Thermomechanical theories for swelling porous media with microstructure

Thermomechanical microstructural dual porosity models for swelling porous m edia incorporating coupled effects of hydration, heat transfer and mechanic al deformation are proposed. These models are obtained by generalizing the three-scale system of Murad and Cushman [56,57] to accommodate heat transfe r effects and their influence on swelling. The microscale consists of macro molecular structures (clay platelets, polymers, shales, biological tissues, gels) in a solvent (adsorbed water), both of which are considered as disti nct nonoverlaying continua, These continua are homogenized to the meso (int ermediate scale) in the spirit of hybrid mixture theory (HMT), so that at t he mesoscale they may be thought of as two overlaying continua. Application of HMT leads to a two-scale model which incorporates coupled thermal and p hysicochemical effects between the macromolecules and adsorbed solvent. Fur ther, a three-scale model is obtained by homogenizing the particles (cluste rs consisting of macromolecules and adsorbed solvent) with the bulk solvent (solvent not within but next to the swelling particles). This yields a mac roscopic microstructural model of dual porosity type. In the macroscopic sw elling medium the mesoscale particles act as distributed sources/sinks of m ass, momentum and energy to the macroscale bulk phase system. A modified Gr een's function method is used to reduce the dual porosity system to a singl e-porosity system with memory. The resultant theory provides a rigorous der ivation of creep phenomena which are due to delayed intra-particle drainage (e.g. secondary consolidation of clay soils). In addition, the model repro duces a class of lumped-parameter models for fluid flow, heat conduction an d momentum transfer where the distributed source/sink transfer function is a classical exchange term assumed proportional to the difference between th e potentials in the bulk phase and swelling particles, (C) 2000 Elsevier Sc ience Ltd. All rights reserved.