Role of Microscopic Physicochemical Forces in Large Volumetric Strains for Clay Sediments

In a clay-water-electrolyte system, each particle is under the influence of van der Waals attraction, electrical double-layer repulsion, Bornʹs repulsion, hydrodynamic viscous drag, and gravity. This study investigates the role of microscopic forces in the volumetric behavior of clay sediments. The microscopic forces are implemented in a 2D discrete element method (DEM) framework that uses spheres to represent clay particles. The model is validated with two well-defined problems: (1) an analytical estimation of force-equilibrium for the system of colloidal particles; and (2) the theoretical settling velocity of spherical particles according to Stokesʹ law. An experimental program is developed to measure the free swell of Georgia kaolinite, Namontmorillonite, and Ca-montmorillonite. The experimental results are used to validate the DEM framework in its ability to correctly model the volumetric strains inherent to clay sediments. A good agreement between the model prediction and the experimental data is obtained, suggesting that the DEM 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 ionic 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 kaolinite by a factor of two.