Rozprawy doktorskie na temat „GRANULAR PILES”

Granular materials are in abundance both in nature and in industry. They are of considerable interest to both the engineering and physics communities, due to their practical importance and many unsolved scientific challenges. This thesis is concerned with the “pressure dip” phenomenon underneath a granular pile (commonly known as the “sandpile problem”) which has attracted great attention in the past few decades. Underneath a sandpile that is formed by funnel feeding, a significant minimum (dip) in the vertical base pressure is often found below the apex where a maximum pressure is intuitively expected. Despite a large amount of work undertaken, a comprehensive understanding of this phenomenon remains elusive. This thesis presents an extensive study investigating the underlying mechanism of this phenomenon and also its implications on pressures in silos. The study started with a laboratory test programme of conical mini iron pellet piles. The results confirmed that the pressure dip is a robust phenomenon. It was shown that, under certain deposition radius with uniform deposition across the deposition area, a dip emerges firstly in a ring shape when the radius of the formed pile is small and comparable to the deposition radius. With the increase of the pile radius upon further deposition, the dip ring gradually evolves to a central dip as the pressure at outer radius eventually overtakes that in the centre. The magnitude of the dip was found to be significantly affected by the deposition rate but almost unaffected by the deposition height.

This thesis explores the design of flexible pipes, buried in shallow trenches with dry sand backfill. The thesis reports the comprehensive analysis of twenty-two full-scale load tests conducted between 1989 and 1991 on pipe installations, mainly within a laboratory facility, at the University of South Australia. The pipes were highly flexible, spirally-wound, uPVC pipes, ranging in diameter from 300 to 450 mm. Guidelines were required by industry for safe cover heights for these pipes when subjected to construction traffic. The tests were designed by, and conducted under the supervision of, the author, prior to the author undertaking this thesis. As current design approaches for pipes could not anticipate the large loading settlements and hence, soil plasticity, experienced in these tests, finite element analyses were attempted. Extensive investigations of the materials in the installations were undertaken to permit finite element modelling of the buried pipe installations. In particular, a series of large strain triaxial tests were conducted on the sand backfill in the buried pipe installations, to provide an understanding of the sand behaviour in terms of critical state theory. Subsequently a constitutive model for the soil was developed. The soil model was validated before implementation in an element of finite element program, AFENA (Carter and Balaam, 1995). Single element modelling of the triaxial tests proved invaluable in obtaining material constants for the soil model. The new element was applied successfully to the analysis of a side-constrained, plate loading test on the sand. The simulation of the buried pipe tests was shown to require three-dimensional finite element analysis to approach the observed pipe-soil behaviour. Non-compliant side boundary conditions were ultimately adjudged chiefly responsible for the difficulty in matching the experimental data. The value of numerical analyses performed in tandem with physical testing was apparent, albeit in hindsight. The research has identified the prediction of vertical soil pressure above the pipe due to external loading as being the major difficulty for designers. Based on the finite element analyses of the field tests, a preliminary simple expression was developed for estimation of these pressures, which could be used with currently available design approaches to reasonably predict pipe deflections.

This thesis explores the design of flexible pipes, buried in shallow trenches with dry sand backfill. The thesis reports the comprehensive analysis of twenty-two full-scale load tests conducted between 1989 and 1991 on pipe installations, mainly within a laboratory facility, at the University of South Australia. The pipes were highly flexible, spirally-wound, uPVC pipes, ranging in diameter from 300 to 450 mm. Guidelines were required by industry for safe cover heights for these pipes when subjected to construction traffic. The tests were designed by, and conducted under the supervision of, the author, prior to the author undertaking this thesis. As current design approaches for pipes could not anticipate the large loading settlements and hence, soil plasticity, experienced in these tests, finite element analyses were attempted. Extensive investigations of the materials in the installations were undertaken to permit finite element modelling of the buried pipe installations. In particular, a series of large strain triaxial tests were conducted on the sand backfill in the buried pipe installations, to provide an understanding of the sand behaviour in terms of critical state theory. Subsequently a constitutive model for the soil was developed. The soil model was validated before implementation in an element of finite element program, AFENA (Carter and Balaam, 1995). Single element modelling of the triaxial tests proved invaluable in obtaining material constants for the soil model. The new element was applied successfully to the analysis of a side-constrained, plate loading test on the sand. The simulation of the buried pipe tests was shown to require three-dimensional finite element analysis to approach the observed pipe-soil behaviour. Non-compliant side boundary conditions were ultimately adjudged chiefly responsible for the difficulty in matching the experimental data. The value of numerical analyses performed in tandem with physical testing was apparent, albeit in hindsight. The research has identified the prediction of vertical soil pressure above the pipe due to external loading as being the major difficulty for designers. Based on the finite element analyses of the field tests, a preliminary simple expression was developed for estimation of these pressures, which could be used with currently available design approaches to reasonably predict pipe deflections.

