Enhancement of river bank shear strength parameters using Vetiver grass root system

Abstract

Vegetation has been used as a bioengineering tool for erosion control and slope stabilization for years. It is accepted that the efficiency of different species of vegetation for slope stabilization is not the same. In this paper, the morphological properties of the Vetiver grass root system including root area ratio (RAR), root diameter ratio (RDR), root diameter and density ratio (RDDR), and root length density (RLD) in a clayey soil are investigated. Also, the effects of morphological characteristics of Vetiver grass root system on the soil shear strength parameters including soil cohesion (C) and soil internal friction factor (φ) are studied. The results showed that RAR, RDDR, and RLD decrease as the soil depth increases. Also, RDR was found to be correlated to the soil depth. The maximum RAR value was found to be 7.99% which is much higher than those reported by previous researchers for other plants used for soil protection. The maximum RDR, RDDI, and RLD values were 72.7, 4.4, and 0.1%, respectively. The results show that among the four root morphological traits studied, RAR and RLD are better correlated to C and φ, respectively. Furthermore, it is found that the plant density is not a significant parameter in the soil reinforcement in the range of densities studied here. Moreover, Vetiver grass roots can increase the soil cohesion and soil internal friction factor up to 119.6% and 81.96%, respectively. Based on regression analysis, some empirical equation are presented for calculation of the soil shear strength parameters as functions of the morphological characteristics of Vetiver grass root. These findings can be used by ecologists for better management of natural waterways by means of a low-cost environmentally friendly technique.