Thermomechanical model of hydration swelling in smectitic clays: II - Three-scale inter-phase mass transfer: Homogenization and computational validation

In Part I-1 a two-scale thermomechanical theory of expansive compacted clay s composed of adsorbed water and clay platelets was derived using a mixture -theoretic approach and the Coleman and Noll method of exploitation of the entropy inequality. This approach led to a two-scale model which describes the interaction between thermal and hydration effects between the adsorbed water and clay minerals. The purpose of this paper is twofold. Firstly, par tial results toward a three-scale model are derived by homogenizing the two -scale model for the clay particles (clusters of clay platelets and adsorbe d water) with the bulk water (water next to the swelling particles). The th ree-scale model is of dual porosity type wherein the clay particles act as sources/sinks of water to the macroscale bulk phase flow. One of the notabl e consequences of the homogenization procedure is the natural derivation of a generalized inter-phase mass transfer equation between adsorbed and bulk water. Further, variational principles and finite element approximations b ased on the Galerkin method are proposed to discretize the two-scale model. Numerical simulations of a bentonitic clay used for engineered barrier of nuclear waste repository are performed and numerical results are presented showing the influence of physico-chemical effects on the performance of the clay buffer. Copyright (C) 1999 John Wiley & Sons, Ltd.