Numerical simulation of dynamic repetitive load test of unbound aggregate using precision unbound material analyzer

This study developed discrete element models to simulate the dynamic repetitive load test using precision unbound material analyzer (PUMA). The simulated aggregate was created with the clump method simulating real particle shape. The parameters of the real particle shape were determined by the smoothness degree of particle shape and the required time-steps, which balanced the accuracy of particle shape and computational efficiency. The rubber ball layer (RBL) was adopted as the boundary conditions of repeated load test according to the features of the PUMA apparatus. Through the comparisons of results between numerical simulation and laboratory tests, the thickness of RBL was found close to the median size of particles resulting in the better simulation. Moreover, the numerical simulation results were verified with the conducted laboratory tests. The predicted permanent deformation was consistent with the laboratory measurement, which showed that discrete element based simulation can obtain the reliable results for the dynamic repetitive load test. The predicted permanent deformation using the real particle model was found much closer to the experimental results, which was greater than the one obtained using the ball model. The analytical results of volumetric-axial strains, directions of displacements, and contact forces indicated that the real particle method can better represent the migration movements of aggregates in the laboratory conditions. The simulation results indicate the importance of considering real aggregate shape in discrete element modelling of unbound material behaviour.