The present work applies the hybrid Voronoi cell finite element method (VCFEM) within geomechanics. Coupled seepage and deformation analysis using the VCFEM incorporating body forces allows accurate analysis of earth dams. The development of a novel approach for simulating granular material behaviour using the combined finite-discrete element method (VCFEM-DEM) provides new insights into strain localization in granular materials. Chapter 1 provides background including summary literature reviews for all concepts in the title including seepage analysis, micromechanical and continuum mechanics theory, Voronoi diagrams, finite elements (FEM), discrete elements (DEM) and combined FEM-DEM. Chapter 1 concludes by detailing the contributions of the present work. Chapter 2 presents the VCFEM for seepage analysis. The numerical examples include an investigation of mesh sensitivity and a comparison of conforming shape functions. Polygonal elements with more than four nodes show a decrease in mesh sensitivity in free surface problems, compared with four-node quadrilateral elements. The choice of conforming shape function within the VCFEM analysis did not affect the results. Chapter 3 formulates and applies the VCFEM-DEM, showing that strain localization effects in granular materials are important at all scales. The VCFEM-DEM captures shear banding in biaxial compression tests, demonstrating that global shear strains and inhomogeneities in the shear stress field present after consolidation are early precursors to the failure mode. At the field scale, strain localization can lead to significant non-uniformity in subsurface stress distribution owing to self-weight. Chapter 4 presents the coupled VCFEM for seepage and deformation. A practical example of the design of an earth dam demonstrates the application of general body forces within a hybrid formulation, notably lacking in the literature. Chapter 5 concludes by summarizing the key observations of the present work, and providing direction for future research. The Appendix provides additional details related to numerical integration within the VCFEM. / Thesis / Doctor of Philosophy (PhD) / The focus of the present work is the simulation of geomechanical behaviour at multiple scales. This ranges from simulating the interaction of grains of sand in a laboratory compression test to the seepage of water through and deformation of a large dam constructed of granular material. The simulations use a numerical tool called the Voronoi cell finite element method (VCFEM), which the present work extends to allow accurate analysis of the flow of fluid through a porous medium, deformation of a granular material under load and coupled analysis of these phenomena. The development and testing of this numerical tool for use in geomechanical analysis is itself a contribution. The present work also contains new insights into how localized stresses and strains in a granular material that are present well before the peak strength can have an important influence on the mode of failure.

Cette thèse s’intéresse à la signature sismique du rôle des fluides dans les mécanismes de déformation des roches fracturées de la croûte supérieure, et plus précisément les failles et les glissements de terrain. S’il est admis que les fluides sont un facteur déclenchant de la rupture dans le cas d’épisodes de forçages climatiques importants ou de glissements très superficiels, leur rôle dans la déstabilisation des grands volumes associée à des forçages faibles est beaucoup moins bien compris. Ainsi, il apparaît nécessaire d’acquérir de nouvelles données synchrones des pressions/débits de fluides, de la déformation et de la sismicité sur le terrain dans des conditions de chargement hydraulique contrôlées pour progresser dans la compréhension des liens entre processus hydromécaniques et sismiques participant à la nucléation de la rupture des roches en partie associée à la réactivation de fractures existantes. Motivé par ce besoin de nouvelles observations, ce travail de thèse concerne l’interprétation de la sismicité produite lors d’expériences originales de stimulation hydraulique (0.3 à 3.5 MPa et 10 à 3000 secondes) de petites zones de faille ou de fractures de taille décamétrique, situées en zones non saturées profonde de versants rocheux. Ces expériences consistaient à produire des déformations menant à l’activation du glissement le long des fractures préexistantes. Le protocole expérimental combine des mesures de déformations/pressions distribuées dans les structures géologiques à des capteurs sismologiques proches (échelle métrique à décamétrique) des zones sources. / This PhD dissertation focuses on the seismic signatures of the role of fluids in the deformation mechanisms of fractured rocks in the upper crust, mainly faults and landslides. While it is generally admitted that fluids are a triggering mechanism for rupture in the cases of episodic and major climate forcing events on shallow landslides, their role in the destabilization of large volumes of rocks, associated to weak forcing, is less understood. Thus, it is primordial to acquire new synchronous data of fluid pressure/flow, deformation and induced seismicity in the field, under controlled conditions of the hydraulic loading, in order to better understand the relationship between seismic and hydromechanical processes involved in the nucleation of rock ruptures, in part associated to the reactivation of existing fractures. Motivated by the need for new observations, this PhD thesis concerns the interpretation of the induced seismicity within unsaturated zones of deep rocky slopes, during original and controlled hydraulic stimulation experiments (0.3 to 3.5 MPa and from 10 to 3000 seconds) of small areas of decameter size. These experiments consisted in triggering rock deformations which lead to the activation of rock sliding along pre-existing fractures where deformation/pressure measurements and seismic sensors were distributed. These experiments were carried out in the Low Noise Underground Laboratory (France), which allows the access to fault zones within a rocky slope (at 250 m depth) and enables accurate geophysical measurements in conditions of very low environmental noise.

