Modelling root-soil interaction in variably saturated fine-grained soil

Plant roots stabilise soil via mechanical reinforcement and by increasing soil matric suction through root-water uptake. However, previous research studies have focused on the mechanical reinforcement without the hydrological effect. In realistic cases, root-soil interaction modelling through hydro-mechanical mechanism is needed. It is known that an increased suction can increase soil shear strength, which will therefore affect the mechanical root reinforcement, but this coupling effect is not quantified. In addition, most of the existing models lack the fundamental features of partially saturated soil behaviour and therefore the real performance is not modelled. This project uses numerical modelling by the Finite Element (FE) Method, employing a sophisticated hypoplastic soil model to realistically capture suction-induced change in soil behaviour in partially saturated clay. Also, the FE analysis considers fully coupled flow deformation behaviour with a definition of the soil water characteristic. FE models of soil translating transversely past a root were developed and validated against saturated cases from the literature. Parametric studies were then performed to identify factors affecting root reinforcement, including root embedment depth, loading rate, loading direction and soil degree of saturation. Based on the simulation results, semi-empirical design charts are proposed to estimate the mechanical strength of root reinforced soil under varying hydrological conditions for different practical applications including slope stabilisation and tree wind throw.