Mechanical reinforcement of soil by willow roots: impacts of root properties and root failure mechanism

Plant roots have considerable impact on the mechanical stability of soil, but to date the underlying mechanisms have been poorly quantified. In this study, controlled laboratory studies of soil reinforced with willow trees (Salix viminalis cv Tora) found a strong correlation between the cross-sectional area of soil covered by roots and shear reinforcement. We separated broken versus pulled-out roots and measured individual root diameters crossing the shear-plane. The shear strength of planted specimens compared with non-planted specimens increased eight-fold at 0.10-m shear depth, more than four-fold at 0.25-m depth, and more than doubled at 0.40-m depth.