Contribution of Vetiver Grass Towards Slope Stability Via Mechanical Root Reinforcement

Soil bioengineering techniques offer an eco-friendly and practically viable alternative for slope stabilization when compared to traditional techniques. In particular, the improvement in slope stability is obtained by planting vegetation that offers an improvement in existing shear strength via mechanical root reinforcement promoted by the presence of roots along failure surface. This study was aimed at evaluating the contribution of the root cohesion for vetiver grass (Chrysopogon zizanioides) on slope stabilization in a tropical and mountainous environmental setting. Various root morphological characteristics of vetiver were obtained experimentally through field and laboratory testing. In general, the vetiver root system comprises of mostly fine roots of diameter varying between 0.11 and 2.22 mm and can offer large tensile strength between 14.4 and 2000 MPa. Results show that the tensile strength offered by vetiver roots increased with decreasing root diameter and a good power-fit relationship was obtained between root diameter and tensile strength. Furthermore, the root morphological characteristics were used with root bundle theory to translate the tensile strength offered by roots into additional root cohesion. Transient seepage analysis was performed on bare and vegetated slope to generate degree of saturation and suction profiles with respect to depth, which were incorporated into a simple infinite slope stability problem to compute the FOS with respect to depth. Analysis of results show that the FOS of shallow depths with presence of vetiver roots increased many folds as compared to bare slope, which demonstrated the potential of vetiver grass in restoration of watersheds along the hill slopes in southern Guam.