O comportamento mecânico de vigas em alvenaria estrutural submetidas ao cisalhamento é abordado de forma aprofundada neste trabalho. São apresentados neste estudo um extensivo levantamento bibliográfico, o qual estabelece um panorama sobre o tema, um programa experimental com ensaios de caracterização do material alvenaria e de vigas em escala natural e um estudo numérico das vigas ensaiadas em laboratório. Na etapa de caracterização dos materiais o comportamento compósito da alvenaria é analisado por meio de prismas submetidos à compressão em duas direções ortogonais, normal e paralela à junta. Para o estudo das vigas são realizados trinta e sete ensaios, nos quais são avaliadas as influências da geometria, das taxas de armaduras e da relação a/d (em que a é a distância da carga aplicada até o apoio e d é a altura útil) na capacidade resistente ao cisalhamento. Posteriormente, é realizada a modelagem numérica através do software DIANA® com o propósito de complementar as análises dos ensaios. A partir dos resultados experimentais e numéricos pôde-se concluir que, com exceção das vigas com armaduras longitudinais de 10 mm de diâmetro, os demais modelos atingiram a ruína por cisalhamento, devido à ausência de estribos ou pela sua insuficiência. O aumento da taxa de armadura longitudinal de 0,45 para 1,18% resultou em um incremento de 18,4% na resistência ao cisalhamento convencional. Para as duas geometrias (vigas com duas e três fiadas) e as duas relações a/d (0,77 e 1,72), constatou-se que não há uma melhora significativa na capacidade resistente quando a taxa de armadura transversal é aumentada de 0,05 para 0,07%. Os mecanismos resistentes, como o efeito de pino, foram efetivos na resistência dos modelos. Por fim, as análises numéricas reproduziram de forma satisfatória os experimentos, tanto no que diz respeito ao comportamento pré e pós-pico quanto na previsão da força última. / This work is an in depth study about the mechanical behaviour of masonry beams subjected to shear forces. An extensive literature review, which establishes a panorama on the subject, an experimental program considering material characterization and full scale beams tests and a numerical study for the tested beams are presented. For the beams, thirty seven tests are carried out in which the influence of geometry, reinforcements ratio and a/d ratio (where a is the distance from the load to adjacent support and d is the effective depth) on the shear strength are evaluated. Computational modelling is performed using the DIANA® software in order to complement the experimental results. From the experimental and numerical results it was possible to conclude that, except for beams with 10 mm diameter steel bar, the other models failed in shear, due to the absence of stirrups or their insufficiency. An increase in longitudinal reinforcement ratio from 0,45 to 1,18% improved the theoretical shear strength in 18,4%. For the beams with two and three courses and for a/d ratios 0,77 and 1,72 it was found that there is no significant improvement on the load capacity when the transverse reinforcement ratio is increased from 0,05 to 0,07%. Shear strength mechanisms, such as the dowel action, were effective in the models load capacity. Finally, the numerical analyzes satisfactorily reproduced the experiments, regarding to the pre and post-peak behaviour and in the prediction of the ultimate load.

