Gradual Residual Coal Pillar Area: A Case Study

Experimental research on increasing effect of water injection in coal seam with chelating agent

ABSTRACT Coal seam water injection has a significant effect on the prevention and control of coal mine rock burst, and the pore characteristics of the coal seam is an important factor affecting the effect of coal seam water injection. With the deep mining of coal mine, the physical and mechanical properties of coal body change, the porosity of the coal seam decreases, and the injectability of the coal seam becomes worse. With the passage of time the minerals and CO2 in coal makes it more difficult to inject water. In order to obtain the reason why the water injection in coal seam becomes worse, the water injection additive with excellent performance is found, and a series of experiments on the impact tendency of coal body are carried out. The results show that the mine water used for coal seam water injection was liable to precipitate more ions, which may react with CO2 dissolved in water to form precipitates, plug coal pore and reduce the fluidity of water in the coal seam, resulting in poor water injection effect. Adding chelating agent IDS in aqueous solution can effectively prevent precipitation formed by the combination of easily precipitated ions and carbonate ions in it. At the same time, the chelating agent IDS can decompose precipitated ions from the surface of coal particles, change from insoluble to soluble, promote pore development, increase the effect of water injection and the pore diameter of the coal, and reduce hydrophobic groups on the coal surface. IDS can reduce the impact tendency of coal, and it is an environmental protection additive that can increase permeability. It can provide reference for prevention and control of composite power disasters by coal seam water injection.

Numerical investigation of impacts of geological faults on coal burst proneness during roadway excavation

Numerical investigation of impacts of geological faults on coal burst proneness during roadway excavation

Predicting roof displacement of roadways in underground coal mines using adaptive neuro-fuzzy inference system optimized by various physics-based optimization algorithms

Due to the rapid industrialization and the development of the economy in each country, the demand for energy is increasing rapidly. The coal mines have to pace up the mining operations with large production to meet the energy demand. This requirement has led underground coal mines to go deeper with more difficult conditions, especially the mining hazards, such as large deformations, rockburst, coal burst, roof collapse, to name a few. Therefore, this study aims at investigating and predicting the stability of the roadways in underground coal mines exploited by longwall mining method, using various novel intelligent techniques based on physics-based optimization algorithms (i.e. multi-verse optimizer (MVO), equilibrium optimizer (EO), simulated annealing (SA), and Henry gas solubility optimization (HGSO)) and adaptive neuro-fuzzy inference system (ANFIS), named as MVO-ANFIS, EO-ANFIS, SA-ANFIS and HGSO-ANFIS models. Accordingly, 162 roof displacement events were investigated based on the characteristics of surrounding rocks, such as cohesion, Young's modulus, density, shear strength, angle of internal friction, uniaxial compressive strength, quench durability index, rock mass rating, and tensile strength. The MVO-ANFIS, EO-ANFIS, SA-ANFIS and HGSO-ANFIS models were then developed and evaluated based on this dataset for predicting roof displacements in roadways of underground mines. The results indicated that the proposed intelligent techniques could accurately predict the roof displacements in roadways of underground mines with an accuracy in the range of 83%–92%. Remarkably, the SA-ANFIS model yielded the most dominant accuracy (i.e. 92%). Based on the accurate predictions from the proposed techniques, the reinforced solutions can be timely suggested to ensure the stability of roadways during exploiting coal, especially in the underground coal mines exploited by the longwall mining. • Roof displacements in underground coal mines were investigated. • Physics-based optimization algorithms were applied in this regard. • ANFIS was applied to determine the relationship of surrounding rocks. • Four AI techniques were proposed to predict roof displacements. • The SA-ANFIS model provided the highest accuracy in predicting roof displacements.

Experimental Study on the Mechanical Behavior of Coal Samples during Water Saturation.

When mining-induced fractures reach overlying aquifers, water enters the mining area and the coal is under different natural water saturation conditions, which significantly affect the mechanical behavior of the coal. In this study, uniaxial compression tests were conducted on dry, partially saturated, quasi-saturated, and fully saturated coal samples. The mechanical parameters, acoustic emission (AE) activities, and failure patterns of differently saturated coal samples were analyzed. The effect of water content on the behavior of coal and suggestions to ensure safe underground coal mining were discussed. The results indicate that the water content in coal increases nonlinearly with intrusion time and can be regarded as a logarithmic function. With increasing water saturation, the mechanical strength of the coal decreases on the whole and the AE activities, crack development, and burst severity are weakened significantly. The failure pattern of the coal samples changes from a dynamic type to a quasi-static one and from a compressive-shear type to a tensile one. Water content has four main effects on the mechanical behavior of the coal samples. These are a liquid bridge force, a water softening effect, a wedge effect, and a lubrication effect. With increasing water saturation, the effect of water gradually increases and predominates the coal failure, leading to a continuous decline in the strength of the coal samples. When the coal around the mining space is subjected to water, the high degree of water saturation in the coal decreases the risks of coal bursts significantly; however, it causes a large deformation and instability of the roadways. To ensure safe mining, more measures should be taken to decrease the amount of inrushing water, reduce the stress, and reinforce the anchor bolting support.

Numerical investigation into impacts of major fault on coal burst in longwall mining – A case study

The presence of geological faults is a significant contributing factor to coal burst in underground mining. In this study, a large-scale discontinuum model was established based on geological and geotechnical conditions in a mine site, where a longwall face passed through a major fault. Four model indicators were calculated during the longwall retreat: model seismic energy (energy released by the model system), fault seismic energy (energy released by fault-slip only), peak abutment stress and maximum strain energy density in coal seam. The change pattern of model seismic energy in the discontinuum model was calibrated against the seismic energy recorded in the mine site. It aims to verify that the model seismic energy can properly demonstrate the seismic energy observed in practice. The model results showed that the peak abutment stress and maximum strain energy density in coal seam increased when the longwall face approached the major fault, and then both of them experienced a most significant reduction when the largest fault-slip event occurred. A coal burst risk classification was then developed using multiple model indicators for the case study. A parametric study was conducted based on the calibrated model, which aims to investigate the impacts of various conditions on both fault-slip behaviour and stress and strain energy distributions around longwall excavations. Four factors were studied: the static friction angle of fault, the cover depth of fault, the dip angle of the coal seam and the mining direction. This study and the proposed model indicators can provide an improved understanding of fault-slip burst mechanisms and insights into the associated coal burst proneness assessment.

Main Roof Breakage and Vibration Induced Coal Burst Occurring in Longwall Roadways

Rock burst is one major threat to mining safety and economy. Rock burst occurring in the longwall mining roadway accounts for 85% of the total amount of burst events. This paper investigates the causality mechanism of rock burst in longwall roadways by establishing a finite elastic beam model in the working face based on the elastic foundation theory. The breakage process of the main roof and related dynamic effects are analysed. The result shows that the movement of the main roof shows free vibration under certain damping resistance. It is also found that the roof dominant vibration frequency increases with the increase in the thickness and elastic modulus of the roof. During roof vibration, the vertical stress applied on the coal mass is unloaded. The destressing of the roof-coal interface causes the coal mass in the roadway rib to slip into the roadway under the horizontal ground stress, resulting in rock burst. The possibility of rock burst increases with increase in the strength and thickness of the roof and horizontal ground stress within the coal mass. This mechanism explains the occurrence of rock burst in the mining roadway; it provides the fundamental theory for the prevention and controlling technologies of longwall roadway rock burst.

Field Monitoring of Delayed Coal Burst in an Advancing Entry of a Deep Coal Mine

Field Monitoring of Delayed Coal Burst in an Advancing Entry of a Deep Coal Mine