Critical State Soil Model for Normally Consolidated Clay revised by SMP Failure Criterion and AJOP Hardening Equation

Abstract

This study presents an enhanced critical state model for normally consolidated clay, developed by improving the Modified Cam Clay (MCC) model to achieve greater accuracy in predicting both shear strength and strain behavior. The proposed model incorporates the Spatial Mobilized Plane (SMP) failure criterion and the Arc Joint via Optimum Parameters (AJOP) hardening formulation into the original MCC framework. A series of comparative analyses were conducted between various models under both drained and undrained conditions in triaxial compression and extension tests. The results reveal that the standard MCC model tends to overestimate pore pressure under undrained conditions due to the use of a linear hardening law. Furthermore, incorporating the SMP criterion addresses the model’s tendency to overpredict shear strength. The proposed MCC+SMP+AJOP model demonstrates improved predictive capability without requiring additional experimental input beyond what is needed for the original MCC model. This makes it a practical and efficient tool for geotechnical analysis and civil engineering design in clayey soils.