Comparison of Vegetation Types for Prevention of Erosion and Shallow Slope Failure Along Roadways

Abstract

Shallow slope failures due to erosion are common occurrences along roadways in Alabama due to the prevalence of high intensity rainfall in the region. The use of vegetative covers is a reasonable solution to stabilize newly constructed steep slopes or repair areas where shallow landslides have occurred. This research aims to evaluate and compare vegetation species that would provide low maintenance and economic slope stabilization and decrease shallow slope erosion at priority sites along roadways. Experiments were conducted to compare the applications of vegetation and to identify the most effective vegetation species for erosion control and stabilization of roadside slopes, by studying plant establishment, surface erosion, depth distribution of root biomass density and increased shear strength of soil due to roots. For this study, five plots with different species were planted on a steep slope at the National Center for Asphalt Technology (NCAT) test track in Opelika, AL. A variety of shrub and grass species were tested and compared individually and in a mix: Parson’s juniper (Juniperus chinensis “Parsoni”), vetiver grass (Vetiveria zizaniodies) and fescue grass (Lolium arundinaceum). The vetiver grass grew and established well. The plot with a juniper and fescue grass mix is also establishing well but has low weed resistance. Erosion pins were used to measure surface erosion and deposition in the shallow slope. Regression and ANOVA analysis have been performed on erosion pin data. In addition, the depth distribution of root biomass density and the increased shear stressed of soil due to roots were determined to evaluate the potential for slope stability. The grass control roots showed the highest average root tensile strength. However, vetiver roots had significantly higher root biomass and increased soil shear strength by a greater amount. This study suggests that vetiver is the most suitable species for slope stabilization. The results from this research will be used to identify suitable plant species that will meet the design objectives and low maintenance requirements for shallow slope stabilization along roadways while also being appropriate for the climate and soil type of Alabama.