Effect of Stern-layer on the compressibility behaviour of bentonites

Abstract

The Stern theory as applicable to interacting parallel clay platelet systems was used to study the compressibility behaviour of bentonites. For a constant surface electrical potential, the distribution of the total electrical charge among the Stern-layer and the Gouy-layer was found to have significant influence on the electrical potential at the midplane between clay platelets. Consideration of the Stern-layer was found to reduce the repulsive pressure or the swelling pressure between clay platelets at large platelet spacing, whereas the repulsive pressure increased significantly when the interacting Gouy-layers were pushed aside. A far greater repulsive pressure was noted for Ca-bentonite than that occurred for Na-bentonite at a platelet distance close to 1.0 nm. Similarly, strong interaction between clay platelets was noted due to suppressed Gouy-layers when the bulk fluid concentration was increased. The repulsive pressure generated due to the overlapping of the Stern-layers was found to be sensitive to changes in the specific adsorption potential, the dielectric constant of the pore fluid in the Stern-layer, and the surface electrical potential. Comparisons of the calculated pressure–void ratio relationships from the Stern theory and the Gouy-Chapman diffuse double layer theory with the experimental consolidation test results of Na- and divalent-rich bentonites showed that, in general, the Stern theory improved the predictions of pressure–void ratio relationships, particularly for pressures greater than 100 kPa; however, strong agreements were lacking in all the cases studied.