The Cam-Clay Models Revised by the SMP Criterion

The Cam-clay models were originally developed through theoretical considerations and experimental results under triaxial compression condition, and extended to three-dimensional models by using stress parameters p and q. A criterion of the Extended Mises type was adopted for the shear yield and failure of clay in Cam-clay models. However, it is well known that the failure of soil is not explained by the Extended Mises criterion but by a criterion of the Mohr-Coulomb type or the SMP (Spatially Mobilized Plane) type and others. Taking the consistency in the shear deformation and the shear failure into account, it is quite natural to introduce the Mohr-Coulomb or SMP criterion for the shear yield as well as the shear failure of soil. In this paper, a transformed stress tensor σ˜ij is proposed, which is deduced from what makes the SMP criterion become a cone in the transformed principal stress space. The transformed stress tensor σ˜ij is applied, as an example, to the Cam-clay models to improve their capability to describe the behavior of soils in general stresses including triaxial compression. The Cam-clay models revised by the transformed stress tensor σ˜ij can explain well the drained and undrained behavior of clay not only under triaxial compression, but also under triaxial extension, plane strain, and true triaxial conditions. The present paper provides a reasonable and simple approach for extending the models using stress parameters p and q to the three-dimensional models by adopting σ˜ij instead of σij.