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17 pages, 6243 KiB

Open AccessArticle

Research on the Testing Method for the Rheological Properties of Large-Particle Gangue Filling Slurry

by Xiaobo Duan, Yucheng Huang, Yuxin Hao and Liao Zhang

Processes 2025, 13(3), 789; https://doi.org/10.3390/pr13030789 - 8 Mar 2025

Viewed by 461

Abstract

Coal mine gangue cementation filling technology has increasingly become an effective and major means of dealing with “coal mining under buildings, railways, and bodies of water” and other complex hard-to-mine coal seams; but also, an important part of a large number of treatments [...] Read more.

Coal mine gangue cementation filling technology has increasingly become an effective and major means of dealing with “coal mining under buildings, railways, and bodies of water” and other complex hard-to-mine coal seams; but also, an important part of a large number of treatments of coal gangue stockpiled on the ground is to realize the green mining of coal mines. Coal mine cement filling often contains gangue particles with particle sizes larger than 15 mm; however, the viscometer and rheometer currently used at home and abroad are unable to accurately measure the rheological parameters of the slurry containing large-particle-sized gangue. In order to accurately measure the rheological parameters of slurry containing large-sized gangue particles combined with the site filling materials, the torque values obtained on the mixing blades at different speeds were generated by the combined action of the slurry between the blade side edge and the mixing drum wall, as well as the slurry between the blade lower edge and the mixing drum bottom. A new type of gangue slurry rheometer was developed. The new type of gangue slurry rheometer mainly included components such as the power system, sensing system, mechanical system, and other auxiliary units. Finally, using Fluent software ANSYS2023 to numerically simulate the fluidity of the slurry under the same conditions, the results obtained after the calculation and the test results showed that the error was within a reasonable range, indicating the correctness of the test principles of the new gangue slurry rheometer and the effectiveness of the instrument. This research offers new insights for accurately measuring the rheological parameters of particles with large sizes. Full article

(This article belongs to the Special Issue Monitoring, Process Control, Simulation, and Optimization in Coal Mining)

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16 pages, 4112 KiB

Open AccessArticle

Automatic Gas Emission Width of Coal Bodies in the Goaf near Outbursting Coal Seams

by Jian Xiao, Ruiqing Bi, Xuexi Chen, Shugang Li, Zhiheng Chen and Jianglong Chen

Processes 2025, 13(3), 715; https://doi.org/10.3390/pr13030715 - 1 Mar 2025

Viewed by 670

Abstract

The influence of coal and gas outbursts from a coal seam adjacent to the working face is crucial for determining its automatic gas discharge width, which is an important basis for the roadway position design of the adjacent working face. This study focuses [...] Read more.

The influence of coal and gas outbursts from a coal seam adjacent to the working face is crucial for determining its automatic gas discharge width, which is an important basis for the roadway position design of the adjacent working face. This study focuses on determining the automatic gas discharge width of the coal body in the neighboring goaf, especially examining the working face of the E₁₀-32040 air mining area and the E₁₀-32060 wind tunnel of the No. 1 Mine operated by Pingmei Company. Theoretical analysis, strain-softening simulation, and field testing were adopted to study the automatic gas discharge width under the current mining conditions, and the results are as follows: (1) Back mining at the working face has a greater impact on the coal body of the neighboring goaf than roadway excavation, and the compression deformation at 50 m from the goaf after back mining is 6.18 times that during roadway excavation. (2) The gas content of the coal body of the neighboring goaf is linearly distributed, and the coefficient of determination (R²) is 0.98024. (3) The extent of compression and deformation of the neighboring coal body follows an exponential distribution, and the coefficient of determination (R²) is 0.99482. (4) Under the current mining conditions, the risk of protrusion can be considered eliminated when the residual gas content is below 4.45 m³/t. The compression deformation is 0.96‰ when the automatic gas discharge width is 30.11 m. The research results can provide theoretical reference and data support for adjacent roadway location design and the selection of gas prevention and control measures in coal seams. Full article

(This article belongs to the Special Issue Monitoring, Process Control, Simulation, and Optimization in Coal Mining)

