Determining the Preconsolidation Stresses of Low Void Ratio, Highly Overconsolidated Clays

Determining the yield stress of low void ratio, heavily overconsolidated clays is fundamental to accurate engineering design. Recent work has shown that these materials often exhibit both a conventional preconsolidation stress (σ′p) and an apparent yield (σ′ya) at a much lower stress. Incremental consolidation (ICON) tests on Cumberland and Humphreys clays revealed two yield stresses, highlighting the challenges of interpreting stress–strain behavior for soils with complex consolidation histories. Using this data, this study investigates and compares the available methods for estimating yield stresses, including Casagrande’s graphical method, Janbu’s constrained modulus approach, and Becker et al.’s work method to determine yield stresses. All of these methods were originally proposed for test results exhibiting a single yield stress. Comparative analysis of these methods underscores their effectiveness and limitations in estimating multiple yield stresses, σ′p and σ′ya. Results provide insights into the behavior of overconsolidated clays and guidance for selecting suitable techniques for advanced geotechnical design.