L’objectif du travail présenté dans cette thèse est l'analyse et modélisation numérique des mécanismes de transfert de charge axiale entre sol-pieu, dans les sols granulaires. En utilisant un modèle élastoplastique tridimensionnel d'élément finis, une attention particulière est prêtée à la modélisation du comportement de l’interface sol-structure. Ainsi, les outils numériques nécessaires ont été mis en place et les outils existants ont été améliorés afin que, l'analyse de l'interaction sol-pieu soit faisable. Deux nouveaux modèles de comportement 3D sont implémentés dans le code d'éléments finis GEFDYN: un modèle d'interface et, pour le sol, une formulation axisymétrique du modèle multimécanismes de l’ECP, déjà existant et également connus sous le nom de Hujeux. La performance des deux modèles de comportement est comparée avec des résultats expérimentaux: d'abord, en utilisant des essais directs de cisaillement sol-structure et ensuite des essais de charge statiques de pieux en modèle physiques de centrifugeuse. La formulation théorique et l'exécution numérique des modèles constitutifs se sont donc avérées adéquats pour l'analyse des mécanismes de transfert de charge de sol-pieux, pour différents états initiaux du sol, différentes rugosités de la surface sol-pieux et différentes géométries. Finalement, l'applicabilité des modèles proposés est également étudiée pour un cas d’étude réel d’essais de charge statique de pieux forés et à tarière continus, menés dans le site expérimental ISC2 à l’occasion de la 2nd International Conference on the Site Characterization. L’identification des paramètres du sol et la simulation des essais de charge in-situ a été réalisé avec succés
The purpose of the work presented in this thesis, which has a theoretical and numerical character, is the analysis and numerical modelling of soil-pile load transfer mechanisms, in granular soils, when the pile is subjected to axial vertical loads. In the three dimensional elastoplastic finite element model used, particular attention is paid to modelling soil-structure interface behavior. The necessary numerical tools were implemented and the existing ones enhanced so that, the analysis of the soil-pile interaction problem is feasible. Two newly implemented 3D constitutive laws, in the GEFDYN finite element code, are proposed: an interface model and, for soil, an axisymmetric formulation of the existing ECP multimechanism model, also known as Hujeux model. The performance of both constitutive models is compared with experimental results. First, using soil-structure direct shear tests and then, using results of static pile load tests of centrifuge physical models. The theoretical formulation and numerical implementation of the constitutive models proved to be adequate for the analysis of the soil-pile load transfer mechanisms for different soil initial states, soil-pile surface roughness conditions, and different geometries. Finally, the applicability of the proposed models, is also studied for a real case study of pile static load tests carried out in the ISC'2 experimental site, at the occasion of the 2nd International Conference on the Site Characterization. Soil’s laboratory characterization tests and in-situ pile static load tests on bored and CFA piles are simulated, and results successfully compared

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2004.
Includes bibliographical references (p. 45-46).
In this thesis, I investigate the static and dynamic properties of a granular heap made cohesive by an interstitial fluid. I present the results of experimental work measuring the maximum angle of stability and the angle of repose of such a pile in a rotating drum geometry. I discuss existing models for the stability of a cohesive granular pile and present a new model that predicts the maximum angle of stability from the pile's geometry and from the cohesive forces between grains. This model agrees well with experiment and suggests that friction is insignificant in determining the maximum angle of stability. In addition, I investigate the effect of the viscosity of the interstitial fluid on the dynamic properties of a granular pile. In particular, I examine the transition from stick-slip motion to continuous motion as well as the effect of viscosity on the angle of repose of the granular pile. I offer a qualitative explanation for my observations of these phenomena.
by Sarah Alice Nowak.
S.B.

No autorizada por el autor para ser publicada a texto completo
La lixiviación en pilas es una de las técnicas más utilizadas en el mundo para la extracción de cobre en minerales de baja ley. Sobre la pila se vierte una solución ácida que separa el cobre de la roca, dicha solución percola hacia los sistemas de drenaje ubicados en la base de la pila compuestos por material granular permeable (denominado “overliner”) y tuberías ranuradas de HDPE (polietileno de alta densidad). El objetivo de la memoria es estudiar el impacto del overliner sobre las tuberías e identificar el parámetro del suelo que tiene mayor influencia sobre la deflexión vertical de éstas al aplicar presiones de hasta 3.6 [MPa] equivalentes a una pila de 200[m] de altura. Para lograr lo anterior, se desarrolló un modelo de diferencias finitas en FLAC 2D, el cual fue calibrado con resultados de ensayos de aplastamiento de gran escala a tuberías de 4” de HDPE. El análisis de sensibilidad permitió concluir que el parámetro más determinante en la deformación vertical de la tubería corresponde al Módulo de Young del material granular protector que recubre las tuberías (overliner). Además se observó que el uso de zanjas para la colocación de las tuberías disminuía la deformación de éstas, facilitando la generación de efecto arco.

