The classical Terzaghi Theory was extended by accounting for the variations of permeability during consolidation. With the aid of X-ray techniques, investigations on the significance of the variation of permeability, as well as the variations of void ratio and effective pressure, were conducted. Effects of the conventional consolidometer boundary on consolidation testing were studied. / Thesis / Master of Engineering (ME)

Strain localization, the phenomenon of large shear deformation within thin zones of intensive shearing, commonly occurs both in-situ and in the laboratory tests on soils specimens. The intriguing mechanism of strain localization and how it will affect the general behavior of soil specimens have been investigated by many researchers. Some of the efforts have focused on finding the links between material properties (void space, fabric tensor) and mechanical behavior (stress, strain, volumetric strain). In the last ten years, several extensive studies have been conducted at Georgia Tech to investigate the mechanism of strain localization and link the microstructural properties with the engineering behavior of Ottawa sands. These studies have included 2-D and 3-D characterization of soil microstructures under either triaxial or biaxial shearing conditions. To extend and complement these previous studies, the current study focuses particularly on 3-D reconstruction, analysis and modeling of specimens of Ottawa sand subject to triaxial or biaxial loading. The 3-D microstructure of biaxial specimens was reconstructed using an optical microscopy based montage and serial sectioning technique. Based on the reconstructed 3-D digital volumes, a series of 2-D and 3-D characterizations and analyses, including local void ratio distributions, extent of shear bands, influence of soil fabrics and packing signature effects, were conducted. In addition to the image analysis based reconstruction and characterization, the 3-D discrete element method (DEM) code, PFC3D, was used to explore both biaxial and triaxial shear related soil behaviors at the global and particulate scale. Void ratio distributions, coordination numbers, particle rotations and displacements, contact normal distributions and normal contact forces as well as global stress and strain responses were investigated and analyzed to help understand the mechanism of strain localization. The microstructures of the numerical specimens were also characterized in the same way as the physical specimens and similar strain localization patterns were identified. Combined with the previous related studies, the current study provides new insights into the strain localization phenomenon of Ottawa sands subject to triaxial and biaxial loading. In addition, the reconstructed digital specimens were subject to a series of dissection studies which revealed exciting new insights into "microstructure signatures" which exist at both meso and micro scales within the real and simulated specimens.

In this study, a two phase investigation of the hydraulic conductivity parameters of silty soils was performed. In the first phase, double-ring infiltrometer tests were used to measure infiltration rates in-situ at two sites in the Piedmont physiographic province of Georgia. The efficacy of predicting saturated hydraulic conductivity for Piedmont soils via published soil surveys from the National Resource Conservation Service and pedotransfer functions was then investigated. Work focused on the development of a consistent test methodology for soils (sandy, to silts and clays) in the Piedmont, and the final test method utilized being the constant head test, using a double-ring infiltrometer with Mariotte tubes to maintain the head. In the second phase of the investigation, laboratory based measurements of the saturated hydraulic conductivity of binary mixtures of fine sand and nonplastic silt were performed to investigate the effects of particle mixtures on hydraulic conductivity. The materials used were ASTM 100/200 sand and Sil-Co-Sil 40 non-plastic silt, chosen based on the ratio of the mean particle diameters. Significant effort was invested in the development and comparison of methodologies to produce uniform specimens of the binary mixtures for hydraulic conductivity testing, with the final being modified dry tubing. Two fixed densities were used to investigate the effects of particle packing on the hydraulic conductivity of binary mixtures, with critical fines contents chosen to ensure the finer particles primarily filled the pore volume of the coarse particles. Incremental fines contents, by mass, up to this theoretical fines content were tested. The measured saturated hydraulic conductivity was evaluated in terms of fines content, global and intergranular void ratio, and confining stress. Models for predicting extreme void ratios and saturated hydraulic conductivity of binary mixtures were also investigated.

