A Unified Bounding Surface Plasticity Model for Both High- and Low-Plasticity Clays Under Low Stress Ratios

A unified bounding-surface plasticity model for clays captures both high- and low-plasticity responses at low stress ratios across a wide range of overconsolidation ratios. The formulation combines a teardrop-shaped yield surface controlled by two parameters (Ψ and ), an explicit form of the plastic potential function yielding a linear stress–dilatancy rule, OCR-aware hardening, and a simple strength correction. Verification against element tests shows close agreement: undrained predictions reproduce the atypically steep, near-linear normally consolidated paths of London Clay and Lower Cromer till (HPLS) while remaining accurate for Boston Blue and Kaolin (LPLS); drained results capture contractive behavior at low OCR and its transition to dilation at higher OCR, with realistic residual strength, in Lower Cromer till, Shanghai clay, and Fujinomori clay. The model offers a single, interpretable, low-parameter framework that is readily calibrated from routine data for everyday geotechnical assessment.