L'objectif de ce travail est de comprendre l'influence des particules très fines sur le phénomène de ré-agglomération lors du broyage. Des billes de verre de taille 0 à 20 µm avec un pourcentage massique variant entre 0 à 1% sont ajoutées dans un tas granulaire de billes de verre de 200 à 300 µm dans un tambour tournant cylindrique de diamètre et longueur 10 cm. La présence des particules fines montre un effet ambivalent sur la stabilité du tas granulaire. Nous avons établi un diagramme de stabilité du milieu granulaire en fonction de la concentration de particules fines et cherché à quantifier l'effet des fines combiné avec d'autres paramètres (humidité relative et vitesse de rotation du tambour). La stabilité d'un tas granulaire dans un tambour tournant est déterminée par la mesure de son angle maximum de stabilité θm. Dans un premier temps, nous avons étudié l'évolution de cet angle à des vitesses de rotation différentes. Les expériences montrent qu'à faible concentration (< 0; 15%), le tas se déstabilise par avalanches lorsque le tambour tourne, θm diminue lorsqu'on augmente la quantité de fines. Quand la vitesse de rotation augmente, le mouvement du tas évolue du régime d'avalanche intermittent au régime d'écoulement continu. En revanche, lorsque la concentration des fines est supérieure à 0,15%, la déstabilisation du tas se traduit par un phénomène de stick-slip à la paroi du tambour, et la quantité de fines augmente la stabilité du tas. Ce comportement apparemment contradictoire est lié au fait que la localisation de la déstabilisation est modifiée. Dans le régime des faibles concentrations, les avalanches commencent à la surface du tas, et le remplissage de l'espace intermédiaire entre les grosses billes par les fines rend la surface de plus en plus lisse, ce qui déstabilise le tas. Par ailleurs, les fines induisent une augmentation de la cohésion du tas par la nucléation des ponts capillaires entre les grains. Ainsi, dans le régime des fortes concentrations, le tas granulaire se comporte comme un corps solide et la déstabilisation a lieu à l'interface tas-tambour. Nous avons également étudié l'influence de l'humidité relative sur la stabilité et montré que dans le régime de faible concentration de particules fines, la déstabilisation est indépendante de l'humidité. D'autre part dans le régime des hautes teneurs en fines, une humidité relative élevée induit une forte cohésion due à la condensation capillaire entre les grains et le tambour ce qui entraîne une augmentation de l'angle maximum de stabilité. / The aim of this work is to understand the effect of very fine particles on the phenomenon of re-agglomeration in the grinding process. Various amount of fine glass beads of 0 to 20 µm (0 to 1% mass concentration) are added to a granular pile of glass beads of 200 to 300 µm rotated in a drum with inner diameter and length of 10 cm. The presence of fine particles shows an ambivalent effect on the stability of the granular heap. We established a stability diagram of the granular medium as a function of fine concentration and quantified the effect of fines combined with other parameters (relative humidity and rotation velocity). The stability of a granular heap in a rotating drum is determined by the measurement of the maximum angle of stability θm. Firstly, we studied the evolution of this angle with different rotation velocities. The experiments indicate that at low fine concentration (< 0:15%), the heap destabilizes through avalanches when the drum rotates, and increasing the fine quantity tends to decrease θm. When the rotation velocity increases, the granular medium transits from intermittent avalanche to continuous flow. In contrast, once the concentration is more than 0:15%, the destabilization of the heap proceeds through a stick-slip phenomenon at the drum wall, and the increase of the fraction of fines tends to increase the stability of the heap. This apparent contradictory behavior is linked to the modification of the destabilization location. In the small concentration regime, the avalanches start at the surface of the heap, and the filling of the interstitial space by the fine particles makes this surface smoother and smoother, thus destabilizing the heap. Besides, the fines induce, through the nucleation of capillary bridges between grains, an increase of the bulk cohesion of the heap. So in the large concentration regime, the heap behaves as a solid body and the destabilization occurs at its bottom. We also studied the influence of relative humidity on the granular stability in our experiment. We found out in the low fine concentration regime, the destabilization is independent of humidity. On the other hand, in the regime of high content of fines, high relative humidity induces a large cohesion due to the capillary condensation between the grains and the wall which induce the increase of the maximum stability angle.

