One of many applications of geohydraulic modelling is assessing the suitability of a site to host a nuclear waste repository. This modelling task is complicated by scale-dependent heterogeneity and coupled thermo-hydro-mechanical (THM) processes. The objective here was to develop methods for (i) upscaling flow and transport in fractured media from detailed-scale data and (ii) accounting for THM-induced effects on regional-scale transport. An example field data set was used for demonstration. A systematic framework was developed where equivalent properties of flow, transport, and stress-effects were estimated with discrete fracture network (DFN) modelling, at some block scale, and then transferred to a regional-scale stochastic continuum (SC) model. The selected block scale allowed a continuum approximation of flow, but not of transport. Instead, block-scale transport was quantified by transit time distributions and modelled with a particle random walk method at the regional scale. An enhanced SC-upscaling approach was developed to reproduce the DFN flow results more simply. This required: (i) weighting of the input well-test data by their conductivity-dependent test volumes and (ii) conductivity-dependent correlation structure. Interestingly, the best-fitting correlation structure resembled the density function of DFN transmissivities. Channelized transport, over distances exceeding the block scale, was modelled with a transport persistence length. A linear relationship was found between this persistence length and the macroscale dispersion coefficient, with a slope equal to a representative mean block-scale dispersion coefficient. A method was also developed to combine well-test data and rock-mechanical data in estimating fracture transmissivities, and its application was demonstrated. Finally, an overall sequential THM analysis was introduced allowing the estimation of the significance of waste-related thermo-mechanical (TM) effects on regional transport; here TM effects are calculated separately and their impact on fracture transmissivities were incorporated into the hybrid framework. For the particular case, their effects on regional-scale transport were small.

Coupled Thermo-Hydro-Mechanical (THM) behavior in geological porous media has been a subject of great interest in many geoengineering disciplines. Many attempts have been made to develop numerical prediction capabilities associated with topics such as the movement of pollutant plumes, gas injection, energy storage, geothermal energy extraction, and safety assessment of repositories for radioactive waste and spent nuclear fuel. This thesis presents a new numerical modeling approach and a new computer code for simulating coupled THM behavior in geological porous media in general, and compacted bentonite clays in particular, as buffer materials in underground radioactive waste repositories. New governing equations were derived according to the theory of mixtures, considering interactions among solid-phase deformation, flows of water and gases, heat transport, and phase change of water. For three-dimensional problems, eight governing equations were formulated to describe the coupled THM processes. A new thermal conductivity model was developed to predict the thermal conductivity of geological porous media as composite mixtures. The proposed model considers the combined effects of solid mineral composition, temperature, liquid saturation degree, porosity and pressure on the effective thermal conductivity of the porous media. The predicted results agree well with the experimental data for MX80 bentonite. A new water retention curve model was developed to predict the suction-saturation behavior of the geological porous media, as a function of suction, effective saturated degree, temperature, porosity, pore-gas pressure, and the rate of saturation degree change with time. The model was verified against experimental data of the FEBEX bentonite, with good agreement between measured and calculated results. A new finite element code (ROLG) was developed for modeling fully coupled thermo-hydro-mechanical processes in geological porous media. The new code was validated against several analytical solutions and experiments, and was applied to simulate the large scale in-situ Canister Retrieval Test (CRT) at Äspö Hard Rock Laboratory, SKB, Sweden, with good agreement between measured and predicted results. The results are useful for performance and safety assessments of radioactive waste repositories. / QC20100720 / THERESA

