An experimental study of seepage properties of gas‐saturated coal under different loading conditions

Wang, Dengke; Lv, Ruihuan; Wei, Jianping; Fu, Qichao; Wang, Yitong; Zhang, Ping; Yu, Chong; Yao, Banghua

doi:10.1002/ese3.309

Cited by 36 publications

(18 citation statements)

References 25 publications

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“…Unfortunately, many researchers seemed to neglect the swelling stress caused by the adsorption of gas when studying the effective stress of coal [48][49][50][51] and also ignore the effective stress when investigating the creep model of coal or rock. Unfortunately, many researchers seemed to neglect the swelling stress caused by the adsorption of gas when studying the effective stress of coal [48][49][50][51] and also ignore the effective stress when investigating the creep model of coal or rock.…”

Section: Discussionmentioning

confidence: 99%

“…There are differences between gas-filled coal and rock as well as soil in terms of effective stress calculation. Unfortunately, many researchers seemed to neglect the swelling stress caused by the adsorption of gas when studying the effective stress of coal [48][49][50][51] and also ignore the effective stress when investigating the creep model of coal or rock. In this article, we demonstrated that the coupling effect of gas pressure and uniaxial (or triaxial) stress should be considered when studying the effective stress of coal.…”

Section: Discussionmentioning

confidence: 99%

“…Unfortunately, many researchers ignored it and treated gascontaining coal as rock or soil, when studying the effective stress of coal [48][49][50][51] under uniaxial (or triaxial) stress and gas pressure. In fact, in this paper, the creep deformation of coal is not only affected by triaxial stress but also by gas pressure during the creep process.…”

Section: Effective Stress For Coal Containing Gasmentioning

confidence: 99%

“…Because of the above two factors, the effective stress of coal containing gas is different from that of rock and soil. Unfortunately, many researchers ignored it and treated gascontaining coal as rock or soil, when studying the effective stress of coal [48][49][50][51] under uniaxial (or triaxial) stress and gas pressure.…”

Section: Effective Stress For Coal Containing Gasmentioning

confidence: 99%

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Creep characteristics and constitutive model of coal under triaxial stress and gas pressure

Zhang

Gao

et al. 2019

Energy Science & Engineering

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Creep behavior is one of the most important mechanical behaviors of coal. In the present study, we systematically carried out a series of creep experiments of briquette samples under triaxial compression and gas pressure. The experimental results showed that the creep deformation characteristics of coal were related to deviatoric stress and gas pressure. The accelerating creep stage initiated when the deviatoric stress reached or exceeded the yield stress until failure took place. In contrast, when the deviatoric stress was less than the yield strength, only transient and steady creep stage occurred. Besides, gas pressure played a positive role in the creep process of coal. The axial strain of coal slightly increased with gas pressure (range from 0.13 to 0.40 MPa) when the effective triaxial stress remained constant. For example, in the steady creep stage (σ 1 = 9 MPa, p = 0.13 MPa), the axial strain of sample S 1 is 2.710% and that of sample S 2 is 3.361%, that is, coal samples with high gas pressure have higher axial strain. Moreover, gas pressure has two main effects on the mechanical behavior of coal. One is that the coal adsorbs gas molecules resulting in swelling strain and swelling stress, and the other is that the gas pressure may compress the coal particles. Considering the swelling stress and gas pressure, we intensively studied the effective stress formula of coal containing gas. Then, the effective stress was taken into consideration in the nonlinear Nishihara creep model. Furthermore, the tertiary creep factor n was introduced in the nonlinear model to control the creep deformation evolution with time so that the nonlinear model could accurately describe the full creep stage of coal. In contrast, due to the lack of such a controlling parameter, the Nishihara model failed to reproduce the accelerating creep stage. K E Y W O R D Scoal, creep model, effective stress, gas pressure, swelling stress, triaxial compression | INTRODUCTIONCreep behavior is one of the fundamental mechanical properties of coal or rock, associated with the stability of many buildings and underground structures in mining and rock engineering, such as roadways, tunnels, and dams. It is important to have a precise understanding of the creep or timedependent behavior of coal or rock, which may prevent coal 502 | ZHANG et Al. Highlights• The coupling effect of triaxial stress and gas pressure on coal was investigated. • The gas pressure played a positive role in the creep process of coal. • The effective stress of gas-filled coal was intensively studied. • The effective stress was considered in the nonlinear Nishihara creep model of coal, which could accurately reproduce the three creep stages, especially the accelerating creep stage.How to cite this article: Zhang L, Li X-C, Gao J-X, An Z-X, Yang X-H, Nie B-S. Creep characteristics and constitutive model of coal under triaxial stress and gas pressure. Energy Sci Eng. 2020;8:501-514. https ://doi.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Effective Stress For Coal Containing Gasmentioning

confidence: 99%

Section: Effective Stress For Coal Containing Gasmentioning

confidence: 99%

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Creep characteristics and constitutive model of coal under triaxial stress and gas pressure

