Development of elasto-plastic constitutive model for unbound granular materials under repeated loads

This study aims to establish an elasto-plastic constitutive model under repeated loads for unbound granular materials (UGM) used in the pavement. Shakedown theory was employed to analyze the deformation behavior of UGM at different stages. The prediction models of plastic strain rate and resilient strain were fitted with the loading repetitions, axial stress, and other factors. Based on the typical stress-strain curves and the models of plastic strain rate and resilient strain, the yield point model was established using the criterion of spatially mobilized plane (SMP). Using this model, the yield stress was obtained conveniently at certain loading conditions, which provided the movement path of yield surface under repeated loads based on kinematic hardening law. Under single loading, the plastic strain hardening was treated as the isotropic hardening. This simplified method made it feasible to establish the elasto-plastic constitutive model under repeated loads. The proposed model was verified with the measured deformation of mixed-size aggregates using precision unbound material analyzer (PUMA) tests. The comparsions of permanent strain and plastic strain rate obtained from laboratory tests and numerical simulation indicated that the proposed elasto-plastic constitutive model can characterize the deformation behavior of UGM.