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26 pages, 7179 KiB

Open AccessArticle

Quantitative Identification of Emission Sources and Emission Dynamics of Pressure-Relieved Methane Under Variable Mining Intensities

by Xuexi Chen, Xingyu Chen, Jiaying Hu, Jian Xiao, Jihong Sun and Zhilong Yan

Processes 2025, 13(3), 704; https://doi.org/10.3390/pr13030704 - 28 Feb 2025

Viewed by 412

Abstract

This study addresses the abnormal emission of pressure-relieved methane under high-intensity mining conditions by integrating geostatistical inversion, FLAC^3D-COMSOL coupled numerical simulations, and stable carbon–hydrogen isotopic tracing. Focusing on the 12023 working face at Wangxingzhuang Coal Mine, we established a heterogeneous methane [...] Read more.

This study addresses the abnormal emission of pressure-relieved methane under high-intensity mining conditions by integrating geostatistical inversion, FLAC^3D-COMSOL coupled numerical simulations, and stable carbon–hydrogen isotopic tracing. Focusing on the 12023 working face at Wangxingzhuang Coal Mine, we established a heterogeneous methane reservoir model to analyze the mechanical responses of surrounding rock, permeability evolution, and gas migration patterns under mining intensities of 2–6 m/d. Key findings include the following: (1) When the working face advanced 180 m, vertical stress in concentration zones increased significantly with mining intensity, peaking at 12.89% higher under 6 m/d compared to 2 m/d. (2) Higher mining intensities exacerbated plastic failure in floor strata, with a maximum depth of 47.9 m at 6 m/d, enhancing permeability to 223 times the original coal seam. (3) Isotopic fingerprinting and multi-method validation identified adjacent seams as the dominant gas source, contributing 77.88% of total emissions. (4) Implementing targeted long directional drainage boreholes in floor strata achieved pressure-relief gas extraction efficiencies of 34.80–40.95%, reducing ventilation air methane by ≥61.79% and maintaining return airflow methane concentration below 0.45%. This research provides theoretical and technical foundations for adaptive gas control in rapidly advancing faces through stress–permeability coupling optimization, enabling the efficient interception and resource utilization of pressure-relieved methane. The outcomes support safe, sustainable coal mining practices and advance China’s Carbon Peak and Neutrality goals. Full article

(This article belongs to the Special Issue Monitoring, Process Control, Simulation, and Optimization in Coal Mining)

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16 pages, 11121 KiB

Open AccessArticle

A Study on the Failure Characteristics of Coal–Rock Structures with Different Bursting Liabilities

by Hongyan Li, Shi He, Yunlong Mo, Zhongxue Sun and Lei Li

Processes 2025, 13(3), 652; https://doi.org/10.3390/pr13030652 - 25 Feb 2025

Viewed by 375

Abstract

Research on the deformation and failure behavior of coal is a key scientific issue in the study of coal–rock dynamic disaster prevention technology. It is a critical means to grasp the structural effect of coal–rock deformation and failure behavior to explore the effects [...] Read more.

Research on the deformation and failure behavior of coal is a key scientific issue in the study of coal–rock dynamic disaster prevention technology. It is a critical means to grasp the structural effect of coal–rock deformation and failure behavior to explore the effects of fracture structure on coal–rock deformation and failure behavior. Our experiment on the failure characteristics of coal–rock and the evolution of deformation–fracture structures before the peak stress of coal–rock primarily investigates the influence of fracture structures on its deformation and failure behavior under loading, with a focus on analyzing the size of the primary fractures. The results indicate that the influence of the primary fracture structure on the physical and mechanical properties of coal–rock varies, and the sensitivity of different properties to these structures also differs. Compared to coal–rock without outburst proneness, the fracture structure evolution of coal–rock with strong outburst proneness before failure is more intense and exhibits significant geometric nonlinearity. The size of the fracture that plays the main role in the pre-peak deformation of coal–rock with strong outburst proneness is about one-third of the size of the specimen, and it is about one-fifth of the size of the specimen for coal–rock without outburst proneness. The fracture structure affects the whole deformation process before the failure of coal–rock with strong outburst proneness, but its influence on coal–rock without outburst proneness is gradually reduced with the loading. Full article

