Swelling of a bentonite plug: A micromechanical approach

Abstract

This paper deals with the swelling due to water of an initially partially saturated sample of bentonite. Homogenization tools are used in order to determine the macroscopic state equation. Bentonite is modelled as the combination of a solid matrix, which is composed of particles made of parallel platelets, and of a porous network. The first part of this paper exposes briefly the mechanical framework of microporoelasticity. In the second part, solid phase of bentonite is modelled with a linear elastic behaviour and capillary effects in the porous network are considered. At the end of this part, comparison with experimental results convinces us to develop a finer model of the solid phase in order to take into account the osmotic effects which exist "inside" the solid phase, in between the particle platelets. This finer model is the aim of the third part at the end of which a state equation for ben-tonite is proposed. Comparison between this equation and the experimental data is very satisfying and brings a qualitative explanation for the different contributions to swelling pressure: swelling of bentonite is the result of mechanical, capillary and electrostatical contributions.