Characterization and Mechanics Modeling of Permanent Deformation of Subgrade Clay Under Cyclic Loading

To ensure comprehensive characterization of the permanent deformation (PD) properties of subgrade clay, a conventional integer-order Newton dashpot was substituted with a fractional-order Abel dashpot within the viscoplastic model. To extend this innovation, a Van Der Poel model was integrated in series to construct a nonlinear viscoelastic-plastic component model of subgrade clay. Based on viscoelastic-plastic mechanics theories, a mechanical model of the subgrade clay's PD was developed and calibrated using the test results of the conventional clay in Changsha. The results show that the fractional-order viscoelastic-plastic mechanical model aligns with the PD test curves. The PD of the subgrade clay exhibits a notable tendency to increase, corresponding to a longer loading action duration and a shorter intermittent loading duration. A critical threshold must be reached for intermittent loading duration to have an effect, and the PD remains constant beyond this threshold. An increased cyclic stress amplitude or a diminished confining pressure increases the PD, followed by an increased cumulative growth rate. Humidity has a significant effect on PD because even a slight increase in moisture content increases the observed PD value twice. Furthermore, as the moisture content progressively transitions from a relatively low to a substantially high threshold, the PD experiences a notable shift in behavior, transitioning from plastic shakedown to plastic creep, resulting in an unconverted development state. The sensitivity analyses of mechanical model parameters show that the viscoelastic parameters d and n exhibit a negligible sensitivity to the associated influence factors. In contrast, the viscoplastic parameters ft and rj? display a robust and significant correlation with the loading action duration, loading intermittent duration, cyclic stress amplitude, confining pressure, and moisture content. Consequently, multiple regression equations were obtained to estimate /3 and m. The verification results show that the mechanical model can accurately capture the PD characteristics of the subgrade clay and be used for the numerical calculation and analysis of the PD of a subgrade filled with clay under cyclic loading. © 2024 Chang'an University. All rights reserved.