Clay media are charged and clay particles coated by an electrical double layer. I will discuss a model of cross-coupled flow in such charged porous media. I start with the local Nernst-Planck and Stokes equations and we use a volume-averaging procedure to obtain the generalized Ohm and Darcy equations with cross-coupling terms at the scale of a representative elementary volume of the porous rock. These coupling terms (representing the effects of streaming current and electro-osmotic pore water flow) obey Onsager's reciprocity. Rather than writing the electrokinetic terms in terms of zeta potential (the electrical double layer potential on the slipping plane located in the pore water), I developed our theory in terms of an effective charge density dragged by the flow of the pore water. This effective charge density is found to be strongly controlled by the permeability, both in saturated and unsaturated conditions, and by the saturation itself. I also developed an electrical conductivity equation including the effect of water content on both the bulk and surface conductivities. Finally, this model is compared with various data from the literature including electrical conductivity data, streaming potential coupling coefficient and electroosmotic permeability data at different saturations. The material properties (with the exception of electrical conductivity) can be aken as the product of a value at saturation and a relative parameter that depends only on saturation. The excellent agreement between the model predictions and the experimental data indicates the possibility to use this model inside numerical codes to predict various effects of interest to water resources including remotely observing unsaturated flow using a network of non-polarizing electrodes or to use electrical fields or electrical currents to move water or contaminants in the vadose zone or to dewater soils just to cite few applications. I wil also discuss the filtering properties of clay membrane in unsaturated conditions.

Couplings properties of partially saturated clayey media

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.