Modelling contaminant transport through deformable semipermeable bentonite-based barriers

The consolidation and contaminant transport equations are derived for bentonite-based barriers that act as semi-permeable membranes. These barriers can generate a water flux in response to a gradient in the chemical composition of the pore solution, a phenomenon known as chemico-osmosis. The derivation starts from the mass balance equations for the water (solvent) and ions (solutes) contained in the pore solution, focusing specifically on a single salt composed of a cation and an anion. The use of virtual variables representing hydraulic pressure and salt concentration in a theoretical bulk solution that is in thermodynamic equilibrium with the pore solution at a specific location in space and moment in time is presented. A linearized version of the obtained equations is compared with a pioneering model proposed in the 1970s. A physical interpretation of the phenomenological coefficient is offered to support the application of the derived equations to field applications aimed at assessing the performance of bentonite-based barriers.