NONLINEAR BEHAVIOR OF CLAY CREEP AND ITS FRACTIONAL DERIVATIVE CREEP MODEL

Creep test is performed on Chengdu clay to study the nonlinear property of clay creep. It is found that instantaneous elastic deformation, attenuated creep deformation, steady creep deformation, and accelerated creep deformation are included in clay deformation. The long-term elastic modulus of clay is nonlinear softening with the increase of time and stress. The viscosity coefficient is nonlinear softening with the increase of stress and nonlinear hardening with the increase of time. Based on the rheology theory, fractional calculus theory and Harris attenuation function, fractional derivative components, nonlinear elastic components and nonlinear viscous components are established, respectively. A nonlinear fractional derivative creep model with simple form, few parameters and clear concept is established. Then, the nonlinear fractional derivative creep model and Burgers creep model are compared. It is found that the fitting effect of nonlinear fractional derivative creep model is better in each stage, and can give more reasonable description of the nonlinear creep of clay, and can accurately reflect the whole process of clay creep. The scientific rationality of the nonlinear fractional derivative creep model is proved.