Cette thèse, composée de deux parties, porte sur l’étude d’instabilités au sein d’un milieugranulaire.La première partie de cette thèse est consacrée à l’instabilité de tôle ondulée, c’est-àdirel’apparition d’un motif de rides sur une piste soumise au passage répété de véhicules.Nos travaux expérimentaux ainsi que des simulations numériques de dynamique moléculairenous ont permis de progresser dans la compréhension de ce phénomène. Pour uneroue rigide tirée à vitesse constante, nous avons étudié quantitativement l’impact de lacohésion du milieu granulaire sur les caractéristiques de l’instabilité : vitesse critique, longueurd’onde et taux de croissance. Nous avons enfin entrepris des études préliminairessur un fluide à seuil simple : un microgel de carbopol.Dans la seconde partie, nous étudions la ségrégation granulaire au sein des astéroïdeslâches. Plusieurs indices montrent qu’un grand nombre d’entre eux sont des empilementsde grains, sans cohésion interne et liés par la gravité. Leur répartition n’est pas homogène,avec des zones lisses recouvertes de fines poussières et d’autres où s’accumulent les grosblocs. Nous avons simulé numériquement un empilement granulaire et nous l’avons soumisà des secousses répétées : nous avons réussi à reproduire la ségrégation. Nous avonsétudié l’influence des paramètres physiques et numériques sur le niveau de ségrégation etla dynamique du phénomène. Nous nous sommes aussi intéressés aux phénomènes physiquespouvant causer la ségrégation : convection granulaire, tamisage cinétique, pressionde déplétion, etc. Enfin, nous avons mis en évidence une instabilité azimutale qui peutexpliquer les observations faites pendant les missions spatiales
This thesis, consisting of two parts, is focusing on instabilities into a granular assembly.The first part deals with washboard road instability, which is the growth of a ripplepattern on a track subjected to repeated passages of vehicles. Our experimental work aswell as soft spheres numerical simulations provide us a better understanding of this phenomenon.In the case of a rigid wheel dragged at constant velocity, we quantitatively studiedthe impact of the cohesion into the granular media on the main features of the instability :critical velocity, wavelength and growth rates. Finally, we have begun preliminary studieson a yield stress fluid, namely a carbopol microgel.The second part is devoted to the granular segregation in asteroids. Several keys showthat a significant part of them are rubble-piles, without internal cohesion and held togetherby their weak self-gravity. The distribution of grains is heterogeneous : while some regionsconsist in fine sand or powder, large boulders seem to accumulate in other parts. Wenumerically simulated a granular pile and subjected it to repeated quakes : we managedto reproduce segregation. We studied the influence of physical and numerical parameterson the segregation level and the dynamics of the phenomenon. We also investigate variouscauses of the segregation : granular convection, kinetic sieving, depletion pressure, etc.Finally, we highlighted an azimuthal segregation which can explain observations duringspatial missions

Etude essentiellement experimentale, comportant, apres un bilan des etudes deja realisees, une etude preliminaire de l'influence des conditions experimentales sur le comportement d'un sable dans un essai triaxial de compression (role de l'antifrottage de et de l'elancement de l'echantillon); ensuite une etude du comportement d'un materiau classique (sable quartzitique de carriere) et d'un materiau a porosite intragranulaire (sable calcaire provenant d'un site petrolier marin). Ebauche aussi d'une approche microstructurale. Le niveau de contrainte envisage (superieur a 10 mpa) peut etre developpe en pointe des pieux battus

