Characterizing Permanent Deformation of Silty Sand Subgrades by Using a Model Based on Multistage Repeated-Load Triaxial Testing

A simple model for the prediction of permanent deformation of unbound pavement material was used to characterize the accumulation of permanent deformation of unsaturated silty subgrade soils from multistage repeated-load triaxial (RLT) tests. The model incorporated the timehardening concept; data obtained from RLT tests with cyclic loading of variable magnitudes, conducted on a single specimen, could be used to calibrate the material model parameters. This feature of the model allowed for characterizing the accumulation of permanent deformation of the material under a wide range of stress conditions. The tests were carried out on two silty sand subgrades and at different moisture contents with pore suction measurements (matric suction) incorporated into the stress state calculations used in the modeling. The shakedown ranges for the permanent deformations for each stress path were calculated, and the material parameters of the predictive models were optimized with the RLT test data. In general, the models performed satisfactorily in capturing the permanent deformation behavior of the selected subgrade materials. The model includes fewer parameters as compared with some existing permanent deformation models and requires reduced testing effort because it is based on results from a multistage RLT test with a single specimen. It can be concluded that the model and the approach have great potential for characterizing and modeling the permanent deformation of subgrade soils.