Climate Resilient Slope Stability Improvement Using Vetiver on a Test Levee

Abstract

Bioinspired slope improvements can achieve outcomes similar to traditional slope improvements for shallow slope failures, while incorporating plant material as a structural component and using a minimum of heavy equipment. Vetiver grass can mitigate the rain-induced slope instability of earthen infrastructure, such as levees, constructed using loess and clay soils. Vetiver grassroots can extend to depths greater than 3 m (10 ft), creating a new composite material with the grassroots and soil, thereby increasing shear strength to combat shallow slope failures. The objective of this study is to determine the feasibility of vetiver as a climate-resilient bioinspired slope stability improvement on a test levee constructed of loess in Vicksburg, Mississippi (MS). Vetiver was planted at 1 ft center-to-center intervals on a 9.1 m wide (30 ft) section of an approximately 12.2 m long (40 ft) downstream slope of a test levee and observed for 2.5 years. To consider the effect of extreme precipitation events, a finite element analysis was completed for a comparable clay slope using 500 year precipitation intensity–duration–frequency curves of Jackson, MS. Precipitation negatively impacts the collapsible and expansive nature of the local loess and clay, respectively. The results demonstrate that vetiver grass is a viable method to increase slope stability for earthen levees constructed with loess and clay, which are prevalent in Vicksburg and Jackson, respectively. Vetiver also holds promise as a climate resilient solution to combat rain-induced shallow slope failures. As society advances toward a more sustainable approach to managing infrastructure, traditional methods of using heavy machinery, concrete, and steel to repair landslides are being replaced with using minimal equipment, earthen and geosynthetic materials, and vegetation. Earthen infrastructure, such as dams and levees, provide protection against the flooding of basins, rivers, lakes, and other bodies of water; however, they are not immune from landslides. One common landslide that can occur in earthen infrastructure is a shallow slope failure, particularly in soil that destabilizes greatly with changes in climate, such as collapsible and expansive soils. The researcher is proposing to use vetiver grass to combat shallow slope failures in earthen infrastructure in MS. Vetiver grassroots can grow to depths greater than 3 m (10 ft), which exceeds the depths of shallow landslides. Vetiver was transplanted on a test levee that was no longer being used in Vicksburg to determine if vetiver could grow in loess. Further, computer modeling was done to predict the performance of vetiver on a levee constructed in clay following storms with an estimated return period of 500 years for Jackson. The use of vetiver was determined to reduce the possibility of shallow slope failures under the conditions specified.