A nonlinear creep model for surrounding rocks of tunnels based on kinetic energy theorem

The initiating condition for the accelerated creep of rocks has caused difficulty in analyzing the whole creep process. Moreover, the existing Nishihara model has evident shortcomings in describing the accelerated creep characteristics of the viscoplastic stage from the perspective of internal energy to analyze the mechanism of rock creep failure and determine the threshold of accelerated creep initiation. Based on the kinetic energy theorem, Perzyna viscoplastic theory, and the Nishihara model, a unified creep constitutive model that can describe the whole process of decaying creep, stable creep, and accelerated creep is established. Results reveal that the energy consumption and creep damage in the process of creep loading mainly come from the internal energy changes of geotechnical materials. The established creep model can not only describe the viscoelastic–plastic creep characteristics of rock, but also reflect the relationship between rock energy and creep deformation change. In addition, the research results provide a new method for determining the critical point of creep deformation and a new idea for studying the creep model and creep mechanical properties.