L’intégrité de surface a un rôle significatif sur la tenue en fatigue des composants usinés. Des spécifications particulières émergent de la part des fabricants et particulièrement de ceux de l’aéronautique. Les trous percés sont des zones critiques à partir desquelles des endommagements peuvent se produire. Néanmoins les contraintes résiduelles sont peu étudiées en perçage. Elles émanent de phénomènes multi-physiques issus de l’opération de perçage difficilement identifiables à cause du confinement du trou. Ce rapport présente les travaux expérimentaux et numériques mis en œuvre au cours de la thèse. Le projet s’est d’abord focalisé autour de l’identification des phénomènes physiques mis en jeu pendant l’opération de perçage pour différents modes de lubrification et sur l’analyse des contraintes résiduelles sur la surface du trou percé. Ce premier volet expérimental a posé les bases de compréhension nécessaires au développement des modèles numériques.Les développements numériques s’articulent autour de deux axes. Le premier consiste à représenter l’opération de perçage. L’état de l’art ainsi qu’une étude préalable ont permis d’identifier les difficultés liées à la modélisation numérique d’une opération de perçage pour des longueurs percées significatives. Le premier modèle développé répond à cette problématique et détermine les sollicitations induites par le perçage nécessaires au calcul des contraintes résiduelles. Le deuxième axe de développement numérique permet de prédire les contraintes résiduelles présentes dans une pièce percée à partir des chargements issus du premier modèle. / The surface integrity has a significant impact on the fatigue life of the machined parts. New requirements appear from manufacturers and especially from aeronautical industrialists. Drilling holes are critical and can damage the component. Nevertheless, residual stresses are not studied a lot in drilling processes. The residual stresses created are a result of multi-physical phenomena during drilling processes. It is difficult to identify them due to the confinement of the hole. In the current study, experimental tests are realized and numerical model of drilling surface integrity was developed. First, experimental works were performed in several lubrication conditions to understand physical phenomena which lead to residual stresses in the drilled workpiece. The numerical developments are set-up about two sections. The first numerical model represents the drilling operation. The state of the art and an initial study were shown that the actual numerical models are not able to simulate a drilling operation in an important drilling depth. So the first numerical model gives an estimation of loads induced by the drilling operation and necessary to compute residual stresses. Finally, the second numerical model simulates residual stresses in a drilled part taking in account loads provided.

There is a growing interest in tidal energy, owing to its predictable nature in comparison to other renewable sources. In the case of the UK, its importance also lies on the availability of exploitable areas as well as their total capacity, which is estimated to cover more than 20% of the country demand. However, the level of development of this kind of technology is still far behind other types of renewable energy. However, several studies focused on a variety of individual devices, followed by more recent research on the deployment of large arrays or tidal farms. Potential sites for energy extraction can be found in narrows between islands and the coast or estuaries. The latter present some advantages for the installation and the connection to the grid but estuaries are often prone to flood risk from tides and surges. Therefore, the objective of this thesis is to evaluate the effect that very large groups of turbines could have on peak water levels during flooding events in the case of being deployed in estuarine areas. For that purpose, a new methodology has been developed, which implies the use of a numerical model (MIKE 21 by DHI), and it has been demonstrated against a real case study in the UK: the Solway Firth estuary. Another objective has consisted of integrating in this thesis the results from detailed CFD modelling and optimisation techniques involved in the project. A literature review has been carried out in order to identify the current state of the art for the different subjects considered in the thesis. Different aspects of the numerical model used for this study (MIKE 21) have been presented and the modelling of the turbines within the code has been validated against experimental and CFD data. The procedure to include large numbers of turbines in the code is also developed. An analysis has been done of the different estuaries existing in the UK suitable for tidal energy extraction, identifying their main geometrical features. Based on this, idealised models of estuaries have been used to assess the influence that the channel geometry could have on the impact of tidal farms under extreme water levels. The effect has been measured by comparing the results of the numerical model between the case with and without turbines under different flooding scenarios. Finally, the same methodology has been applied to a real case study selected from the previous group of estuaries namely the Solway Firth. An initial model has been created, according to the available data at the start of the research, which contained some errors related to the water depth at the intertidal areas in the upper estuary. Therefore, when a more realistic dataset became available, an improved model was created. The improved model has been used to assess the effects of tidal farms in the estuary under a coastal flooding event. It is concluded that there is significant influence of the channel geometry over the locations where the maximum changes in water levels due to the tidal farms will happen. Nevertheless, the effects seem to be more relevant in terms of the decrease rather than the increase of peak water levels for all geometries and the maximum changes seem to be in the order of dm. This is in agreement with the results of the Solway Firth models and can be summarised as a positive net effect over flood risk. On the other hand, a concern has been raised about the impact on intertidal areas, which could be the subject of future research.

