Triaxial creep properties and model of red sandstone under freeze-thaw environment

In order to study the time-effectiveness mechanical properties of rock mass engineering in cold regions under the coupling of freeze-thaw cycles and long-term loads, the triaxial multi-level loading and unloading creep tests are carried out on saturated red sandstone under different freeze-thaw cycles. The results show that the effects of freeze-thaw cycles on the creep deformation of red sandstone are related to the loading stress level. At low stress levels, the viscoelastic strain of rock increases approximately linearly and slowly with the increasing freeze-thaw cycles, and at high stress levels, it increases nonlinearly. The viscoplastic strain increases linearly with increasing freeze-thaw cycles. The fourth-level loading stress level (70%${\sigma }_{\text{c}}$) is the boundary point of the creep deformation characteristics of red sandstone. The steady-state creep rate of red sandstone increases exponentially with the increase of the freeze-thaw cycles. Based on the creep test results of the red sandstone, the freeze-thaw-damage creep model considering the effects of freeze-thaw cycles and creep damage is established. The creep equation for rock under three-dimensional stress is obtained. The proposed model is verified and its parameters are identified. The theoretical and experimental data are in good agreement. The influences of freeze-thaw cycles on the model parameters are analyzed. The research results may provide a theoretical basis for the construction of rock mass engineering and long-term stability analysis in cold regions.