Mechanisms controlling volume change of saturated clays and the role of the effective stress concept

This investigation deals with the mechanisms con- trolling the one-dimensional volume change beha- viour of saturated kaolinite and montmorillonitic clays. An attempt has been made to explain the behaviour of the clays in the light of the modified effective stress concept which takes into considera- tion the interparticle electrical attractive and repul- sive forces. Eight organic pore fluids of different dielectric properties and water have been used to vary the interparticle forces in the one-dimensional consolidation tests. In order to further confirm the nature of the mechanisms, tests have also been con- ducted in which the existing pore fluid was replaced by another of different dielectric properties, to change the force system at interparticle level. The experimental results clearly indicate that the volume change behaviour of these clays is controlled basi- cally by two mechanisms which are governed by the modified effective stress concept. In mechanism 1, the volume change is controlled by the shearing resistance at interparticle level and in mechanism 2, primarily by the long range diffuse double layer repulsive forces. Although these effects operate simultaneously, the results indicate that mechanism 1 primarily governs the volume change behaviour of non-expanding lattice type clays like kaolinite, and mechanism 2, that of the expanding lattice type clays like montmorillonite