Small Scale Toppling Tests on Simplified Tree Root Prototypes

The root plate of trees, from a Geotechnical point of view, plays the role of the “living” foundation of a tall structure, subject to complex loading histories essentially deriving from environmental actions (e.g., wind loads). Its mechanical response to toppling loads (which represent a noticeable source of risk in urban areas), is not yet fully understood by the current interpretative models. In the paper, with the aim of highlighting the main features of the mechanical behavior of such systems, some small-scale 1g tests are presented. A simplified root prototype has been conceived, by combining elementary structural elements aimed at exhibiting both flexural and pullout properties of real-like flat root systems. Toppling loads (at constant vertical load and zero horizontal load) have been applied to the prototype and three different granular materials have been employed to reproduce the soil layer. The results highlight a certain positive correlation between a representative secant stiffness of the tests and their ultimate toppling resistance in case of very deformable soils. More uncertain trends are instead observed in case of stiffer granular materials. Although still not referred to real working conditions of tree roots, the experimental campaign may contribute to a deeper geotechnical understanding of the tree toppling phenomenon.