A simple elastoplastic model for normally and over consolidated soils with unified material parameters

An isotropic hardening elastoplastic model for soil, which can describe typical deformation and strength behavior of normally and over-consolidated soils in general stress conditions, is presented. This model can take into consideration the influence of density and/or confining pressure on the deformation and strength characteristics of soils. Further, it also takes into account the influence of intermediate principal stress'on the deformation and strength of soil and the stress path dependency on the plastic flow, as did other previous versions of this model. For considering the intermediate principal stress on the deformation and strength, the concept of modified stress t(ij) is employed in the same way as the previous models. With respect to the subloading surface concept, the previous models are revised and extended into one in which the influence of density and/or confining pressure on the deformation and strength of soil can be considered. Furthermore, the influence of stress path dependency of the direction of plastic flow is considered by dividing the plastic strain increment into two components - i.e., a component satisfying associated flow rule and a component of isotropic compression. In the present model, only one material parameter a for representing the influence of density and/or confining pressure is added to the parameters of the previous model, which are fundamentally the same as those of the Cam clay model. The validity of the present model is checked by monotonic and cyclic loading tests not only on normally and over-consolidated clay but also on loose and dense sands in three-dimensional stresses.