(This article belongs to the Special Issue Monitoring, Process Control, Simulation, and Optimization in Coal Mining)

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18 pages, 7291 KiB

Open AccessArticle

Gas Desorption Characteristics of Different Coal Ranks

by Huigang Xu, Xuyao Qi, Haidong Wang, Zhongqiu Liang, Tao Yang, Yongming Zou, Qi Jiang and Lei Jin

Processes 2025, 13(2), 570; https://doi.org/10.3390/pr13020570 - 18 Feb 2025

Viewed by 426

Abstract

It is crucial to understand the desorption and diffusion characteristics of coal seam gas to prevent gas disasters in coal mines. This study conducted constant-temperature gas dispersion tests on lignite, fiery coal, and anthracite to uncover the complexities of gas diffusion in coal [...] Read more.

It is crucial to understand the desorption and diffusion characteristics of coal seam gas to prevent gas disasters in coal mines. This study conducted constant-temperature gas dispersion tests on lignite, fiery coal, and anthracite to uncover the complexities of gas diffusion in coal samples under the influence of coal metamorphism. The main focus was on determining their gas desorption and diffusion characteristics and analyzing the mathematical models of gas dispersion for coal samples with varying degrees of metamorphism over different durations. The results indicated that highly metamorphosed coal samples reached the desorption limit quickly, while low-rank lignite required more time to reach the limit. The gas desorption diffusion rate was notably sensitive to the level of coal metamorphism. In the first 10 min, the gas desorption rate remained stable for lignite and fiery coal, whereas anthracite exhibited a rapid desorption rate in the initial 4 min followed by stability in the subsequent 6 min. Additionally, the effective gas diffusion coefficient showed a strong negative linear correlation with the degree of metamorphism, indicating reduced gas diffusion ability with increased metamorphism. The empirical formulas applied to anthracite showed stable correlation indices, with Formula 3 considered more suitable for describing the gas desorption processes of lignite and fiery coal. Full article

(This article belongs to the Special Issue Monitoring, Process Control, Simulation, and Optimization in Coal Mining)

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17 pages, 4205 KiB

Open AccessArticle

Mechanical and Permeability Characteristics of Gas-Bearing Coal Under Various Bedding Angles

by Xiaojun Tang, Feng Xu, Yewu Bi, Ruiqing Bi, Yangyang Guo and Ningning Huo

Processes 2025, 13(1), 176; https://doi.org/10.3390/pr13010176 - 10 Jan 2025

Viewed by 631

Abstract

Coal structures are commonly found in coal rock formations. Understanding the evolutionary laws of mechanics, deformation, and permeability of gas-bearing coal rock during the failure process at different bedding angles is crucial for studying the prevention and control techniques of coal and rock [...] Read more.

Coal structures are commonly found in coal rock formations. Understanding the evolutionary laws of mechanics, deformation, and permeability of gas-bearing coal rock during the failure process at different bedding angles is crucial for studying the prevention and control techniques of coal and rock gas dynamic disaster mitigation. In this study, a mechanical seepage test of gas-bearing coal under various bedding angles was conducted using the fluid–solid coupling triaxial servo test system. The results indicate the following corrections: ① Both axial peak strain (ε₁) and radial peak strain (ε₃) initially increase and then decrease, reaching their maximum values at 45°, indicating that the specimen eventually slips along the bedding plane and fails. ② As the bedding angle increases, the peak stress of the coal body shows a “V”-shaped distribution, with the peak strength of the gas-bearing coal sample being the lowest at 60°. ③ The minimum permeability of the coal sample increases with the rise in the bedding angle. The bedding direction of the coal samples at 90° and 75° aligns with the axial direction, leading to more seepage channels. ④ At a bedding angle of 60°, the minimum dissipated energy (U_d) is required for sample failure, indicating that the sample is highly prone to failure. Full article

(This article belongs to the Special Issue Monitoring, Process Control, Simulation, and Optimization in Coal Mining)

