Correlation of Fully-Softened Shear Strength of Clay Soil with Index Properties, Phase I

Abstract

Shallow slope failures in clay soils cause many millions of dollars of damage annually on highway embankments and cut slopes and necessitate difficult and expensive repairs that negatively impact budgets, traffic flow, and the environment. The embankments typically fail when clay soils become “fully softened” due to shrink-swell action during wet-dry-wet cycles and experience downhill creep. Slope analyses using either peak or residual strength properties do not properly model most slope failure or potential failure conditions. The use of peak strength in the analyses tends to overestimate the factor of safety (stability) and the use of residual shear strength in the analysis tends to underestimate the factor of safety (stability). The use of fully-softened shear strength values results in a more accurate analysis and leads to designs or repair methods that provide long-term stability at reasonable costs. Understanding the mechanisms of these slope failures and being able to economically predict the fully softened shear strength of clay soils is key to successful design, repair, and stabilization of clay slopes.