[pt] Nesse trabalho é avaliada a solução numérica do colapso na frente de escavação em túneis rasos, através da teoria de análise limite numérico, usando o teorema do limite inferior, a partir da condição de equilíbrio para as condições plásticas, além de considerar o comportamento do material rígido perfeitamente plástico. O teorema de limite inferior implica em maximizar o fator multiplicador na carga atuante, por isso a análise limite se torna um problema de otimização, nele tem que se usar a programação matemática para ser resolvido. É avaliada a solução numérica tridimensional da análise limite através do método dos elementos finitos, usando malha de elementos hexaédricos de oito nós, a análise dos elementos finitos é feita com o próprio código gerado na linguagem de programação do MATLAB 2017.As metodologias de programação matemática empregadas são: programação cônica de segunda ordem e programação semidefinida. Antes deve-se adaptar os critérios de ruptura de Drucker Prager à programação cônica de segunda ordem e Mohr-Coulomb tridimensional à programação semidefinida. Para a otimização se usa o algoritmo comercial MOSEK Aps 7.1 baseado no método do ponto interior em grande escala, na linguagem do MATLAB 2017. Além disso, obteve-se o mecanismo de colapso através da propriedade da dualidade do problema de otimização, dualidade que é cumprida pelos teoremas de limite superior e inferior. / [en] In this work the numerical solution of the collapse in the front of excavation in shallow tunnels is evaluated through the theory of numerical limit analysis, using the lower limit theorem, from the equilibrium condition for the plastic conditions, considering the behavior of the perfectly plastic rigid material. The lower limit theorem implies maximizing the multiplier factor in the acting load, so that the limit analysis becomes an optimization problem. The three-dimensional numerical solution of the limit analysis using the finite element method is evaluated using a mesh of eight-node hexahedral elements. The finite element analysis is done using the code generated in the MATLAB 2017 programming language. The mathematical programming methodologies used are: second order conic programming and semidefinite programming. The Drucker-Prager three-dimensional criteria should be adapted to the conic programming of the second order and Mohr-Coulomb three-dimensional to the semidefinite programming. For the optimization, the MOSEK Aps 7.1 commercial algorithm based on the large-scale interior point method is used in the MATLAB 2017 language. In addition, the collapse mechanism was obtained through the duality property of the optimization problem, duality that is fulfilled by the upper and lower limit theorems.

[pt] A produção de petróleo em alta vazão a partir de reservatórios formados por arenitos friáveis requer a instalação de sistemas de contenção de sólidos para preservar equipamentos de superfície e subsuperfície. Os projetos de explotação para campos constituídos por estes reservatórios têm na completação uma etapa fundamental na construção do poço. Dentre as diversas operações de completação, a instalação de sistemas de contenção de sólidos é uma das mais complexas e envolve uma ampla gama de recursos humanos e financeiros. A alteração no estado de tensões atuante sobre a formação é uma das principais fontes de carregamento dos sistemas de contenção mecânica de sólidos instalados em poços horizontais. O objetivo deste trabalho é desenvolver um modelo para avaliação do desempenho de sistemas de contenção de sólidos do tipo gravel pack quando submetidos aos esforços relacionados ao comportamento geomecânico das formações produtoras e a variação de pressões durante a vida produtiva de um poço de petróleo, permitindo a otimização de projetos destes sistemas sob a ótica da resistência ao colapso das telas. O carregamento imposto sobre estes sistemas é avaliado através da implementação do modelo de Mohr Coulomb solucionado numericamente através do método de elementos finitos (MEF). O programa comercial ABAQUS™ é utilizado em função da sua flexibilidade para solução de modelos não-lineares. Foram analisados sistemas de contenção de areia com os conjuntos de telas tipicamente utilizados na indústria de petróleo. Em nenhum cenário analisado foram verificados indícios de colapso dos tubos indicando a possibilidade de redução da sua resistência mecânica. / [en] Global increase in energy demand and the lack of opportunities on shore or in shallow waters are driving production of hydrocarbons towards deep and ultra deepwater basins, where reservoirs are usually formed by weak and unconsolidated sandstones that require sand control methods to prevent damage in surface and subsurface equipments. Guidelines to select sand control systems are primarily based on sand exclusion, seeking to optimize balance between oil rate and fines production. Another aspect, often overlooked, is collapse strength of the system formed by the sand control equipment and the formation itself, subjected to mechanical loadings that change during life of the well. This contribution presents a method to evaluate collapse strength of sand control systems taking into account mechanical interaction between the formation and sand control screens. Elastoplastic models are used to represent granular materials. Three sand control systems were studied: gravel pack with premium screens, stand alone premium screens and pre-packed screens. A model to describe contact between granular materials (gravel and formation) and soil-pipe interaction is proposed. Results demonstrate that perforated base pipes used in premium screens may be oversized for applications under regular operating conditions.

