A MULTISCALE THEORY OF SWELLING POROUS-MEDIA .2. DUAL-POROSITY MODELSFOR CONSOLIDATION OF CLAYS INCORPORATING PHYSICOCHEMICAL EFFECTS

A three-scale theory of swelling clay soils is developed which incorpo rates physicochemical effects and delayed adsorbed water flow during s econdary consolidation. Following earlier work, at the microscale the clay platelets and adsorbed water (water between the platelets) are co nsidered as distinct nonoverlaying continua. At the intermediate (meso ) scale the clay platelets and the adsorbed water are homogenized in t he spirit of hybrid mixture theory, so that, at the mesoscale they may be thought of as two overlaying continua, each having a well defined mass density. Within this framework the swelling pressure is defined t hermodynamically and it is shown to govern the effect of physico-chemi cal forces in a modified Terzaghi's effective stress principle. A homo genization procedure is used to upscale the mesoscale mixture of clay particles and bulk water (water next to the swelling mesoscale particl es) to the macroscale. The resultant model is of dual porosity type wh ere the clay particles act as sources/sinks of water to the macroscale bulk phase flow. The dual porosity model can be reduced to a single p orosity model with long term memory by using Green's functions. The re sultant theory provides a rational basis for some viscoelastic models of secondary consolidation.