An NCL-dependent state parameter for constitutive modeling of clays

In this study, a novel state parameter is proposed to establish a realistic relationship between the mechanical behavior of overconsolidated (OC) clays and their stress history. This state parameter is defined as the vertical distance between the intersection of the yield surface with the p-axis and the normal consolidation line (NCL) in the e-lnp space, where e is the void ratio and p is the mean effective stress. When this state parameter is incorporated into constitutive modeling, it eliminates the need for bounding surface and pre-consolidation pressure, as the stress history is inherently represented through the current density state of the clay. Moreover, it offers a unified characterization of stress history effects on both compression and shear behavior. Based on the proposed state parameter and supporting experimental evidence, an enhanced dilatancy relation and a hardening rule are developed, enabling accurate predictions of shear dilatancy and peak strength evolution with varying overconsolidation ratios (OCRs). Comparative analyses against several classical and recent constitutive models confirm that the proposed model provides a robust and accurate description of the strength and deformation behavior of OC clays over a wide range of OCRs and loading paths, outperforming existing approaches in predictive capability.