A DUAL POROSITY MODEL FOR CONTAMINANT TRANSPORT IN EXPANSIVE CLAYS

摘要

A three-scale model based on a modified convection-diffusion-reaction equation wherein the partition coefficient governing the instantaneous adsorp-tion/desorption of the species in the micro-pores appears appears coupled with the local electric potential sastisfying a Poisson-Boltzmann equation, is proposed to describe contaminant transport in swelling clays characterized by two levels of porosity (micro and macro-pores). At the microscale the medium is composed of charged clay particles saturated by a binary monovalent aqueous electrolyte solution. At the intermediate (meso) scale the two-phase system is represented in a homogenized fashion with movement of the ionic charges governed by the Nernst-Planck relations. At the macroscale, the mesoscale mixture of clay clusters is homogenized with the bulk solution in the macro-pore system. A notable consequence of the approach proposed herein is the microscopic representation for the partition coefficient which can be exploited to derive the constitutive behavior for this quantity.