Les modèles numériques sont un outil complémentaire pour la prédiction de la corrosion. L'objectif de cette thèse est de développer un modèle de corrosion reposant sur la méthode des automates cellulaires pour l'étude de l'évolution morphologique des surfaces, ainsi que de la cinétique de corrosion. Le modèle développé couple les demi-réactions électrochimiques d'oxydation et de réduction. Au niveau cinétique, la simulation par automates cellulaires peut alors reproduire les courbes intensité-potentiel d'une réaction redox sur électrode inerte. L'échelle spatio-temporelle choisie décrit des phénomènes de corrosion à l'échelle mésoscopique, niveau intermédiaire par rapport aux approches habituelles. Dans notre modèle, les probabilités rendent compte de la nature stochastique des réactions anodiques et cathodiques. Cette étude nous a permis de décrire l'évolution de la morphologie de la corrosion dans différents contextes: corrosion généralisée, corrosion par piqûre et corrosion en milieu confiné. Deux régimes de corrosion ont été observés: un régime de corrosion uniforme dans lequel les demi-réactions sont distribuées de manière homogène suivi par un régime de corrosion localisée, caractérisé par une séparation spatiale des zones cathodiques et anodiques. / Numerical modelling is complementary tool for corrosion prediction. The objective of this work is to develop a corrosion model by means of a probabilistic cellular automata approach at a mesoscopic scale. In this work, we study the morphological evolution and kinetics of corrosion. This model couples electrochemical oxydation and reduction reactions. Regarding kinetics, cellular automata models are able to describe current as a function of the applied potential for a redox reaction on an inert electrode. The inclusion of probabilities allows the description of the stochastic nature of anodic and cathodic reactions. Corrosion morphology has been studied in different context: generalised corrosion, pitting corrosion and corrosion in an occluded environment. A general tendency of two regimes is found. A first regime of uniform corrosion where the anodic and cathodic reactions occur homogeneously over the surface. A second regime of localized corrosion when there is a spatial separation of anodic and cathodic zones, with an increase of anodic reaction rate.

No description available.

La congélation artificielle des terrains est une technique d'imperméabilisation et de renforcement des terrains régulièrement employée dans le génie civil et l'industrie minière. Dans un objectif de prédiction fiable de l'évolution de la congélation dans le milieu poreux, cette recherche propose deux nouveaux modèles numériques permettant la simulation du problème global de la congélation artificielle des terrains. Un premier modèle a pour objectif la représentation des mécanismes couplés thermo-hydrauliques associés à la congélation du matériau tandis qu'un deuxième modèle se concentre sur l'estimation des échanges de chaleur entre un puits de congélation et le terrain environnant. Le modèle thermo-hydraulique, en plus d'être cohérent sur le plan thermodynamique, a été vérifié à la fois par rapport à des solutions analytiques et par rapport à des résultats expérimentaux obtenus à grande échelle en conditions d'écoulements importants. Le modèle puits-terrain adopte une approche innovante par rapport à la bibliographie. Il permet de déterminer les conditions aux limites des modèles de congélation des terrains, difficiles à connaître en pratique, et d'optimiser les conditions opératoires du système grâce à des temps de simulation limités. De par les hypothèses considérées, leur fiabilité et leur praticité d'utilisation, ces deux modèles sont particulièrement adaptés à des sites industriels comme celui de la mine d'uranium de Cigar Lake (Canada) qui présente deux contraintes majeures : la présence potentielle d'écoulements importants et la forte hétérogénéité des terrains à congeler. Dans de tels contextes, des applications d'utilisation conjointe des deux modèles ou non sont présentées par rapport à des cas simples et au cas industriel de Cigar Lake. Ils peuvent ainsi être employés pour prédire l'évolution de la congélation dans le terrain en tenant compte des interactions thermo-hydrauliques, pour optimiser le système de congélation, ou encore pour évaluer l'impact sur la progression des zones congelées de conditions géologiques, hydrogéologiques et opératoires particulières. / Artificial ground freezing is a ground sealing and reinforcement technique regularly used in civil and mining engineering. In order to reliably predict the freezing evolution in the porous medium, this research offers two new numerical models allowing the simulation of the global problem of artificial ground freezing. A first model aims at representing the thermo-hydraulic coupled mechanisms associated with the material freezing while a second model focuses on the estimation of heat transfers between a freeze pipe and the surrounding ground. The thermo-hydraulic model, in addition to being thermodynamically consistent, has been verified both with respect to analytical solutions and large- scale experimental results