Scaling of plant roots for geotechnical centrifuge tests using juvenile live roots or 3D printed analogues

Geotechnical centrifuge modelling of vegetated slopes requires appropriately scaled plant roots. Recent studies have independently suggested that juvenile live plants or 3D printing to fabricate root analogues could potentially produce representative prototype model root systems. This paper presents a critical comparison of juvenile versus 3D printed approaches in terms of their representation of root mechanical properties, root morphology and distribution of the additional shear strength generated by the roots with depth. For the 3D printing technique, Acrylonitrile Butadiene Styrene (ABS) plastic material was used, while for live plants, three species (Willow, Gorse and Festulolium grass), corresponding to distinct plant group functional types (tree, shrub and grass), were considered. The tensile strength and Young's modulus of the 'roots' were collected from uniaxial tension tests and shear strength data of rooted soil samples was collected in direct shear. The prototype root characteristics as modelled were then compared with published results for field grown species and the benefits and challenges of using these two modelling approaches is discussed. Finally, some recommendations on realistically modelling plant root systems in centrifuge tests are given.