Mechanism controlling permeability change in clays due to changes in pore fluid

When a water-saturated clayey soil is leached with an organic fluid such as heptane, it has been found that under some conditions the hydraulic conductivity (or the permeability) increases manyfold. While it is generally agreed that physicochemical changes (e.g., compression of double-layer thickness) and the consequent alterations to the internal fabric (e.g., shrinkage of clusters) are responsible in most cases for such an increase, the underlying mechanism is not clearly understood. Two possible mechanisms are (1) formation of a few macrocracks due to shrinkage of clusters and (2) uniform increase in intercluster porosity throughout the volume of the soil due to shrinkage of clusters. The objective of the study presented here is to examine the most plausible mechanism of permeability increase caused by leaching. With the aid of Olsen’s permeability equation based on the cluster model, Poiseuille’s law for laminar fluid flow between two parallel plates, physicochemical theories, and experimental permeability data, it is shown that the formation of macrocracks is the most plausible mechanism of permeability increase.