Material coordinates and solute movement in consolidating clay

Use of material coordinates often simplifies analysis and offers physical i nsights into one-dimensional flow in porous media. Their use also ensures t hat material balance is preserved. This paper identities common elements in material approaches to water flow in saturated swelling systems and to sol ute movement during non-steady water flow in unsaturated porous materials. It then shows that solute transport during non-steady flow of water in a sw elling system can be described in terms of a water-based coordinate system which, in turn, is based on the distribution of the solid. The coordinates are simply defined and measured and their use results, for a non-reactive s olute, in a non-linear diffusion equation, solutions of which are available for many practically important initial and boundary conditions. The approa ch is illustrated using transient profiles involving Na+/Ca2+/Mg2+ measured during constant pressure filtration experiments with bentonite. (C) 1999 E lsevier Science Ltd. All rights reserved.