Vertical loading tests on a simplified tree root prototype

The increasing number of extreme weather events, often accompanied by very intense wind gusts, can cause diffuse damages to arboreal heritage, which hence represents a severe hazard in urban areas for buildings, cars, structures, infrastructures and even human lives. From a geotechnical perspective, assessing the stability of a tree against uprooting represents a problem of interaction between the soil and the root system, subject to complex loading conditions. The experimental study presented in this paper approaches such a problem by considering a 1D vertical loading condition, both under compressive and tensile loads, for a simplified small-scale tree prototype with a flat root system, resting in a dry mid-loose Ticino sand deposit. The root system is conceptually assimilated to a direct foundation, and the role of the bending and the tensile behaviour of the different root components is highlighted, by considering both monotonic and non-monotonic quasi-static loading paths. The influence of several geometrical parameters is investigated, and the results highlight the need of a large displacement approach, also considering second order geometrical effects, to correctly interpret the results. These latter can be considered preparative to the development of more complex 3D experimental tests and theoretical interpretative frameworks.