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Characterizing layered rock's anisotropic creep is crucial for assessing the potential effect of anisotropic creep on the long-term stability of engineering structures. This study establishes a new anisotropic viscoelastic-plastic model involving the nonlinear creep characteristics of the rock matrix and the bedding plane, which can describe the three-stage anisotropic creep characteristics of layered rock. In the anisotropic creep model, the nonlinear Burgers model describes the creep features of the bedding planes, and the nonlinear Nishihara model describes the rock matrix's creep features are coupled in series. To verify the rationality and accuracy of the newly proposed creep model, a series of uniaxial compression creep tests of chlorite schist with different inclination angles are conducted. On the one hand, the experimental results show that there is a geometrical similarity of the creep curves for the samples with inclination angles of 0°, 50°, and 90°, exhibiting apparent instantaneous strain, attenuation creep, stability creep, and accelerated creep, which shows the bedding planes with different inclination angles do not affect the creep curves' shape, mainly affecting the magnitude of instantaneous strain and creep strain. The long-term strengths of three different types of inclined rock specimens are 0.67–0.88 times the corresponding uniaxial compressive strengths. On the other hand, the new creep model can agree well with the experimental results, which proves that it can describe the anisotropic creep characteristics of layered rock mass well. Further, the sensitivity analysis results of mechanical parameters in the creep model show that the failure modes of layered rock masses are controlled by inclination angle within the range of β 1 ∼ β 2 . Moreover, the accelerated creep time of rock specimens with different inclination angles increases with the increment of deviatoric stress, n1, n3, and creep rate, contrary to the law of confining pressure and parameters n2, n4. Highlights: A three-dimensional anisotropic creep model is established considering the nonlinear creep characteristics of the rock matrix and bedding planes. The creep test results show that the bedding planes with different inclination angles do not affect the creep curves' shape, mainly affecting the magnitude of instantaneous strain and creep strain. [ABSTRACT FROM AUTHOR]

To reasonably describe the time-dependent characteristics of rock under true triaxial stresses and analyze the long-term stability of deep underground engineering, based on the understanding of time-dependent mechanical properties of rock under true triaxial stresses, a new fractional-order damage element and the method in which the crack initiation stress is taken as the starting point of creep and the crack damage stress as the starting point of creep accelerating stage were established. Then, combined with the Mogi-Coulomb strength criterion, a fractional-order creep damage model of rock under true triaxial stresses was proposed. The proposed model was further verified based on uniaxial, conventional triaxial and true triaxial creep test results. The theoretical curves of the model are highly consistent with the test curves, indicating that the proposed model has wide applicability and rationality. Meanwhile the sensitivity of true triaxial stress states and model parameters to the creep characteristics was further investigated. Finally, based on the proposed creep model, the time-dependent characteristics of rock under untested true triaxial stress levels were predicted. The research provides a theoretical basis for the prediction of time-dependent disasters and the long-term stability analysis of surrounding rock in deep engineering. [ABSTRACT FROM AUTHOR]