<p>In this thesis, fractured rock masses are treated asequivalent continua for large-scale analyses of rockengineering projects. Systematic developments are made for thedetermination of equivalent mechanical and hydraulic propertiesof fractured rock masses using a hybrid discrete fracturenetwork - distinct element method (DFN-DEM) approach. Thedetermined equivalent properties are then used for a far-fieldfinite element analysis of the thermo-mechanical impacts on thestress, deformation and permeability of fractured rockssurrounding a hypothetical geological repository of nuclearwaste. The geological data were extracted from the results ofan extensive site investigation programme at Sellafield, UK,conducted by Nirex UK Ltd.</p><p>The scale dependencies of the hydraulic and mechanicalproperties were investigated by using multiple realizations ofthe fracture system geometry with increasing model sizes untilproperly defined hydraulic and mechanical representativeelementary volumes (REVs) were reached. The validity of thesecond order permeability tensor and the fourth-ordermechanical compliance tensor were tested for continuum analysesat larger scales. The REV was determined to be around 5 m formechanical and hydraulic data in this study.</p><p>Analysis of the stress-dependent mechanical and hydraulicproperties shows that the effect of rock stresses is crucial.The elastic moduli increase significantly with the increase ofstress and an empirical equation of stress-dependent elasticmodulus is suggested based on results of numerical experiments.Calculations of the Poisson's ratios suggest greater valuesthan are normally assumed in practice. Depending on the stateof stress, permeability decreases or increases with increasingcompressive stress. Stress-induced flow channeling effect iscaptured by numerical modeling for the first time and detailedmechanisms of shear dilation of fractures are provided. Basedon the numerical experiments, a set of empirical equations wassuggested for the stress-dependent permeability, consideringboth normal deformation and shear dilation of fractures.</p><p>Thermo-mechanical impact on the performance of ahypothetical repository at a far-field scale (5 km by 1 km) wasinvestigated with the stress-dependent equivalent propertiesdetermined at the REV scale. This analysis shows thatmechanical responses vary significantly depending on how themechanical properties were determined. The change ofpermeability due to the thermal loading is, however, notsignificant in this particular case.</p><p>The thesis provides a framework for systematic analysis oflarge-scale engineering applications in fractured rock masses,such as geological repositories of nuclear wastes.</p><p><b>Keyword:</b>Fractured rock masses, Equivalent Continuum,Discrete Fracture Network (DFN), Distinct Element Method (DEM),Finite Element Method (FEM), Nuclear Waste Disposal, CoupledThermo-Hydro-Mechanical Processes</p>

Le béton est un matériau très utilisé dans l'industrie de construction. Une limite essentielle à un usage de ce matériau est sa dégradation par écaillage lorsqu’il est exposé au feu. Le phénomène d'écaillage consiste en une éjection du béton sous forme d'écailles à la surface du béton exposée à l'incendie. La section de béton s'en trouve progressivement réduite. De plus, ce phénomène expose les armatures et peut conduire à une rupture prématurée de structures telles que les tunnels, les gratte-ciels, les centrales nucléaires etc. De nombreuses recherches ont été consacrées à la mise au point de méthodes de prévention de l'écaillage et à la détermination des paramètres qui ont une influence sur ce phénomène. Cependant, la physique qui contrôle l'écaillage n'est pas encore entièrement comprise. L'objectif principal de la thèse est de fournir une meilleure compréhension des mécanismes impliqués dans l’écaillage du béton en utilisant une approche numérique-expérimentale, i.e., la tomographie neutronique couplée à la modélisation numérique avancée à une échelle adéquate.Dans ce travail, les premières mesures 3D de la teneur en eau du béton (grandeur locale indispensable au suivi du processus de déshydratation potentiellement responsable de l’écaillage) soumis à un chargement thermique sévère ont été réalisées à l'aide de tomographies neutroniques rapides. Le suivi de la déshydratation rapide du béton a été possible en réalisant un scan 3D toutes les minutes grâce à la source neutrons de l'Institut Laue Langevin (leader mondial), à Grenoble, France. Cette vitesse d'acquisition est dix fois plus rapide que toute autre étude tomographique rapportée dans la littérature. Un dispositif, adapté à l'imagerie neutronique et aux essais à haute température, a été développé pour réaliser de telles expériences. L'influence de la taille des agrégats sur la distribution de l'humidité au sein de l'échantillon est présentée. Les résultats quantitatifs sur l'accumulation d'humidité derrière le front de déshydratation, connue sous le nom de 'moisture-clog" et considérée comme un des facteurs principaux engendrant un excès de pression, sont également présentés et discutésEn parallèle, un modèle thermo-hydro-mécanique (THM) entièrement couplé a été mis en œuvre sur le logiciel élément fini Cast3M afin d'étudier et prédire le comportement du béton à haute