JRMGE / Vol 17 / Issue 4
True triaxial unloading test on the mechanical behaviors of sandstone: Effects of the intermediate principal stress and structural plane
Fan Feng, Zhiwei Xie, Shaojie Chen, Diyuan Li, Siyu Peng, Tong Zhang
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a College of Energy and Mining Engineering, Shandong University of Science and Technology, Qingdao, 266590, China
b State Key Laboratory of Mining Response and Disaster Prevention and Control in Deep Coal Mines, Anhui University of Science and Technology, Huainan,
232001, China
c School of Resources and Safety Engineering, Central South University, Changsha, 410083, China
d Department of Civil and Structural Engineering, Kyushu University, Fukuoka, 8190395, Japan
2025, 17(4): 2208-2226. doi:10.1016/j.jrmge.2024.04.005
Received: 2024-02-04 / Revised: 2024-03-18 / Accepted: 2024-04-27 / Available online: 2024-06-01
2025, 17(4): 2208-2226.
doi:10.1016/j.jrmge.2024.04.005
Received: 2024-02-04
Revised: 2024-03-18
Accepted: 2024-04-27
Available online: 2024-06-01
A series of true triaxial unloading tests are conducted on sandstone specimens with a single structural plane to investigate their mechanical behaviors and failure characteristics under different in situ stress states. The experimental results indicate that the dip angle of structural plane (θ) and the intermediate principal stress (σ2) have an important influence on the peak strength, cracking mode, and rockburst severity. The peak strength exhibits a first increase and then decrease as a function of σ2 for a constant θ. However, when σ2 is constant, the maximum peak strength is obtained at θ of 90°, and the minimum peak strength is obtained at θ of 30° or 45°. For the case of an inclined structural plane, the crack type at the tips of structural plane transforms from a mix of wing and anti-wing cracks to wing cracks with an increase in σ2, while the crack type around the tips of structural plane is always anti-wing cracks for the vertical structural plane, accompanied by a series of tensile cracks besides. The specimens with structural plane do not undergo slabbing failure regardless of θ, and always exhibit composite tensile-shear failure whatever the σ2 value is. With an increase in σ2 and θ, the intensity of the rockburst is consistent with the tendency of the peak strength. By analyzing the relationship between the cohesion (c), internal friction angle (φ), and θ in sandstone specimens, we incorporate θ into the true triaxial unloading strength criterion, and propose a modified linear Mogi-Coulomb criterion. Moreover, the crack propagation mechanism at the tips of structural plane, and closure degree of the structural plane under true triaxial unloading conditions are also discussed and summarized. This study provides theoretical guidance for stability assessment of surrounding rocks containing geological structures in deep complex stress environments.
Keywords: True triaxial unloading, Dip angle of structural plane, Intermediate principal stress, Mechanical behaviors, Cracking modes, Failure criterion
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Author(s) Information
Fan Feng
Fan Feng obtained his PhD degree in Mining Engineering from Central South University in 2018. He worked as Research Assistant in Earth Mechanics Institute, Colorado School of Mines from 2017 to 2018. He is currently an Associate Professor in Shandong University of Science and Technology. His research interests include (1) deep hard rock mechanics and engineering; (2) prevention and control of mine ground pressure disasters; and (3) underground metal mining methods and crafts. He hosted a total of 15 scientific projects, including two National Natural Science Foundation of China (NSFC). As the first author/corresponding author, he has published 30 papers indexed by SCI/EI. He has won the Green Mine Innovation Contribution Award and 12 provincial and ministerial science and technology awards.