Study on shear strength of root-soil composite for slope stabilization using grass vegetation

Abstract

Bio-engineering or utilizing plants to reinforce slopes and prevent erosion, for stabilization of both natural and man-made slopes is a cost-effective and sustainable alternative, especially in developing countries like Sri Lanka. Several factors influence the plant roots' ability to increase shear strength. This study investigates influence of Chrysopogon zizanioides (Vetiver grass) roots on soil’s shear strength, focusing on its application in slope stabilization. Shear strength characteristics of soil and soil reinforced with various concentrations of Vetiver grass roots were investigated using large direct shear tests conducted utilizing reconstituted test specimens, to assess their impact on soil shear strength. Stress-strain curves show that, root-reinforced soil exhibit higher shear strength compared to soil-only specimens. Results indicate a proportional increase in shear strength with higher RAR values, with root-permeated soil specimens demonstrating an average shear strength enhancement of approximately 2.5–4 kPa compared to unreinforced specimens, with the increase in RAR up to 1%. The findings suggest that presence of Vetiver roots in soil significantly enhances its shear strength parameters, leading to higher cohesion in root-reinforced soil specimens compared to soil-only specimens. As the RAR increases, indicating a higher density of roots in soil, cohesion of root-reinforced soil specimens also increases proportionally. For the applied normal stress range, observed increase in cohesion of 2 kPa with the increase in RAR up to 1%. Specifically, with a 1% RAR, the study indicates a potential 6% increase in factor of safety, which is a significant improvement of slope stability