Effect of Rotation on Seeds' Self-Burial Process: Insights from DEM Simulations

Seeds of some flowering plants such as Erodium and Pelargonium can bury itself into the ground for future germination. The self-burial behavior is realized due to hygroscopic coiling and uncoiling of the awns. It is hypothesized that the rotating motion due to the changing of the helical structure of the awn reduces penetration resistance of the seed via breaking the local force chains in soil. In this study, this hypothesis is tested using a DEM model, which allows investigating the interaction between a penetrator and the granular material at different scales. The DEM model was first calibrated and validated using existing laboratory triaxial test data of Ottawa sand. A cone was then penetrated into the calibrated soil sample vertically with different rotational speeds. It was observed that the rotational movement can significantly reduce the penetration resistance, and the reduction becomes more pronounced at higher rotational speeds. From particle scale analysis, the force chain and particle velocity field of the soil sample were investigated, and comparisons were made among cases, which shed light on the fundamental mechanism of the reduction effect.