Fractal derivative creep constitutive model of rock considering hardening and damage effects

The creep of rock is the result of the evolution of its internal hardening effect and damage effect. Based on the modeling idea of the classical element model, the initial yield strength of rock is taken as the stress threshold of creep hardening. The long-term strength of rock is used as the stress threshold of damage softening. The hardening function that can reflect the hardening effect of rock and the damage variable that can reflect the damage effect are introduced. The results show that the established nonlinear creep model of rock is in good agreement with the creep test results. This shows the correctness of the rock creep model. At the same time, it can fully reflect the creep hardening and damage softening mechanism of the whole process of rock creep. The model can not only describe the existing salt rock creep test, but also provide a theoretical basis for the prediction of creep deformation under other stress states. The model curve established in this paper can better describe the creep curve with accelerated creep than the original model and the test curve. It can also accurately captures the variation of decay creep and stable creep. The model effectively captures the coupled effects of hardening and damage.