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24 pages, 38222 KiB

Open AccessArticle

Borehole Failure Mechanics and Influencing Factors in a Gas-Bearing Soft Coal Seam Under Complex Geological Conditions

by Xuexi Chen, Zhilong Yan, Jiaying Hu, Tao Yang, Jihong Sun, Yunqi Tao and Xingyu Chen

Processes 2025, 13(1), 146; https://doi.org/10.3390/pr13010146 - 7 Jan 2025

Viewed by 607

Abstract

The present research focuses on the mechanical properties and stress evolution of gas-bearing soft coal seams during drilling, which are affected by a multitude of complex factors such as high ground stress, gas pressure, and pre-existing fractures. In this study, a combination of [...] Read more.

The present research focuses on the mechanical properties and stress evolution of gas-bearing soft coal seams during drilling, which are affected by a multitude of complex factors such as high ground stress, gas pressure, and pre-existing fractures. In this study, a combination of PFC2D (Particle Flow Code in 2 Dimensions) numerical simulation and theoretical analysis is employed to investigate the borehole mechanics and fracture evolution characteristics under diverse complex conditions and to determine the factors influencing different forms of borehole failure in soft coal seams. The principal outcomes are as follows: (1) At a horizontal displacement of 0.1 m from the borehole orifice of the soft coal seam, a stress peak value of 13.9 MPa is attained; the peak value of the coal body contact force is 15.8 MPa; the peak value of the displacement is 0.008 m; and the porosity of the coal body around the borehole ranges from 0.14 to 0.35. (2) With an increase in the number of pre-existing fractures, the inclination progressively aligns with that of the pre-existing fractures. Maximum values of contact force (5.13–51.9 MPa), stress (3.19–37.2 MPa), shape dimension, and fracture angle (140–150°) are achieved under the highest lateral pressure coefficient and gas pressure (1.5 MPa). (3) The borehole energy is directly proportional to the number of pre-existing fractures, the lateral pressure coefficient, and gas pressure. The number of pre-existing fractures has the most significant impact on the damage degree, followed by the lateral pressure coefficient and then the gas pressure. (4) Two types of failure are identified: fracture-dominated failure, which is controlled by the geometric distribution of pre-existing fractures, and stress-dominated failure, wherein the failure zone gradually extends both upward and downward with an increasing lateral pressure coefficient. Full article

(This article belongs to the Special Issue Monitoring, Process Control, Simulation, and Optimization in Coal Mining)

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17 pages, 9468 KiB

Open AccessArticle

Non-Pillar Coal Mining by Driving Roadway During Mining Period in High-Gas Top-Coal-Caving Working Face

by Haisheng Shen, Zhongshun Chen, Yong Yuan, Bo Li and Samuel Kofi Anamor

Processes 2024, 12(11), 2607; https://doi.org/10.3390/pr12112607 - 20 Nov 2024

Cited by 1 | Viewed by 795

Abstract

To solve the problem of the inability to achieve Y-shaped ventilation in the boundary coal mining of high-gas mines and the problem of gas accumulation in the upper corner of a fully mechanized mining face, non-pillar coal mining technology is proposed by a [...] Read more.

To solve the problem of the inability to achieve Y-shaped ventilation in the boundary coal mining of high-gas mines and the problem of gas accumulation in the upper corner of a fully mechanized mining face, non-pillar coal mining technology is proposed by a driving roadway during the mining period. A high-gas working face requires Y-shaped ventilation to achieve upper corner gas control, but Y-shaped ventilation conditions are not available at the boundary coal body. In order to handle this challenge, studies have suggested non-pillar coal mining technology, which involves excavating roadways while mining in order to achieve non-pillar coal extraction and use recoverable wide coal pillars. During the simultaneous excavation of a working face and roadway, studies analyzed the distribution characteristics of the complicated stress environment. Following an evaluation of the impact of coal pillar width on the quality of an excavation roadway, this study’s development is in terms of an effective technique for retaining coal pillars as established. During the mining period of a working face, in the goaf of the working face, the research analyzed the distribution properties of the gas flow field, and findings from the study indicate that the width of the recovered coal pillar influences the distribution of gas. Finally, the width of the coal pillar was comprehensively determined, forming non-pillar coal mining technology by a driving roadway during the mining period. The on-site practice has shown that using a wide coal pillar with a width of 70 m to protect the roadway significantly reduces the deformation of the surrounding rock in the mining roadway, the gas concentration at the return airway is lower than the safety production standard, and by decreasing the mining succession time by 15 months, studies achieved improving the working face’s coal extraction rate by 12.6%. Full article

