Unsaturated hydro-mechanical-electro-chemical coupling based on mixture-coupling theory: a unified model

Electro-kinetic remediation and electro-kinetic consolidation play an important role in soil reinforcement and remediation. Although they are interrelated in mechanism, modeling of the two technologies is often separated due to the knowledge and multiple-scale gap between geo-mechanics and electro-chemistry, including electro-osmosis, hydraulic-osmosis, chemical osmosis, and mechanical deformation. This paper develops a unified hydro-mechanical -electro-chemical (HMEC) constitutive model for unsaturated soil by using a non-equilibrium thermo-dynamics-based approach, mixture-coupling theory, to study the two technologies in one framework. Entropy production during the dissipative process is considered, and Helmholtz free energy is used to bridge the interactions between mechanical deformation at the macroscale scale and electro-chemical transport at the molecular scale. A new term, electric-induced stress coef-ficient, has been introduced into the stress-strain relationship to reflect the effects of electric field on the solid matrix. Meanwhile, the classic Darcy's law has been fundamentally extended to consider the electro and chemical osmosis phenomena. The model is verified by comparing with existing equations and models. Finally, parameter analyses and case studies show that chemical transport and mechanical deformation are significantly influenced by electrical parameters and physical-chemical properties. In the unsaturated state, the chemical concentration distribution is affected by the coupling effects between electro-osmosis consolidation and chemical osmosis.