Les bétons lourds sont des bétons spéciaux de haute densité qui dépasse les 3000 kg/m3 comparativement aux bétons ordinaires (2350 kg/m3). Généralement, ils sont utilisés comme des écrans de protection contre les rayonnements ionisants au niveau des installations nucléaires ce qui permet de réaliser des ouvrages porteurs assurant une protection contre les rayons Gamma et d’autres rayons radioactifs. Ils sont utilisés aussi comme des lests dans les applications nécessitant un contre poids important. Des granulats de forte densité sont utilisés pour la fabrication de ces bétons comme la barytine (sulphate de baryum), l’hématite et la magnétite (minerais à base d’oxydes de fer), des déchets ferreux, grenailles de fer ou d’acier… grâce aux propriétés particulières qui les caractérisent tel que la haute densité, la faible abrasivité et la neutralité chimique. Cette étude porte sur l’influence de ces additions utilisées sur le comportement rhéologique (viscosité plastique et seuil de cisaillement) et mécanique des bétons lourds confectionnés. Les résultats obtenus ont montré que l’augmentation du pourcentage d’ajout d’addition (de 38% jusqu’à 54%) provoque une augmentation de la viscosité plastique et du seuil de cisaillement. L’objectif principal de cette présente recherche, est d’étudier la faisabilité d’utiliser ces bétons lourds dans les fondations profondes et plus précisément dans le bétonnage des pieux forés. Afin de répondre à cet objectif, un dispositif équivalent reproduisant à échelle réduite le bétonnage des pieux forés et permettant donc d’établir des corrélations entre la mise en place du béton avec le dispositif proposé et la mise en place réelle du béton sur les chantiers, a été mis en place. Plusieurs configurations de fixation du tube plongeur ont été étudiées. L’ensemble des résultats obtenus a permis de régler la hauteur de fixation du tube plongeur à 15 cm du fond du pieu afin de favoriser la sortie du premier béton et l’évacuation du fluide de forage. Des simulations numériques de l’écoulement d’un fluide à seuil en présence d’un deuxième fluide ont étés réalisées en utilisant COMSOL Multiphysics. L’influence des paramètres rhéologiques et de la densité des bétons utilisés dans le bétonnage des pieux a été étudiée à travers ces simulations. Il a été montré que l’augmentation du béton utilisé (de 2435 kg/m3 à 3064 k/m3) augmente le volume de fluide évacué c’est-à-dire, plus le béton est dense plus, il arrive à chasser le fluide et le remplacer dans le tube.Mots
Heavy concretes are special concretes of high density, which is almost 3000 kg/m3 instead of 2350 kg/m3 in the case of ordinary concretes. Usually, they are used as shields against ionizing radiation at nuclear facilities, which allows the construction of load-bearing structures providing protection against Gamma and other radioactive rays. They are also used as ballast in structures requiring a high weight. Aggregates and heavy additions are used for the manufacture of these concretes such as barite, hematite, magnetite, ferrous waste, granules of iron and steel, thanks to their particular properties such as high density, low abrasivity and chemical neutrality. This study deals with the influence of these additions used on the rheological (plastic viscosity and yield stress) and mechanical behavior of the heavy concretes made in order to highlight the effect of the density of the additions on the behavior of the concretes. The results obtained showed that the increase in the addition percentage (from 38% to 54%) causes an increase in the plastic viscosity and the yield stress. The main objective of this research is to study the feasibility of using these heavy concretes in deep foundations specifically in the concreting of bentonite-bored piles. In order to meet this objective, equivalent tests have been set up through the development of a device that simulates the concreting techniques applied at construction sites. Numerical simulations of concreting bentonite-bored piles have been performed using Comsol Multiphysics, through which the influence of rheological parameter and density of concretes was studied. It has been shown that increasing the concrete density from 2435 kg/m3 to 3064 kg/m3, increases the evacuated volume of drilling fluid

