Root-soil-water hydrological interaction and its impact on slope stability

Vegetation is known to provide mechanical reinforcement and hydrological influences on soils, thus affecting the soil shear strength and the stability of rooted soil slopes. Professor Tien H. Wu pioneered the research on the root mechanical reinforcement effect. This study focuses on hydrological influences of vegetation. Factors including species-specific genetic features and soil conditions that control the transpiration process are often varying, leading to significant uncertainty in the transpiration process. The primary objective of this paper is to investigate the influence of the uncertainty of the maximum transpiration rate E_tp on the pore-water pressure distributions in and the stability of a vegetated slope. Random field theory is applied to model the spatial variation of E_tp, which maintains constant along the vertical direction by its definition but varies along the slope surface. A modified Richards equation governing water flow in unsaturated media is employed to incorporate a sink term that models the root-water uptake. Three idealised types of root geometry, i.e. uniform, triangular and parabolic types, are considered, along with the spatial variation of E_tp. The uniform root geometry shows the most significant impact on enhancing the slope factor of safety through transpiration, compared with the triangular and parabolic geometry types.