A Mixture Coupling Theory based model for solute transport in deformable dual-porosity media

Rock, soil and many porous-like materials are often fractured or structured media, which can exhibit dual-porosity behaviour. Studies on solute transport in deformable dual-porosity media remain challenging due to the multi-physics coupled effects and the complex interaction between fracture (or macropore) and porous matrix. Though several studies exist on constitutive modelling of coupled behaviour in deformable dual-porosity, the previously developed models are not systematic in thermodynamical frameworks. This paper proposes a Mixture Coupling Theory approach based on nonequilibrium thermodynamics to develop the solute transport model with consideration of hydro-mechanical coupling in dual-porosity media (referred to as the ST-HM model). This paper derives the constitutive equations of fully hydro-mechanical coupled behaviour in dual-porosity media and considers the pore and fracture porosity evolution influenced by both hydro and mechanical fields. Therefore, the governing equations of ST-HM are capable of predicting non-reactive solute transport with a fully hydro-mechanical coupled effect in dual-porosity media. Then, the model was verified against existing models and validated by relevant experimental results. Further, a numerical example shows that the presented model significantly improves the accuracy of the prediction of porosity, fluid pressure, and solute concentration compared with previous models, which ignore the fully hydro-mechanical coupled effects on solute transport.