température. Le code nouvellement implémenté est remarquablement plus rapide (20-30 fois) que le code existant sur lequel il est basé. Une approche mésoscopique a été adaptée au modèle pour prendre en compte l'hétérogénéité du béton. D'abord, le modèle est appliqué à des expériences de la littérature, qui étu-dient les paramètres standards tels que la température, la pression du gaz et la perte de masse. En-suite, des profils d'humidité 1D obtenus à partir d'expériences de radiographie neutronique sont utili-sés pour vérifier et améliorer le modèle en termes de lois de comportement critiques telles que les courbes de déshydratation et de rétention d'eau. Enfin, le modèle est utilisé pour prédire la distribution d'humidité 3D mesurée dans ce travail de doctorat par tomographie neutronique. Entre autres, des simulations THM mésoscopiques sont effectuées pour étudier l'influence d'un agrégat sur le front de séchage. / Concrete has been extensively used in the construction industry as a building material. A major drawback of this material is its instability at high temperature, expressed in the form of violent or non-violent detachment of layers or pieces of concrete from the surface of a structural element. This phenomenon, known as fire spalling, can lead to the failure of concrete structures such as tunnels, high rise buildings, nuclear power-plants, underground parkings etc. because the reinforcement steel is directly exposed to high temperature and the designed cross section of the concrete elements (e.g., columns, beams, slabs) is reduced. A lot of research has been dedicated on developing preventing methods for spalling and also on determining the parameters that have an influence on it. However, the physics behind this phenomenon is not yet fully understood.In this doctoral, the first 3D measurements of moisture content in heated concrete, which is believed to be one of the processes directly related to spalling, have been performed using in-situ neutron tomography. In order to follow the fast dehydration process of concrete, one 3D scan (containing 500 radiographs) per minute was captured thanks to the world leading flux at the Institute Laue Langevin (ILL) in Grenoble France. This acquisition speed, which is ten times faster than any other experiment reported in the literature, was sufficient to follow the dehydration process. A dedicated setup, adapted to neutron imaging and high temperature, has been developed for performing such kind of experiments. Concrete samples with different aggregate size have been tested. Quantitative analysis showing the effect of the aggregate size on the moisture distribution is presented. Results on the moisture accumulation behind the drying front, known as the moisture-clog, are also presented and discussed.In parallel, a numerically-efficient coupled thermo-hydro-mechanical (THM) model has been implemented in the finite element software Cast3M for understanding and predicting the complex behavior of concrete at high temperature in the context of spalling. The newly implemented code is remarkably faster (20-30 times) than an existing one, on which it is based. A mesoscopic approach has been adapted to the model for taking into account the heterogeneity of concrete. First the model is applied to experiments from literature monitoring standard parameters such as temperature, gas pressure and mass loss. Then, 1D moisture profiles obtained from neutron radiography experiments are used for verifying and improving the model in terms of some critical constitutive laws such as dehydration and water retention curves. Finally, the model is employed for predicting the 3D moisture distribution measured in this doctoral work via neutron tomography. Among others, mesoscopic THM simulations are performed for investigating the influence of an aggregate on the drying front.

Les roches argileuses profondes de très faible perméabilité (10-20 m2), telles que l’argilite du Callovo-Oxfordien (COx) en France ou l’Argile à Opalinus en Suisse, sont des roches hôtes potentielles pour le stockage géologique des déchets radioactifs. Lors des différentes phases du stockage, ces roches seront soumises à des sollicitations thermo-hydro-mécaniques (THM) couplées. La détermination de leurs caractéristiques THM reste à compléter pour une meilleure compréhension de la réponse du champ proche des galeries de stockage.L’étude expérimentale des matériaux de faible perméabilité est délicate et plusieurs questions sur leur comportement THM restent posées. Dans ce contexte, deux systèmes expérimentaux originaux avec mesures précises des déformations locales et chemin de drainage (H) réduit ont été développés et utilisés pour la réalisation d’essais saturés drainés : une cellule de compression isotrope (H = 10 mm) et une cellule triaxiale standard dont le chemin de drainage a été réduit à l’aide d’un géotextile placé autour de l’échantillon (H = 19 