Le comportement thermomécanique des géomatériaux est un sujet de recherche qui touche un nombre important de domaines d'application : le stockage des déchets radioactifs en couche géologique profonde, le comportement des structures géothermiques, le stockage de chaleur, le comportement des matériaux à proximité des câbles à haute tension, le comportement saisonnier des matériaux asphaltiques, l'origine des tremblements de terre, etc. Dans le contexte du stockage des déchets radioactifs en couches géologiques profondes, un intérêt particulier a récemment été accordé à l'étude du comportement thermomécanique de l'argile de Boom, l'argile à Opalines, l'argilite du Callovo-Oxfordien et la diorite d'Äspö. L'ensemble de ces études montre qu'une exposition à des températures élevées peut altérer les propriétés physiques et mécaniques des géomatériaux : l'angle de frottement, la cohésion, la perméabilité-porosité, les modules élastiques, la résistance, le comportement volumique, le comportement post-pic, le comportement à long terme, etc. Depuis une trentaine d'années, un nombre important de modèles de comportement ont été développés dans le but d'intégrer les effets de la température à des modèles élasto-plastiques dérivés de la théorie de l'état critique. Cependant, peu de ces modèles intègrent les effets du temps sur le comportement thermomécanique des géomatériaux ; lequel apparaît essentiel au dimensionnement de structures à long terme. L'objectif de ces travaux de thèse est de répondre à cette problématique en intégrant les effets de la température au modèle de comportement mécanique L&K. Le modèle de comportement L&K est un modèle à deux mécanismes, l'un dit "plastique" permettant de décrire le comportement mécanique instantané des matériaux, l'autre dit "viscoplastique" permettant de décrire le comportement différé. Après un état des lieux détaillé concernant les comportements thermomécaniques instantané et différé des géomatériaux, les effets de la température ont été pris en compte à travers l'évolution des paramètres d'écrouissage des deux mécanismes. Ce modèle thermomécanique a été validé sur des applications expérimentales en support de ce travail de thèse. Les résultats montrent que la formulation proposée permet de reproduire fidèlement le comportement thermomécanique des géomatériaux. Les applications à venir concernent des calculs sur ouvrage dans le contexte du stockage des déchets radioactifs / The effect of temperature on the behaviour of geomaterials is a crucial issue in geotechnical and underground engineering. The thermo-mechanical behaviour of rocks and soils contains many applications in the fields of high-level nuclear waste disposal, heat storage, geothermal structures, petroleum drilling, zones around buried high-voltage cables, bituminous materials, and geological research. In the context of nuclear waste disposal at great depths, the thermo-mechanical behaviour of Boom clay, Opalinus clay, Callovo-Oxfordian argillite and Äspö diorite has recently received special attention in Europe. Research in these areas has demonstrated that rocks and soils may suffer from changes in their mechanical properties during short-to long-term exposure to an elevated temperature. These changes include effects on the friction angle, permeability/porosity, elastic moduli, shear strength, dilatancy, softening, brittle-to-ductile transition, creep, etc... Since Prager's first works on the modelling of non-isothermal plastic deformation, many constitutive models have been developed to include these phenomena in computational inelasticity. Most models generalize the critical-state model to include the effects of temperature on the short-term behaviour of clays and rocks. However, the effect of time on the thermo-mechanical behaviour is often not coupled to the rate-independent plasticity even if the long-term behaviour appears essential for ensuring the safety and stability during the design and construction analysis in many fields, such as the storage of nuclear waste and more generally underground excavations. Thus, it appears important to combine both instantaneous and delayed thermo-mechanical effects to obtain appropriate constitutive equations to model such problems. In this Ph.D thesis, a unified thermo-plastic/viscoplastic constitutive model has been developed for this purpose. This model is a straightforward extension of the unified elasto-plastic/viscoplastic L&K constitutive model which was developed in previous Ph.D works. The updated thermo-mechanical model includes the evolutions of the two yield limits and the fluidity coefficient with temperature. The model was validated under several thermo-mechanical conditions on clayey rocks. The typical features of the thermo-mechanical behaviour of geomaterials were well reproduced. The numerical predictions of the triaxial compression tests and creep tests clearly indicate that the model can predict the overall behaviour of geomaterials under deviatoric and non-isothermal stress paths

