Triaxial Creep Damage Model for Salt Rock Based on Fractional Derivative

Abstract

The long-term stability of underground energy reserves is closely linked to salt rock creep. To study the creep behavior of salt rock, creep tests were conducted on salt rock specimens under various confining pressures and axial stresses. The test results reveal that the creep of salt rock is influenced by the combined effect of confining pressure and deviatoric stress, which represents the difference between axial and confining pressure. Subsequently, a long-term strength and time-controlled viscoplastic damage body is proposed by considering the plastic deformation in the steady-state creep stage. The viscoplastic damage body is connected in series with the fractional-order Maxwell model to form a new six-element nonlinear creep model generalized to three-dimensional form. The applicability of the new model was verified using triaxial creep test data of salt rock, and it was found to describe the creep curve more accurately compared to the Nishihara model. A sensitivity analysis of the model parameters indicates that different parameters affect various creep stages, and creep curves under different loads can be adjusted by changing these parameters.