Study of the Fundamentals of Expansive Clays through Discrete Element Modeling

The double-layer and inter-layer forces are generally considered to be responsible for the expansion of swelling clay minerals upon water saturation. However, the validity of these assumptions has not been quantitatively verified in the past. Focusing on the double-layer repulsive force, in the present paper, the factors influencing swelling of montmorillonite are studied using the discrete element method (DEM). Numerical specimens of dry clay powders, one-dimensionally compressed to the desired void ratio, are flooded with an electrolyte (salt-water) of known properties and the ensuing swelling pressure is monitored under constant volume condition. A systematic series of numerical simulations is carried out to examine the importance of cation exchange capacity and Hamaker constant on the swelling of clays. The numerically predicted constant-volume swelling pressure values are verified with laboratory experimental data. It is shown that the double-layer repulsion alone can quantitatively account for the observed swelling pressure for the range of void ratios considered (0.7 to 2.0).