An elasto-viscoplastic constitutive model for clay using a transformed stress tensor

Abstract

It is well-known that the behavior of natural clay is anisotropic. One of the reasons is that the behavior is strongly affected by the history of stress, strain, temperature and chemical reactions. This type of anisotropy is called ‘stress induced anisotropy’ or ‘structural anisotropy’. On the other hand, the behavior of clay also strongly depends on the current stress state. The current stress sensitivity is one of the salient features of granular materials. An anisotropic stress state causes results in anisotropic and pseudo-anisotropic deformation behavior. The objective of the present paper is to propose a constitutive model for clay to describe the rate-dependent anisotropic and/or the current stress induced pseudo-anisotropic behavior of clay based on a transformed stress tensor. It is shown that the proposed constitutive model is noncoaxial and applicable to explain the current stress induced pseudo-anisotropy, the effect of the intermediate stress dependency of the soil behavior and the deviatoric flow rule. In addition, an objective formulation of the constitutive model for large deforamations is discussed.