This paper proposes new an original technique aiming to go further towards the 3D characterization in clay microstructure. To achieve this, an approach using FIB-SEM imaging coupled with image processing techniques has been developed allowing to generate a three-dimensional microstructure from digital 3D reconstruction.(Ding et al., 2023). The tests using FIB-SEM technique were carried out on remolded saturated clay samples submitted to one-dimensional compression. Particular emphasis was placed on how to rebuild, with sufficient accuracy, the pore network of an observed micro-volume. Then, pores properties were investigated in terms of pore size distribution, morphology, and spatial orientations. Finally, Pore size distribution deduced from FIB-SEM was then superimposed to mercury intrusion porosimetry results allowing more discussions around the FIB-SEM technique efficiency.

Ding, Y ., Bennai, F., Jrad, M., Guyon, J., Hattab, M. 2023. Three-dimensional pore network of kaolin using FIB-SEM imaging. Particulate Science and Technology. https://doi.org/10.1080/02726351.2023.2292271

Both granular materials and human societies are dynamic and nonlinear that can be regarded as illustrations of complex systems. An important feature in granular materials under external loading is force transmission through particle contacts, whereas in populations during epidemic varying quantities of circulating pathogens are transmitted during social interactions [1, 2].

An assembly of granular materials consisting of interacting particles shows emergent properties on the macroscopic scale under external loading. The mechanism behind emergent properties can be illustrated by network-related statistics. For example, the emergence of asymptotic states such as the critical state agrees with the evolution of the number of grain loops as mesostructures [3] that ensue in this stress-strain regime. Similarly, the population network is a key to understanding the spread and evolution of epidemics and the use of network-driven strategies has been regarded as an important pathway for structuring responses, i.e. discrete outbreaks into clusters versus generalized, diffuse ones [1, 4].

In this research, we interpret the upscaling processes of the two complex systems within a thermodynamic framework [5] as both address the laws of macroscopic quantities versus microscopic entities through the ontology of activity or change of state. We explore how stress transmission in granular materials and pandemic spreading in human society can be described with a similar conceptual framework, as they both consist in information transmission based on a network composed of individual components and their interactions that upscale to a larger population and scale. The comparison gives us new insights into the two systems.

[1] Radjai, Farhang, et al. 1998. (https://doi.org/10.1103/PhysRevLett.80.61)

[2] Cevik, Muge, and Stefan D. Baral. 2021. (https://doi.org/10.1126/science.abg0842)

[3] Deng, Na, et al. 2021. (https://doi.org/10.1016/j.jmps.2021.104300)

[4] Rohani, Pejman, et al. 2010. (https://doi.org/10.1126/science.1194134)

[5] Nicot, François, et al. 2023. (https://doi.org/10.1016/j.jmps.2023.105394)

Most soils and rocks contain varying fractions of clay minerals within their solid matrix. These geomaterials can exhibit a significant swelling potential toward chemo-thermo-hydromechanical loadings. To ascertain their swelling behavior across various scales, several multiscale modeling techniques have been developed, with molecular dynamics, micromechanics-based approaches and double-porosity models being the most common. Molecular dynamics simulation is a computational technique that applies Newton's second law of motion to depict the movement of particles within a granular system. Micromechanics-based approaches upscale the poro-elasticity law from the clay layer level to the sample scale through homogenization. Dual-porosity models are generally based on elasto-plasticity, incorporating different hydro-mechanical laws at two distinct scales. Although their significant contribution to the understanding of clay swelling behaviour, these techniques have been insufficiently reviewed, compared and discussed mutually in the literature. This paper aims to provide a cross-look at these multiscale approaches by presenting the theoretical background of existing formulations, highlighting breakthrough results, discussing major differences, current challenges and proposing future perspectives.