Creep Parameter Determination and Model Establishment Considering Stress and Time Effects

In order to better study the creep properties of rock under different stress and time, the creep test was taken from the surrounding rock of the roadway. First, a model that describes the whole process of rock creep was introduced so that it could correspond to the various stages of creep. Then, a new method for determining creep parameters was proposed. The calculated creep parameters were processed by combining the stress difference and the time product, and the relationship between the creep parameters and the overstress difference and time product was analyzed. A creep model considering stress and time effects was obtained. Finally, the model was verified by the experimental data and calculation results, and the rationality and correctness of the method for determining the parameters of the creep model were analyzed. The results shown that the special point of creep curve and the definition of creep deformation were combined with the model equation and experimental data to determine the creep parameters under different stress and time. The improved creep model could better describe the creep damage process of rock under different stress states, and provided a new idea for establishing the unsteady creep model and determining the model parameters. The product of E₂ controlled the limit of viscoelastic deformation gradually decreased with the product of time and overstress difference. The shear viscoelastic coefficient η₁ gradually decreased as the product of time and overstress difference increases. The product of η₂ controlling the steady creep rate decreased with time and the overstress difference. The higher the stress level, the greater the steady creep rate, but the overall stable creep rate was less than the accelerated creep rate. The nonlinear viscous coefficient η₃ mainly controled the accelerated creep deformation of rock and gradually decreased with the increase of stress and time. The trend of creep parameters as a whole indicated that stress and time had certain degrading effects on rock creep parameters.