La réaction alcali-silice (RAS) est une réaction de dégradation des bétons. Le lithium est connu pour ses qualités d’inhibiteur de la RAS, malheureusement les quantités nécessaires à l’inhibition sont variables et les mécanismes par lesquels il agit sont encore mal connus. Les travaux menés au cours de cette thèse ont pour but d’évaluer l’efficacité du lithium à inhiber la RAS, ainsi que d’améliorer la compréhension de ses mécanismes d’action. L’efficacité de cinq composés de lithium a tout d’abord été évaluée en milieu modèle (milieu simplifié simulant la RAS), à l’aide d’un granulat réactif : le silex. Le suivi de paramètres physico-chimiques traduisant l’altération de la silice avec l’ajout de lithium a révélé que l’inhibition de la RAS n’évolue pas de manière linéaire avec la quantité de lithium introduite (effet seuil) et que le contre-ion accompagnant le lithium n’a pas d’effets sur l’inhibition. Le suivi de l’expansion d’éprouvettes de mortier contenant différentes quantités de LiOH pour trois granulats différents a également révélé la présence d’un effet seuil à l’efficacité du lithium. Afin de valoriser des déchets industriels, deux scories lithinifères ont été employées dans des mortiers et l’une d’elles s’est avérée capable d’inhiber la RAS par son contenu en lithium. Pour améliorer la compréhension des mécanismes d’inhibition, des éprouvettes de mortier dopées en LiOH ont été caractérisées par des techniques permettant de détecter le lithium telles que la ToF-SIMS. Celle-ci a révélé la présence du lithium au cœur des grains de silex dans une formulation inhibée, suggérant ainsi que le lithium inhibe la RAS en accroissant la stabilité de la silice réactive
Alkali-silica reaction (ASR) is a deleterious reaction taking place in concrete. Lithium is known to inhibit ASR, unfortunately the quantities of lithium required to enable inhibition fluctuate with the experimental conditions and the materials tested and the mechanisms by which this element inhibits ASR are not fully understood. The study presented in this report has two goals : assessing the quantities of lithium required to inhibit ASR and improving the understanding of the inhibition mechanisms. The influence of different lithium compounds on the inhibition of ASR was studied using model reactors (concrete sub-system simulating ASR) containing a reactive flint aggregate. The degradation of silica due to ASR was assessed by different chemical and physical reaction degrees. The results led to the following conclusions: the inhibition of ASR by lithium ions evolves nonlinearly with the quantity of lithium (threshold effect) and the counter-ion accompanying the lithium does not have a significant influence on ASR inhibition. The expansive behaviour of three different aggregates in mortars containing LiOH also displayed the threshold effect observed previously. In order to recycle industrial waste, two lithium-containing slags were used in mortar bars and one of them happened to be effective to inhibit ASR. Finally, to improve the understanding of ASR inhibition, mortar bars containing LiOH were analysed by techniques capable of detecting lithium such as ToF-SIMS. The latter revealed the presence of lithium within flint particles in a non-expansive bar, which suggests that lithium inhibits ASR by stabilising reactive silica

Soft soil reinforcement by inclusion is a growing technique caracterized by a pile grid and a granular embankment introduced between the reinforced soil and the structure. Unlike traditionnal methods, the load is partially transferred to the pile heads by arching in the embankment. The application area of this research focuses on the shallow foundations case, in which the thickness of the embankment is small. The litterature review shows that only a few studies were dedicated to that case, and that fundamental questions remains concerning the load transfer in the embankment. Chosen method for this research consists in two-dimensionnal physical modelling, analysis of the conducted simulations, and development of an analytical model in order to predict the load transfer to the piles by arching in the embankment. The results of this PhD thesis provide original elements of evidence of the load transfer in the studied system, proposes an analytical model based on block division of the granular embankment by shear bands - which is in good agreement with experimental data - and lead to a better understanding of arching in soils.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

