A Simple Soil Model for Complex Loadings

After having many practical applications using a complex soil constitutive law (Wang et al, 2006), we discovered that there is a need for a simple model that can simulate clay type of soils under cyclic loading conditions. In the current geotechnical engineering practice under such conditions, the shear strength of clay, named as undrained strength, is considered to be not affected by the mean confining stress changes. Based on the framework of the bounding surface plasticity, a very simple soil model is formulated for clay type of soils under cyclic loading conditions. The failure surface now is similar to the classical Von Mises yield surface. The accompanying virgin loading surface, reverse loading surface and projection center changes are formulated in the same way as the above mentioned model for sand (Wang et al.,, 1990). But, this model has only four model parameters; each of them has clear physical meaning. Thus, the model is very easy to use. Single element responses are presented first to show how this model can predict deformation under monotonic and cyclic loadings. A site response example is presented next to compare with the results from using conventional equivalent linear approach. Finally, a complex earthquake deformation analysis for a typical earth dam is presented. This paper demonstrates that this simple soil model, which has only one more model parameter than the conventional Mohr-Coulomb model, is capable of simulating the non-linear soil behavior under complex loading conditions.