Microstructural approach and transfer water modelling in highly compacted unsaturated swelling clays

A compacted smectite clay was studied in order to understand the swelling phenomenon. The influence of the sample initial state on the swelling mechanisms was demonstrated. A complete physical–chemical and mineralogical characterization of the clay was achieved using X-ray by reflexion and thermal methods. The X-ray diffraction by transmission method allowed to describe the various levels of the hydrated clay organization and the microstructure evolution. The pore distribution and the water partition are shown. Other important parameters: water retention, inter-layer distances, particle size, number of layers per particle were examined. This information gives the ability to follow the swelling which occurred in two steps, and to calculate the swelling potential versus the water content, or the void ratio. In application to this study, a water transfer in unsaturated clay was studied with the laws of continuous medium mechanics. A finite difference program was used to examine two cases: prevented and free swelling in an oedometer. In order to take into account the material deformation, the swelling potential was introduced in the diffusion coefficients. The simulation results of the water transfer obtained on this basis, were in good agreement with the experiments. Copyright © 2000 John Wiley & Sons, Ltd.