mm) .Une caractérisation poroélastique détaillée de l’argilite du COx en cellule isotrope a permis, par des approches directes et indirectes compatibles, une détermination fiable des paramètres poroélastiques isotropes transverses du matériau, identifiés dans un cadre théorique permettant de déterminer les composantes du tenseur de Biot (coefficients b1 et b2, respectivement perpendiculaire et parallèle au litage). Un paramètre clé peu documenté à ce jour est le module de compression des grains solides, déterminé à l’aide d’un essai de compression sans membrane (Ks = 21.7 GPa).Un contrôle de température et un étalonnage précis de ces effets parasites ont permis l’étude de la réponse volumique thermique de l’argilite du COx lors d’un essai de chauffage drainé sous confinement isotrope constant proche de l’état in-situ. Une expansion thermoélastique suivie d’une contraction thermoplastique a été observée, avec une température de transition à 48°C, proche de la plus grande température supportée pendant l’histoire géologique de l’argilite. On confirme ainsi le fait que les argilites gardent en mémoire la température maximale supportée. La précision des mesures de déformations a aussi permis d’identifier un fluage volumique, dont l’amplitude est accentuée à 80°C.Des calculs poroélastiques avec les conditions aux limites du système de drainage amélioré ont permis de déterminer l’ordre de grandeur des taux de déformations axiales permettant un bon drainage lors du cisaillement triaxial (6.6×10-8 s-1). Les essais drainés sur l’argilite du COx présentent une bonne compatibilité avec un critère déjà publié. Des résultats cohérents ont aussi été obtenus sur le critère de rupture de l’Argile à Opalinus, par rapport auquel ont été comparés ceux d’essais de compression simple à différentes vitesses sur des échantillons équilibrés à 94% d’humidité relative qui a mis en évidence une dépendance de la résistance au pic vis-à-vis du taux de déformation axial.L’ensemble de ces résultats permet de réduire l’incertitude concernant les propriétés THM des argilites et devrait permettre une meilleure estimation de la réponse du champ proche des galeries au cours des différentes phases de leur période service.Mot clés : argilites, perméabilité, drainage, saturation, poroélasticité, coefficients de Biot, isotropie transverse, cisaillement triaxial, chauffage, fluage / Deep low permeability claystones (10-20 m2), such as Callovo-Oxfordian claystone (COx) in France or the Opalinus Clay in Switzerland, are potential host rocks for deep geological radioactive waste disposal. During the various phases of the storage, these rocks will be subjected to thermo-hydro-mechanical (THM) coupled effects. The determination of their THM parameters remains to be completed for a better understanding of the near-field response of the storage galleries.The experimental study of low permeability geomaterials is difficult and several questions about their THM behavior still remain. In this context, two original experimental systems with high precision local strain measurements and reduced drainage lengths (H) were developed and used for saturated drained tests: an isotropic compression cell (H = 10 mm) and a standard triaxial cell with a reduced drainage length using a geotextile placed around the sample (H = 19 mm).A detailed poroelastic characterization of the COx argillite in the isotropic cell provided a set of compatible transverse isotropic poroelastic parameters of the material, identified in a theoretical framework allowing to determine the Biot tensor components (coefficients b1 and b2, perpendicular and parallel to bedding plans, respectively). A key parameter not well documented to date is the unjacketed modulus that was determined by means of an unjacketed compression test (Ks = 21.7 GPa).A temperature control and an accurate calibration of thermal parasite effects allowed the investigation of the thermal volumetric response of the COx argillite during a drainage test under constant isotropic confining stress close in-situ state conditions. A thermoelastic expansion followed by a thermoplastic contraction was observed, with a transition at a temperature of 48 °C, close to the highest temperature supported during the geological history of the claystone. It is thus confirmed that such claystones keep in memory the maximum supported geological temperature. The precision of the deformation measurements also made it possible to identify a volumetric creep that is enhanced at 80 °C.Poroelastic calculations with the boundary conditions of the improved drainage system allowed to determine the magnitude of axial strain rates allowing good drainage during triaxial drained shearing (6.6×10-8 s-1). The drained tests carried out on the COx claystone showed a good compatibility with a criterion already published. Coherent data were also obtained on the Opalinus Clay failure criterion, that were compared to those of uniaxial compression tests at different speeds on samples equilibrated at 94% relative humidity, that exhibited a dependence of the peak strength on the shear rate.These results make it possible to reduce the uncertainties concerning the THM properties of claystones and should allow a better estimation of the response of the near field close to the galleries during the different phases of their service period.Key words: claystone, permeability, drainage, saturation, poroelasticity, Biot coefficient, transverse isotropy, triaxial testing, heating, creep