Tese de doutoramento em Engenharia Mecânica, no ramo de Aerodinâmica Industrial e Engenharia do Vento, apresentada ao Departamento de Engenharia Mecânica da Faculdade de Ciências e Tecnologia da Universidade de Coimbra
The transport of soil particles by wind is of enormous relevance in a wide range of events from those related to agriculture (e.g., seed transport) to the formation and modification of the landscape. A classic example is sand dunes, which can be formed, moved, or entirely eroded due to aeolian processes. Still, aeolian transport of particles may cause serious damage in transportation, communications and severe environmental problems, such as the degradation of air quality due to dispersion of pollutants from stockpiles. The wind exposure will lead to the particles movement through several mechanisms, such as, suspension, creeping, saltation, and saltation bombardment. Consequently, the free surface will change over time due to entrainment and deposition phenomena. The main objective of this study is assessing the airflow characteristics over and around granular material complex three-dimensional piles when subjected to the wind erosion and its influence in the behavior of the free surface, as well as, in the sand emission rate. A literature review was made over the main subjects of interest to the present work, from the basics, such as granular material and aeolian transport mechanisms, to the key magnitudes involved in the wind erosion phenomena. Studies performed to calculate the dust emission from stockpiles are presented and reviewed along with the widely applied methodology from United States Environmental Protection Agency (USEPA). This methodology estimates the emission of particles from stockpiles only during specific erosion events, such as bursts, when in reality emissions occur in many other occasions. The present work offers the possibility of conducting the determination of emissions from stockpiles along time; this approach makes viable to follow the time-dependent evolution of the free surface enhancing in this way the accuracy of the predictions. Therefore, studies that are related to free surface progress are also reviewed. The present work has a significant experimental component, and the thesis describes in considerable detail the experimental apparatus and procedures, including wind tunnel, granular material, tested pile configurations and performed tests – in particular, erosion and shear stress (with Irwin probes) measurements. In addition, the use of Computational Fluid Dynamics (CFD) plays an important role in the present study; therefore, for completeness, key concepts related to CFD are included in this thesis along with a brief survey of studies that employ CFD methodology to evaluate aeolian erosion. The present CFD studies were conducted by using an open source CFD code – OpenFOAM (OF). The motivation for the selection of OF, as the CFD tool, is related to its wide acceptance in the scientific community; moreover, its application to the prediction and study of wind erosion is an original contribution to this field of research. Full description of the numerical model and its implementation are given along with the methodology used in the model validation. Two different pile configurations were studied - a two-dimensional triangular pile and a three-dimensional oblong pile. The increasing geometrical complexity of the piles allowed gaining gradual experience with the procedures and methodologies involved. The experimental and numerical studies for these cases and their results are analyzed and discussed. In what concerns the oblong piles, the numerical results are correlated with the registered free surface deformation of the piles and compared against other study available in the literature, in which oil film visualization tests were conducted and a different CFD tool was used. Considering that the model validation is partly performed against experimental results, particular attention was given to their accuracy. For the triangular piles, the comparison is primarily against the wall shear stress results obtained using the Irwin probes, which were built and calibrated for this work. The study of these probes was extensive and it led to an innovative and significant contribution to this field of research, which justifies an integrated, but autonomous Part B of this thesis. Due to the versatility of experimental apparatus built to assist the calibration of the Irwin probes, a more in-depth study was also carried out on the flow through rectangular ducts with a constant and variable cross-section. Finally, the main findings resulting from the present work are summed up and some recommendations for future work are given.
O transporte de partículas do solo pelo vento é de enorme relevância numa ampla gama de eventos, desde os relacionados com a agricultura (por exemplo, o transporte de sementes) até a formação e modificação da paisagem. Um exemplo clássico são as dunas de areia, que se podem formar, mover ou erodir totalmente devido a processos eólicos. Por outro lado, o transporte de partículas pode provocar sérios danos no sector dos transportes, comunicações e graves problemas ambientais, como a degradação da qualidade do ar devido à dispersão de poluentes provenientes de pilhas de armazenamento. A exposição ao vento pode levar ao movimento das partículas através de vários mecanismos, tais como, suspensão, arrastamento, saltação e bombardeamento das partículas em saltação. Consequentemente, a superfície livre irá mudar ao longo do tempo devido aos fenómenos de arrastamento e deposição. O objetivo principal deste estudo é investigar as características do fluxo de ar sobre e ao redor de pilhas tridimensionais (3D) complexas de material granular quando sujeitas à erosão do vento e avaliar a sua influência no comportamento da superfície livre, bem como na taxa de emissão. Uma revisão bibliográfica foi feita sobre os principais temas de interesse para o presente trabalho, desde o básico, como material granular e mecanismos de transporte eólicos, até às grandezas chave envolvidas nos fenómenos de erosão do vento. Estudos realizados para calcular a emissão de poeira de pilhas de armazenamento são apresentados e revistos juntamente com a metodologia, amplamente aplicada, da Agência de Proteção Ambiental dos Estados Unidos (United States Environmental Protection Agency - USEPA). Esta metodologia estima as emissões de partículas a partir de pilhas de armazenamento apenas durante eventos de erosão específicos, tais como rajadas, quando as emissões na realidade ocorrem em muitas outras ocasiões. O presente trabalho oferece a possibilidade de realizar a determinação de emissões de pilhas de armazenamento ao longo do tempo; esta abordagem torna viável seguir a evolução dependente do tempo da superfície livre, aumentando assim a precisão das previsões. Portanto, estudos relacionados com a evolução da superfície livre são também revistos. O presente trabalho tem uma componente experimental significativa, e a tese descreve em considerável detalhe a montagem experimental e os procedimentos, incluindo o túnel de vento, material granular, as configurações de pilhas testadas e os testes executadas – em particular, testes de erosão e de medição da tensão de atrito (com sondas Irwin). Adicionalmente, o uso da Dinâmica de Fluidos Computacional (em inglês: Computational Fluid Dynamics — CFD) desempenha um papel importante no presente estudo, assim sendo, para completar, conceitos chave relacionados a CFD estão incluídos nesta tese, juntamente com uma breve pesquisa de estudos que empregam a metodologia CFD para avaliar a erosão eólica. Os presentes estudos CFD foram realizados usando um software CFD de código aberto - OpenFOAM (OF). A motivação para a seleção do OF, como ferramenta CFD, está relacionada com a sua ampla aceitação na comunidade científica; e além disso, a sua aplicação na previsão e estudo da erosão eólica é uma contribuição original para este campo de pesquisa. A descrição completa do modelo numérico e da sua implementação são dadas juntamente com a metodologia utilizada na validação do modelo. Foram estudadas duas configurações de pilha diferentes - uma pilha triangular bidimensional (2D) e uma pilha tridimensional (3D) oblonga. A crescente complexidade geométrica das pilhas permitiu ganhar experiência de forma gradual com os procedimentos e metodologias envolvidos no estudo. Os estudos experimentais e numéricos para estes casos, bem como os seus resultados, são analisados e discutidos No que diz respeito às pilhas oblongas, os resultados numéricos são correlacionados com a deformação de superfície livre das pilhas e comparados com outro estudo disponível na literatura, no qual foram realizados testes de visualização de filmes de óleo e utilizada uma ferramenta CFD diferente. Considerando que a validação do modelo é parcialmente realizada através da comparação dados experimentais; especial atenção foi dada à sua precisão. Para as pilhas triangulares, a comparação é feita, principalmente, com resultados da tensão de atrito da parede medidos através das sondas Irwin, as quais foram construídas e calibradas para este trabalho. O estudo efetuado com estas sondas foi extenso e contribuiu de forma inovadora e significativa para esta área de pesquisa, o que justifica uma Parte B integrada, mas autónoma desta tese. Devido à versatilidade da montagem experimental construída para auxiliar a calibração das sondas Irwin, um estudo mais aprofundado foi também realizado sobre escoamentos em condutas retangulares com seção transversal constante e variável. Finalmente, as principais conclusões que resultam do presente trabalho são resumidas e sugerem-se algumas recomendações para o trabalho futuro.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1988.
Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 123-136).

