DISCRETE ELEMENT MODELING OF LEACHING-INDUCED APPARENT OVERCONSOLIDATION IN KAOLINITE

A. ANANDARAJAH

ABSTRACT: Elasto-plastic behavior of a material depends on the past loading history, and for clays, the most important process representing the past loading history is overconsolidation. The deformation behavior of clays including the general stress-strain relation, shear strength, and  compressibility all depend on overconsolidation. A soil is generally referred to as overconsolidated soil when the existing stress is smaller than the maximum stress experienced by the soil in the past  (i.e., preconsolidation pressure); otherwise, the soil is referred to as normally consolidated soil. In many circumstances, even when the soil is normally consolidated by this definition,  the soil may behave like an overconsolidated soil, exhibiting an ``apparent overconsolidation.'' Various factors such as  cementation, desiccation, aging, bonding, etc., have been suggested as possible causes of ``apparent overconsolidation.'' In this paper, using a particle-level numerical simulation technique known as the discrete element method (DEM), a study is performed to examine the microscopic mechanism responsible for overconsolidation in clays. The stress-based overconsolidation, and a leaching induced ``apparent overconsolidation'' are numerically simulated and studied. It is shown that there are many similarities at the microscopic level between stress-based and leaching-induced overconsolidations. It is further found that the change in void ratio during the process of leaching-induced overconsolidation is negligible.

Key words: clay, cohesion, double-layer repulsive force, interparticle cohesion, normal consolidation, overconsolidation, shear strength, stress-strain behavior, van der Waals attractive force (IGC:D4/D5/D6)