Hydromechanical Effects of Vegetation on Improving Slope Stability

Slope protection measures often include the use of different types of geosynthetics as soil reinforcements or as soil nails. But such materials are not biodegradable and might have some adverse effect on the soil in the near future. On the other hand, vegetation roots can function as reinforcement within the soil, utilizing the tensile strength of the roots, and while doing so, they also increase the apparent cohesion of the soil. In this study, concerning hydromechanical effects of vegetation, two methods have been used to estimate the improvement in slope stability in terms of factor of safety (FOS), namely, the apparent cohesion method (method 1), a simplified method most commonly used in the literature, and the root geometry method (method 2), a newly developed (Mondal, Hydro-mechanical effect of vegetation on improving slope stability, National Institute of Technology Jamshedpur, Jharkhand, 2023) and more realistic method. Further, the aging effect of the root is also considered, keeping in view the fact that the tensile strength of the root decreases over the lifespan of the root. Accordingly, the finite element models for both these methods have been developed using PLAXIS 2D. For a suitably chosen slope example, the results obtained from the slope stability analyses using both methods have been found to be in agreement with the expected significant improvement in the FOS as compared to the bare slope. More specifically, application of method 1 results in an improvement of nearly 45% and compared to method 2, method 1 overestimates the FOS by nearly 8%. As regards the aging effect of the root, the FOS is seen to be quite sensitive to the root decay as well as tensile strength.