South Africa, as one of the world’s largest gold producing countries, also generates large amounts of tailings. These tailings are disposed in tailings dams, which pose great threat to the environment in the case of failure, in particular, liquefaction. In order to evaluate the potential of liquefaction, the void ratio of the tailings is required and is often impossible to obtain. Seismic methods allow an indirect method to estimate void ratio of in situ deposits of which tailings are examples of. Currently, the use of seismic methods to estimate void ratio of tailings rely on shear wave velocity – void ratio relationships derived for sands. It is thus uncertain whether this relationship holds for gold tailings, which is classified as a sandy silt or silt. The measurement of shear wave velocity of tailings is done in the laboratory using a triaxial apparatus modified to accommodate bender element. Shear wave velocities are measured using wide square pulses and continuous sinusoidal waves. The results show that there is a near linear relationship between void ratio and shear wave velocity normalized against effective stress. The position of this relationship lies below the previously published results for sands. Shear wave velocity of gold tailings is more sensitive to changes in effective stress than changes in void ratio or over-consolidation ratio. Furthermore, using phase sensitive detection of continuous waves, we can conclude that shear wave velocity of gold tailings is also frequency dependent. / Dissertation (MEng)--University of Pretoria, 2006. / Civil Engineering / MEng / Unrestricted

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A new measurement technique called fiber optic reflectometer (FOR) was developed to investigate multiphase flows. The principle and setup of the FOR technique were introduced and applied to various experiments. Based on the coherently mixed signal between the Fresnel reflection off the fiber-liquid interface and the scattered signal off the object, such as a gas bubble, and a solid particle, this single probe technique is capable of simultaneously measuring the velocity of the object with a high accuracy and the phase of the fluid. In addition, bubble diameter, velocity, and void fraction were measured directly. By means of a simple modification of the FOR technique, solute concentration and refractive index change were measured with a greatly improved accuracy. This modified technique was used for measuring of a NaCl concentration in deionized water to validate a new normalization technique. In the second part of this thesis, a plunging breaking wave in deep water has been studied. Using the wave focusing method, a strong plunging breaker was generated with accuracy in the deep water condition in a two-dimensional wave tank. It was possible to describe the breaking process in detail using a high speed camera with a frame rate of 500 or 1000 fps. Four kinds of experimental techniques were employed or developed to investigate the plunging breaker. Bubble image velocimetry (BIV) and particle image velocimetry (PIV) were used to measure the velocity fields. The velocity fields of the highly aerated region were obtained from the BIV measurements. In addition, the modified PIV technique is capable of measuring the velocities in the entire flow field including the aerated region. Mean and turbulent properties were obtained by the ensemble average. The mean velocity, mean vorticity, and mean kinetic energy were examined over the entire flow field. In addition, the Reynolds stresses and turbulent kinetic energy were calculated with high temporal and spatial resolutions. Free surface elevation was obtained from wave gauge measurements. BIV and PIV images were also used to obtain the free surface elevation and the boundary of the aerated region for more accurate results. The FOR technique was used to obtain the void ratio at each splash-up region. Compressibility of the plunging breaker was considered. Mass flux, momentum flux, kinetic energy, and Reynolds stresses at each FOR station were recalculated using the void ratio obtained from the FOR measurements. All terms at the first splash-up region were highly overestimated more than 100 percent unless the void ratio was applied to the calculation of fluxes and energies. Compared with the fully developed first splash-up region, the overestimation at the second and third splash-up was less significant. However, most terms were overestimated by 20~30 percent when the void ratio was not considered.

Particulate materials are ubiquitous in the natural environment and have served throughout human history as one of the basic materials for developing civilizations. In terms of human activity, the handling of particulate materials consumes approximately 10% of all the energy produced on earth. Advances in the study and understanding of particulate materials can thus be expected to have a major impact on society. Geotechnical engineers have a long history of studying particulate materials since the fundamental building blocks of the profession include sands, silts, clays, gravels and ores, all of which are in one form or another particulates. The interface between particulates and other engineered materials is very important in determining the overall behavior of many geotechnical systems. Laboratory experimental studies into interface shear behavior has until now, been largely confined to systems involving uniformly graded sands comprised of a single particle size. This study addresses these potential shortcomings by investigating the behavior of binary particle mixtures in contact with surfaces. The binary nature of the mixtures gives rise to a changing fabric state which in turn can affect the shear strength of the mixture. Accordingly, packing limit states and the shear strength of binary mixtures were investigated across a range of mixtures, varying in particle size ratio and the proportion of fine particles to provide a reference. Binary mixtures in contact with smooth surfaces were investigated from both a global shear response and a contact mechanics perspective. A model was developed that allowed for the prediction of an interface friction coefficient based on fundamental material properties, particle and mixture parameters. Surface roughness changes as a result of shearing were also examined. The interface shear behavior with rough interfaces was examined in the context of the relative roughness between particles and surface features. The interpretation of traditional measures of relative roughness suffer from the need for a definitive average particle size, which is ambiguous in the case of non-uniform mixtures. Measures of an applicable average particle size for binary mixtures were evaluated.

