A simple approach for estimating contribution of vetiver roots in shear strength of a soil–root system

Bio-engineering technology, using vegetation, is an innovative and low-cost measure to address slope failure-related problems. To quantify the contribution of vegetation roots for increasing the strength of soil, several laboratory and field investigations have been conducted in this study. At first, the morphological characteristics of vetiver (Chrysopogon zizanioides) were studied. It was found that vetiver root can grow up to 1 m in three months in sandy soil. The average tensile strength of full-grown vetiver root was 27 MPa, and with the increase in root diameter, root tensile strength decreases. A correlation was developed between the tensile strength and diameter of the root, which was compared with previous studies. Laboratory tests were conducted on root mixed soil and found that the shear strength of rooted soil increases with the increase in root length and decrease in soil water content. Also, an attempt has been made to estimate the improved shear strength of rooted soil by developing a correlation between the additional shear strength of rooted soil and the tensile strength of roots per unit area of soils. To evaluate the shear strength of vetiver-rooted soil, in situ tests were conducted in naturally grown vetiver land for both rooted soil and bare soil. An approximately linear relationship was observed between the additional shear strength of rooted soil and the mobilized tensile strength of roots. Finally, a mathematical model was developed based on the experimental outcomes. This simple model can be used to estimate the shear strength parameters of rooted soil.