Evaluation of rainfall induced moisture variation depth in highway embankment made of Yazoo clay

Abstract

Yazoo clay is highly plastic and has been associated in Mississippi with swelling problems and causes significant maintenance problems to the highway slopes. The infiltration of rainwater may create a perched water condition within the slopes, which may reduce the shear strength of the soil at the vadose zone. However, limited data is available on the wetting depth of highway slopes constructed on Yazoo clay in Mississippi. The objective of the current study is to determine the active moisture variation zone of highway embankment slopes constructed on Yazoo clay soil in Jackson, Mississippi. In this study, three highway slopes in the Jackson metroplex were considered as referenced slopes, which were monitored by using a rain gauge, moisture sensors, water potential probes in each slope. At each slope, sensors are installed at three different depths (1.5 m (5 ft.), 3 m (10 ft.), and 5 m (15 ft.)) at the crest, middle, and toe of the slope. The 3D flow analysis was also conducted using the Finite Element Method (FEM) in Plaxis 3D. The depth of moisture variation of the highway slopes was determined based on simulation of the unsaturated moisture flow and saturation of the slope existing soil test data and field instrumentation results. The field monitoring data indicated that the highest infiltration occurred at the crest of the slope, and the moisture variation zone continues up to 3.5 m (12 ft.). The 3D analysis showed that with the low-intensity long-duration rainfall, the progressive rainfall saturated the near-surface soil.