Plant root-inspired penetration experiments in layered sand profiles

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Soil characterization is a vital step preceding the development of any site. During site investigation (SI) activities, penetration through stiff or deep layers poses challenges due to the required large vertical reaction forces. To provide these, rigs for SI are typically large and heavy, creating challenges in accessing sites or with soft surficial soils, increasing mobilization costs and carbon footprint. This paper investigates a plant root-inspired strategy called circumnutation-inspired (CI) penetration which reduces the vertical penetration resistance. The CI probes have a bent tip and are rotated and vertically advanced at constant rates while recording the mobilized forces (F_z) and torques (T_z). CI penetration in layered deposits were investigated by performing a set of tests at varying relative velocities, defined by the ratio of tangential to vertical velocity of the tip of the CI probe. The F_z and T_z mobilized in the layered deposit are compared with those mobilized in respective uniform sand deposits that make up the layered deposit. Cone Penetration Test (CPT) soundings were performed in each of these deposits as well. In all cases, CI penetration resulted in an exponential decrease in F_z  with increasing relative velocity, while the T_z increases with initial increases in relative velocity before reaching a stable value. Both CPT and non-rotational CI penetration mobilize similar F_z in the layered and uniform sand deposits. The total work done during CI penetration at low relative velocity in layered and uniform deposits has similar magnitudes as conventional testing (98-118% of CPT), while mobilizing significantly lower F_z (46-65% of CPT). Thus, CI penetration can facilitate the use of more compact and lightweight rigs to conduct SI tasks, such as classifying soils or installing sensors.

2025 International Conference on Bio-mediated and Bio-inspired Geotechnics (ICBBG2025)

General session: Bio-inspired methods for subsurface exploration and excavation