Molecular-level behavior induction in the constitutive modeling of swelling clayey soils – A review

Swelling soils are considered one of the most problematic soils due to their volume changes resulting from variations in the moisture regime. Such volume change tendencies in swelling soils have caused short- and long-term stability issues for civil engineering. The swelling-mechanical behavior is also central in the design of industrial/nuclear waste containment barriers, slope stability of the mudrocks, and gas shale extraction. Several valuable efforts have been undertaken to predict the mechanical behavior of swelling soils at the macro and molecular levels. Still, these models have some limitations due to the partial consideration of complex fabric and structure of natural and compacted swelling soils. Moreover, all macro-level constitutive models require a complete matrix of strength and volume change tests which restrict their application in engineering practice. This paper covers a review, including key features and limitations, of existing models for the mechanical behavior of swelling soils at the macro and molecular levels. Finally, a framework of a nano-level hydro-mechanical constitutive model has also been presented through molecular-level simulations of the structure of the swelling soils. The proposed model can be utilized to predict stiffness moduli for all possible variations in the fabric and structure of swelling soils.