Numerical simulation of porosity and tortuosity effect on the permeability in clay: Microstructural approach

This study presents an analysis of the association between the coefficient of permeability of active clays and their porosity and tortuosity. Montmorillonite was selected because it is used as a barrier in geo-environmental projects and its sensitive structure results in wide variations in permeability when in contact with pore fluids. The microstructural approach was selected for a numerical simulation using the discrete element method (DEM). A DEM code was developed by considering the mechanical force, diffuse double-layer repulsion, and van der Waals attraction as the inter-particle interaction. The coefficient of permeability was calculated by simulating consolidation tests, and the DEM simulations were compared with the experimental data. The results show that the coefficient of permeability decreased as the void ratio decreased. At the same void ratio, there was a deviation between the coefficient of permeability for clay-electrolyte systems caused by the micro-fabric and variations in tortuosity. Micro-fabric evolution during loading showed that increasing the stress state caused a reorientation of the particles perpendicular to the direction of loading and increased the anisotropy of the particle orientation, increasing the tortuous flow path. A dispersed or oriented structure can occur at the same void ratio for different clay-electrolyte systems, causing variations in the coefficient of permeability.