[pt] Este trabalho tem por objetivo a avaliação da estabilidade de taludes de solo quando sometidos a processos de infiltração de chuva, utilizando conceitos de Análise Limite e Análise de Confiabilidade. Primeiramente, determina-se a variação da sução no solo, para isto, emprega-se o Método dos Elementos Finitos e o Método de diferenças finitas na solução da equação de Richards. O modelo de Van Genuchten (1980) é utilizado para a curva característica. Na solução da nãolinearidade, emprega-se o método Picard Modificado. A instabilidade de taludes é estudada mediante o método de Análise Limite Numérica com base no Método de Elementos Finitos e o critério de Mohr Coulomb como critério de escoamento. A solução do problema matemático será realizada no espaço cônico quadrático com o objetivo de tornar a solução mais computacionalmente eficiente. Considerando as propriedades do solo como variáveis aleatórias foi incluída a determinação do Índice de Confiabilidade utilizando as formulações dos métodos de Monte Carlo e FORM (first order reliability method). Inicialmente são introduzidos conceitos básicos associados ao fluxo saturado-não saturado. A seguir são apresentados alguns conceitos. Sobre Análise Limite e sua formulação pelo Método de Elementos Finitos. Finalmente são introduzidos os fundamentos da Análise de Confiabilidade. Análises de confiabilidade das encostas de Coos Bay no estado de Oregon nos Estados Unidos e da Vista Chinesa no Rio de Janeiro Brasil, são apresentadas devido a que estes taludes sofreram colapso quando submetidos a processos de infiltração de água de chuva. Os resultados deste trabalho mostram que a falha das encostas ocorre quando o índice de confiabilidade atinge um valor perto de dois. / [en] This thesis aims to perform a reliability analysis of the stability of 2D soil slopes when they are submitted to water infiltration due to the rains.The time variation of the soil matric suctions is calculated first. The Finite Element Method is used to transform the Richards differential equation into a system of nonlinear first order equations. The nonlinearity of the problem is due to the use of the characteristic curve proposed by van Genuchten (1980). The Modified Picard Method is applied to solve de time-dependent nonlinear equation system. The responses of the flux-problem are transferred to the stability problem in some instants using the same time-interval (normally days).To estimate the stability of the slopes, limit analysis is used. The limit analyses are performed based on the Inferior Limit Theorem of the Plasticity Theory. The problem is defined as an optimization problem where the load factor is maximized. The equilibrium equations are obtained via Finite Element discretization and the strength criterion of Mohr-Couomb is written in the conic quadratic space. Therefore, a SOCP (Second Order Conic Programming) problem is generated. The problem is solved using an interior point algorithm of the code Mosek.Since the soil properties are random variables a reliability analysis can be performed at each instant of the time-dependent problem. In order to perform the reliability analyses, Response Surfaces for the failure function of the slope are generated. In this work, the Stochastic Collocation Method is used to generate Response Surfaces. The Simulation Monte Carlo Method and the FORM (First Order Reliability Method) are used to obtain both the reliability index and the probability of failure of the slopes.Reliability analyses of the Coos Bay Slope in the state of Oregon in USA and in the Vista Chinesa Slope in Rio de Janeiro, Brazil, are presented because they collapse due to rainfall infiltration. The results show that the soil slope fails when the related reliability index is close to two.

