Understanding Shallow Slope Failures on Expansive Soil Embankments in North Texas Using Unsaturated Soil Property Framework

Abstract

Slopes constructed with expansive soils are prone to shallow slope failures when subjected to seasonal wetting-drying. This article presents a field experimental study and corresponding modeling analysis to understand slope failures at shallow depths, typically ranging from 1 to 5 ft (0.3–1.5 m) from the surface. Previous studies revealed that the major cause of shallow slope failures for earthen dams is due to the formation of surficial cracks due to rapid matric suction change occurring during cyclic wetting-drying from seasonal changes. The purpose of this study is to identify the influential factors such as soil matric suction on the stability of unsaturated soil slopes. In this study, soil from a test section at Joe Pool Lake dam, Texas is considered. Test soil was subjected to basic soil characterization and later studied for their engineering behavior. Unsaturated soil properties for Joe Pool Lake soil are obtained by evaluating the soil water characteristic curve (SWCC) using pressure cell and filter paper technique. Rainfall and temperature data collected at the site were utilized for modeling the unsaturated condition of the slope using VADOSE/W software. Results showed that consistent matric suction variation contributed to the reduction in the stability of the slopes. This analysis also provided valuable insight into the formation of fully softened zones at shallow depths due to the formation of desiccation cracks.