Modeling Macro-Scale Clay Secondary Compression at Micro-Scale Clay Particle Interfaces

Clay consolidation has generally been considered from a macro-scale perspective by measuring the macro-scale compression of a clay soil over time. Clay particles in consolidation tests experience shear and normal forces at the inter-particle level due to force applied to the soil at the macro-scale. These shear and normal forces cause the particles to slide at the micro-scale and produce macro-scale changes in soil volume and shape. By considering the inter-particle interactions at the micro- scale interfaces, the shear force - normal force - velocity relationship can be described by the theoretically derived Rate Process Theory (RPT). This paper presents a Discrete Element Method (DEM) model to numerically calculate thin, disk-shaped clay particle movement in three dimensions during compression using the RPT contact model. The coefficient of secondary compression obtained from the DEM model using RPT parameters supported by previous research was 0.059. The coefficient of secondary compression obtained from macro-scale consolidation tests for a montmorillonite clay was 0.031. Differences between the numerical model and experimental measurements are attributed to particle shape, size distribution, and particle number. The influence of the number of bonds and bond strength on clay creep behavior are also quantified and discussed.