Le présent travail propose et développe une méthodologie complète d’identification des propriétés mécaniques locales d’un matériau hétérogène à l’échelle des phases constitutives. Il s’agit d’une combinaison de compétences très diverses, à la fois en théorique, en simulation numérique et en expérimentation. Plus précisément, la partie théorique concerne la détermination des relations nano-micro pour le module d’indentation homogénéisé par des techniques de changement d’échelle; la partie numérique basée sur la théorie du calcul à la rupture est réalisée en vue de trouver de ces dernières relations applicables pour la dureté; et la dernière partie est effectuée pour récupérer les propriétés homogénéisées par la voie expérimentale à l’aide de la technique de nano-indentation. L’étude expérimentale de la thèse est pour l’objectif de déterminer des propriétés d’indentation de différents échantillons de pâte de ciment. Un programme expérimental complet, est développé, qui permet de caractériser des phases principales à l’échelle micrométrique de ce matériau, parmi lesquelles nous nous intéressons surtout à celles plus importantes correspondantes à des phases de la matrice C-S-H. La modélisation du problème lié à l’enfoncement d’une pointe d’indentation dans un matériau est étudiée. Pour cela, la première voie, basée sur l’approche cinématique du calcul à la rupture, consiste à tenter de construire des mécanismes de ruine analytiquement, puis à les faire évoluer en fonction du changement de la géométrie initiale, afin d’obtenir la charge de ruine correspondante. La seconde voie consiste ensuite à suivre la même approche, mais en construisant numériquement ces mécanismes de ruine. La charge obtenue dépend naturellement des paramètres de critères retenus, que l’on détermine grâce à la combinaison avec les résultats expérimentaux. Les critères de résistance de Von-Mises et de Tresca valables pour des matériaux purement cohérents ainsi que celui de forme elliptique sont examinés dans ce travail / The present work proposes and develops a complete methodology for identifying the local mechanical properties of a heterogeneous material at the scale of the constitutive phases. It is a combination of very diverse skills in theory, in numerical simulation and in experimentation. More precisely, the theoretical part concerns the determination of the nano-micro relations for the indentation module; the numerical part based on the yield design theory is carried out to find the last relations applicable for the hardness; and the last part is performed to obtain homogenized properties by the experimental way using the nano-indentation technique. The experimental study of the thesis is for the purpose of determining indentation properties of different cement paste samples. A complete experimental program, is developed, which allows characterizing the main phases at the micrometric scale of this material, among which we are mainly interested in the C-S-H matrix phases. The modeling of the problem related to the penetration of an indentation point into a material is studied. For this, the first way, based on the kinematic approach of the yield design theory, consists in trying to construct ruin mechanisms analytically, then to make them evolve according to the change of the initial geometry, in order to obtain the corresponding ultimate load. The second way is then to follow the same approach, but by building numerically these ruin mechanisms. The obtained load depends naturally on the retained criteria parameters, which are determined by the combination with the experimental results. The Von-Mises and Tresca strength criteria for purely coherent materials as well as the elliptical one are examined in this work

La conception d’une coque de sous-marin est cruciale pour son opérabilité et la sécurité de l’équipage, mais également complexe. En effet, les ingénieurs doivent prendre en compte à la fois la légèreté, la discrétion acoustique et la résistance de la coque à la pression d’immersion et aux attaques extérieures. Les explosions sous-marines représentent une menace de premier ordre pour l’intégrité de la coque, dont le comportement doit être correctement analysé. Les travaux présentés dans cette thèse portent sur le développement d’une méthode simplifiée, basée sur des formulations analytiques, pour étudier la réponse mécanique d’un cylindre profondément immergé à une explosion sous-marine. Le but de cette méthode est de fournir aux ingénieurs une estimation rapide des dommages subis par la coque cylindrique, leur permettant de simuler un grand nombre de scénarios d’explosion. Dans ce travail de thèse, le modèle de la corde plastique sur fondation plastique est repris et adapté à l’étude d’un cylindre immergé soumis à un chargement explosif, pour lequel les effets de pression d’immersion et d’interaction fluide-structure sont à prendre en compte. Une modélisation simplifiée de l’interaction fluide-structure est couplée avec le modèle de corde plastique sur fondation plastique, en considérant d’une part les effets de la pression d’immersion et d’autre part le raidissage circonférentiel du cylindre. Des expressions analytiques sont développées pour calculer l’enfoncement de la coque ainsi que son énergie de déformation plastique. Les résultats obtenus sont comparés à des résultats d’essais et de simulations numériques, ce qui permet de valider progressivement la méthode simplifiée, mais aussi de mettre en évidence ses limitations. / The design of a hull of submarine is crucial for its operability and the safety of the crew, but also complex. Indeed, the engineers have to take into account at the same time lightness, acoustic discretion and resistance of the hull to immersion pressure and to environmental attacks. Underwater explosions represent a first-rate threat to the integrity of the hull, whose behavior needs to be properly analyzed. The works presented in this thesis concern the development of a simplified method, based on analytical formulations, to study the mechanical behavior of a cylinder deeply immersed subjected to an underwater explosion. The purpose of this method is to give engineers a fast estimation of the damage undergone by the cylindrical shell, allowing them to compute a large number of scenarios of explosion.In the scope of this thesis, the model of the plastic string on plastic foundation is picked up and adapted to the study of an immersed cylinder subjected to an explosive load, for which the effects of immersion pressure and fluid-structure interaction are to be taken into account. This simplified model of the fluid structure interaction is coupled with the model of a plastic string resting on plastic foundation, by considering on one hand the effects of the immersion pressure and on the other hand the circumferential stiffening of the cylinder. Analytical expressions are derived in order to calculate the final deflection of the shell as well as its energy of plastic deformation. The obtained results are compared with results obtained with numerical simulations, which allows to validate gradually the simplified method, but also to highlight its limitations.