La maintenance, la réparation et le renforcement de murs en maçonnerie par matériaux composites collés nécessitent le développement de méthodes et techniques d'évaluation de l'aptitude au service et de requalification tant pour leur restauration fonctionnelle que pour leur adaptation à de nouvelles contraintes (évolution du zonage sismique par exemple). Le présent travail de thèse a pour objectif de proposer un outil d'évaluation par calcul de l'état limite ultime de murs en maçonnerie, renforcés par composites collés, chargés dans leur plan.Les travaux effectués concernent la modélisation par homogénéisation de murs en maçonnerie et une campagne expérimentale de caractérisation du transfert de charge entre un renfort en tissu de fibres de carbone et un support en blocs creux de béton par le biais d'un joint de colle. Pour modéliser la résistance des murs maçonnés, nous proposons une loi élastique parfaitement plastique pour le comportement dans le plan d'une maçonnerie constituée de blocs liés par des joints de mortier. Le convexe de plasticité est obtenu par une technique d'homogénéisation périodique qui prend en compte la nature tridimensionnelle de la cellule de base. On obtient alors un convexe limité par plusieurs surfaces de charge. Un algorithme numérique original est ensuite proposé et programmé dans le logiciel aux Eléments Finis ABAQUS. Des simulations numériques utilisant le module développé sont présentées / Maintenance, repair and reinforcing of masonry walls with composite materials glued require the development of methods and techniques for evaluating the suitability for service and retraining for both their functional restoration for their adaptation to new constraints (changes seismic zoning for example). This thesis aims to propose an evaluation tool by calculating the limit state of masonry walls,reinforced bonded composite, loaded in their plane.The work done on modeling by homogenization of masonry walls and acampaign experimental characterization of charge transfer between a reinforcement of carbon fiber fabric and a backing of hollow blocks concrete by means of an adhesive joint. To model the resistance of masonry walls, we propose a law for elastic perfectly plastic behavior in the plane formed of masonry blocks connected by mortar joints. The convex plasticity is obtained byperiodic homogenization technique which takes into account the three dimensional nature of the basic cell. This gives a convex bounded by several surfaces of charge. An algorithm digital original is then proposed and programmed in the finite element software ABAQUS. Numerical simulations using the developed module are presented

L'objectif de ce travail est de comprendre l'influence des particules très fines sur le phénomène de ré-agglomération lors du broyage. Des billes de verre de taille 0 à 20 µm avec un pourcentage massique variant entre 0 à 1% sont ajoutées dans un tas granulaire de billes de verre de 200 à 300 µm dans un tambour tournant cylindrique de diamètre et longueur 10 cm. La présence des particules fines montre un effet ambivalent sur la stabilité du tas granulaire. Nous avons établi un diagramme de stabilité du milieu granulaire en fonction de la concentration de particules fines et cherché à quantifier l'effet des fines combiné avec d'autres paramètres (humidité relative et vitesse de rotation du tambour). La stabilité d'un tas granulaire dans un tambour tournant est déterminée par la mesure de son angle maximum de stabilité θm. Dans un premier temps, nous avons étudié l'évolution de cet angle à des vitesses de rotation différentes. Les expériences montrent qu'à faible concentration (< 0; 15%), le tas se déstabilise par avalanches lorsque le tambour tourne, θm diminue lorsqu'on augmente la quantité de fines. Quand la vitesse de rotation augmente, le mouvement du tas évolue du régime d'avalanche intermittent au régime d'écoulement continu. En revanche, lorsque la concentration des fines est supérieure à 0,15%, la déstabilisation du tas se traduit par un phénomène de stick-slip à la paroi du tambour, et la quantité de fines augmente la stabilité du tas. Ce comportement apparemment contradictoire est lié au fait que la localisation de la déstabilisation est modifiée. Dans le régime des faibles concentrations, les avalanches commencent à la surface du tas, et le remplissage de l'espace intermédiaire entre les grosses billes par les fines rend la surface de plus en plus lisse, ce qui déstabilise le tas. Par ailleurs, les fines induisent une augmentation de la cohésion du tas par la nucléation des ponts capillaires entre les grains. Ainsi, dans le régime des fortes concentrations, le tas granulaire se comporte comme un corps solide et la déstabilisation a lieu à l'interface tas-tambour. Nous avons également étudié l'influence de l'humidité relative sur la stabilité et montré que dans le régime de faible concentration de particules fines, la déstabilisation est indépendante de l'humidité. D'autre part dans le régime des hautes teneurs en fines, une humidité relative élevée induit une forte cohésion due à la condensation capillaire entre les grains et le tambour ce qui entraîne une augmentation de l'angle maximum de stabilité.