obtained under conditions of high water flow velocity. The pipe-ground model adopts an innovative approach compared with literature. It allows to determine the boundary conditions of the ground freezing models, not readily available in practice, and to optimize the operating conditions of the system thanks to limited simulation times. By the considered assumptions, their reliability and their practicality, these two models are particularly well adapted to industrial sites like the uranium mine Cigar Lake (Canada) which presents two major constraints: the potential presence of high seepage-flow velocities and the strong ground heterogeneity. In these contexts, applications of the two models, jointly used or not, are presented with respect to simple cases and to the industrial case of Cigar Lake. They can be employed to predict the freezing evolution in the ground considering the thermo-hydraulic interactions, to optimize the freezing system, or to evaluate the impact of specific geological, hydrogeological and operating conditions on the freezing progress.

Le traitement des sols à la chaux est une méthode couramment utilisée pour améliorer les propriétés mécaniques de sols aux performances insuffisantes. Cependant, ces améliorations mécaniques ne sont pas prises en compte dans les calculs de dimensionnement. Cette thèse propose une méthodologie pour pallier à ce problème. Un programme expérimental approfondi est réalisé afin de décrire avec précision le comportement mécanique d’un sol traité et les processus associés à la structuration introduite par le traitement. La composition chimique, et notamment la quantité de composés cimentaires hydratés, est déterminée par analyses thermogravimétriques et thermodifférentielles. Un couplage non-linéaire entre la quantité d’hydrates et la limite élastique se basant sur ces résultats expérimentaux est proposé. À partir de ces résultats, une nouvelle formulation a été développée afin de modéliser la dégradation de la structure en plasticité, et a servi au développement d’une nouvelle loi de comportement élasto-plastique basée sur le modèle de Cam Clay Modifié. Cette dernière a montré reproduire correctement les principaux traits de comportement spécifiques aux sols traités. Il est démontré que ce modèle est également adapté aux sols naturellement structurés. Afin de prendre en compte les effets du traitement et la présence de structure dans le dimensionnement, un programme basé sur la méthode des éléments finis, comprenant le pré- et le post-processing de la géométrie et des résultats du problème, a été développé. Une validation rigoureuse a confirmé l'implémentation correcte de la méthode et son potentiel pour l’optimisation du dimensionnement des ouvrages / The effects of lime treatment on the mechanical properties of soils are usually not accounted for in the design of geotechnical structures. As a result the potential of lime treatment has not been fully exploited. In this thesis, a comprehensive experimental program has been carried out to identity the key features of the mechanical behaviour of structured materials. The chemical modifications arising from lime treatment were quantified using thermal analysis methods. From these results a non-linear chemo-mechanical coupling was established between the concentration of cementitious compounds and the yield stress. Using these results, a new formulation to model the degradation of the structure at yield has been developed and implemented in a constitutive model for structured materials. This new model, developed in the framework of the Modified Cam Clay model, requires a limited number of additional parameters that all have a physical meaning and can all be determined from a single isotropic compression test. The model has proven to be successful in reproducing the key features of structured materials and for the modelling of the mechanical behaviour of lime treated specimens under various stress paths. Due to similarities in behaviour, it is shown that the formulation is also suitable for naturally structured soils. To account for a structured material in the design of geotechnical structures, a fully functional finite element program for elasto-plastic problems was developed including the pre- and post-processing of the results. A thorough validation has confirmed the good implementation of the finite element method and its suitability for the modelling of complex geometries involving structured materials

