Constitutive model for fatigue of rock under cyclic loading

In order to investigate the mechanical behavior of rock subjected to cyclic loading, the basic components based on the creep theory are performed to study the fatigue behaviors, of rock, and hereby both stationary fatigue (modified Kelvin model and Burgers model) and non-stationary fatigue (nonlinear viscoelastoplastic model for fatigue) are proposed to describe their fatigue behaviors. The model can simulate reduction, constant and acceleration if and only if n>1. The predicted fatigue behaviors are consistent with the observations in tests. It is shown that the model is capable of describing the fatigue behaviors of rocks. If the development of irreversible deformation can be divided into three phases, that is, initial phase, uniform velocity phase and accelerated phase, the accelerated fatigue parameter gradually decreases with the increase of uniaxial compressive strength of rock．It is more important to design fatigue parameters using the stress ratio rather than the threshold for fatigue failure.