A Robust Constitutive Model for Clays over a Wide Range of Plasticity

This study presents a robust constitutive model for clays capable of capturing mechanical behavior over a wide range of plasticity and overconsolidation ratios (OCR). The model is formulated within a bounding-surface plasticity framework and employs a teardrop-shaped yield surface controlled by two shape parameters, Ψ and Ω, which regulate yield-surface skewness and shear strength, respectively. An explicit plastic potential is introduced to eliminate the stress–dilatancy paradox and to obtain a linear, physically interpretable stress–dilatancy relation. Model parameters are calibrated using conventional laboratory data and are linked to standard oedometer indices, preserving practical applicability. Validation against triaxial test results for clays with contrasting plasticity demonstrates that the model consistently reproduces both curved and nearly linear stress paths at low stress ratios, as well as a smooth transition from normally consolidated to overconsolidated behavior. The proposed formulation provides a unified and robust framework suitable for numerical implementation and geotechnical engineering applications.