A Viscoelastic-Plastic Constitutive Model of Creep in Clay Based on Improved Nonlinear Elements

A Triaxial creep experiment was performed with Chengdu clay. The results demonstrate that the deformation of clay includes instantaneous elastic strain, attenuated creep deformation, steady creep deformation, and accelerated creep deformation. In view of the nonlinear properties of creep, an improved nonlinear viscous element describing attenuating creep and an improved fractional order viscous element describing accelerating creep are established, and a one-dimensional nonlinear fractional order five-element creep model is developed with the two improved elements. The model can theoretically describe the entire process of creep. The nonlinear fractional order five-element model and the traditional five-element model were employed to verify the creep test. Compared with the traditional five-element creep model, the nonlinear fractional order creep model more faithfully reproduces the experimental data and more accurately describes the deformation trend in each stage, especially the accelerated creep stage.