A creep damage model for yellow sandstone under the action of wetting-drying cycles

Regarding the issue of creep characteristics of the rock mass following excavation or excavation with graded loading and unloading under external forces. This study performs uniaxial compression and step loading and unloading creep tests on rock samples under different wetting-drying cycles with yellow sandstone to investigate the creep characteristics of rock bodies after excavation or excavations with step loading and unloading under external forces. Moreover, it constructs a creep damage model based on the nonlinear rheological theory and damage mechanics to describe the instantaneous elastic strain, instantaneous plastic strain, nonlinear viscoelastic strain, and nonlinear viscoplastic strain of rocks. Besides, it proposes a creep model parameter identification method based on the creep curve characteristics. The results have shown that the action of wetting-drying cycles causes a weakened decrease in elastic modulus, uniaxial compressive strength, and long-term compressive strength of yellow sandstone, in line with the exponential function change relationship. The specimen damage type evolves from shear damage of a single oblique section to conical shear damage of a double oblique section. Additionally, the creep rate is not constant in the steady-state creep stage but constantly changes with time, and the fluctuation range increases with the increase in the wetting-drying cycles. The creep damage model parameters do not differ much under the same stress condition, and each parameter is influenced by the creep stress at a specific law. The instantaneous modulus of elasticity of the elastomer and plastic body and the creep stress have a linear relationship, whereas the modulus of elasticity and viscosity coefficient and the creep stress have an exponential one.