[Thesis defense] Mohamed El Shamieh ‘Évolution de la perméabilité des sols granulaires dans un contexte d’érosion interne par suffusion’

Abstract :

Hydraulic earth structures are susceptible to internal erosion, with suffusion being one of the most complex and least understood mechanisms. Suffusion alters the microstructure of granular soils by selectively eroding fines, leading to significant changes in permeability, even when porosity or grain size distribution remain unchanged. This thesis develops a comprehensive multiscale analysis of permeability changes in suffusion-affected granular soils through a combined numerical investigation and analytical modeling. 
The numerical investigation relies on the Discrete Element Method (DEM) for sample generation, Delaunay-based techniques for pore space characterization and a Fast Fourier Transform (FFT)-based full field homogenization method for permeability estimation. Systematic analyses of three microstructural configurations, isotropically compacted (M0), gravity-modified (M1) and flow-modified (M2), identify critical descriptors governing permeability variations, such as porosity and a weighted constriction diameter D_cw. A new permeability-microstructure relation is proposed, inspired by the classical Kozeny-Carman model. The developed model is calibrated and validated on a wide set of numerical specimens, both uniform and gap-graded. The results highlight the robustness of the model, especially in flow-modified configurations, for which it outperforms existing models. 
To reduce computational cost, a self-consistent micromechanical analytical model is then developed within a mean-field homogenization framework, based on Brinkman inhomogeneity problems. The solid phase is represented by zero permeability spherical inhomogeneities from the entire grain size distribution, while the pore phase is represented by purely fluid inhomogeneities with one or two equivalent diameters constrained by the specific surface area. Four key parameters, grain size distribution, porosity, pore size ratio and fine pore fraction, define a unified analytical model capable of representing both mono- and bimodal pore families, thereby describing microstructural configurations from isotropic compacted (M0) to flow-modified (M2). Model results show good agreement with numerical simulations for all gradings and compaction states, successfully capturing permeability and the modifications in flow-modified systems. Overall, the combination of the numerical investigation with the analytical modeling provides a physically grounded and computationally efficient tool for predicting permeability changes in granular soils under suffusion, with direct implications for assessing internal erosion in hydraulic earth structures.

Composition of the jury

Christian GEINDREAU, Professeur des Universités, Université Grenoble Alpes 
Antoine WAUTIER, Ingénieur en Chef des Ponts, des Eaux et des Forêts HDR, INRAE- Aix-en-Provence 
Éric VINCENS, Professeur des Universités, Ecole Centrale de Lyon 
Luisa ROCHA DA SILVA, Professeure des Universités, Ecole Centrale de Nantes 
Ariane ABOU CHAKRA, Maîtresse de Conférences HDR, INSA Toulouse 
     
Thesis supervisor : Didier MAROT, Professeur des Universités, Nantes Université   
Co-supervisor : Rachel GELET, Maîtresse de Conférences HDR, Nantes Université   
Advisor : François BIGNONNET, Maître de Conférences, Nantes Université