Submitted by Israel Vieira Neto (israel.vieiraneto@ufpe.br) on 2015-03-04T17:54:03Z No. of bitstreams: 2 DISSERTAÇÃO Oscar Bezerra Pezo.pdf: 5982903 bytes, checksum: b9759670a74301d6ab644f498ad40ad1 (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) / Made available in DSpace on 2015-03-04T17:54:03Z (GMT). No. of bitstreams: 2 DISSERTAÇÃO Oscar Bezerra Pezo.pdf: 5982903 bytes, checksum: b9759670a74301d6ab644f498ad40ad1 (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Previous issue date: 2013-07-02 / CAPES / A presente dissertação analisa, em termos do comportamento carga-recalque, um banco de dados organizado por Wilson Cartaxo Soares (2011), de fundações em grupo de estacas e radier estaqueados, executados em solo arenoso de várias camadas da área litorânea de João Pessoa/PB, com 07 provas de carga, estáticas, em estacas do tipo Hollow Auger, construídas em escala real, com 300 mm de diâmetro e 4,5 m de comprimento. Os dados foram retroanalisados com o Método dos Elementos Finitos (MEF 3D), utilizando o programa CESAR-LCPC v4 (Cleo 3D versão 1.07). Na modelagem do comportamento tensão-deformação do solo foi utilizado o modelo constitutivo de Mohr-Coulomb. Os parâmetros geotécnicos iniciais utilizados em cada um desses modelos foram obtidos através de correlações a partir de valores de NSPT obtidos por SOARES (2011). Os resultados dessas simulações numéricas foram comparados com os resultados experimentais, medidos nas provas de carga. Definiu-se os parâmetros geotécnicos do solo a partir da retroanálise por meio da modelagem numérica para serem empregados em futuras simulações no maciço. Análises paramétricas são executadas com o intuito de obter um maior conhecimento do comportamento da fundação em radier estaqueado, usando o modelo elásticoplástico de Mohr-Coulomb. Isso ocorre mediante algumas alterações de sua configuração que inclui a espessura do radier, número, diâmetro, espaçamento e comprimento das estacas embutido no solo. Carga vertical central está sendo considerada para a análise paramétrica. O recalque máximo, recalque diferencial e distorção angular do radier diminuem, com o aumento da espessura do radier, do número, comprimento e diâmetro das estacas.

A nonlinear Mohr-Coulomb constitutive model with a strain dependent yield surface and non-associated flow was employed to study the plastic soil properties which affect the rate of surface fault rupture propagation in reverse events. These numerical simulations show a trend for soils with higher stiffness to have a higher rate of rupture propagation. Additionally the study shows the effects of strain softening and hardening on the rate of rupture propagation. Soils which strain harden exhibiting ductile behavior typically require more basal offset to rupture to the surface than soils which strain soften exhibiting brittle behavior. These results agree with our previous fault box studies, which showed that soils with higher near surface shear wave velocity were more likely to propagate rupture to the surface for a given reverse event. The numerical modeling allowed for a more comprehensive evaluation of material types and fault angles than the fault box, and provided confidence in these findings.

