Application of a three-surface kinematic hardening model to the repeated loading of thinly surfaced pavements
Little effort has been made to apply the Critical State Soil Mechanics concept to the prediction of pavement response. The aim of this research is to apply soil mechanics principles, particularly the kinematic hardening concept, to the prediction of the response of lightly trafficked pavements to repeated loading. For this purpose, the finite element critical state program CRISP is used. A comparison is made between the predictions given by the three-surface kinematic hardening (3-SKH) model and a layered elastic analysis BISAR for the resilient deformation produced by repeated loading of a thinly surfaced pavement, and the models are found to be in good agreement. The ability of the 3-SKH model to predict soil behaviour under cyclic loading, and under one-dimensional loading, unloading and reloading is also evaluated. A comparison between model predictions and experimental data obtained by other researchers shows that the 3-SKH model over-predicts the value of K0,nc and hence shear strain during monotonic loading. This problem is magnified when the model is applied to cyclic loading behaviour where large numbers of cycles are involved. The model also predicts an accumulation of negative shear strain with increasing number of cycles under some stress conditions. This will lead to unrealistic predictions of rutting in pavements. However, the model is suitable for obtaining resilient parameters for input to a layered elastic analysis program. A new model, which is a modified version of the 3-SKH model, is therefore proposed by modifying the flow rule and the hardening moduli. This model can correctly predict the value of K0,nc and reduce the amount of shear strain predicted. The model also eliminates the problem of accumulation of negative shear strain with increasing number of cycles. The new model introduces two additional parameters, one of which can be determined by one-dimensional normal compression test, and the other by fitting a set of cyclic loading data. The new model is used to design the required thickness of granular material using the permissible resilient subgrade strain and permanent rut depth criteria during construction. It is found that the new model predicts a realistic granular layer thickness required to prevent excessive rutting, thus showing much promise for use in design of thinly surfaced pavements.