[pt] Problemas de engenharia geotécnica onde a resistência ao cisalhamento é fator determinante para o projeto são geralmente avaliados com base no critério de ruptura de Mohr-Coulomb; no entanto, modelos constitutivos avançados são necessários para abordar grande parte de problemas geotécnicos onde estimativas de deformação são necessárias. Lade e Kim propuseram um modelo constitutivo elastoplástico avançado para investigar o comportamento tensão vs. deformação de materiais com atrito, sob condição drenada ou não drenada. Nesta dissertação, este modelo foi implementado no programa computacional de diferenças finitas FLAC3D com o objetivo de estudar o comportamento elasto-plástico de aterros. As equações governantes do modelo constitutivo de Lade-Kim são apresentadas e um algoritmo explícito de integração de tensões foi implementado na presente pesquisa. Os resultados numéricos obtidos com o modelo de Lade e Kim foram comparados com aqueles publicados na literatura, envolvendo ensaios triaxiais de laboratório realizados em areia e análises numéricas 2D do comportamento de barragem. Finalmente, após validação da implementação do modelo, análises do comportamento 2D e 3D de aterros foram executadas, verificando a influência destes tipos de análise nos valores calculados, bem como resultados numéricos foram também comparados com aqueles determinados pelo tradicional modelo elasto-plástico de Mohr-Coulomb. / [en] Geotechnical engineering problems, where the design is mainly influenced by the shear strength, can be successfully analyzed considering a traditional constitutive model; however, advanced constitutive models must be used when the estimative of deformation is an important factor to be considered. Lade and Kim proposed the Lade-Kim model in order to model a granular material stress-strain constitutive relation under different combinations of effective stress and drained or undrained conditions. In this dissertation, this model is implemented and validated in the FLAC3D finite volume program, in order to study the elasto-plastic behavior of embankments. The governing equations of the constitutive model of Lade-Kim are presented and, using an appropriate stress integration algorithm, it is implemented in FLAC3D. This procedure is validated by using experimental results of triaxial tests performed on the sand of the Sacramento River and performing two-dimensional deformation analyzes of embankments and comparing the results with the literature. Finally, the Lade-Kim model is used in two-dimensional and three-dimensional deformation analyses of embankments in order to analyze the influence of the three-dimensional condition. On the other hand, the same analyzes were carried out using the Mohr- Coulomb constitutive model in order to compare the results and analyze the efficiency of the Lade-Kim constitutive model. Thus, it is concluded that the Lade-Kim constitutive model was successfully implemented and that it provides accurate results regarding modeling geomechanical behavior under different combinations of effective stresses.

This study investigates the tensile behavior of anchor pull-out tests from super early age concrete(less than 12h) by finite element(FE) software ANSYS Workbench. In previous experiment, several series of pull-out tests were finished and analyzed. In each per hour, different speeds(1mm/s, 0.2mm/s, 0.1mm/s and 0.833mm/s) were evaluated, getting the results about correlation of pull-out force and displacement(F-D curve). It is difficult to evaluate the specific development of tensile strength in super young concrete, due to the super plasticity that makes itself soft and unstable. The first step of this study is to collect relevant empirical formula, theoretical varying material properties with time and pull-out force of experimental applied anchors. Comparison of simulation analysis results and empirical formulas determines whether the establishment of the finite element model and adapted constitutive model of known natural hardened concrete(NHC) are valid or not. The second procedure is that the material properties of NHC are replaced by different age values and modified until getting the same simulation results as experiment outcome. The propose of this paper is to investigate a more accurate modified formula to describe the development of tensile behavior in super early age concrete:1. Introduction 2. Background 2.1 Modes of failure 2.2 A new failure mode 2.3 Finite Element Numerical Simulation 3. Research Questions 4. Aims/Objectives of the Research 5. Proposed Research Method 5.1 Previous Empirical theory 5.1.1 Cubic Compressive strength of Early Age Concrete 5.1.2 Tensile Strength of Early Age Concrete 5.1.3 Modulus of Elasticity in Early Age Concrete 5.1.4 Prediction of pull-out maximum force to headed studs from concrete 5.2 Pervious Experiment 5.3 Numerical Simulation 6. Significance/Contribution to the Discipline 7. Experiment Program 7.1 Experiment Setup 7.2 Experiment Result 8. Numerical simulation and analysis 8.1 Material Properties 8.2 Modelling Setup 8.3 The first pull-out test 8.4 Comparison Results at different stages 9. Discussion and Results 10. Summary and Conclusion 11. Recommendation for future studies 12. References 13. Appendix