O conhecimento de zonas potencialmente instáveis no fundo do mar é de fundamental importância para o desenvolvimento das estruturas marinhas, pois permite posicionar estruturas offshore em áreas mais seguras, reduzindo-se possíveis danos, custos e eventual poluição ambiental. Nesse contexto, o objetivo do presente trabalho é investigar, através de uma abordagem analítico-numérica, a estabilidade de maciços submarinos submetidos ao carregamento cíclico da onda. O efeito das ondas de água sobre o leito submerso é descrito pela propagação de uma onda de pressão ao longo de sua superfície, empregando-se a teoria linear de Stokes. São considerados maciços com superfície superior horizontal e inclinada, constituídos por material coesivo (argilas) e material granular (areias). Em maciços constituídos por solos finos, a capacidade resistente do material é modelada pelo critério de Tresca não-homogêneo e a análise da estabilidade é desenvolvida em condição não drenada. Por outro lado, em leitos granulares, a resistência do meio depende explicitamente do valor da poropressão, sendo descrita classicamente pelo critério de Coulomb sem coesão. A análise de estabilidade é então desenvolvida em tensões efetivas e o gradiente de poropressão atua como uma força volumétrica sobre o esqueleto, caracterizando o modo de carregamento principal deste material. Em razão da tendência a se densificar quando submetido a um estado de tensões desviadoras cíclicas, ocorre, em geral, a acumulação de excesso de poropressão no maciço granular. Consequentemente, o acoplamento entre o comportamento do material e o carregamento cíclico tem fundamental importância sobre o cálculo do excesso de poropressão desenvolvido. Para determinação das forças de percolação, considera-se uma abordagem simplificada baseada na partição das deformações em contribuições reversível e irreversível, que permite desacoplar o cálculo da pressão intersticial induzida pela onda. Aplicando-se conceitos da teoria da Análise Limite é possível formular limites inferiores e superiores da máxima amplitude segura do carregamento da onda. Finalmente, os efeitos da declividade da superfície do leito e da espessura de camada de solo sobre a estabilidade são analisados. / The knowledge of potentially unstable areas on the seabed is of fundamental importance to the development of marine structures, because it allows to install offshore structures in safer areas, reducing possible damages, costs and eventual environmental pollution. In this context, the objective of the present work is to investigate the stability of submarine soil masses subjected to the wave cyclic loading through analytical-numerical approaches. The effect of water waves on the submerged bed is described by the propagation of a pressure wave along its surface, using the Stokes’s linear theory. Soil masses with horizontal and sloped upper surface, composed of cohesive material (clays) and granular materiais (sands) are considered in this study. In soil masses constituted of fine soil, the material strength capacity is modeled by the non-homogeneous Tresca criterion and the stability analysis is carried out in undrained condition. On the other hand, in granular beds, the strength explicitly depends on the pore pressure value, being classically described by the Coulomb criterion without cohesion. Then, the stability analysis is developed in effective stress and the pore pressure gradient acts as a volumetric force on the skeleton, characterizing the main charging mode of this material. Due to the tendency to densify when subjected to a cyclic deviatoric stress state occurs, in general, the build-up of pore pressure excess in the granular mass. Consequently, the coupling between the material behavior and the cyclic loading has fundamental importance in the calculation of the pore pressure excess generated. In order to define the seepage forces, a simplified approach based on the partition of deformations in reversible and irreversible contributions is considered, which allows to decouple the wave-induced pore pressure calculation. Applying the concepts of the limit analysis theory it is possible to formulate upper and lower boundaries of the maximum safe amplitude of the wave loading. Finally, the effects of the seabed surface steepness and of the soil layer thickness on the stability are analyzed.

