A Mathematical Model for Shear Strength Prediction of Vetiver Rooted Soil
Mohammad Shariful Islam, Faria Fahim Badhon
Abstract
The role of vegetation in the stability of slopes has expanded recognition in the last few decades. Performance of plants in stabilizing slopes is closely linked to the variation of the shear strength of root-reinforced soils. Vetiver grass (locally known as binna or binna shoba) is mostly available in Bangladesh. An attempt has been made in this study to develop a mathematical model for predicting the shear strength contribution by root of vetiver rooted soil. The mean tensile strength of matured vetiver root was found to be 27 MPa. The shear strength parameters of vetiver rooted soil were determined by in situ shear strength tests. Tests were conducted in the field on 9 block samples under same normal load at same soil depth using a special device developed in the study. Additional shear strength for rooted soil was determined by comparing with bare sample. The obtained relationship between the additional shear strength provided by roots (Δs) and the tensile strength of roots per unit area of soils (tR) is approximately linear. Based on the experimental observation, a mathematical model (Δs=5.14tR) was developed to predict the additional shear strength of soil-root system. This simple, straightforward model will provide a convenient mean for stability analysis of vegetated slopes.