Firstly, a series of field surveys of root morphology and mechanical tests of root material were carried out on Trema orientalis (L.) Blume (India charcoal trema), a plant species commonly used for slope land vegetation in Taiwan. Subsequently, a three-dimensional (3-D) numerical model of the soil-root system was established to simulate an in-situ pull-out test of the soil-root system. The validities of the 3-D numerical model, simulation procedures and various input
material parameters in the model were also verified. Subsequently, a 3-D numerical model identical to the soil-root system used in pull-out test was repeatedly adopted for the simulation of a direct shear test to estimate the shear strength increment of the soil-root system due to root ΔSr. Eventually, a mechanical conversion model was developed to correlate the ΔSr with the basal diameter of plant D
and the simulation of ultimate pull-out resistance of root Pus, namely, the relationship function ΔSr =f(D) and ΔSr =f(Pus). In addition, the proposed model can be used to determine the required strength parameters for the stability analysis of vegetated slopes and quantitatively evaluate the contribution of a root system to the stability of a slope.
Key Words : Soil-root system, 3-D numerical model, increment of shear strength due to roots, ultimate pull-out resistance.