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International audience; The paper is concerned with a micromechanical formulation of force transmission within an unsaturated soil as a three-phase system composed of idealized spherical particles connected by a pore water menisci network. It is proposed here a tensorial effective stress equation that can be viewed as a generalized Bishop's equation in which the elusive effective stress parameter X is elucidated. The latter can be expressed as an explicit function of the number of water menisci, particle packing and degree of water saturation. Also, interparticle forces are found to be dependent on the distribution of pore fluid pressure and the contractile skin arising from the interaction of interfaces. Two major findings of this work are: (1) the determination of the analytical relationship between X and degree of saturation, and (2) the identification of a suction based internal shear effect even under isotropic external loading. The understanding of suction stress and its dependency on the degree of saturation is a longstanding problem both theoretically and experimentally.

International audience; Modelling and understanding water fluxes in the vadose zone are important in regards to water management and require appropriate characterization methods of soil hydraulic properties. The presented work studies three common methods for characterization of soil hydraulic properties based on the inverse modelling of Beerkan water infiltration experiments: the CI method for Cumulative Information method and two BEST methods for Beerkan Estimation Soil pedotransfer methods. These methods estimate the soil sorptivity and saturated hydraulic conductivity by fitting infiltration data using infiltration models. The CI method directly fits the experimental cumulative infiltration to the usual short time expansion of the complete analytical model proposed by Haverkamp et al. (1994). The BEST methods are based on a specific algorithm that splits the experimental curves into two parts; the first part being fitted to the short time expansion and the second part to the long time expansion. To test the methods, several subsets of infiltration data were generated using the complete analytical model for several radii of the disc source and for times ranging from zero to several truncation times. The methods were then applied and the ratio between their estimations and the target values were evaluated to quantify their related accuracy. The results clearly demonstrated that the CI method must be used only to short time infiltration data. Yet, this method is usually used without any truncation of the experimental data, whereas the truncation should certainly be required. The BEST methods proved efficient and robust, provided the steady state was reached at the end of the infiltration experiment and both short and long time data solutions were used. The gain in accuracy of the BEST methods was all the more important when the disc radius was small.

Ce rapport présente le travail effectué au sein de l’UMR EMMAH à Avignon sur le code éléments finis Fafemo. Ce code donne une solution numérique des équations non linéaires de Richards traduisant les écoulements dans les milieux poreux non saturés. J’ai d’abord amélioré le code séquentiel en utilisant des méthodes itératives pour résoudre les systèmes linéaires creux (PETSc) et le mailleur Gmsh. Les coûts de calcul ont été significativement réduis. Cependant, l’objectif principal de ce stage a été de concevoir une version parallèle et efficace de Fafemo. J’ai effectué les tests de cette version parallèle sur deux clusters (Migale et Jade, le plus puissant cluster français). Ce travail a permis de faire un premier pas vers la modélisation du comportement de milieux poreux fortement hétérogènes comme les substrats des toitures terrasses végétalisées, This manuscrit presents the work done on Fafemo software based on finite element methods at the EMMAH laboratory in Avignon. This software gives us numerical solutions of Richards non linear equations for water flow in unsaturated porous media. First I improved the software using iterative methods to solve sparse linear systems (PETSc) and Gmsh as mesher. Computational costs have been significantly reduced. But the main goal of this training course was to develop a parallel version of Fafemo. This version was tested on Migale and Jade (the most powerful French cluster). This works leads to a first step in simulating water flow in heterogeneous ground with application to green roofs

The present work is based on a published calorimetric method for the determination of the specific surface area of minerals, especially quartz. These previously obtained calorimetric data have been used here to show the variation in thermodynamic properties of adsorbed water at different prints along the adsorption isotherm of water on quartz. A solid solution type model allows the extrapolation of this isotherm to the region near the saturation point and also to very low partial water vapour pressures., Dans un travail récent, une méthode calorimétrique a été utilisée pour déterminer la surface spécifique des minéraux et notamment du quartz. Les données calorimétriques ainsi obtenues ont été utilisées dans le présent travail pour calculer les fonctions thermodynamiques de l'eau adsorbée à la surface du quartz. Une expression analogue à celle des solutions solides est utilisée pour décrire l'isotherme d'adsorption et pour permettre son extrapolation au voisinage de la saturation, ainsi qu'au voisinage des très faibles pressions partielles de vapeur d'eau., Trolard Fabienne, Valles Vincent, Partyka Stanislas, Tardy Yves. Propriétés thermodynamiques de l'eau adsorbée à la surface du quartz. In: Bulletin de Minéralogie, volume 109, 3, 1986. pp. 199-218.