Nonlinear Variation Parameters Creep Model of Rock and Parametric Inversion

Traditional Nishihara model is a linear constant parameters model, and it is difficult to describe nonlinear accelerated creep characteristics of rock with this model. Therefore, an improved Nishihara model is proposed in the way of replacing, cascading elements and substituting parameters in the original model. Firstly, fractional differential elements are used to replace viscous elements in the traditional Nishihara model; then a viscous plastic element with assumption exponential relationship between the rock nonlinear rheological deformation and time power function is cascaded; finally, the viscosity coefficient of the traditional model is rewritten to a variable parameter related to stress and time, thus obtaining the nonlinear variation parameters creep model of rock. The improved model is verified with data from creep test to frozen soft rock during Cretaceous period, which shows that this model can describe the rock nonlinear accelerated creep characteristics more accurately and more comprehensively.