Ce travail tente de développer des outils numériques efficaces pour une approche plus rationnelle et moins empirique du dimensionnement à la ruine des ouvrages de génie civil. Contrairement aux approches traditionnelles reposant sur une combinaison de calculs élastiques, l'adoption de coefficients de sécurité et une vérification locale des sections critiques, la théorie du calcul à la rupture nous semble être un outil prometteur pour une évaluation plus rigoureuse de la sécurité des ouvrages. Dans cette thèse, nous proposons de mettre en œuvre numériquement les approches statique par l'intérieur et cinématique par l'extérieur du calcul à la rupture à l'aide d'éléments finis dédiés pour des structures de plaque en flexion et de coque en interaction membrane-flexion. Le problème d'optimisation correspondant est ensuite résolu à l'aide du développement, relativement récents, de solveurs de programmation conique particulièrement efficaces. Les outils développés sont également étendus au contexte de l'homogénéisation périodique en calcul à la rupture, qui constitue un moyen performant de traiter le cas des structures présentant une forte hétérogénéité de matériaux. Des procédures numériques sont spécifiquement développées afin de déterminer puis d'utiliser dans un calcul de structure des critères de résistance homogènes équivalents. Enfin, les potentialités de l'approche par le calcul à la rupture sont illustrées sur deux exemples complexes d'ingénierie : l'étude de la stabilité au feu de panneaux en béton armé de grande hauteur ainsi que le calcul de la marquise de la gare d'Austerlitz / This work aims at developping efficient numerical tools for a more rational and less empirical assessment of civil engineering structures yield design. As opposed to traditionnal methodologies relying on combinations of elastic computations, safety coefficients and local checking of critical members, the yield design theory seems to be a very promising tool for a more rigourous evaluation of structural safety. Lower bound static and upper bound kinematic approaches of the yield design theory are performed numerically using dedicated finite elements for plates in bending and shells in membrane-bending interaction. Corresponding optimization problems are then solved using very efficient conic programming solvers. The proposed tools are also extended to the framework of periodic homogenization in yield design, which enables to tackle the case of strong material heterogeneities. Numerical procedures are specifically tailored to compute equivalent homogeneous strength criteria and to use them, in a second step, in a computation at the structural level. Finally, the potentialities of the yield design approach are illustrated on two complex engineering problems : the stability assessment of high-rise reinforced concrete panels in fire conditions and the computation of the Paris-Austerlitz railway station canopy

Ce travail tente de développer des outils numériques efficaces pour une approche plus rationnelle et moins empirique du dimensionnement à la ruine des ouvrages de génie civil. Contrairement aux approches traditionnelles reposant sur une combinaison de calculs élastiques, l'adoption de coefficients de sécurité et une vérification locale des sections critiques, la théorie du calcul à la rupture nous semble être un outil prometteur pour une évaluation plus rigoureuse de la sécurité des ouvrages. Dans cette thèse, nous proposons de mettre en œuvre numériquement les approches statique par l'intérieur et cinématique par l'extérieur du calcul à la rupture à l'aide d'éléments finis dédiés pour des structures de plaque en flexion et de coque en interaction membrane-flexion. Le problème d'optimisation correspondant est ensuite résolu à l'aide du développement, relativement récents, de solveurs de programmation conique particulièrement efficaces. Les outils développés sont également étendus au contexte de l'homogénéisation périodique en calcul à la rupture, qui constitue un moyen performant de traiter le cas des structures présentant une forte hétérogénéité de matériaux. Des procédures numériques sont spécifiquement développées afin de déterminer puis d'utiliser dans un calcul de structure des critères de résistance homogènes équivalents. Enfin, les potentialités de l'approche par le calcul à la rupture sont illustrées sur deux exemples complexes d'ingénierie : l'étude de la stabilité au feu de panneaux en béton armé de grande hauteur ainsi que le calcul de la marquise de la gare d'Austerlitz / This work aims at developping efficient numerical tools for a more rational and less empirical assessment of civil engineering structures yield design. As opposed to traditionnal methodologies relying on combinations of elastic computations, safety coefficients and local checking of critical members, the yield design theory seems to be a very promising tool for a more rigourous evaluation of structural safety. Lower bound static and upper bound kinematic approaches of the yield design theory are performed numerically using dedicated finite elements for plates in bending and shells in membrane-bending interaction. Corresponding optimization problems are then solved using very efficient conic programming solvers. The proposed tools are also extended to the framework of periodic homogenization in yield design, which enables to tackle the case of strong material heterogeneities. Numerical procedures are specifically tailored to compute equivalent homogeneous strength criteria and to use them, in a second step, in a computation at the structural level. Finally, the potentialities of the yield design approach are illustrated on two complex engineering problems : the stability assessment of high-rise reinforced concrete panels in fire conditions and the computation of the Paris-Austerlitz railway station canopy