Prolonger la durée de vie d’un parc nucléaire impose de garantir la pérennité des enceintes de confinement, troisième et dernière barrière de protection contre les potentielles émissions radioactives. Ces structures sont attentivement auscultées depuis la construction grâce à un dispositif de mesures spécifiques incluant des extensomètres noyés dans le béton. De conception intrinsèquement fiable et bien que largement éprouvés, ces capteurs de déformation commencent à présenter des taux de défaillance significatifs, nécessitant, de fait, le recours à des chaînes de mesure de substitution. En ne pouvant être mises en œuvre qu’au voisinage de la surface du béton, ces solutions ne permettent qu’un accès indirect à la déformation initialement observée. Des doutes peuvent dès lors être émis sur la représentativité des mesures et par conséquent sur la qualité de la surveillance.Pour analyser l'influence de la localisation de la mesure, le développement et l'exploitation de deux modèles numériques éléments finis complémentaires sont proposés. Il s’agira principalement, pour l’un, de quantifier les possibles écarts de comportement sur le long terme et en épreuve liés aux gradients de température et d’humidité ; et pour l’autre, la variabilité liée au caractère hétérogène et particulier de la géométrie des enceintes. Suite à la calibration des modèles de comportement thermo-hydro-mécanique, s’appuyant sur des résultats d'essais matériaux en laboratoire, une prévision à l'échelle de la structure, utilisant des chargements sur ouvrage reconstruits à partir de données historiques ou de synthèses fondées sur le retour d’expérience du parc nucléaire français exploité par EDF, est menée. L'historique de déformation est ainsi reconstruit en tout point de l'enceinte pour en déduire un modèle analytique des variations spatiales dans l'enceinte des déformations afin de faciliter son exploitation.En mettant en évidence de faibles écarts sur le long terme entre position à cœur et en surface, il est d'abord démontré que des chaînes de mesure de substitution sont utilisables avec un bon niveau de confiance en dehors des zones singulières. Par ailleurs, l’usage de fonctions de correction basées sur les transferts physiques régnant dans la structure permet de minimiser l’influence des changements de position de mesure dans l’épaisseur. / Extending the life of nuclear plant needs to ensure the sustainability of containment, third and last barrier against potential radioactive emissions. These structures are closely monitored from construction through a specific measuring system including strain gauges embedded in the concrete. Inherently reliable, though widely proven technology, these strain sensors start presenting significant failure rates, requiring the use of substitution measure chains. These solutions, which can only be placed near surface of concrete, allow only an indirect access to the initially observed strain. Doubts may therefore be issued on the representativeness of measurements and therefore on the quality of monitoring.To analyze the influence of the location of the measurement, the development and exploitation of two finite elements numerical models are proposed. This will be mainly for one to quantify the possible misbehavior in the long term and during tests related to temperature and moisture gradients; and for the other, the variability related to heterogeneous and particular nature of the geometry of nuclear power plant. As a result of the calibration of the thermo-hydro-mechanical behavior models, based on laboratory materials test, a forecast throughout the structure is conducted, using reconstructed loads from historical data or syntheses based on feedback from the french nuclear power plant operated by EDF. The history of deformation is thus reconstructed in any enclosure point to settle an analytical model of the spatial variations of the enclosure deformation to facilitate its operations.Highlighting small long-term differences between embedded and surface position, it is first shown that alternative measuring systems can be used with a high confident level outside singular position. Furthermore, the use of correction functions based on physical transfers prevailing in the structure makes it possible to minimize the influence of position measurement of changes in thickness.

