Mechanical Characteristics of Coal Samples under Triaxial Unloading Pressure with Different Test Paths

Zhang, Yang; Yang, Yongjie; Ma, Depeng

doi:10.1155/2020/8870821

Cited by 7 publications

(6 citation statements)

References 12 publications

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“…Triaxial tests have been extensively employed in the investigation of deformation, failure, and mechanical behavior of coal or rock, allowing for the replication of complex stress conditions encountered in the field [8,9]. For example, Zhou et al [10] conducted a study on the failure characteristics and mechanisms of coal under different confining pressures and graded loads.…”

Section: Introductionmentioning

confidence: 99%

Mechanical Behaviors and Precursory Characteristics of Coal-Burst in Deep Coal Mining for Safety-Sustainable Operations: Insights from Experimental Analysis

Wang,

Zhou

et al. 2024

Sustainability

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Coalburst, a frequent and severe dynamic disaster, poses significant challenges to the safety and sustainable development of coal mines during deep excavation. To investigate the mechanical behaviors and precursory characteristics of coalburst subjected to in situ stress conditions, multiaxial cyclic loading experiments were conducted on cubic coal specimens, and the effects of different confining pressures on the mechanical parameters and energy evolution were analyzed. Acoustic emission (AE) technology was utilized to study the accumulation process of stress-induced damage and identify the source modes of microcracks. Then, nonlinear fractal theory and critical slowing theory were used to investigate the time-varying precursory characteristics of catastrophic failure in coalburst. The results show that as the confining pressure increases, the coal samples exhibit higher levels of elastic strain energy and dissipative energy, indicating an enhancement of plasticity. The AE count and accumulated energy show a strong correlation with cyclic loads. With an increasing number of cycles, the AE Felicity ratio gradually decreases, indicating a progressive increase in irreversible damage. Shear-mode microcracks also become more prominent with applied stress and confining pressures, as supported by varying AF/RA values of AE signals. The AE signals also follow the Hurst statistical law, and increasing applied stress and confining pressure strengthen this statistical pattern with a higher Hurst index. Throughout the cyclic loading process, certain AE varying trends were observed: the autocorrelation coefficient increased, the fractal dimension gradually decreased, and the variance suddenly increased. These trends serve as early, middle, and short–imminent warning signals, respectively, for the catastrophic failure of the loaded coal sample. These research findings contribute to a deeper understanding of coal failure evolution and provide a basis for early detection and warning of coalburst disasters, which are also essential for promoting the safe and sustainable development of deep coal mining operations.

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Section: Introductionmentioning

confidence: 99%

Mechanical Behaviors and Precursory Characteristics of Coal-Burst in Deep Coal Mining for Safety-Sustainable Operations: Insights from Experimental Analysis

Wang,

Zhou

et al. 2024

Sustainability

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“…Comparing the triaxial unloading test with the conventional triaxial compression test, a reduction in the coal specimen’s cohesive force and an increase in internal friction were noted. Moreover, Wang et al [ 10 ] analyzed how the confining pressure and unloading rate impacted crack propagation; the results indicated that under greater confining pressure, crack formation post-failure, and the rate of crack expansion, increased with higher unloading rates. Takeda et al [ 11 ] examined the semi-permeability evolution of Wakkanai mudstones during cyclic loading and unloading, emphasizing the importance of considering the applied stresses when estimating argillite semi-permeability.…”

Section: Introductionmentioning

confidence: 99%

Study on the Strength and Failure Characteristics of Silty Mudstone Using Different Unloading Paths

