Viscoelastic plastic creep constitutive model based on energy conservation law and strain energy theory

On the basis of the law of conservation of energy, the three stages of rock creep are analyzed. The reasons for the difficulty in studying the accelerated creep stage of rocks using the traditional creep model are expounded. The triaxial creep deformation law and critical point parameter values of rocks are obtained by carrying out rock creep tests under different confining pressures. Based on strain energy theory, the law of conservation of energy, and Perzyna viscoplastic theory, a creep constitutive model, which can describe the whole process of primary creep, steady-state creep, and accelerated creep, is established. Results show that the model can well reflect the creep characteristics of rocks, especially when the load of rocks is greater than the long-term strength. It has an obvious effect on highlighting the accelerated creep stage of rocks. The fitting degree of the creep model curve and test curve is considerably greater than that of the Nishihara model curve and test curve. The model not only describes the whole process of rock primary creep, steady-state creep, and accelerated creep thoroughly but also compensates for the shortcomings of traditional models in describing accelerated creep. This model can provide a theoretical basis for further revealing the objective law of rock creep.