Effect of tree roots on a shear zone: modeling reinforced shear stress

Tree roots provide important soil reinforcement that improves the stability of hillslopes. After trees are cut and roots begin to decay, the frequency of slope failures can increase. To more fully understand the mechanics of how tree roots reinforce soil, fine sandy soil containing pine roots was placed in a large shear box in horizontal layers and sheared across a vertical plane. The shapes of the deformed roots in the sheared soil were explained satisfactorily by an equation that had been developed to model the deformed shape of artificial reinforcement elements, such as wood dowels, parachute cord, Bungy cord, and aluminum rods. Root deformation in sheared soil is influenced by the diameter and concentration of roots. A model is proposed that uses root strain to estimate the shear stress of soil reinforced by roots. The shear resistance measured from the shear tests compared quite well with the model simulation.