Wang

Zhang

et al. 2023

Materials

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To investigate the strength and failure characteristics of silty mudstone using different stress paths, silt-like mudstone specimens were subjected to triaxial unloading tests. The results indicate the following. (1) When subjected to equivalent initial deviator stress levels and differing confining pressures, the peak stress, residual stress, and elastic modulus, exhibited during unloading, increased concordantly with greater initial confining pressure. Both the peak strain and residual strain increased with rising initial confining pressure. The increase in peak strain and residual strain initially decelerated, then noticeably increased, before ultimately decreasing again. Additionally, the unloading failure time and strain rate demonstrated a negative correlation as the confining pressure increased. (2) Under different initial deviatoric stress conditions, the peak stress, residual stress, and residual strain, under unloading confining pressure conditions, decreased as the initial deviatoric stress levels elevated. Conversely, the peak strain and elastic modulus initially increased, then decreased under increasing initial deviatoric stress conditions. The unloading failure time and strain rate were both observed to decrease as the initial deviatoric stress levels increased. (3) Utilizing the Mohr stress circle enabled the characterization of the shear strength variation in the specimens during the unloading process. The cohesion and internal friction angle remained relatively consistent across the different unloading stress paths appraised, with cohesion being greater in path I versus path II, whereas the internal friction angle exhibited an inverse relationship. (4) The specimen failed during unloading due to lateral expansion caused by unloading confining pressure and collapse failure. The failure fracture surfaces predominantly manifested shear failure morphologies.

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“…The existing studies have revealed that as high as 80% of the failure strength under the corresponding confining pressure is generally selected at the unloading point [15][16][17][18]. Under the same loading and unloading stress path, (1) a higher initial confining pressure tends to lead to more energy stored in the coal body and severer damages; (2) a higher unloading rate tends to lead to less energy stored in the coal body, which is more prone to brittle failure and the more complex the damage degree [19][20][21]; Xue et al [19] indicated that the energy required for rock failure is a definite value under certain conditions and is not affected by the stress loading path. Regarding the researches on the engineering properties of excavation rock mass, in addition to the above-mentioned influencing factors, the loading axial pressure rate is also a critical factor and mainly reflects the speed of stress concentration in the construction environment.…”

Section: Introductionmentioning

confidence: 99%

A Study on the Effects of Loading Axial Pressure Rate on Coal Mechanical Properties and Energy Evolution Law

Guo

Sun

et al. 2022

Geofluids

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Due to the unique nature of the coal mining industry, safety is always one highly upheld premise of high production and high efficiency. According to the stress adjustment characteristics of the surrounding rocks in roadway excavation under a nondisruptive environment, the stress paths of unloading confining pressure and loading axial pressure were designed creatively and vividly, and the coal mechanical properties and energy evolution law under different loading axial pressure rates were studied through a series of experiments. As the loading axial pressure rate increases, the mechanical parameters at the time of coal failure show a nonlinear increase in the peak strength, the confining pressure, and the axial strain, while the variation laws of lateral strain and volumetric strain are not obvious. In addition, the failure mode transfers from the brittle failure to the ductile failure. In terms of energy, the positive work done by the axial pressure, the total work, and the elastic strain energy tend to increase nonlinearly, while the negative work done by the confining pressure and the plastic strain energy increase conversely. The elastic strain energy conversion rate increases logarithmically, indicating that a higher loading axial pressure rate tends to increase the probability and strength of coal instantaneous failure and subsequent dynamic behaviors. The research results reveal that providing an appropriate pressure relief and timely support after the roadway excavation in the actual production process can effectively reduce the energy level of the environment at the location of the surrounding rock support system, which is conducive to the roadway support and the surrounding rock stability control. Furtherly, it has important reference value for the roadway excavation and other underground engineering excavation and support operations and is of great significance to promote the development of deep resources.

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Mechanical Characteristics of Coal Samples under Triaxial Unloading Pressure with Different Test Paths

Cited by 7 publications

References 12 publications

Mechanical Behaviors and Precursory Characteristics of Coal-Burst in Deep Coal Mining for Safety-Sustainable Operations: Insights from Experimental Analysis

Mechanical Behaviors and Precursory Characteristics of Coal-Burst in Deep Coal Mining for Safety-Sustainable Operations: Insights from Experimental Analysis

Study on the Strength and Failure Characteristics of Silty Mudstone Using Different Unloading Paths

A Study on the Effects of Loading Axial Pressure Rate on Coal Mechanical Properties and Energy Evolution Law

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