Made available in DSpace on 2014-12-17T14:48:13Z (GMT). No. of bitstreams: 1 FranciscoMGL_DISSERT.pdf: 2920200 bytes, checksum: c9c74c01a86db791fd1fef40b8b653c2 (MD5) Previous issue date: 2012-03-09 / Soil improved with the addition of cement have been utilized as an alternative to the construction of various types of geotechnical works, almost always present economic and environmental advantages. This paper presents a study on the usage of cement in the improvement of mechanical properties of sandy soils, characteristic of the region of Natal, collected from its dunes. This research was made in order to analyze the influence of cement content, voids, and also including water immersion and confining pressure. Samples molded from cement-soil mixtures were tested for unconfined compression tests and triaxial tests. The samples had the percentage of cement mixed in 2.5%, 5% and 10% by weight. The cement agent used was the Portland Cement of High Early strength(CPV-ARI), which promoted agility to the experimental procedure for presenting a rapid gain in strenght. The void ratio used ranged from 0.7 (more compact), 0,9 and 1,1(softer). The soil under study can be considered as pure sand. In general, it can be stated that the larger the amount of cement added to the sand studied is, the greater ultimate strength will be. Likewise, as more compact the soil is, the less void ratio and more resistant it will be present. The confining pressure tends to increase the resistance of the specimens. The cementing adopted grades showed that the use of different criteria for failure did not significantly alter the stress-strain parameters for the sand studied. The angle of friction values were found within the typical range of medium and compact sands. Cementing acted in the sand providing an intercepted cohesion which increased enhancing the potential cementation. In triaxial compression tests, the sand with void ratio is equal to 0.7 and showed the expected behavior for a compact sand while the stress-strain behavior of the same sand with the void ratio of 0.9 tended to be expected for the soft sand as well / Solos melhorados com adi??o de cimento t?m sido bastante utilizados como alternativa na constru??o de diversos tipos de obras geot?cnicas, quase sempre por apresentar vantagens econ?micas e ambientais. Este trabalho apresenta um estudo sobre a utiliza??o de cimento no melhoramento das propriedades mec?nicas de solos arenosos caracter?sticos da regi?o de Natal, coletados em dunas. Foi avaliada a influ?ncia do teor de cimento, do ?ndice de vazios, da inunda??o e da tens?o confinante. Corpos-de-prova moldados a partir de misturas de solo-cimento foram submetidos a ensaios de resist?ncia ? compress?o simples e ? compress?o triaxial convencional. Nas amostras as porcentagens de cimento foram variadas em 2,5%, 5% e 10% em peso. O agente cimentante utilizado foi o Cimento Portland de Alta resist?ncia inicial (CP-V ARI), que promoveu agilidade ao procedimento experimental por apresentar um processo de cura mais r?pido.Os ?ndices de vazios utilizados variaram de 0,7 (mais compacto), 0,9 e 1,1(mais fofo). O solo estudado pode ser considerado como uma areia pura. De uma forma geral, pode-se afirmar que quanto maior a quantidade de cimento adicionado ? areia estudada, maior a sua resist?ncia final. Da mesma forma, quanto mais compacto estiver esse solo, isto ?, quanto menor o ?ndice de vazios, mais resistente ele se apresentar?. A tens?o confinante tende a aumentar a resist?ncia dos corpos de prova. Nos graus de cimenta??o adotados, a utiliza??o de diferentes crit?rios de ruptura n?o alterou significativamente os par?metros tens?o-deforma??o para a areia estudada. Os valores de ?ngulo de atrito encontrados estavam dentro dos valores t?picos para areias m?dias e compactas. A cimenta??o agiu na areia de modo a proporcionar um intercepto de coes?o que aumentou com o incremento da cimenta??o. Nos ensaios de compress?o triaxial, a areia com ?ndice de vazios igual a 0,7 apresentou o comportamento esperado para uma areia compacta, enquanto o comportamento tens?o deforma??o da mesma areia com ?ndice de vazios de 0,9 tendeu ao esperado para a areia fofa