Railways are one of the largest transportation networks in the world that play an important role in the mass transportation of both the passengers and freight. The speed of trains and as well as the axial load carrying capacity have been increasing significantly during the past few decades to keep in pace with the population and economy growth and to compete with other modes of transportation such as the road, air and water transportation system. Billions of dollars are spent annually for maintenance of rail tracks in the world. The efficient and optimum use of these funds is a challenging task that demands innovative and cutting edge technologies in railway engineering. The railway subgrade is an important part of railway foundation and should be capable of providing a suitable base supporting the ballast and subballast to accommodate the stresses due to traffic loads without failure or excessive deformation. The progressive shear failure is a well-known and age old challenging problem for railways over the world for centuries. The subgrade of railway track which typically constitutes of fine-grained material tends to fail through the accumulation of soil movements up- and sideward developing a path for the least resistance along which progressive shear failure occurs under repeated train-induced loads and due to the effects of climate factors. To-date, limited number of studies have addressed failure mechanism associated with the progressive shear failure, especially using the mechanics of unsaturated soils. In this thesis, a novel and first of its kind, Visual Basic program developed in AutoCAD environment based on Mohr-Coulomb failure criteria and unsaturated soil mechanics theory. This program is capable of taking account of the influence of matric suction and simulate progressive shear failure in the subgrade under moving train. Simulation results suggest several parameters that include stress distribution, matric suction, cohesion, coefficient of lateral earth pressure at rest, and coefficient of residual friction as well as the angle of internal friction have a significant effect on the progressive shear failure and the shape of failure planes in the subgrade. The progressive shear failure in subgrade can be reduced by increasing matric suction, cohesion, coefficient of lateral earth pressure at rest, and coefficient of residual friction as well as the angle of internal friction, and optimizing combination of these parameters. The simulation results suggest the progressive shear failure can be well simulated with the Mohr-Coulomb failure criteria. Several suggestions are made for railway subgrade construction and maintenance based on the results of this study.

In dense cities, the interactions between all structures, from tall skyscrapers to complex underground tunnel systems, need to be carefully analysed as soon as a new project is considered. This is necessary because of the stress changes in the soil induced by each new construction. Demolishing a building could cause heave at the base of the excavation, deflections in supporting structures and settlements of the surroundings. The behaviour can be modelled in order to predict how large the deformations will be. This thesis investigates the effectiveness of such models. This is done through the application of a parameter sensitivity analysis on models created in Plaxis. The purpose of the analysis is to identify which factors cause discrepancies between the models and the actual displacements monitored on site. The project being examined is located in central London. The analysis focuses on the displacements of existing tunnels below the site caused by the demolition of two buildings. An analysis was carried out to investigate the significance of different parameters, of different material models and methods of analysis, of 3D effects and of inaccurate groundwater data. Ground investigations, laboratory tests and published data were the main sources used to collect reliable initial input parameters for the material models. A model was created in Plaxis 2D using the Mohr-Coulomb and the Hardening Soil with small-strain stiffness material models, using two types of undrained analysis. A model using the Mohr-Coulomb material model was created in Plaxis 3D as well. A sensitivity analysis was then carried out on the 2D models to identify which input parameters were most significant to the tunnel displacements. The results were compared to monitoring data and a back-analysis was carried out to produce more accurate results. The initial and adjusted input parameters were also tested on the 3D model. Finally, the groundwater level was altered. The results indicate that soil stiffness and effective cohesion are the most significant. Small-strain stiffness is shown to be especially important when analysing small tunnel deformation. The 3D model generally yielded more accurate results than the 2D model, while the groundwater level did not appear to affect the deformations. / I