O conhecimento de zonas potencialmente instáveis no fundo do mar é de fundamental importância para o desenvolvimento das estruturas marinhas, pois permite posicionar estruturas offshore em áreas mais seguras, reduzindo-se possíveis danos, custos e eventual poluição ambiental. Nesse contexto, o objetivo do presente trabalho é investigar, através de uma abordagem analítico-numérica, a estabilidade de maciços submarinos submetidos ao carregamento cíclico da onda. O efeito das ondas de água sobre o leito submerso é descrito pela propagação de uma onda de pressão ao longo de sua superfície, empregando-se a teoria linear de Stokes. São considerados maciços com superfície superior horizontal e inclinada, constituídos por material coesivo (argilas) e material granular (areias). Em maciços constituídos por solos finos, a capacidade resistente do material é modelada pelo critério de Tresca não-homogêneo e a análise da estabilidade é desenvolvida em condição não drenada. Por outro lado, em leitos granulares, a resistência do meio depende explicitamente do valor da poropressão, sendo descrita classicamente pelo critério de Coulomb sem coesão. A análise de estabilidade é então desenvolvida em tensões efetivas e o gradiente de poropressão atua como uma força volumétrica sobre o esqueleto, caracterizando o modo de carregamento principal deste material. Em razão da tendência a se densificar quando submetido a um estado de tensões desviadoras cíclicas, ocorre, em geral, a acumulação de excesso de poropressão no maciço granular. Consequentemente, o acoplamento entre o comportamento do material e o carregamento cíclico tem fundamental importância sobre o cálculo do excesso de poropressão desenvolvido. Para determinação das forças de percolação, considera-se uma abordagem simplificada baseada na partição das deformações em contribuições reversível e irreversível, que permite desacoplar o cálculo da pressão intersticial induzida pela onda. Aplicando-se conceitos da teoria da Análise Limite é possível formular limites inferiores e superiores da máxima amplitude segura do carregamento da onda. Finalmente, os efeitos da declividade da superfície do leito e da espessura de camada de solo sobre a estabilidade são analisados. / The knowledge of potentially unstable areas on the seabed is of fundamental importance to the development of marine structures, because it allows to install offshore structures in safer areas, reducing possible damages, costs and eventual environmental pollution. In this context, the objective of the present work is to investigate the stability of submarine soil masses subjected to the wave cyclic loading through analytical-numerical approaches. The effect of water waves on the submerged bed is described by the propagation of a pressure wave along its surface, using the Stokes’s linear theory. Soil masses with horizontal and sloped upper surface, composed of cohesive material (clays) and granular materiais (sands) are considered in this study. In soil masses constituted of fine soil, the material strength capacity is modeled by the non-homogeneous Tresca criterion and the stability analysis is carried out in undrained condition. On the other hand, in granular beds, the strength explicitly depends on the pore pressure value, being classically described by the Coulomb criterion without cohesion. Then, the stability analysis is developed in effective stress and the pore pressure gradient acts as a volumetric force on the skeleton, characterizing the main charging mode of this material. Due to the tendency to densify when subjected to a cyclic deviatoric stress state occurs, in general, the build-up of pore pressure excess in the granular mass. Consequently, the coupling between the material behavior and the cyclic loading has fundamental importance in the calculation of the pore pressure excess generated. In order to define the seepage forces, a simplified approach based on the partition of deformations in reversible and irreversible contributions is considered, which allows to decouple the wave-induced pore pressure calculation. Applying the concepts of the limit analysis theory it is possible to formulate upper and lower boundaries of the maximum safe amplitude of the wave loading. Finally, the effects of the seabed surface steepness and of the soil layer thickness on the stability are analyzed.

