Abstract: This study presents an investigation on the effect of the osmotic potential due to chemical solute concentration changes by the use of the net mean stress, suction and chemical concentration elastic constitutive relationship to represent the deformation behavior exhibited by expansive clays. The impact of such changes on stress/strain behavior of the soil has been accommodated by the development of a non linear elastic constitutive relationship, a state surface, which includes the effects of chemical solute concentration. In particular, it was suggested that the determination of the stiffness of the soil with respect to chemical solute concentration could be achieved via a theoretical approach. In this study, the double layer theory is investigated and the ability of the proposed numerical model to represent it is shown.