SMP Criterion-Based Unified Constitutive Model for Geomaterials

A unified and simple constitutive model for both clay and sand under three-dimensional stress conditions is presented. The model was developed from the modified Cam-clay model, and the following two points are considered. First, a so-called transformed stress tensor based on the SMP criterion is applied to the modified Cam-clay model to improve the model capability in describing the behavior of soils in general stresses including triaxial compression. The transformed stress tensor is deduced from what we transform the SMP criterion to a circle in the transformed π-plane. The model realizes the consistency from the shear yield to the shear failure and the combination of the critical state theory with the SMP criterion. Secondly, a new hardening parameter is introduced in order to develop a unified constitutive model for both clay and sand. It can not only describe the dilatancy from lightly to heavily dilative sand, but also be reduced to the plastic volumetric strain for normally consolidated clay. The results predicted by the presented model are compared in detail with the test results of sand and clay in triaxial compression, true triaxial, plane strain and triaxial extension. It is shown that the presented model can describe well the drained and undrained behavior of clay and sand along various stress paths including triaxial compression, triaxial extension, plane strain, and true triaxial conditions. Only five conventional soil parameters are needed in the model.