A creep constitutive model is developed by incorporating visco-elasticity, visco-plasticity and visco-damage to simulate the time- and rate-dependent nonlinear mechanical behaviors of salt rock. Based on the small deformation assumption and the effective stress concept in the theory of continuum damage mechanics (CDM), the Kelvin-Voigt model accounting for viscoelasticity, Duvaut-Lions model accounting for visco-plasticity and Darabi’s visco-damage model are incorporated. The constitutive model is calibrated by experimental data to determine the parameters of visco-elasticity, visco-plasticity, and visco-damage. It is indicated by the model validation and parametric study that: The Kelvin-Voigt model is able to model the recoverable creep deformation effectively. The Duvaut-Lions mode is able to model the un-recoverable creep deformation and has a remarkable advantage over the Perzyna model because it easily accounts for non-smooth yield surfaces. The Darabi’s visco-damage model is able to model the damage creep accurately. In a word, the unified constitutive model is able to effectively simulate the mechanical response of salt rock under different loading conditions.

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