Root Biomechanics Testing Challenges: Findings from Experiments on Native Australian Trees

¹ The University of Sydney, School of Civil Engineering, Australia
² The University of Sydney, School of Geosciences, Australia
³ School of Professional Practice and Leadership, University of Technology Sydney, Sydney, Australia

^* Corresponding author: jiale.zhu@sydney.edu.au

Abstract

Root biomechanical properties are critical for soil reinforcement and slope stability, yet the lack of standard tensile testing procedures creates significant variability in results. This study examines three key challenges—clamping mechanisms, root irregular morphologies, and root moisture content—through experiments on four native Australian tree species. Of the three tested clamping methods, two failed: the finger-trap mechanism lacked grip on small-diameter roots, while epoxy reinforcement caused excessive moisture loss. The flat clamp with a rough surface performed best but damaged large roots under excessive force. Unexpected root irregularities, such as nodal joints and tortuous points, led to localised stress concentrations, reducing tensile strength and increasing variability. While root moisture content has been qualitatively discussed, its quantitative effects remain underexplored, with fewer than five studies addressing it. This study demonstrates that moisture content and root diameter explain up to 71% of tensile strength variability, underscoring the need for its control in testing. These findings highlight the necessity of standardised testing procedures to improve measurement reliability. While preliminary guidelines are proposed, further refinement is needed to advance predictive modelling and bioengineering applications in unsaturated soils.