Historical evolution and new trends for soil-intruder interaction modeling

Soil is a crucial resource for life on Earth. Every activity, whether natural or man-made, that interacts with the sub or deep soil can affect the land at large scales (e.g. geological risks). Understanding such interactions can help identify more sustainable and less invasive soil penetration, exploration, and monitoring solutions. Over the years, multiple approaches have been used in modeling soil mechanics to reveal soil behavior. This paper reviews the different modeling techniques used to simulate the interaction between a penetrating tool and the soil, following their use over time. Opening with analytical methods, we discuss the limitations that have partially been overcome by the finite element method (FEM). FEM models are capable of simulating more complex conditions and geometries. However, they require the continuum mechanics assumption. Hence, FEM analysis cannot simulate the discrete processes occurring during soil deformation (i.e. the separation and mixing of soil layers, the appearance of cracks, or the flow of soil particles). The discrete element method (DEM) has thus been adopted as a more promising modeling technique. Alongside models, experimental approaches have also been used to describe soil-intruder interactions, complementing or validating simulation results. Recently, bioinspired approaches have been considered promising to improve sustainability and reduce the invasiveness of classical penetration strategies. This review highlights how DEM-based models can help in studying the interaction mechanisms between bioinspired root-like artificial penetrometers and the soil. Bioinspired designs and the merging of multiple analysis approaches can offer new perspectives. These may be pivotal in the design of highly optimized soil robotic explorers capable of adapting their morphology and penetration strategies based on their surrounding conditions.