Compte tenu de l’évolution démographique et climatique planétaire, la gestion de la ressource en eau constitue un défi majeur auquel la communauté internationale devra faire face au cours du XXIème siècle. A cet effet, l'identification de la continuité hydrique entre les eaux de surface et les eaux souterraines permet l'introduction de la notion de gestion intégrée de la ressource. L'application de ce principe de gestion au bassin de la Seine, à travers l'estimation des échanges nappe-rivière, est rendue possible par la mise en pratique du concept d'interface nappe-rivière emboitées au sein de travaux de modélisation. Pour cela une procédure de modélisation multi-échelles peut être mise en place. Elle vise à intégrer des informations locales au sein de modélisation à une échelle supérieure. Dans ce mémoire, une procédure de modélisation multi-échelles est mise en œuvre. Ce protocole de modélisation est initié par une estimation des flux d'eau régionaux au sein de l'hydrosystème Seine. La cohérence globale de ces flux est garantie par le développement d'une méthodologie de calibration de modèles couplés en deux étapes. Ensuite les informations locales, que sont les hétérogénéités de la plaine alluviale de la Bassée et de la représentation des interfaces nappe-rivière du réseau secondaire, sont intégrées au modèle régional par une procédure de modélisation emboitée et de changement d'échelle des paramètres hydrauliques. La mise en place de cette procédure a finalement permis l'estimation fine des échanges nappe-rivière sur la quasi-totalité (83%) du réseau hydrographique naturel du bassin de la Seine et ainsi de répondre aux recommandations de gestion intégrée de la ressource faites par la directive cadre sur l'eau. / Given the current climate and anthropogenic evolutions, water management becomes one of the greatest challenges of the 21st Century. For that purpose, by identifying hydraulic continuity between surface and subsurface water, the concept of integrated water management can be introduced. In this work this management concept is applied on the Seine basin by quantizing hydrological processes occuring at the nested stream-aquifer interface. The implementatin of the nested interface concept can bedone through multi-scale modeling. This modelling procedure, aimed at embody the local characteristics of the interfaces (such as structural or hydrodynamic heterogeneities) in large scale models. A multi-scale modelling procedures is applied to the regional Seine basin model (70000 km²) in order, to study the hydrodynamic behaviour of the Bassée alluvial plain, and to quantify the stream-aquifer exchanged fluxes at the basin scale. The modelling protocol is initiated with regionals fluxes estimation over Seine hydrosystem. Regional fluxes consistency are assured by a two-step calibration procedure of fully coupled models. Then, the local characteristics of the Bassée alluvial plain, are implemented in the regional model by nested modelling methodology associated with upscaling procedure of hydraulics properties. Finally, the multi-scale modelling procedure lead to quantify distributed stream-aquifer exchanged water fluxes over 83% of the natural river network of the Seine basin, and thus, achieve to answer the integrated water resources management recommandations of the water framework directive.