Centrifuge modelling of root-soil interaction of laterally loaded trees under different loading conditions

Understanding the stability of trees under lateral loads arising from natural hazards (e.g. extreme weather and debris flows) is important, as fallen trees can become a potential threat to life and infrastructure. Two 1: 20 scale three-dimensional printed analogue root system models, with architectures from field-surveyed root architecture data, were used to simulate the push-over behaviour of trees in silty sand under different conditions in the centrifuge. The peak overturning moments obtained were verified against data from field winching tests. Horizontal roots orientated in the loading direction and the central taproot complex contributed most to the overturning resistance. Increasing soil matric suction due to a lowering of the water table, increasing the loading rate and considering the presence of the fine root fraction all resulted in higher moment capacity and rotational stiffness of the root systems. The overturning behaviour was ductile in fully saturated soil and more brittle in partially saturated cases, with more root breakages in the windward horizontal roots and the taproot complex in the latter. These results suggest that it is important to measure the groundwater conditions when conducting winching tests and demonstrate a connection between soil effective stress, total root breakage area and peak moment resistance.