The Florida Everglades has a long history of anthropogenic changes which have impacted the quantity and quality of water entering the system. Since the construction of Tamiami Trail in the 1920's, overland flow to the Florida Everglades has decreased significantly, impacting ecosystems from the wetlands to the estuary. The MIKE Marsh Model of Everglades National Park (M3ENP) is a numerical model, which simulates Everglades National Park (ENP) hydrology using MIKE SHE/MIKE 11software. This model has been developed to determine the parameters that effect Everglades hydrology and understand the impact of specific flow changes on the hydrology of the system. As part of the effort to return flows to the historical levels, several changes to the existing water management infrastructure have been implemented or are in the design phase. Bridge construction scenarios were programed into the M3ENP model to review the effect of these structural changes and evaluate the potential impacts on water levels and hydroperiods in the receiving Northeast Shark Slough ecosystem. These scenarios have shown critical water level increases in an area which has been in decline due to low water levels. Results from this work may help guide future decisions for restoration designs. Excess phosphorus entering Everglades National Park in South Florida may promote the growth of more phosphorus-opportunistic species and alter the food chain from the bottom up. Two phosphorus transport methods were developed into the M3ENP hydrodynamic model to determine the factors affecting phosphorus transport and the impact of bridge construction on water quality. Results showed that while phosphorus concentrations in surface waters decreased overall, some areas within ENP interior may experience an increase in phosphorus loading which the addition of bridges to Tamiami Trail. Finally, phosphorus data and modeled water level data was used to evaluate the spectral response of Everglades vegetation to increasing phosphorus availability using Landsat imagery.

For the design of deep excavations, codes and standards advise to base estimates of wall deflections and ground movements on empirical data. Due to the limited number of case studies on circular excavations it is nearly impossible to find comparable projects under similar conditions. Therefore designers have to adopt conservative approaches, which predict larger ground movements than probably occur in reality and thus lead to more expensive structures and protective measures. Further uncertainty is induced for diaphragm wall shafts. The discontinuous nature of the wall due to the joints between the individual panels may cause anisotropic wall behaviour. There is a complete lack of understanding if, and how, the design of diaphragm wall shafts should consider anisotropic wall stiffness. The construction of Thames Water's Abbey Mills shaft in East London provided a unique opportunity to monitor the structural performance and the ground movements of one of the largest shafts ever built in the UK. The 71 m deep excavation penetrates a typical London strata and one third is in unweathered medium to hard Chalk. The monitoring scheme included distributed fibre optic strain sensing instrumentation and conventional inclinometers in the shaft wall to measure bending and hoop strains, as well as wall deflections during several construction stages. Further inclinometers and extensometers were installed around the shaft to monitor surface and sub-surface ground movements. The monitoring results were then compared to the initial PLAXIS design predictions. A further numerical investigation was conducted in FLAC2D which allowed a more flexible parametric study. The measured bending moments during shaft excavation exceeded the predictions mainly in the wall sections in the Chalk group. It was found that this was caused by assigning a low cohesion to the Chalk to induce conservative ground movements, so that the Chalk yielded in the analysis. In reality however, it remained elastic and hence induced larger bending moments in the wall. For future excavations in Chalk it is recommended to investigate the effect of a low and a high cohesion of the Chalk on the wall bending moment. The hoop strain measurements indicate that the shaft has undergone a three-dimensional deformation pattern during a dewatering trial prior to shaft excavation. The parametric study on wall anisotropy suggests that the shaft wall behaved like a cylindrical shell with isotropic stiffness, where the joints between the panels do not reduce the circumferential stiffness. Further numerical simulations varied the shaft wall thickness and the at rest lateral earth pressure coefficient in the Chalk. The results showed that the wall thickness has a minor influence on its deflection and hence thinner walls might be feasible for future shafts. The at rest lateral earth pressure coefficient of the Chalk appeared to be appropriately picked with 1.0 in the initial design. Above all, it was shown that wall deflections were very small with less than 4 mm. Correspondingly small ground movements were measured throughout shaft excavation. Empirical formulas on the other hand predict large settlements between 40 and 105 mm. Numerical predictions were much closer to the measurements and showed that small heaves occurred due to soil swelling caused by removal of overburden pressure. For future shaft designs it is hence advised against the use of empirical formulas derived from case studies under different conditions. It may furthermore not be necessary to implement expensive large-scale monitoring schemes, as it has been confirmed that ground movements around diaphragm wall shafts are minimal and that risks are low. The findings from this study provide valuable information for future excavations, which can be applied to the shafts constructed for the forthcoming Thames Tideway Tunnel project.

