Effect of root age on the slope stability using vetiver grass

Abstract

This study aims to investigate the impact of the increasing age of vetiver grass on the factor of safety (FS) of slopes. Data were gathered from previous studies to establish a mathematical relationship between root cohesion—a key factor influencing FS—and the plant’s age. Finite element modeling using PLAXIS 2D software was conducted on a 45-degree slope to calculate FS in the absence and presence of vetiver grass at ages 5, 10, 15, and 20 years. Results indicate that root cohesion (c_r) and root area ratio (RAR) significantly affect FS values. Over 20 years, soil cohesion increased by 67%, and the FS of a 45-degree slope improved by 6.7%. A constant internal friction angle (K) was considered to create a graph for calculating root cohesion values across different ages with varying K values. Additionally, a simple mathematical model was developed to predict root cohesion based on plant age, considering other critical factors such as RAR. The study also found that while root cohesion increases with age, the rate of increase diminishes over time. Overall, the shear strength of rooted soil enhances with higher RAR and mobilized tensile strength of roots. This research highlights the substantial role of vetiver grass in improving slope stability, providing valuable insights for the application of vetiver in soil conservation and slope stabilization projects.