tätbebyggda städer bör samspelet mellan olika konstruktioner, från skyskrapor till tunnelsystem, analyseras noga så fort ett nytt projekt ska påbörjas. Detta är kritiskt på grund av den förändrade spänningsfördelning som uppstår i marken vid varje ny byggnation. Marken häver sig, stödmurar deformeras och den omkringliggande marken sätter sig när en byggnad rivs. Denna process kan modelleras för att uppskatta hur stora deformationerna kommer att bli. Det här examensarbetet utvärderar hur effektiv en sådan modell är. En känslighetsanalys utfördes på modeller skapade i Plaxis. Syftet med denna analys är att undersöka vilka faktorer som orsakar skillnader mellan modellerna och mätdata. Projektet ligger i centrala London och analysen fokuserar på tunneldeformationer orsakade av att två byggnader rivs. Tunnlarna befinner sig i ett lager av Londonlera under byggarbetsplatsen. En analys utfördes för att undersöka huruvida olika parameterar, olika materialmodeller och analysmetoder, 3D effekter och grundvattennivån påverkar tunnelförflyttningarna. Markundersökningar, labbtester och publicerad data användes som grund för att bestämma indatavärden. En 2D modell skapades i Plaxis genom att använda materialmodellerna Mohr-Coulomb och ”Hardening Soil with small-strain stiffness”. En Mohr-Coulomb modell skapades dessutom i Plaxis 3D. En känslighetsanalys utfördes sedan på 2D modellen för att identifiera vilka parametrar som påverkade tunnelförflyttningarna mest. Resultaten jämfördes med mätdata och viktiga parameterar ändrades för att ge bättre resultat. Inverkan av att ändra dessa värden undersöktes även i 3D modellen. Slutligen undersöktes påverkan av en förhöjd grundvattennivå. Resultaten antyder att jordens styvhet och den effektiva kohesionen har störst inverkan på resultaten. Styvheten vid små töjningar visar sig vara särskilt viktigt eftersom deformationerna år små. 3D modellen gav generellt sätt mer korrekta resultat än modellen i 2D. En högre grundvattennivå påverkade inte resultaten nämnvärt.

Esta dissertação apresenta em primeira etapa o trabalho desenvolvido para averiguar a adequação dos modelos reológicos de Mohr-Coulomb e de Endurecimento de solo, para representar as deformações e distorções que ocorrem no sistema soloestrutura, quando do processo de escavação de valas escoradas. Além disto, em uma segunda etapa fazem-se estimativas de previsão de danos causados em edificações, em decorrência das escavações de uma vala escorada da linha 1 do Metropolitano de São Paulo (Metrô S.P.). A primeira e a segunda etapa foram feitas através de 810 simulações numéricas, em elementos finitos utilizando-se o software PLAXIS, associadas a retroanálise por processo direto do módulo de deformabilidade a 50% da tensão de ruptura dos solos utilizando-se para isto o processo direto. Apresenta-se também uma síntese da formação e dos tipos de solos que constituem a bacia sedimentar de São Paulo, onde se localiza a seção experimental nº1 objeto de estudo desta dissertação. Faz-se uma breve revisão bibliográfica a respeito das técnicas de retroanálise. Apresentam-se critérios para escolha de intervalos de parâmetros geotécnicos que representem o sistema solo-estrutura no processo de escavação. Foram feitas análises paramétricas para determinar os parâmetros geotécnicos que mais influenciam o sistema solo-estrutura. Comparam-se os modelos constitutivos de Mohr-Coulomb e de endurecimento na previsão das deformações. Por fim, faz-se a previsão do nível de danos causados pelas escavações da vala, a um edifício hipotético / This dissertation presents, in a first part, the work done to verify how appropriate are the Mohr-Coulomb and hardening soil constitutive models to represent the strains and the distortions associated with escavations of braced wall process. In the second part, estimates are made of the damages in constructions due to the braced excavations of line one of Sao Paulo Subway (Metrô S.P.). In the two phases, 810 numeric simulations were made, in finite elements using the software PLAXIS, associated the back analysis for direct process. It is presented a synthesis of the formation and the types of soils that constitute the basin of the sediments of the city of São Paulo, where is located the section experimental nº1, object of study of this dissertation. It is presented an short bibliographical revision regarding the back analysis techniques. Criteria for choice of intervals of parameters geotechnical that represent the system soil-structure in the excavation process are presented. Parametric analyses are made to determine which the parameters have larger influence in the behavior of the system soil-structure. The behavior of the soil-structure system is simulated using the Mohr-Coulomb and hardening soil constitutive models. The Mohr-Coulomb and hardening soil constitutive models are compared in the forecast of the deformations. Finally, it is made the forecast of the level of damages to a hypothetical building caused by the braced excavations