The drainage behaviour of sports pitches is not well understood nor has performance been measured in the past. Within planning authorities there is a perceived contribution of pitch water discharge to local flood risk; whereby all the rainfall surface runoff is rapidly channelled through the drainage system to the pitch outfall. However, empirical evidence from industry suggested that this may not be a realistic assumption from observations of low drainage volumes yielded from pitch drainage systems. Furthermore, discharge constraints imposed have in many cases resulted in grossly over-designed off-line drainage attenuation systems for new sports developments through lack of understanding. In contrast, sports pitches indeed have the potential to enhance the attenuation performance of the subsoils and provide localised effective management of surface water runoff, and a significant storage volume if designed appropriately The findings in this thesis confirm that pitch bases demonstrate the key functions that are in fact reflected in the design requirements of Sustainable Urban Drainage Systems (SuDS). This PhD research project was conducted to investigate and document the performance of common pitch construction and drainage systems to better characterise the key drainage mechanisms that occur and control the flow of surface rain water through the pitch to the discharge outfall. The project developed a triangulated approach to the investigations, comprising: field measurements of climate and discharge behaviour at a range of artificial and natural turf pitches in England; laboratory physical model testing of pitch component hydraulics; and predictive mathematical modelling of how a pitch system may be expected to perform hydraulically based on key material and system drainage principles. The field monitoring systems were developed as part of the research, as was bespoke laboratory physical simulation of a pitch construction. It was found that very variable yields (% out versus % in) of water were detected from the monitored field sites. The values varied across a range of < 1 to 88%, with the natural turf providing higher yields in general. The antecedent weather patterns did not show a clear relationship with yield as might have been expected. However, it was not always possible to retrieve detailed information on the subsoil conditions or hydraulic capability reducing the conclusiveness of the discharge flow measurements. The scaled laboratory testing of pitch materials established the importance and magnitude of barriers to percolation of surface water through the layers of the pitch constructions, in particular artificial pitch profiles. It was found that a significant proportion of the total rainfall head was required to instigate percolation of surface water through the carpet and into the pitch i.e. breakthrough head. In addition, several constituent pitch materials exhibited water retention characteristics that reduced that rate of free percolation of surface water through the pitch profile. The net impact is to reduce the net available head of water to further drive flow through the layers to the pipe network drainage system. A conceptual hydraulic model, developed from the literature, was further developed into a simple numerical model. The model was informed by parameters determined from the laboratory measurements and key groundwater drainage flow theory to attempt to replicate a pitch drainage system. It was envisaged that the models would be validated by the field data, although this proved challenging as a result of the field data variability and the multivariate nature of the influences on flows measured. A key finding of the modelling was further establishing the likely head of water generated at the interfaces between the bottom of the granular sub-base and the pipe collection drainage system beneath. This resulted in limited pipe infiltration and low total flows to the outfall, further corroborating the project field results and the anecdotal observations from practitioners. The combined unique data sets provide a refined model for sports pitch drainage to both reinforce understanding and inform practical design and operation.