Zhang

Gao

et al. 2019

Energy Science & Engineering

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“…In the mining process, the original stress distribution is destroyed by the mining activities and forms the stress concentration zone, resulting in the change of permeability. The permeability of initial undamaged coal is intensely sensitive to the effective stress and decreases with the increase of the effective stress, and it is also affected by the swelling stress of coal [10][11][12]. There is an exponential relationship between the permeability and the effective stress, and the permeability anisotropy of undamaged coal under effective stress shows a dynamic development change law [13,14].…”

Section: Introductionmentioning

confidence: 99%

Experimental Study on the Permeability Evolution and Gas Flow Law of Post-Strength Soft Coal

Hou

Jin

et al. 2020

Applied Sciences

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Permeability is an essential indicator for predicting gas drainage yield and preventing mine gas disasters, which is significantly influenced by the stress paths and the integrity of coal. Conventional research on permeability mainly focused on the permeability evolution of initial undamaged or fractured (prefabricated fractures) coal under various stress paths; little attention has been paid to post-strength coal (stress-induced damage), especially for soft coal. To determine the permeability evolution and gas flow law of post-strength soft coal samples under various stress paths, we used the experimental method combined with the numerical method in this study. The results showed that when the confining pressure and axial pressure of post-strength soft coal samples were unloaded, the permeability increased by 1.25–1.32 times; when the coal samples were loaded into the secondary damage, the permeability first decreased and then increased. The simulation part in this study found that the development of the fracture of coal samples under triaxial compression was divided into four stages. Gas flow law of post-strength soft coal was significantly influenced by fracture locations, and the gas pressure and gas flow field near the fracture were disturbed.

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Damage caused by freeze‐thaw treatment with liquid nitrogen on pore and fracture structures in a water‐bearing coal mass

Lin

Yan

et al. 2020

Energy Science & Engineering

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The purpose of the study was to explore the microscopic and mesoscopic damage mechanisms of water‐bearing coal mass in the freeze‐thaw process with liquid nitrogen. For this purpose, by using a Zeiss microscope, a nonmetal ultrasonic velocity detector and a nuclear magnetic resonance (NMR) spectrometer, the changes in the structures of surface fractures and pores before and after coal masses with different moisture contents when subjected to freeze‐thaw treatment with liquid nitrogen (FTTLN) were tested. The result showed that under the freeze‐thaw effect of liquid nitrogen, the structures of surface fractures and internal pores of coal mass were both changed. Upon increasing the moisture content of the coal, the width of surface fractures increased; the surface fractures showed significant fractal characteristics: The higher the moisture content of the coal, the greater the rate of change of fractal dimension after FTTLN; the ultrasonic wave velocity in the coal mass gradually decreased after FTTLN, and the greater the moisture content, the more significant the decrease in ultrasonic wave velocity; under the freeze‐thaw effect of liquid nitrogen, the pore structure in the coal mass was transformed from micropores and small pores to mesopores and macropores and certain new micropores and small pores were generated. Upon increasing the moisture content of the coal mass, the peak area of micropores and small pores and their proportion decreased at first and then increased (reaching the minimum at 9.12% of moisture content); the peak area, peak area proportion, and porosity of mesopores and macropores always increased. The damage factor attained based on the width of fractures, longitudinal wave velocity, fractal dimension of surface fractures, and porosity was favorably correlated with the moisture content: With increasing moisture content, the coal mass became more severely damaged.

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An experimental study of seepage properties of gas‐saturated coal under different loading conditions

Cited by 36 publications

References 25 publications

Creep characteristics and constitutive model of coal under triaxial stress and gas pressure

Creep characteristics and constitutive model of coal under triaxial stress and gas pressure

Experimental Study on the Permeability Evolution and Gas Flow Law of Post-Strength Soft Coal

Damage caused by freeze‐thaw treatment with liquid nitrogen on pore and fracture structures in a water‐bearing coal mass

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