La simulation numérique des écoulements turbulents cavitants revêt de nombreuses difficultés tant dans la modélisation des phénomènes physiques que dans le développement de méthodes numériques robustes. En effet de tels écoulements sont caractérisés par un changement de phase associé à des gradients de la masse volumique, des variations du nombre de Mach causées par une chute de la vitesse du son, des zones de turbulence diphasique et la présence d'instationnarités.Les travaux de la présente thèse s'inscrivent dans la continuité des études expérimentales et numériques menées au sein du Laboratoire des Ecoulements Géophysiques et Industriels (LEGI),qui visent à améliorer la compréhension et la modélisation d'écoulements cavitants. Les simulations s'appuient sur un code compressible associé à une technique de pré-contionnement bas-Mach qui permet de traiter les zones incompressibles. Les écoulements diphasiques sont reproduits à l'aide d'un modèle de mélange homogène 1-fluide avec discrétisation implicite en pas de temps dual. Enfin la résolution adopte l'approche moyennée RANS qui couple le système des équations de conservation avec des modèles de turbulence du premier ordre basés sur la notion de viscosité turbulente.Dans les zones diphasiques, le calcul des variables thermodynamiques nécessite l'introduction d'équations d'état. La pression au sein du mélange est ainsi reliée aux grandeurs conservatives soit à partir d'une équation d'état de mélange des gaz raides, soit par une relation sinusoïdale incorporant la fraction volumique de vapeur (le taux de vide). La valeur ajoutée de ces travaux de thèse repose sur l'introduction d'une équation de transport pour le calcul du taux de vide. Celle-ci incorpore un terme source dont le transfert de masse entre les phases est fermé grâce à une hypothèse de proportionnalité à la divergence du champ de vitesse. Outre l'amélioration des phénomènes de convection, de dilatation et de collapse, cette équation supplémentaire permet de relaxer l'équilibre thermodynamique local et d'introduire un état métastable pour la phase vapeur.Les simulations 2D et 3D sont réalisées sur des géométries de type Venturi caractérisées par le développement de poches de cavitation partielle instables. L'objectif consiste à reproduire les instationnarités inhérentes à chaque profil telles que la formation d'un jet rentrant liquide à proximité de la paroi ou la production de nuages de vapeur convectés par l'écoulement principal.Les résultats numériques mettent en avant une variation de la fréquence des instationnarités en fonction du calcul de la vitesse du son en zone de mélange. D'autre part, la prise en compte de déséquilibre de la phase vapeur amplifie les phénomènes de propagation d'ondes de pression générées par le collapse des structures cavitantes et participe à la déstabilisation de la poche. Enfin, l'influence de l'équation de transport de taux de vide est analysée en confrontant les résultats des simulations à ceux obtenus ultérieurement à partir d'un modèle à seulement trois équations de conservation. / The computation of turbulent cavitating flows involves many difficulties both in modeling the physical phenomena and in the development of robust numerical methods. Indeed such flows are characterized by phase transitions and large density gradients, Mach number variation due to speed of sound decrease, two-phase turbulent areas and unsteadiness.This thesis follows experimental and numerical studies led at the Laboratoire des Ecoulements Géophysiques et Industriels which aim to improve the understanding and modeling of cavitating flows. Simulations are based on a compressible code coupled with a pre-conditionning technique which handles low-Mach number areas. The two-phase flows are reproduced using a one-fluid homogeneous model and temporal discretisation is performed using an implicit dual-time stepping method . The resolution is based on the RANS approach that couples conservation equations with firts-order closure models to compute eddy viscosity.In two-phase flows areas, the computation of thermodynamic quantities requires to close the system with equations of state (EOS). Thus, two formulations are investigated to determine the pressure in the mixture. The stiffened gas EOS is written with conservative quantities while a sinusoidal law deduces the pressure from the volume fraction of vapor (the void fraction). The present study improves the homogeneous equilibrium models by including a transport equation for the void ratio. The mass transfer between phases is assumed to be proportional to the divergence of the velocity. In addition to a better modeling of convection, expansion and collapse phenomenon, this added transport equation allows to relax the local thermodynamic equilibrium and to introduce a mestastable state to the vapor phase.2D and 3D simulations are performed on Venturi type geometries characterized by the development of unstable partial cavitation pockets. The goal is to reproduce unsteadiness linked to each profile such as the formation of a re-entrant jet or the quasi-periodic vapor clouds shedding. Numerical results highlight frequency variations of unsteadiness depending on the speed of sound computation. Moreover, the simulation conducted with a relaxed vapor density increase the pressure wave propagation magnitude generated by the collapse of cavitating structures. It contributes to the destabilization of the pocket. Finally, the role of the void ratio equation is analyzed by comparing the simulation results to those obtained subsequently from a model involving only three conservation equations.