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Article

Study on Mechanism and Constitutive Modelling of Secondary Anisotropy of Surrounding Rock of Deep Tunnels

1
College of Mining Engineering, Taiyuan University of Technology, Taiyuan 030024, China
2
CCTEG Coal Mining Research Institute, Beijing 100013, China
3
State Key Laboratory of Intelligent Coal Mining and Strata Control, Beijing 100013, China
*
Author to whom correspondence should be addressed.
Symmetry 2025, 17(8), 1234; https://doi.org/10.3390/sym17081234
Submission received: 20 June 2025 / Revised: 17 July 2025 / Accepted: 1 August 2025 / Published: 4 August 2025
(This article belongs to the Section Engineering and Materials)

Abstract

Crack initiation, propagation, and slippage serve as the key mesoscopic mechanisms contributing to the deterioration of deep tunnel surrounding rocks. In this study, a secondary anisotropy of deep tunnels surrounding rocks was proposed: The axial-displacement constraint of deep tunnels forces cracks in the surrounding rock to initiate, propagate, and slip in planes parallel to the tunnel axial direction. These cracks have no significant effect on the axial strength of the surrounding rock but significantly reduce the tangential strength, resulting in the secondary anisotropy. First, the secondary anisotropy was verified by a hybrid stress–strain controlled true triaxial test of sandstone specimens, a CT 3D (computed tomography three-dimensional) reconstruction of a fractured sandstone specimen, a numerical simulation of heterogeneous rock specimens, and field borehole TV (television) images. Subsequently, a novel SSA (strain-softening and secondary anisotropy) constitutive model was developed to characterise the secondary anisotropy of the surrounding rock and developed using C++ into a numerical form that can be called by FLAC3D (Fast Lagrangian Analysis of Continua in 3 Dimensions). Finally, effects of secondary anisotropy on a deep tunnel surrounding rock were analysed by comparing the results calculated by the SSA model and a uniform strain-softening model. The results show that considering the secondary anisotropy, the extent of strain-softening of the surrounding rock was mitigated, particularly the axial strain-softening. Moreover, it reduced the surface displacement, plastic zone, and dissipated plastic strain energy of the surrounding rock. The proposed SSA model can precisely characterise the objectively existent secondary anisotropy, enhancing the accuracy of numerical simulations for tunnels, particularly for deep tunnels.
Keywords: surrounding rock failure; surrounding rock deformation; strain-softening; true triaxial test; numerical simulation surrounding rock failure; surrounding rock deformation; strain-softening; true triaxial test; numerical simulation

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MDPI and ACS Style

Yi, K.; Gong, P.; Lu, Z.; Su, C.; Duan, K. Study on Mechanism and Constitutive Modelling of Secondary Anisotropy of Surrounding Rock of Deep Tunnels. Symmetry 2025, 17, 1234. https://doi.org/10.3390/sym17081234

AMA Style

Yi K, Gong P, Lu Z, Su C, Duan K. Study on Mechanism and Constitutive Modelling of Secondary Anisotropy of Surrounding Rock of Deep Tunnels. Symmetry. 2025; 17(8):1234. https://doi.org/10.3390/sym17081234

Chicago/Turabian Style

Yi, Kang, Peilin Gong, Zhiguo Lu, Chao Su, and Kaijie Duan. 2025. "Study on Mechanism and Constitutive Modelling of Secondary Anisotropy of Surrounding Rock of Deep Tunnels" Symmetry 17, no. 8: 1234. https://doi.org/10.3390/sym17081234

APA Style

Yi, K., Gong, P., Lu, Z., Su, C., & Duan, K. (2025). Study on Mechanism and Constitutive Modelling of Secondary Anisotropy of Surrounding Rock of Deep Tunnels. Symmetry, 17(8), 1234. https://doi.org/10.3390/sym17081234

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