(This article belongs to the Special Issue Monitoring, Process Control, Simulation, and Optimization in Coal Mining)

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19 pages, 12300 KiB

Open AccessArticle

Initial Desorption Characteristics of Gas in Tectonic Coal Under Vibration and Its Impact on Coal and Gas Outbursts

by Maoliang Shen, Zhonggang Huo, Longyong Shu, Can Zhao, Huijie Zhang and Weihua Wang

Processes 2024, 12(11), 2548; https://doi.org/10.3390/pr12112548 - 14 Nov 2024

Viewed by 747

Abstract

The rapid desorption of gas in coal is an important cause of gas over-limit and outbursts. In order to explain the causes of coal and gas outbursts induced by vibration, this paper studies the gas desorption experiments of tectonic coal with different particle [...] Read more.

The rapid desorption of gas in coal is an important cause of gas over-limit and outbursts. In order to explain the causes of coal and gas outbursts induced by vibration, this paper studies the gas desorption experiments of tectonic coal with different particle sizes and different adsorption equilibrium pressures under 0~50 Hz vibration. High-pressure mercury intrusion experiments were used to measure the changes in pore volume and specific surface area of tectonic coal before and after vibration, revealing the control of pore structure changes on the initial desorption capacity of gas. Additionally, from the perspective of energy transformation during coal and gas outbursts, the effect of vibration on the process of coal and gas outbursts in tectonic coal was analyzed. The results showed that tectonic coal has strong initial desorption capacity, desorbing 29.58% to 54.51% of the ultimate desorption volume within 10 min. Vibration with frequencies of 0~50 Hz increased both the gas desorption ratios and desorption volume as the frequency increased. The initial desorption rate also increased with the vibration frequency, and vibration can enhance the initial desorption capacity of tectonic coal and delay the attenuation of desorption rate. Vibration affected the changes in the initial gas desorption rate and desorption rate attenuation coefficient by increasing the pore volume and specific surface area, with the changes in macropores and mesopores primarily affecting the initial desorption rate and 0~10 min desorption ratios, while the changes in micropores and minipores mainly influenced the attenuation rate of the desorption rate. Vibration increased the free gas expansion energy of tectonic coal as the frequency increased. During the incubation and triggering processes of coal and gas outbursts, vibration has been observed to accelerate the fragmentation and destabilisation of the coal body, while simultaneously increasing the gas expansion energy to a point where it reaches the threshold energy necessary for coal transportation, thus inducing and triggering the coal and gas protrusion. The study results elucidate, from an energy perspective, the underlying mechanisms that facilitate the occurrence of coal and gas outbursts, providing theoretical guidance for coal and gas outburst prevention and mine safety production. Full article

(This article belongs to the Special Issue Monitoring, Process Control, Simulation, and Optimization in Coal Mining)

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20 pages, 7628 KiB

Open AccessArticle

Combined Effect of Multiple Slotting Spatial Parameters on Gas Extraction Efficiency: Numerical Analysis and Field Verification

by Xuexi Chen, Xinyu Ma, Jiaying Hu, Tao Yang, Aitao Zhou, Ruiqing Bi and Jihong Sun

Processes 2024, 12(11), 2482; https://doi.org/10.3390/pr12112482 - 8 Nov 2024

Viewed by 947

Abstract

Hydraulic slotting is an effective technology that enhances gas extraction operations and prevents gas disasters in coal mines. Slotting parameters and spatial arrangements substantially affect permeability enhancements. The pressure-release range and effective extraction area under different slotting spatial parameters were obtained by constructing [...] Read more.

