A coupled constitutive model for modelling small strain behaviour of soils

Laboratory experiments on soils have shown that the deviatoric stress – deviatoric strain relationship in soils is highly non-linear, especially in the small strain range. That led to several formulations quantifying that nonlinearity. However, the constitutive models which aim to replicate the small strain nonlinearity are often complex and rarely used in geotechnical engineering practice. The goal of this study is to offer a simple way for updat-ing the existing constitutive models to take into account small strain stiffness changes. The study use an existing small-strain relationship to derive a yield surface. When the yield surface is introduced to an existing soil model, it enhances the model with the nonlinear deviatoric stress- deviatoric strain relationship in the small strain range. Subsequently, the paper gives an example of such a model enhancement by combining the new yield surface with the Modified Cam Clay constitutive model. The simulations with the upgraded constitutive model of the undrained triaxial tests on London Clay replicate the experiments in clearly better than the base model.