Application of Lades Criterion to Cam-Clay Model

Ladeʹs criterion is one of the best criteria for describing the shear yield and failure behavior of soils in 3D stresses, and the original Cam-clay model is the most popular and fundamental elastoplastic model for normally consolidated clays. In this paper, a transformed stress tensor is proposed for combining Ladeʹs criterion and the Cam-clay model. The transformed stress is deduced from what makes the curved surface of Ladeʹs criterion become a cone with the axis being the space diagonal, i.e., Ladeʹs criterion becomes the extended Mises type criterion in the transformed principal stress space. The Cam-clay model revised by Ladeʹs criterion is capable of describing the mechanical behavior of soils in general stresses. It is presented that the revised model can simulate well the drained and undrained behavior of soils, not only under triaxial compression conditions, but also under plane strain, true triaxial, and hollow cylinder conditions. The elastoplastic models for soils, in which only the first and second stress invariants are used, can be extended simply to the model, including the third stress invariant by adopting Ladeʹs criterion.