Coupled Hydro-Mechanical Analysis of Highway Slope on Expansive Soil Subjected to Rainfall

Because of intensive precipitation and the presence of high-plastic Yazoo clay in central Jackson in Mississippi, shallow highway slope failures are a reoccurring phenomenon. Annually, the majority of highway slopes in central Mississippi experience shallow slope failures. The major objective of the current study is to evaluate the performance of two repaired highway slopes in the Jackson Metroplex neighborhood in Mississippi. The highway slope ratios are 3H:1V (Terry Road) and 6H:1V (McRaven Road). Soil boring and CPT testing were conducted as part of site investigations. Vertical slope inclinometers and precipitation gauge were also installed at the site slopes to record and detect displacement along the slope and real precipitation, respectively. One year after monitoring the slops, consecutive shallow slope movements were observed in late 2019. Based on the field monitoring results, the slopes became fully saturated. Impacting factors and potential failure conditions were verified with back analysis using the 3D Finite Element Method in the Plaxis. Based on the 3D coupled flow-deformation analysis results, the progressive precipitation infiltrated in the top soil which significantly impacted the reduction in soil matric suction and creates a perched water zone, which reduced the factor of safety closed to 1.0. Based on the field and numerical observations, the development of the perched water zone as a result of continuous precipitation led to slope surficial layer movements.