Hydraulic slotting is an effective technology that enhances gas extraction operations and prevents gas disasters in coal mines. Slotting parameters and spatial arrangements substantially affect permeability enhancements. The pressure-release range and effective extraction area under different slotting spatial parameters were obtained by constructing a hydraulic slotting pressure-release permeability and three-dimensional (3D) slotting numerical models. These models quantitatively characterized the influence rules of multiple slotting spatial arrangement parameters on the extraction efficiency at a 3D scale, clarified the interactions of multiple slottings and their combined effects on pressure relief and permeability enhancement, and verified the results using field engineering tests. The results showed that hydraulic slotting significantly alters local stress and strain distributions, creating high-strain and high-stress zones with clear spatial attenuation. The process enhances fracture development, reducing gas pressure from 1 MPa to 0.08 MPa, thereby improving extraction efficiency. Enlarging the slot dimensions from 1.5 to 2.5 m increases the gas pressure-relief efficiency by up to 41% and nearly triples the impact radius. Wider slot spacing (1.5 m to 3.5 m) and additional slots (from one to three) further reduce the borehole gas pressure by 23% to 25%, optimizing hydraulic slotting technology for practical applications. Full article

(This article belongs to the Special Issue Monitoring, Process Control, Simulation, and Optimization in Coal Mining)

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21 pages, 14008 KiB

Open AccessArticle

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

by Maoliang Shen, Zhonggang Huo, Longyong Shu, Qixian Li, Pengxin Zhang and Weihua Wang

Processes 2024, 12(8), 1701; https://doi.org/10.3390/pr12081701 - 14 Aug 2024

Cited by 2 | Viewed by 922

Abstract

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. [...] Read more.

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 (D_e) 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 D_e 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. Full article

(This article belongs to the Special Issue Monitoring, Process Control, Simulation, and Optimization in Coal Mining)

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20 pages, 10455 KiB

Open AccessArticle

Experimental Study on the Effect of Unloading Paths on Coal Damage and Permeability Evolution

by Congmeng Hao, Youpai Wang and Guangyi Liu

Processes 2024, 12(8), 1661; https://doi.org/10.3390/pr12081661 - 7 Aug 2024

Cited by 2 | Viewed by 1218

Abstract

Coal seam cavitation is one of the most effective techniques for gas disaster control in low-permeability coal. Due to the difference in cavitation method and process, the damage degree and fracture development range of the coal body around the cavern are greatly different, [...] Read more.

Coal seam cavitation is one of the most effective techniques for gas disaster control in low-permeability coal. Due to the difference in cavitation method and process, the damage degree and fracture development range of the coal body around the cavern are greatly different, and the effect of increasing the permeability of the coal body is further changed. In order to further understand the permeability enhancement mechanism of cavitation technology on low-permeability coal and effectively guide engineering applications, this paper conducted experimental research on the unloading damage and permeability evolution characteristics of coal under different cavitation paths using a coal-rock “adsorption-percolation-mechanics” coupling test system. Through the analysis of coal strength and deformation characteristics, coal damage characteristics, and the evolution law of coal permeability combined with the macroscopic damage characteristics of coal, the strength degradation mechanism of unloaded coal and the mechanism of increased permeability and flow were revealed. The results show that unloading can significantly reduce the strength of coal, and the greater the unloading rate, the more obvious the reduction. The essence of this is that unloading reduces the cohesion and internal friction angle of coal—damage and breakage are the most effective ways to improve the permeability of the coal body. Unloading damaged coal bodies not only significantly improves the permeability of the coal body but also improves the diffusion ability of gas, and finally, shows a remarkable strengthening effect of gas extraction. Full article

(This article belongs to the Special Issue Monitoring, Process Control, Simulation, and Optimization in Coal Mining)

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17 pages, 6075 KiB

Open AccessArticle

Study on the Damage Mechanism of Coal under Hydraulic Load

by Hongyan Li, Yaolong Li, Weihua Wang, Yang Li, Zhongxue Sun, Shi He and Yongpeng Fan

Processes 2024, 12(5), 925; https://doi.org/10.3390/pr12050925 - 1 May 2024

Cited by 1 | Viewed by 1161

Abstract

Hydraulic fracturing is extensively utilized for the prevention and control of gas outbursts and rockbursts in the deep sections of coal mines. The determination of fracturing construction parameters based on the coal seam conditions and stress environments merits further investigation. This paper constructs [...] Read more.

