Contribution of Vetiver Root on the Improvement of Slope Stability

Bio-engineering technology, using vegetation, offers an effective solution to slope protection, as the roots of the vegetation reinforce the earthen slopes and enhance their stability. This study attempts to evaluate the improved shear strength parameters of rooted soil and to determine the stability of vegetated slopes. The influence of vetiver grass (Chrysopogon zizanioides) root on shear strength of soil was studied. Extensive laboratory tests were performed to characterize the behavior of soil-root matrix. Laboratory direct shear tests were performed on reconstituted root mixed soil samples and also on undisturbed rooted soil samples for both clayey and sandy soils. Reconstituted soil samples were prepared by mixing the roots having different root lengths and root arrangements at varying moisture content of soil samples. Test results indicate that vetiver root has a significant contribution in enhancing the shear strength parameters of soil-root matrix. A maximum of 50% increase in shear strength was observed. Based on the test results of undisturbed rooted soil samples, a numerical analysis was conducted to evaluate the stability of vegetated slopes using PLAXIS 2D. Results show that the factor of safety of vegetated sandy slopes increased up to 20.6%. For clayey soil, the increase in factor of safety was insignificant due to the deep-seated failure. However, the presence of vetiver root increased the shear strength of soil and reduced the surface erosion which will increase the overall stability of the slopes. Therefore, utilization of vegetation can be a sustainable and environment-friendly technique against slope failure-related problems.