Date of Award
Fall 2025
Document Type
Open Access Dissertation
Department
Civil and Environmental Engineering
First Advisor
Enrica Viparelli
Abstract
Earthen embankments are the most common type of embankment due to the relatively low cost, simplicity, and material availability. However, they are also the most prone to erosion related failure, typically due to overtopping and piping. Research has been conducted to identify ways to control soil erosion and protect earthen embankments with different approaches such as addition of chemicals and biopolymer to the soil, installation of protective layering (geotextiles, concrete), increased soil compaction, and use of vegetation. This thesis considers the use of Bermuda Grass to increase resistance to erosion and protect embankments from failure during overtopping. Grass coverage and root prevalence have been shown to significantly reduce erosion rate and erodibility of soils. More research, however, is needed to understand how Bermuda Grass covered soil erodes and how characteristics such as grass coverage, root depth, and percent of the soil area taken up by roots known as root area ratio (RAR) affect the mode of erosion. To answer these questions, erosion experiments were conducted in a flume in the Hydraulics Laboratory at the University of South Carolina with flow velocities that ranged from 0.88 m/s to 2 m/s. Main findings of the experiments were: RAR contributed to increased resistance to erosion by adding root-cohesion and shear strength. In addition, root depth increased erosion resistance. Grass coverage shielded soil from the erosive water shear force. Long grass blades and strong roots promoted deposition of soil eroded from the upstream. Erosion generally progressed downstream as grass was displaced and soil was exposed. Erosion thresholds were identified and corresponded to the increase in root resistance as roots were displaced by the flow. After the maximum resistance of a root had been surpassed, uprooting occurred when the root fractured or slipped. To quantify erosion results a normalized displacement index was defined relying on cumulative change in percent coverage, with a score of 1 indicating full erosion and 0 indicating no erosion. This contrasts with typical categorizations of erosion in the format of depth/time. However, categorizing results with the displacement index is advantageous because grass samples did not erode in a layered manner unlike bare soils. The displacement index also captures the time-dependent nature of grass erosion. Additionally, the displacement index was used to estimate average erosion rates for different grass percent coverage and RAR. The experimental results indicate that Bermuda Grass has the potential to be a viable solution for increasing erosion resistance and may be useful for protecting against overtopping failure.
Rights
© 2025, Oru-Ntui Johnwatters Nkiri
Recommended Citation
Nkiri, O. J.(2025). Erosion of Bermuda Grass Covered Soils. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/8661