A new three-dimensional theoretical model for analysing the stability of vegetated slopes with different root architectures and planting patterns

Abstract The influence of root hydro-mechanical reinforcement on slope stability has commonly been modelled two-dimensionally. Moreover, the differentiation between primary and secondary roots is always ignored. This paper proposes a new three-dimensional (3D) theoretical model describing the effects of hydro-mechanical reinforcement of root systems on the stability of initially unsaturated soil slopes. Primary and secondary roots are differentiated within the root system. Root water uptake is modelled by considering root-soil hydraulic interactions. The theoretical model is implemented using the finite element method and calibrated with previous centrifuge results for a 3D vegetated slope. Three series of parametric analyses are carried out by considering (a) secondary root architecture, (b) plant spacing, and (c) planting pattern. The results show that, after 5-day transpiration, the conical root architecture induces higher suction and plant-plant interactions than the cylindrical root architecture. After rainfall with 1000-year return period, the differences in hydrological reinforcement vanish, while a lower factor of safety is found for the conical root architecture, mainly due to the smaller mechanical root reinforcement it provides. Additionally, the staggered row planting pattern with a large plant spacing of 2 m is recommended for bioengineering applications, as it affords greater mechanical reinforcement than does the regular pattern.