[pt] Visando avaliar uma ferramenta numérica efetiva para resolução de problemas de estabilidade tridimensionais, a análise limite numérica foi estudada neste trabalho. Sua abordagem numérica requer o uso tanto do método dos elementos finitos quanto de programação matemática. Isto porque os teoremas da plasticidade, base da análise limite, podem ser colocados como problemas de otimização. No teorema do limite inferior, por exemplo, se deseja maximizar o fator de colapso, com o solo sujeito a condições de equilíbrio e ao critério de ruptura. O critério de ruptura utilizado foi o de Drucker-Prager. Neste trabalho, fez-se uso da programação cônica quadrática, conhecida por possibilitar a resolução de problemas de grande escala com muita eficiência. Empregou-se, para tanto, o solver Mosek. Além de ser possível determinar o fator de colapso, também se desenvolveu um método para calcular o fator de segurança da encosta. Ele reduz sucessivamente os parâmetros de resistência do solo, através do método de Newton-Raphson. Em casos de geometrias mais complexas, a formulação do problema teve que ser modificada. Uma força horizontal fictícia foi adicionada na condição de equilíbrio e unicamente ela foi majorada com o fator de colapso. Foi apenas através desta formulação que se pode simular a estabilidade de solos submetidos ao efeito de poropressão. A análise de fluxo foi simulada a parte no programa de elementos finitos desenvolvido por Miqueletto (2007). A resistência do solo depende dos valores de poropressão, que caracterizam os solos como saturados ou não saturados. / [en] Numerical limit analysis was studied in order to evaluate an effective numerical procedure to solve three-dimensional slope stability problems. This numerical approach utilizes finite element method and mathematical programming. Mathematical programming is needed because the plasticity theorems, basic theorems for limit analysis, can be cast as optimization problems. The lower bound theorem consists of finding the maximum collapse multiplier that will lead the soil to the imminence of collapse. The soil will still be restricted to equilibrium conditions and the yield criterion will have to be satisfied everywhere. Drucker- Prager was the yield criterion chosen. In this thesis, the optimization problem is reformulated as a second order cone programming (SOCP). SOCP is known to solve large-scale problems with great computational efficiency and we used the solver Mosek. The model calculates not only the collapse multiplier, but also the safety factor for the slope. A strength reduction scheme was proposed, based on the Newton-Raphson method. For complex geometries cases, a novel formulation was developed. A fictitious horizontal force was added at the equilibrium equation and uniquely this force was increased by the multiplier factor. It was only through this reformulation that it was possible to assess stability of slopes subjected to porepressure effects. The groundwater flow was simulated separately in a finite element program developed by Miqueletto (2007). The soil strength depends on porepressure values, which define soils as saturated or unsaturated.

Les capacités de résistance de l'argilite Callovo-Oxfordian (COx), qui est une roche hôte potentielle pour le dépôt souterrain profond de déchets radioactifs de haute activité en France, sont étudiées. À une échelle microscopique, des micros pores peuvent être observés dans la matrice. Une première étape d'homogénéisation a été réalisée afin d'évaluer le critère de résistance de la matrice. L'analyse microstructurale de ce matériau à quelques centaines d'échelle, référencée échelle échelle mésoscopique, montre une matrice argileuse et une distribution aléatoire d'inclusions minérales (quartz et calcite).Dans le but de déterminer le domaine de résistance à l'argilite COx, un premier outil numérique a été développé dans le contexte du comportement élastoplastique de la matrice. Plusieurs modèles morphologiques du volume élémentaire représentatif ont été considérés, et soumis à un chargement incrémental dans des conditions périodiques jusqu'à la charge limite. A la suite de ce calcul élastoplastique, un point de la frontière du domaine de résistance est obtenu. Ce dernier est alors obtenu par des calculs élastoplastiques successifs.Une alternative aux simulations élastoplastique directes, des approches cinématiques et statiques du calcul à la rupture sont réalisées. Une méthode du type éléments finis basée sur la construction d'un champ de contrainte (dans l'approche statique) et d'un champ de vitesse (dans l'approche cinématique) est développé dans un outil numérique permettant de calculer une limite inférieure et une limite supérieure de domaine de résistance / The strength capacities of Callovo-Oxfordian (COx) argillite which is a potential host rock for the deep underground repository of high-level radioactive waste in France are investigated. At a micro-scale, micro-pores can be observed in the matrix. A first strength homogenization step has been performed in order to evaluate the matrix strength criteria. The microstructure analysis of this material at some hundreds of micromet scale, referred at meso-scale, shows a clay matrix and a random distribution of