[pt] Atrelado aos cenários cada vez mais complexos de extração de energia, o estudo de fenômenos acoplados em meios porosos - notadamente térmicos, hidráulicos, químicos e mecânicos - tem se apresentado como essencial na previsão de comportamento de meios geológicos no que diz respeito à disposição de rejeitos radioativos, armazenamento de dióxido de carbono, engenharia de reservatórios geotérmicos e geomecânica de reservatórios. Assim, este trabalho objetiva desenvolver um esquema de acoplamento termo-hidro-mecânico-químico iterativo visando a simulação do armazenamento geológico de dióxido de carbono, empregando um simulador de fluxo composicional (GEM) e um programa de análise de tensões (ABAQUS ou CHRONOS). A idealização das metodologias de acoplamento foi efetuada através dos processos hidro-mecânico, termo-hidro-mecânico e termo-hidro-mecânico-químico, bem como as validações e aplicações em casos reais. Os casos de validação, realizados empregando modelos simplificados monofásicos, apresentaram resultados satisfatórios quanto ao comportamento hidro-mecânico e termo-hidro-mecânico. Adicionalmente às validações, os esquemas termo-hidro-mecânico e termo-hidro-mecânico-químico foram aplicados em dois casos reais de armazenamento de CO2 apresentados na literatura, projeto In Salah (Argélia) e aquífero Utsira (Noruega), respectivamente. De maneira geral, os resultados encontrados, para ambos os casos estudados, representaram acuradamente as respostas encontradas em campo, fato que evidencia a qualidade, robustez e aplicabilidade dos esquemas de acoplamento propostos neste trabalho. / [en] Considering the increasingly complex scenarios of energy extraction, the study of coupled phenomena in porous media - notably thermal, hydraulic, chemical and mechanical - has been considered as essential in order to predict the behavior of geological media with regard to radioactive waste storage, CO2 geological storage, geomechanics of geothermal reservoirs and reservoir geomechanics. Thus, this work aims to develop a thermo-hydro-mechanical-chemical iterative coupling scheme in order to simulate the geological storage of CO2, employing a compositional flow simulator (GEM) and a stress analysis program (ABAQUS or CHRONOS). The idealization of the coupling methodologies was carried out through the processes hydro-mechanical, thermo-hydro-mechanical and thermo-hydro-mechanical-chemical, as well as the validations and applications in real cases. The validation cases, performed employing simplified single-phase models, presented satisfactory results regarding the hydro-mechanical and thermo-hydro-mechanical behaviors. Additionally to the validations, the thermo-hydro-mechanical and thermo-hydro-mechanical-chemical schemes were applied in two real cases of CO2 geological storage reported by the literature, In Salah project (Algeria) and Utsira aquifer (Norway), respectively. In general, the results found, in both cases studied, accurately represented the behavior observed in the field, which in turn highlights the accuracy, robustness and applicability of the coupling schemes proposed in this work.

To uilize the shallow geothermal energy, heat pumps are often coupled with borehole heat exchangers (BHE) for heating and cooling buildings. In cold regions, soil freezing around the BHE is a potential problem which can seriously influence the underground soil temperature distribution, inlet and outlet fluid temperature of the BHE, and thus the efficiency of the whole GSHP system. The influence of the freezing process on the overall system performance is investigated by comparing different BHE configuration with and without latent heat effect from the frozen groundwater. The coefficient of performance (COP) of the heat pump will alter when freezing process in taken into account and lead to various electricity consumption. Except for the efficiency aspect, the freezing behavior can also lead to the redistribution of pore pressure and fluid flow, and in some extreme cases can even result in frost damage to the BHEs. A fully coupled thermohydro-mechanical model is required for advanced system design and scenario analyses. Based on the framework of the Theory of Porous Media, a triphasic freezing model is derived and solved with the finite element method. Ice formation in the porous medium results from a coupled heat and mass transfer problem with phase transition and is accompanied by volume expansion. The model is able to capture various coupled physical phenomena through the freezing process including the latent heat effect, groundwater flow with porosity change and mechanical deformation. With this kind of THM freezing model, we are also able to solve different kinds of engineering problem, e.g. geotechnics, construction engineering and material engineering.

Le présent travail est consacré à l'étude du comportement thermo-hydro-mécanique linéaire et non linéaire des roches poreuses de type argilites par approche de changement d'échelle. A partir des observations microstructurales de ces matériaux, un modèle conceptuel a été proposé. Dans ce modèle, le volume élémentaire représentatif du milieu hétérogène est composé d'une phase matricielle argileuse contenant des inclusions sphériques de minéraux de quartz et de calcite et des inclusions ellipsoïdales aplaties représentant l'espace poreux. Dans un premier temps, le procédé de la modélisation a été exploité par la détermination des propriétés effectives isotropes et isotrope transverses des argilites : la conductivité thermique et les propriétés thermo-hydro-mécanique croisées. En outre, de nombreuses études numériques ont mis en évidence l'influence de la morphologie de l'espace poreux, de la minéralogie et des