Role of microscopic physicochemical forces in large volumetric strains forclay sediments

In a clay-water-electrolyte system, each particle is under the influence of van der Waals attraction, electrical double-layer repulsion, Born's repuls ion, hydrodynamic viscous drag, and gravity. This study investigates the ro le of microscopic forces in the volumetric behavior of clay sediments. The microscopic forces are implemented in a 2D discrete element method (DEM) fr amework that uses spheres to represent clay particles. The model is validat ed with two well-defined problems: (1) an analytical estimation of force-eq uilibrium for the system of colloidal particles; and (2) the theoretical se ttling velocity of spherical particles according to Stokes' law. An experim ental program is developed to measure the free swell of Georgia kaolinite, Na-montmorillonite, and Ca-montmorillonite. The experimental results are us ed to validate the DEM framework in its ability to correctly model the volu metric strains inherent to clay sediments. A good agreement between the mod el prediction and the experimental data is obtained, suggesting that the DE M can be used to predict large volumetric strains for clay sediments. It is also shown, through numerical simulations, that ionic strength of the pore fluid is an important controlling factor for volumetric strain. For low io nic strength, montmorillonite can experience a void ratio increase up to 2. 0 compared with high ionic strengths. For ionic strength ranging from 0.001 to 2.0, changes in void ratio for montmorillonite are higher than kaolinit e by a factor of two.