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La thèse vise à étudier le comportement mécanique des sables sous la condition de cisaillement simple et à son application au calcul des pieux. Tout d'abord, un modèle de sable récemment développé (SIMSAND) prenant en compte l'état critique est introduit avec une procédure directe de détermination des paramètres. Le modèle est implanté dans un code de calcul aux éléments finis qui a fait l’objet de différentes validations. Ensuite, le modèle est amélioré en considérant l'anisotropie inhérente lors de la rotation des contraintes principales sous la condition de cisaillement simple et a été validé en utilisant les résultats des essais tri axiaux et de cisaillement simple sur le sable de Fontainebleau. Les essais de cisaillement simple sont analysés en imposant les conditions de sollicitations réelles tridimensionnelles appliquées par l’appareillage utilisé. L'inhomogénéité de l'échantillon avec l'effet de la taille de l'échantillon est également étudiée. Puis, des essais de cisaillement simple cycliques drainés et non-drainés sur le sable de Fontainebleau sont effectués pour étudier les caractéristiques sous charges cycliques, telles que la dégradation de la contrainte normale effective et l'accumulation de la déformation volumique, compte tenus de certains facteurs comme l’indice des vide initial, la contrainte normale appliquée, le rapport de contrainte de cisaillement cyclique et le rapport de contrainte de cisaillement moyenne. Sur la base de ces résultats, deux modèles analytiques sont proposés pour prédire la dégradation à long terme de la contrainte normale effective et l'accumulation des déformations volumiques en fonction du nombre de cycles. En outre, les essais cycliques de cisaillement simple sont simulés par le modèle SIMSAND amélioré en utilisant une technique d'inversion de contrainte. Enfin, on simule une série de pieux modèles sous charges monotone et cyclique pour laquelle la résistance en pointe du pieu est évaluée ainsi que la réponse du sol entourant le pieu. / The thesis aims to study the mechanical behaviour of sand under simple shear condition and to apply the results to the numerical simulation of pile foundation. First, a recently developed critical state sand model (SIMSAND) is introduced with a straight forward procedure of parameters determination, implemented into a finite element code and then subjected to a series of validations. Then, the model is enhanced by considering the inherent anisotropy during the principal stress rotation under the simple shear condition and validated by using results of both triaxial tests and simple shear tests on Fontainebleau sand. Simple shear tests are analysed by simulating in three-dimensions the real conditions imposed by the simple shear apparatus. The inhomogeneity of the samples with the effect of sample size is also investigated. Furthermore, undrained and drained cyclic simple shear tests on Fontainebleau sand are conducted to investigate the cyclic responses, such as the effective normal stress degradation and the volumetric strain accumulation, respectively, considering some impact factors such as the initial void ratio, the normal stress, the cyclic shear stress ratio and the average shear stress ratio. Based on these results, two analytical models are proposed to predict the long-term degradation of the effective normal stress and the accumulation of the volumetric strain with the number of cycles. Moreover, the cyclic simple shear tests are simulated by the enhanced SIMSAND model by incorporating the stress reversal technique. Finally, a series of model pile tests under monotonic and cyclic loadings are simulated based on which the cone resistance of the piles is evaluated as well as the response of the soil surrounding the pile.

Esta tese apresenta os princípios e a formulação de um modelo não-linear de atrito estático em interface de concreto areia. A hipótese básica para desenvolvimento das equações consiste na ocorrência do atrito de deslizamento (atrito verdadeiro), do atrito de rolamento (rearranjo das partículas) e da dilatância (variação de volume durante o cisalhamento). A solução analítica do modelo considera o efeito da rugosidade da superfície de contato, da curva granulométrica da areia e do seu estado de compacidade inicial. Foram realizados ensaios de cisalhamento direto com carga normal constante em interface de contato entre concreto e areia com seção de 500 mm x 500 mm com o objetivo de permitir a calibração do modelo proposto. É discutida e sugerida a incorporação da equação constitutiva desse modelo em análises de interação solo-estrutura via método dos elementos finitos. Sua aplicabilidade é demonstrada através da análise 1D e 2D de estacas de atrito executadas em areia e submetidas a carregamentos de compressão / This thesis presents the principles and formulation underlying a concrete-sand interface nonlinear static friction model. The basic hypothesis employed in the development of the model equation takes into account the interface sliding friction (true friction), a rolling friction (particle rearrangement) and dilatancy(volume variation during shear). The model analytical solution considers the effect of roughness of the contact surface, the grain size distribution and its initial state of compactness of the sand. To calibrate the proposed model, a direct shear stress test under constant load was carried out along a 500mm x 500mm section concrete-sand interface. Furthermore, a discussion and suggestion of the inclusion of the model constitutive equation applied to the analysis of soil-structure interaction using the finite element method are presented. The applicability of the proposed model is proven through the analysis of 1-D and 2-D skin friction piles made of sand mass subjected to compression load

