Meeting Abstract
Annelids such as the earthworm Lumbricus terrestris achieve underground locomotion via synchronized expansion-contraction cycles (peristalsis) of their segmented bodies. These animals advance in the subsurface at higher rates than current tunnel boring machines. While the mechanics of their locomotion has been broadly studied from the animal perspective, the soil response – critical to their ability to propel themselves – is poorly understood. The present study is aimed at bridging this gap, by investigating the micromechanical response of granular materials (soil) surrounding the body of a worm in peristalsis. For this purpose, a set of two-dimensional and three-dimensional discrete element model (DEM) simulations were performed. In these numerical models, soil particles are modeled as discrete circles (2-D) or spheres (3-D) subject to contact forces and Newton’s laws of motion. For each simulation, a domain representing a volume of soil was generated around a segmented cylinder. Once the domain dynamic forces equilibrated, the segments were expanded following a peristaltic motion akin to that of earthworms. Contact forces between particles and their displacements were tracked, allowing for a deep understanding of how the soil responds to such movement. The results reveal how the anchorage mechanism of worms develops, as well as quantifying the forces supporting the advancement into the subsurface. Finally, the results show that the expansion ratio is fundamental in generating anchorage resistance by inducing different soil responses. It was observed that for small expansion ratios (nearly cylindrical shape), interface friction is the most significant contributor to the anchorage force. As the expansion becomes more accentuated, passive resistance is mobilized resulting in remarkably higher anchorage forces.
