A triaxial creep model for salt rocks based on variable-order fractional derivative

This paper intend to describe the entire creep process of a salt rock under triaxial loading, especially the creep characteristics in the accelerated creep stage, by replacing the Newtonian dashpot in the Maxwell model with the variable-order fractional derivative component and extending it from one to three dimensions. The experimental data were obtained from the creep of salt rock under multistage loading for approximately five months to examine the applicability of the new model. The fitting results show that the new model can accurately describe the creep behavior of the salt rock and can fully reflect the accelerative rheological property of the salt rock. Compared with the traditional nonlinear rheological model, the new model has fewer parameters and increased accuracy of the fitting results, and is anticipated to have an increased application area.