NON-STATIONARY BURGERS CREEP MODEL OF ROCK AND ITS PARAMETER IDENTIFICATION

In view of the nonlinear characteristics of rock creep, a nonlinear viscous component is proposed to replace the two linear viscous components in the Burgers model. Accordingly, a non-stationary Burgers model is established. The one-dimensional creep equation of the non-stationary Burgers model is deduced and the concomitant influence of the range of parameters λ₁ and λ₂ in the model is analyzed. Then, the non-stationary model is theoretically determined to describe the three stages of creep. On this basis, the creep equation of non-stationary Burgers model is extended to three-dimensional stress state. Triaxial compression creep test curve of rock in Xiangjiaba is fitted and its parameters are identified based on the Levenberg-Marquardt algorithm. By comparing the fitted curve and correlation coefficient between stationary and non-stationary Burgers models, it can be found that the fitted results of the non-stationary Burgers model are much better and can accurately describe the creep features in three stages including the accelerated creep status. The applicability and rationality of the established nonlinear model are verified.