Micromechanical approach to swelling behavior of capillary‐porous media with coupled physics

Summary A detailed multiscale analysis is presented of the swelling phenomenon in unsaturated clay‐rich materials in the linear regime through homogenization. Herein, the structural complexity of the material is formulated as a three‐scale, triple porosity medium within which microstructural information is transmitted across the various scales, leading ultimately to an enriched stress‐deformation relation at the macroscopic scale. As a side note, such derived relationship leads to a tensorial stress partitioning that is reminiscent of a Terzaghi‐like effective stress measure. Otherwise, a major result that stands out from previous works is the explicit expression of swelling stress and capillary stress in terms of micromechanical interactions at the very fine scale down to the clay platelet level, along with capillary stress emerging due to interactions between fluid phases at the different scales, including surface tension, pore size, and morphology. More importantly, the swelling stress is correlated with the disjoining forces due to electrochemical effects of charged ions on clay minerals and van der Waals forces at the nanoscale. The resulting analytical expressions also elucidate the role of the various physics in the deformational behavior of clayey material. Finally, the capability of the proposed formulation in capturing salient behaviors of unsaturated expansive clays is illustrated through some numerical examples.