Experimental Research on Anisotropy Characteristics of Shale under Triaxial Incremental Cyclic Loading and Unloading
Shale is a common rock type that is associated with underground engineering projects, and several important factors, such as bedding structure, confining pressure, and the loading and unloading path, significantly influence the anisotropy of shale. Triaxial monotonic loading tests and triaxial incre...
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MDPI AG
2024-03-01
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| Online Access: | https://www.mdpi.com/2076-3417/14/6/2602 |
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| author | Yangbing Cao Qiang Yan Sui Zhang Fuming Cai |
| author_facet | Yangbing Cao Qiang Yan Sui Zhang Fuming Cai |
| author_sort | Yangbing Cao |
| collection | DOAJ |
| description | Shale is a common rock type that is associated with underground engineering projects, and several important factors, such as bedding structure, confining pressure, and the loading and unloading path, significantly influence the anisotropy of shale. Triaxial monotonic loading tests and triaxial incremental cyclic loading and unloading tests of shale under three kinds of confining pressures and five types of bedding inclination angles (<i>θ</i>) were thus performed to investigate the anisotropy of shale in terms of mechanical behavior, acoustic emission (AE), and energy evolution, and reveal the mechanism by which shale anisotropy is weakened. The results show that (1) the compressive strength and elastic modulus of shale decrease and then increase as the <i>θ</i> increases, and that both <i>σ</i><sub>3</sub> and incremental cyclic loading and unloading reduce the anisotropy in terms of the compressive strength and elastic modulus of shale, with the ratio of plastic strain to total strain reaching its maximum at a <i>θ</i> of 60° during each loading and unloading cycle. (2) The failure modes of shale with <i>θ</i> of 0°, 30°, and 90° under triaxial monotonic loading are similar to the counterparts under triaxial incremental cyclic loading and unloading, while the failure modes of shale with <i>θ</i> of 45° and 60° differ significantly under the two loading conditions, and interestingly, the degree to which the bedding plane participates in shale crack evolution under incremental cyclic loading and unloading is considerably lower than that under triaxial monotonic loading. (3) The cumulative AE count and AE <i>b</i>-value of shale first decrease and then increase as the <i>θ</i> increases, while the Felicity ratio decreases as the number of cycles increases. (4) As the <i>θ</i> increases, the total energy density <i>U</i><sub>0</sub> and the parameter <i>m</i>, which reflects the accumulation rate of elastic energy, first decrease and then increase, with both reaching a minimum at a <i>θ</i> of 60°. (5) The mode by which cyclic loading and unloading leads to failure in shale with a <i>θ</i> of 60° is similar to that at a <i>θ</i> of 0° and is the main mechanism by which shale anisotropy weakening occurs as a result of cyclic loading and unloading. The results provide experimental support and a theoretical basis for safer and more efficient underground engineering projects that involve shale. |
| first_indexed | 2024-04-24T18:34:33Z |
| format | Article |
| id | doaj.art-81daad14b391462d85f7d5ab1a774836 |
| institution | Directory Open Access Journal |
| issn | 2076-3417 |
| language | English |
| last_indexed | 2024-04-24T18:34:33Z |
| publishDate | 2024-03-01 |
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| spelling | doaj.art-81daad14b391462d85f7d5ab1a7748362024-03-27T13:20:13ZengMDPI AGApplied Sciences2076-34172024-03-01146260210.3390/app14062602Experimental Research on Anisotropy Characteristics of Shale under Triaxial Incremental Cyclic Loading and UnloadingYangbing Cao0Qiang Yan1Sui Zhang2Fuming Cai3Zijin School of Geology and Mining, Fuzhou University, Fuzhou 350108, ChinaZijin School of Geology and Mining, Fuzhou University, Fuzhou 350108, ChinaEngineering Technology Innovation Center of Mineral Resources Explorations in Bedrock Zones, Ministry of Natural Resources, Guiyang 550081, ChinaZijin School of Geology and Mining, Fuzhou University, Fuzhou 350108, ChinaShale is a common rock type that is associated with underground engineering projects, and several important factors, such as bedding structure, confining pressure, and the loading and unloading path, significantly influence the anisotropy of shale. Triaxial monotonic loading tests and triaxial incremental cyclic loading and unloading tests of shale under three kinds of confining pressures and five types of bedding inclination angles (<i>θ</i>) were thus performed to investigate the anisotropy of shale in terms of mechanical behavior, acoustic emission (AE), and energy evolution, and reveal the mechanism by which shale anisotropy is weakened. The results show that (1) the compressive strength and elastic modulus of shale decrease and then increase as the <i>θ</i> increases, and that both <i>σ</i><sub>3</sub> and incremental cyclic loading and unloading reduce the anisotropy in terms of the compressive strength and elastic modulus of shale, with the ratio of plastic strain to total strain reaching its maximum at a <i>θ</i> of 60° during each loading and unloading cycle. (2) The failure modes of shale with <i>θ</i> of 0°, 30°, and 90° under triaxial monotonic loading are similar to the counterparts under triaxial incremental cyclic loading and unloading, while the failure modes of shale with <i>θ</i> of 45° and 60° differ significantly under the two loading conditions, and interestingly, the degree to which the bedding plane participates in shale crack evolution under incremental cyclic loading and unloading is considerably lower than that under triaxial monotonic loading. (3) The cumulative AE count and AE <i>b</i>-value of shale first decrease and then increase as the <i>θ</i> increases, while the Felicity ratio decreases as the number of cycles increases. (4) As the <i>θ</i> increases, the total energy density <i>U</i><sub>0</sub> and the parameter <i>m</i>, which reflects the accumulation rate of elastic energy, first decrease and then increase, with both reaching a minimum at a <i>θ</i> of 60°. (5) The mode by which cyclic loading and unloading leads to failure in shale with a <i>θ</i> of 60° is similar to that at a <i>θ</i> of 0° and is the main mechanism by which shale anisotropy weakening occurs as a result of cyclic loading and unloading. The results provide experimental support and a theoretical basis for safer and more efficient underground engineering projects that involve shale.https://www.mdpi.com/2076-3417/14/6/2602shaleanisotropyincremental cyclic loading and unloadingfailure modeacoustic emissionenergy evolution |
| spellingShingle | Yangbing Cao Qiang Yan Sui Zhang Fuming Cai Experimental Research on Anisotropy Characteristics of Shale under Triaxial Incremental Cyclic Loading and Unloading Applied Sciences shale anisotropy incremental cyclic loading and unloading failure mode acoustic emission energy evolution |
| title | Experimental Research on Anisotropy Characteristics of Shale under Triaxial Incremental Cyclic Loading and Unloading |
| title_full | Experimental Research on Anisotropy Characteristics of Shale under Triaxial Incremental Cyclic Loading and Unloading |
| title_fullStr | Experimental Research on Anisotropy Characteristics of Shale under Triaxial Incremental Cyclic Loading and Unloading |
| title_full_unstemmed | Experimental Research on Anisotropy Characteristics of Shale under Triaxial Incremental Cyclic Loading and Unloading |
| title_short | Experimental Research on Anisotropy Characteristics of Shale under Triaxial Incremental Cyclic Loading and Unloading |
| title_sort | experimental research on anisotropy characteristics of shale under triaxial incremental cyclic loading and unloading |
| topic | shale anisotropy incremental cyclic loading and unloading failure mode acoustic emission energy evolution |
| url | https://www.mdpi.com/2076-3417/14/6/2602 |
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