schémas d'estimation sur les résultats prédictifs. Dans un deuxième temps, nous avons modélisé le comportement mécanique non linéaire (élasto-plastique, élasto-viscoplastique) des roches argileuses. La comparaison entre les simulations numériques et les résultats expérimentaux disponibles (essai de compression triaxiale, essai de fluage) a confirmé la validation du modèle développé / The present work deals with the linear and non-linear thermo-hydro-mechanical behaviour of porous rocks such as the argillite by the multiscale modelling approach. Based on microstructure observations, a conceptual model was proposed. In this model, the representative elementary volume of a heterogeneous medium is composed of an argillaceous matrix containing spherical inclusions of minerals quartz and calcite and ellipsoidal inclusions representing the pore space. In a first step, the process of modelling has been exploited by determining the isotropic and transversely isotropic effective properties of the argillite: thermal conductivity and thermo-hydro-mechanical properties. Furthermore, many numerical studies have highlighted the influence of the morphology of the pore space, of the mineralogy and of the estimate schemes to the predictive results. In a second step, we modelled the non linear mechanical behaviour (elasto-plastic, elasto-viscoplastic) of argillaceous rocks. The comparison between numerical simulations and available experimental results (triaxial compression test, creep test) confirmed the validation of the model developed

Les structures en béton des centrales nucléaires peuvent être soumises à des contraintes thermo- hydriques modérées, caractérisées par des températures de l’ordre de la centaine de degrés aussi bien en conditions de service qu’accidentelles. Ces contraintes peuvent être à l’origine de désordres importants notamment la fissuration qui a pour effet d’accélérer les transferts hydriques dans la structure. Dans le cadre de l’étude de la durabilité de ces structures, le modèle THMs a été développé au Laboratoire d’Etude du Comportement des Bétons et des Argiles (LECBA) du CEA Saclay pour simuler le comportement du béton face à des sollicitations couplées thermo-hydro-mécaniques. Dans cette thèse on s’est intéressé à l’amélioration dans le modèle THMs d’une part de l’estimation des paramètres mécaniques et hydromécaniques du matériau en conditions partiellement saturées et en présence de fissuration et d’autre part de la description de la fissuration. La première partie a été consacrée à la mise au point d’un modèle basé sur une description multi-échelle de la microstructure des matériaux cimentaires, en partant de l’échelle des principaux hydrates (portlandite, ettringite, C-S-H, etc.) jusqu’à l’échelle macroscopique du matériau fissuré. Les paramètres investigués sont obtenus à chaque échelle de la description par des techniques d’homogénéisation analytiques. Dans la seconde partie on s’est attaché à décrire numériquement de façon précise la fissuration notamment en termes d’ouverture, de localisation et de propagation. Pour cela une méthode de réanalyse éléments finis/éléments discrets a été proposée et validée sur différents cas-test de chargement mécanique. Enfin la procédure a été mise en œuvre dans le cas d’un mur chauffé et une méthode de recalcul de la perméabilité a été proposée permettant de montrer l’intérêt de la prise en compte de l’anisotropie du tenseur de perméabilité lorsqu’on s’intéresse à l’étude des transferts de masse dans une structure en béton fissurée. Mots clés : matériaux cimentaires, homogénéisation, modélisation multi-échelle, microfissures, éléments discrets, éléments finis, chargements thermo-hydro-mécaniques. / The concrete structures of nuclear power plants can be subjected to moderate thermo-hydric loadings characterized by temperatures of the order of hundred of degrees in service conditions as well as in accidental ones. These loadings can be at the origin of important disorders, in particular cracking which accelerate hydric transfers in the structure. In the framework of the study of durability of these structures, a coupled thermo-hydro-mechanical model denoted THMs has been developed at Laboratoire d’Etude du Comportement des Bétons et des Argiles (LECBA) of CEA Saclay in order to perform simulations of the concrete behavior submitted to such loadings. In this work, we focus on the improvement in the model THMs in one hand of the assessment of the mechanical and hydromechanical parameters of the unsaturated microcracked material and in the other hand of the description of cracking in terms of opening and propagation. The first part is devoted to the development of a model based on a multi-scale description of cement-based materials starting from the scale of the main hydrated products (portlandite, ettringite, C-S-H etc.) to the macroscopic scale of the cracked material. The investigated parameters are obtained at each scale of the description by applying analytical homogenization techniques. The second part concerns a fine numerical description of cracking. To this end, we choose to use combined finite element and discrete element methods. This procedure is presented and illustrated through a series of mechanical tests in order to show the feasibility of the method and to proceed to its validation. Finally, we apply the procedure to a heated wall and the proposed method for estimating the permeability shows the interest to take into account an anisotropic permeability tensor when dealing with mass transfers in cracked concrete structures. Keywords : cement-based materials, homogenization, multi-scale modelling, microcracks, discrete elements, finite elements, thermo-hydro-mechanical loadings.