Variable Parameter Creep Model Based on the Separation of Viscoelastic and Viscoplastic Deformations

The MTS815.02 rock test system is used for performing triaxial compression creep experiments on sandstone to reveal the rheological properties of the rock in deep roadways. Instantaneous elastic, viscoelastic, and viscoplastic strains are separated, and the relationship between the model parameters and the stress and time is established by combining the characteristics of the creep curve. According to non-linear rheological theory, the constitutive equation of a creep model of the rock under a three-dimensional stress state is deduced, and the validity of the model is verified by the experimental data. Results show that the improved creep model comprehensively considers instantaneous elastic, non-linear viscoelastic, and viscoplastic strains, making the theoretical curve of the model highly consistent with the experimental curve. The model can describe the non-linear creep during the loading of sandstone. It can also reflect the creep parameters during the deformation. The correlation coefficients of the experimental curve and the theoretical curve under the same stress are both greater than 0.90. The comparison results verify the validity and feasibility of the creep model.