Determination of effective diffusion properties based on 3D FIB/SEM images of clays

This article presents a numerical approach aiming to estimate the effective diffusion properties of clay using real 3D images obtained through Focused Ion Beam and Scanning Electron Microscopy (FIB/SEM). A description of the original FIB/SEM procedure, specifically developed for observing remoulded clays at the particle scale, is presented. Image processing allowed the reconstruction of a micro-volume extracted from a clay sample subjected to an oedometric loading with an effective vertical stress of 1000 kPa. Numerical calculations of effective diffusivity were performed on the real 3D images using periodic homogenization technique. The results revealed anisotropy in the diffusion phenomena of the studied clay: the effective diffusion coefficient is lower along the direction of the mechanical loading and higher in the plane normal to the stress axis. These findings are consistent with quantitative pore orientation results obtained through image processing, where it was shown that, after mechanical loading, the pores tend to orient towards the plane normal to the axis of the effective vertical stress. These results demonstrate that incorporating the real geometry of clay microstructure into diffusion property calculations allows for a better consideration of the complexity of the clay fabric in relation to mechanical loading.