Previous research has shown that cyclic wetting and drying can reduce the shear strength of compacted highly plastic clays to the fully softened shear strength. Consolidated-undrained triaxial testing procedures were used to determine the fully softened shear strength of Eagle Ford Shale, which is a highly plastic clay found in central Texas. The measured secant friction angles of Eagle Ford Shale were also compared to a graphical relationship and an equation for computing the fully softened secant friction angle to verify the applicability of these correlations for the purpose of selecting strengths for design. Slope stability analyses were also performed to determine the pore water pressures and shear strength conditions that existed at the time of failure in the slope where the Eagle Ford Shale was obtained.