Hydraulic fracturing is extensively utilized for the prevention and control of gas outbursts and rockbursts in the deep sections of coal mines. The determination of fracturing construction parameters based on the coal seam conditions and stress environments merits further investigation. This paper constructs a damage analysis model for coal under hydraulic loads, factoring in the influence of the intermediate principal stress, grounded in the octahedron strength theory analysis approach. It deduces the theoretical analytical equation for the damage distribution of a coal medium subjected to small-flow-rate hydraulic fracturing in underground coal mines. Laboratory experiments yielded the mechanical parameters of coal in the study area and facilitated the fitting of the intermediate principal stress coefficient. Leveraging these datasets, the study probes into the interaction between hydraulic loads and damage radius under assorted influence ranges, porosity, far-field crustal stresses, and brittle damage coefficients. The findings underscore that hydraulic load escalates exponentially with the damage radius. Within the variable range of geological conditions in the test area, the effects of varying influence range, porosity level, far-field stress, and brittle damage coefficient on the outcomes intensify one by one; a larger hydraulic load diminishes the impact of far-field stress variations on the damage radius, inversely to the influence range, porosity, and brittle damage. The damage radius derived through the gas pressure reduction method in field applications corroborates the theoretical calculations, affirming the precision of the theoretical model. These findings render pivotal guidance for the design and efficacy assessment of small-scale hydraulic fracturing in underground coal mines. Full article

(This article belongs to the Special Issue Monitoring, Process Control, Simulation, and Optimization in Coal Mining)

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Review

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44 pages, 8150 KiB

Open AccessReview

Theories, Techniques and Materials for Sealing Coalbed Methane Extraction Boreholes in Underground Mines: A Review

by Ruiqing Bi, Miaomiao Guo, Shuai Wang, Yunguang Zhang, Xiaopeng Si, Xuexi Chen and Liang Zhang

Processes 2024, 12(9), 2022; https://doi.org/10.3390/pr12092022 - 19 Sep 2024

Cited by 2 | Viewed by 1197

Abstract

To further enhance the intelligent technology, platformisation, and systematisation of coalbed methane extraction sealing technology, this paper analyses the research progress of theories, technologies, and sealing materials related to coalbed methane extraction sealing and systematically summarises the latest achievements of the basic theories, [...] Read more.

To further enhance the intelligent technology, platformisation, and systematisation of coalbed methane extraction sealing technology, this paper analyses the research progress of theories, technologies, and sealing materials related to coalbed methane extraction sealing and systematically summarises the latest achievements of the basic theories, key technologies, and sealing materials of coalbed methane extraction. Considering the increasing mining depth, advancements in intelligent technology, and the evolving landscape of coalbed methane development, it is particularly important to establish a more comprehensive coalbed methane extraction borehole sealing system. Based on this, future development trends and research prospects are proposed: In terms of coalbed-methane-extraction-related theories, there should be a stronger focus on fundamental research such as on gas flow within the coal matrix. For coalbed methane extraction borehole sealing technologies and devices, efforts should be made to enhance research on intelligent, platform-based, and systematic approaches, while adapting to the application of directional long borehole sealing processes. In terms of coalbed methane extraction borehole leakage detection, non-contact measurement and non-destructive monitoring methods should be employed to achieve dynamic monitoring and early warning of methane leaks, integrating these technologies into coalbed methane extraction system platforms. For coalbed methane extraction borehole sealing materials, further development is needed for liquid sealing materials that address borehole creep and the development of fractures in surrounding rock, as well as solid sealing materials with Poisson’s ratios similar to that of the surrounding rock mass. Full article

(This article belongs to the Special Issue Monitoring, Process Control, Simulation, and Optimization in Coal Mining)

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