O presente trabalho de pesquisa aborda a aplicação de análise por elementos finitos a maciços escavados por túneis, revisando relevantes estudos sobre análise numérica deste tipo de obra e realizando modelagem numérica própria, bi e tridimensional, voltada ao caso do Túnel Paraíso do Metrô de São Paulo (obra com dados de instrumentação e de ensaios), com uso do consagrado programa de elementos finitos Imperial College Finite Element Program (ICFEP), desenvolvido nos últimos trinta anos no Imperial College de Londres. Dentre os modelos constitutivos adotados nestas análises, destaca-se o Cinemático com Duas Superfícies Modificado do Imperial College, modelo elasto-plástico com endurecimento cinemático e isotrópico, baseado no estado crítico, com grande capacidade de representar as características de rigidez de argilas sobreadensadas (como são as argilas da região do Túnel Paraíso), cujas principais características são levantadas através de revisão bibliográfica. Da observação da etapa de reprodução numérica de ensaios e dos resultados conseguidos com as análises da escavação do túnel, são feitas considerações sobre o desempenho de todos os modelos constitutivos adotados (além do Cinemático com Duas Superfícies Modificado, o Cam-Clay Modificado e o elasto perfeitamente plástico com critério de ruptura de Mohr-Coloumb), bem como sobre a performance dos modelos numéricos desenvolvidos. / This research approaches the application of finite element analysis to tunnel excavation, making a survey of some numerical relevant studies of this kind of construction and performing a range of plane-strain and three-dimensional analyses, focused on the Paraíso Tunnel from Sao Paulo Underground (with field instrumentation and lab tests), using a powerful finite element program, the Imperial College Finite Element Program (ICFEP), developed in the last thirty years at Imperial College London. Among the constitutive models adopted in those analyses, it is highlighted the Modified Two Surfaces Kinematic from Imperial College, a elasto-plastic model with kinematic and isotropic hardening, based on the critical state, with great ability to represent the pre-failure stiffness of overconsolidated clays (as are the clays around Paraíso Tunnel), whose main features are raised through a literature survey. From the results of numerical simulation of lab tests and from the predictions of the tunnelling analyses, it is discussed the performance of all constitutive models adopted (including Modified Cam-Clay and elastic perfectly plastic model with Mohr-Coloumb failure criterion) and of the numerical models developed.

Fundação Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro / Estudos de fundações de obras de arte, como barragens de concreto-gravidade e barragens de terra, devem contemplar todos os esforços atuantes no maciço de fundação, principalmente as tensões e as deformações esperadas durante todo o processo construtivo e no período pós-construtivo. Quando essas estruturas são apoiadas sobre rochas de boa sanidade, a escolha do barramento geralmente favorece a implantação de barragens de concreto. Entretanto, quando os maciços de fundação são formados por solos, a opção técnica geralmente mais bem aceita é quanto à utilização de barragens de terra. Em ambos os casos, as análises de estabilidade e de deformação são desenvolvidas por métodos analíticos bem consolidados na prática. Nas condições mais adversas de fundação, seja em rochas ou em solos com marcante anisotropia e estruturas reliquiares herdadas da rocha-mãe, a utilização de modelos constitutivos anisotrópicos em análises por elementos finitos propicia simulações mais realistas dessas feições estruturais, contribuindo para o seu melhor conhecimento. O presente trabalho teve por objetivo demonstrar a utilização de um modelo constitutivo anisotrópico no estudo da fundação da Barragem San Juan, localizada na República Dominicana, que foi concebida como uma estrutura tipo concreto-gravidade apoiada sobre solos residuais jovens altamente anisotrópicos. Nessa obra, apesar de sua pequena altura, a presença marcante de descontinuidades ensejou um estudo mais detalhado do comportamento tensão-deformação da fundação, levando em conta o levantamento detalhado da atitude das descontinuidades presentes no maciço e os resultados de ensaios de resistência em planos paralelos e normais às descontinuidades. Para a estimativa de deformações, os respectivos módulos de Young (Es) foram estimados com base em correlações com a resistência à penetração SPT desenvolvidas nesta dissertação, a partir de um estudo estatístico baseado em várias publicações disponíveis na literatura. As análises numéricas por elementos finitos foram desenvolvidas através do programa Plaxis 2D, utilizando-se como modelo constitutivo aquele denominado The Jointed Rock Model, que é particularmente recomendado para análises de estabilidade e deformação de materiais anisotrópicos. Os resultados das análises numéricas foram comparados com as análises de equilíbrio limite elaboradas para o projeto executivo da referida barragem, pelo programa Slope, utilizando o método rigoroso de Morgenstern e Price, que se mostrou conservador. Os resultados das análises numéricas mostraram sua inequívoca versatilidade para a escolha de opções de reforço da fundação, através de dentes que objetivavam o aumento das condições de estabilidade da barragem.