Stone columns or granular piles can have widespread application in the field of ground improvement. It is a cost effective measure used to improve bearing capacity of weak soils for supporting a wide variety of structures such as residential, commercial and industrial buildings, raft foundations, oil storage tanks, highways and other applications. It also helps in reducing settlements. The stone columns derive its load carrying capacity mainly from confinement of the surrounding soil. In the present investigation, load versus settlement response of silty clay bed is compared with the load versus settlement response of silty clay bed reinforced with stone column for different aggregate mixes and different depth of stone column with and without encasement. The plate load tests were carried out on a single column in a large rectangular tank (1.5m×0.6m×0.9m). The test bed was prepared using locally available silty clay soil. Investigations were carried out by varying the size of aggregate in the stone column as well as mixing different size aggregates. The results from the tests indicated a clear improvement in load carrying capacity of silty clay bed due to stone column as well as a reduction in settlement. The bearing capacity improvement factors have been found out to be 1.11, 1.23, 1.32 for stone columns with 20mm aggregates; 1.08, 1.22, 1.31 for stone columns with 10mm aggregate; 1.15, 1.24,1.41 for stone columns with a mixture of 10mm and 20mm aggregates in the ratio of 1:1 by weight for depths of 250mm, 500mm and 750mm respectively at 25mm settlement. It has been observed that for encased stone column the bearing capacity improvement factors at 25mm settlement for full depth of silty clay bed i.e. 750mm has been observed as 1.87,1.83 and 1.91 for stone columns with 20mm, 10mm and a mixture of 10mm and 20mm aggregate respectively.

Granular pile, also popularly known as stone column, is an economical and efficient ground improvement technique to treat variety of soils. Depending on loading, geometry and spacing pattern, granular pile may fail individually or as a group. Bulging failure of granular pile is the most common failure criterion among the possible failure mechanisms – punching failure, shear failure and bulging failure. In this study, Finite Element analyses have been performed using commercially available software PLAXIS 2D to understand the bulging and the load-settlement behavior of both single floating granular pile and granular piled raft embedded in a soft clay deposit. Elastic-perfectly plastic response (Mohr-Coulomb criterion) is used to model both the granular pile and the soft clay. Parametric study is carried out by varying the properties of clay and granular pile to understand and quantify (a) the bulging along the depth of the pile with and without raft, and (b) the load-carrying capacity of granular pile and piled raft. Critical length of granular pile is also proposed for the cases considered in the study.

碩士
國立成功大學
土木工程學系碩博士班
91
Abstract An elastic-plastic, dynamic three-dimensional (3-D) Finite Difference Method (FDM) is adopted to investigate the effects of granular pile improvement on dissipation of excess pore water pressure and mitigation of ground settlement during earthquake. To verify the appropriateness of dynamic model, undrained dynamic triaxial tests were simulated under different experiment conditions. The numerical predictions and laboratory measurement shows a similar tendency. Subsequently, a 3-D finite difference dynamic analysis was implemented on a sandy layer with and without granular pile treatment. The analysis was conducted incorporated with dynamic pore-water pressure calculation and fluid flow modeling. Numerical results with and without granular pile improvement were then compared to illustrate the improvement effect of granular pile on high liquefaction potential sandy stratum. Eventually, a series of parametric studies were performed on installation parameters of granular pile includes pile configurations, pile permeability, pile diameter and pile length. The effect of various installation parameters were discussed in terms of dissipation of excess pore water pressure and reducing of ground settlement during earthquake. In this study, it was found that the improvement effect of granular pile on reducing the ground settlement may not be as beneficial as in the case of excess pore water pressure dissipation. The dissipation ratio of excess pore water pressure DR value varies from 9.16% to 88.5% for various improvement cases violently while the improvement ratio of ground settlement IR value alters mildly from 2.19% to 18.61%. This implies that the granular pile is predominantly capable of dissipating the induced excess pore water pressure to mitigate the liquefaction potential rather than reduce the ground settlement during the earthquake.

