Small-scale modelling of root-soil interaction of trees under lateral loads

Aim: (1) To understand the tree root-soil interaction under lateral and moment loading using a physical modelling technique; (2) To detect the possible factors (e.g. root architecture, water condition, and stress level) influencing a tree’s push-over behaviour; (3) To identify suitable scaling laws to use in physical modelling. Methods: Two 1:20 scaled root models with different architectures (namely, deep and narrow, and shallow and wide) were reconstructed and 3D printed based on the field-surveyed root architecture data. Push-over tests were performed both in elevated-gravity (centrifuge 20-g) and normal-gravity (1-g) conditions. Results: The shallow and wide model showed higher anchorage strength than the deep and narrow model. Regardless of the root architecture, the root anchorage strength measured from dry soil was higher than that from saturated soil. However, once the effective stress was the same, regardless of water conditions, the root anchorage strength would be the same. Conclusions: The presence of water decreasing the soil effective stress and key lateral roots extending along the wind direction play a significant role on a tree’s push-over resistance. Centrifuge tests showed comparable results to the field pull-over measurements while 1-g model tests overestimated the root-soil interaction, which could be corrected for soil strength by using modified scaling laws.