mineral inclusions (quartz and calcite).Aiming to the determination of COx argillite strength domain, an FEM numerical tool has been developed in the context of the elastoplastic behavior of the matrix. Several morphological patterns of the representative elementary volume have been considered and subjected to an incremental loading in periodic conditions until collapse occurs. As a result of such elastoplastic calculation, one point of the boundary of the strength domain is obtained. The latter then could be reached by successive elastoplastic calculations.As an alternative to direct elastoplastic simulations, kinematic and static approaches of limit analysis are performed. The stress-based (static approach) and the velocity-based (kinematic approach) finite element method are used to develop a numerical tool able to derive a lower bound and upper bound of strength domain, respectively

O conhecimento de zonas potencialmente instáveis no fundo do mar é de fundamental importância para o desenvolvimento das estruturas marinhas, pois permite posicionar estruturas offshore em áreas mais seguras, reduzindo-se possíveis danos, custos e eventual poluição ambiental. Nesse contexto, o objetivo do presente trabalho é investigar, através de uma abordagem analítico-numérica, a estabilidade de maciços submarinos submetidos ao carregamento cíclico da onda. O efeito das ondas de água sobre o leito submerso é descrito pela propagação de uma onda de pressão ao longo de sua superfície, empregando-se a teoria linear de Stokes. São considerados maciços com superfície superior horizontal e inclinada, constituídos por material coesivo (argilas) e material granular (areias). Em maciços constituídos por solos finos, a capacidade resistente do material é modelada pelo critério de Tresca não-homogêneo e a análise da estabilidade é desenvolvida em condição não drenada. Por outro lado, em leitos granulares, a resistência do meio depende explicitamente do valor da poropressão, sendo descrita classicamente pelo critério de Coulomb sem coesão. A análise de estabilidade é então desenvolvida em tensões efetivas e o gradiente de poropressão atua como uma força volumétrica sobre o esqueleto, caracterizando o modo de carregamento principal deste material. Em razão da tendência a se densificar quando submetido a um estado de tensões desviadoras cíclicas, ocorre, em geral, a acumulação de excesso de poropressão no maciço granular. Consequentemente, o acoplamento entre o comportamento do material e o carregamento cíclico tem fundamental importância sobre o cálculo do excesso de poropressão desenvolvido. Para determinação das forças de percolação, considera-se uma abordagem simplificada baseada na partição das deformações em contribuições reversível e irreversível, que permite desacoplar o cálculo da pressão intersticial induzida pela onda. Aplicando-se conceitos da teoria da Análise Limite é possível formular limites inferiores e superiores da máxima amplitude segura do carregamento da onda. Finalmente, os efeitos da declividade da superfície do leito e da espessura de camada de solo sobre a estabilidade são analisados. / The knowledge of potentially unstable areas on the seabed is of fundamental importance to the development of marine structures, because it allows to install offshore structures in safer areas, reducing possible damages, costs and eventual environmental pollution. In this context, the objective of the present work is to investigate the stability of submarine soil masses subjected to the wave cyclic loading through analytical-numerical approaches. The effect of water waves on the submerged bed is described by the propagation of a pressure wave along its surface, using the Stokes’s linear theory. Soil masses with horizontal and sloped upper surface, composed of cohesive material (clays) and granular materiais (sands) are considered in this study. In soil masses constituted of fine soil, the material strength capacity is modeled by the non-homogeneous Tresca criterion and the stability analysis is carried out in undrained condition. On the other hand, in granular beds, the strength explicitly depends on the pore pressure value, being classically described by the Coulomb criterion without cohesion. Then, the stability analysis is developed in effective stress and the pore pressure gradient acts as a volumetric force on the skeleton, characterizing the main charging mode of this material. Due to the tendency to densify when subjected to a cyclic deviatoric stress state occurs, in general, the build-up of pore pressure excess in the granular mass. Consequently, the coupling between the material behavior and the cyclic loading has fundamental importance in the calculation of the pore pressure excess generated. In order to define the seepage forces, a simplified approach based on the partition of deformations in reversible and irreversible contributions is considered, which allows to decouple the wave-induced pore pressure calculation. Applying the concepts of the limit analysis theory it is possible to formulate upper and lower boundaries of the maximum safe amplitude of the wave loading. Finally, the effects of the seabed surface steepness and of the soil layer thickness on the stability are analyzed.