DEM model calibration and contact force network analysis of sand-EPS (rigid-soft) granular system subjected to one-dimensional compression

Compressibility of Expanded Polystyrene (EPS) beads in mixtures of sand and EPS beads is considered by discrete element modeling of beads as clumps of particles bonded by a cohesive contact model. A calibration scheme is devised where input microparameters are calibrated stepwise, using experimental results and available data. The calibrated model is used to investigate the effect of parameters, namely normal pressure, EPS bead content and bead relative size on the compressibility and lateral stresses of the mixtures. Results showed an increase in mixture compressibility with the addition of EPS, which coincided with an increase in total coordination number. The increase in EPS bead size was observed to decrease compressibility. Microscale results showed a reduction in the overall, EPS-EPS and sand-EPS coordination numbers with the increase in bead relative size, resulting in the contact network being more dominated by sand-sand contacts which resulted in stiffer mixtures. However, this reduction in compressibility was negligible for larger EPS bead contents where coordination numbers showed that enough contacts are formed between EPS beads to create a continuous network across the sample, thus curtailing the effect of EPS bead size. Contact force networks showed that despite the increase in the number of sand-EPS and EPS-EPS contacts, the majority of forces are transferred through sand-sand contacts.