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Date of Award

2018

Document Type

Campus Access Master's Report

Degree Name

Master of Science in Geology (MS)

Administrative Home Department

Department of Geological and Mining Engineering and Sciences

Advisor 1

John Gierke

Committee Member 1

Thomas Oommen

Committee Member 2

Molly Cavaleri

Abstract

The highlands of Ethiopia, which contain the most densely populated and the most intensely farmed areas in the country, have been known to exhibit characteristics that make them highly prone to risks associated with slope instability; such as intense rainfall events, rugged terrain, and high levels of anthropogenic activity. Because Eucalyptus trees are the most commonly planted tree in this region, they can potentially be used to mitigate slope instability. In this study, root-area ratios were measured on three types of Eucalyptus plantations and root tensile strength tests were conducted in Abajale, Ethiopia. Using the Wu and Waldron model, the mechanical reinforcement of each root system was calculated, and added to a 2-dimentional, slope-stability model (RocScience Slide) in order to determine their contribution to slope stability. Precipitation and temperature data were also obtained from the Were Illu Meteorology station in order to identify the soil saturation potential and the most hazardous months of the year for slope instability using the Thornthwaite and Mather monthly water balance model. Because roots potentially provide more shear strength than unconsolidated regolith, it was hypothesized that higher root area ratios would correspond to greater slope stability, and that coppiced plantations would contribute more to soil cohesion than timber plantations, due to their increased concentration of biomass in their root systems. This study found that mechanical reinforcement of Eucalyptus root structures on these slopes showed an improvement of 10% in the safety factor during the dry season, and of 7% during the wet season, when the risk of slope failure was the greatest. Little difference was found with regards to management techniques, suggesting that Eucalyptus plantations have the ability to maintain a healthy root system after being harvested.

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