碩士
國立中央大學
土木工程研究所
100
Flume experiment were employed to examine granular collapses by using ballistic mill stone. The flow characteristics and pore water pressure variation during the collapse of particle piles are analyzed. The effect of aspect ratios of the granular piles under different water content both saturated and unsaturated, is examined by measuring the dynamic pore water pressure and the flow characteristics. Aspect ratio (a=hi /?i), sliding speed and passive failure are all related to the thickness of the fluidization. Both the deposit geometric morphology and landslide process depend on basal conditions, sill height, aspect ratio and water content. The dry granular flow velocity profiles can be described by the Super Stable Heap(SSH) model. While in the saturated granular flows, the velocity profile can be described by Bagnold rheology. The variation of pore water pressure is associated with the particle collapse patterns. Heavy rainfall induced infiltration increases the pore water pressure and may cause slope collapse.

Dissertação de Mestrado Integrado em Engenharia Mecânica apresentada à Faculdade de Ciências e Tecnologia
Há muitas empresas que têm necessidades de armazenamento em estaleiros abertos de materiais granulares em pilhas. Tal facto leva a que esses materiais estejam sujeitos à erosão provocada pelo vento, o que implica que eles possam contaminar o ar, criando-se problemas económicos, ambientais e de saúde para as populações. O formato da pilha em estudo nesta dissertação é o oblongo. As dimensões do modelo são 74 mm de altura, 635 mm de comprimento e 226 mm de largura. Fizeram-se ensaios de erosão em túnel de vento, uma vez que existem poucos estudos experimentais da erosão de pilhas com este formato. Assim, mostram-se os resultados experimentais da erosão provocada pelo vento, que vai deformar a pilha, bem como da taxa de erosão da pilha. Estes resultados são apresentados para vários instantes de tempo de erosão. São usadas duas velocidades de escoamento incidente nestes ensaios: 9.08 e 9.90 m/s. A medição da erosão provocada na pilha é feita usando duas grelhas de medição distintas: uma mais refinada e outra mais grosseira. Verificou-se que não havia diferença, a nível qualitativo na taxa de erosão nem na medição da deformação da pilha, entre a grelha de medição grosseira e a refinada.São usadas duas direções de escoamento incidente: perpendicular à pilha e formando um ângulo de 60º com a pilha. Observa-se que a erosão da pilha é simétrica, para o caso do escoamento incidente ser perpendicular à pilha e que a taxa de erosão da pilha é maior para a velocidade mais elevada. Para além disso, a rotação da pilha tende a reduzir a sua deformação, sendo este efeito mais notório para a velocidade de escoamento incidente de 9.08 m/s.
There are many industries who has needs of storage in open yards of granular materials in stockpiles. This fact leads to these materials will be potentially subject to erosion provoked by the wind, what will lead those materials to contaminate the air, creating economic, environment and health problems for the populations.The pile shape in study of this dissertation is the oblong. The dimensions of the model are 74 mm of height, 635 mm of length and 226 mm of width. Erosion tests in wind tunnel have been done, because there are few experimental studies of erosion of piles with this shape. Thus, wind erosion experimental results are shown, illustrating deformation of the pile, as well as the erosion rate. These results are shown for several instants of erosion. Two wind flow speeds are used in these experiments: 9.08 and 9.90 m/s. The erosion rate of the pile is computed for two distinct grids of measurement: one refined and the other coarser. It was found that there was no qualitative difference in erosion rate of the pile nor in his deformation, between the coarser grid measurement and the refined.Two wind flow directions are used: perpendicular to the pile and doing an angle of 60º with it. It was found that there was no qualitative difference in erosion rate of the pile nor in his deformation, between the coarser grid measurement and the more refined. It is observed that the erosion of the pile is symmetrical, for the case of wind flow perpendicular to the pile and the erosion rate of the pile is greater for the higher wind speed. Furthermore, the wind direction tend to reduce his deformation, being this effect more notorious for the wind flow speed of 9.08 m/s.