Horizontal penetration of a finite-length intruder in granular materials

In recent years, bio-inspired burrowing robots and other intruder problems in granular media have attracted significant attention. Many of these, especially related to traditional penetration problems in geotechnical engineering, cover vertical penetration. Modelling these types of problems numerically using the discrete element method (DEM) is typically done ignoring gravity by controlling the stresses in the selected representative volume. Additionally, most problems involve infinitely long intruders from a modelling point of view. However, in horizontal penetration there is enough evidence to show that intruders are affected by an uplift force that affects the penetration and needs to be considered. In this paper we use the DEM to demonstrate the impact of considering vertical uplift and gravity for a finite-length intruder penetrating in a dense granular media through particle level and macro-behaviour. Additionally, through the numerical study, important mechanisms emerge during horizontal penetration, including four different distinct stages on the surrounding soil, or the extent of disruption, that are fundamentally distorted when gravity is ignored.