Civil engineers are at times required to stabilize sulfate bearing clay soils with calcium based stabilizers. Deleterious heaving in these stabilized soils may result over time. This dissertation addresses critical questions regarding the consequences of treating sulfate laden soils with calcium-based stabilizers. The use of a differential scanning calorimeter was introduced in this research as a tool to quantify the amount of ettringite formed in stabilized soils. The first part of this dissertation provides a case history analysis of the expansion history compared to the ettringite growth history of three controlled low strength mixtures containing fly ash with relatively high sulfate contents. Ettringite growth and measurable volume changes were monitored simultaneously for mixtures subjected to different environmental conditions. The observations verified the role of water in causing expansion when ettringite mineral is present. Sorption of water by the ettringite molecule was found to be a part of the reason for expansion. The second part of this dissertation evaluates the existence of threshold sulfate levels in soils as well as the role of soil mineralogy in defining the sensitivity of soils to sulfate-induced damage. A differential scanning calorimeter and thermodynamics based phase diagram approach are used to evaluate the role of soil minerals. The observations substantiated the difference in sensitivity of soils to ettringite formation, and also verified the existence of a threshold level of soluble sulfates in soils that can trigger substantial ettringite growth. The third part of this dissertation identifies alternative, probable mechanisms of swelling when sulfate laden soils are stabilized with lime. The swelling distress observed in stabilized soils is found to be due to one or a combination of three separate mechanisms: (1) volumetric expansion during ettringite formation, (2) water movement triggered by a high osmotic suction caused by sulfate salts, and (3) the ability of the ettringite mineral to absorb water and contribute to the swelling process.

Total suction of unsaturated soils is contributed by matric and osmotic suctions. Matric suction arises from capillary actions in the soil structure and varies with changes in moisture content of the soil. Pore fluid osmotic suction is related to the dissolved salt content in soil water (soil water salinity) and increases with pore water salinity. Exposure of clay soils to chemical solutions (example landfill leachate, brine pond solutions) induces osmotic suction difference between soil water and the chemical reservoir. Soil water refers to the aqueous solution residing in soil pores that is chemically composed of H2O molecules and dissolved salt molecules. Osmotic suction difference between soil water and the chemical reservoir is dissipated through the following modes. Salt molecules diffuse from the chemical reservoir to the soil water and H2O molecules from soil water flows to chemical reservoir to equalize salt concentrations in the two chambers. This flow of H2O molecules is called an osmotic flow. During osmotic flow, if the clay particles behave as perfect semi-permeable membranes, only water exchanges between clay voids and the external solution in response to chemical concentration gradients. Clay particles however function as imperfect semi-permeable membranes and transfer dissolved salts in addition to water. The outward flow of H2O molecules from soil water (dilute solution chamber) to chemical reservoir (concentrated solution chamber) causes negative pore fluid pressures to develop within the compacted clay, which then leads to increase in effective stress and the consequent volume decrease is termed as osmotic induced consolidation. Conversely, diffusion of salt molecules from chemical reservoir to soil water in response to chemical concentration gradient reduces the thickness of the diffuse ion layers around the clay particles causing a decrease in the electrical repulsion forces between them. This in turn reduces the separation of the clay particles and, consequently, compresses the clay sample to a lower void ratio; the process being termed as osmotic consolidation. Tests described by researchers show that osmotic consolidation usually has a larger effect than the osmotically induced one. Review of the literature shows that most of the available theoretical and experimental analysis in literature only focuses on the behaviour of clay samples reconstituted from slurries and not on the one of compacted clays. Compacted clays are exposed to osmotic suction gradients under field situations such as landfills and brine ponds where compacted clay liners are in contact with leachate/brine solutions. Examining the impact of osmotic suction dissipation on the swell/compression behaviour of compacted clays forms the focus of the present thesis. Statement of Problem Compacted clays differ from clay samples reconstituted from slurries as they are characterized by both matric suction and osmotic suction. As a result, besides dissipating osmotic suction gradients by diffusion of salt molecules and flow of H2O molecules, compacted clays absorb salt solution in their partly saturated void spaces to dissipate matric suction and in the process may develop swelling strains. However, absorption of salt solution to dissipate matric suction and salt diffusion in response to osmotic suction difference will alter the diffuse double layer (DDL) thickness as the latter is affected by the dissolved salts concentration of soil water; alterations in DDL thickness will in turn affect the swelling behaviour of the compacted clays. The influence of alterations in DDL thickness from dissipation of matric suction and osmotic suction difference on the swelling magnitudes of compacted expansive clays exposed to salt solutions needs to be examined. The direction of salt diffusion in response to dissipation of osmotic suction difference will also impact the swelling behaviour of compacted clays exposed to osmotic suction gradients. Diffusion of salts from external reservoir to soil water (salinization path) in response to osmotic suction gradients will reduce the swell potential of the compacted expansive clay from increased dissolved salts concentration in soil water. Conversely, diffusion of salts from soil water to external reservoir (desalinization path) should facilitate the compacted clay to swell more from reduction in its dissolved salts concentration. The influence of direction of salt diffusion during dissipation of osmotic suction gradient on the swell behaviour of compacted expansive clays needs to be examined. The volumetric response of compacted clays exposed to salt solutions may be different compared with identically compacted specimens wetted with distilled water at same total vertical pressure value. As previously mentioned, exposure of compacted clays to salt solutions, besides destroying capillary bonds will alter the soil water chemistry of the compacted clay specimens from absorption of salt solution to dissipate matric suction and salt diffusion in response to osmotic suction gradients. Alterations in soil water chemistry in turn alter the swell pressures of compacted clay specimens from concomitant changes in electrical repulsion forces. If the modified swell pressure of the compacted specimen exceeds the total vertical pressure, diminished swelling strains result at the macroscopic level. Conversely, the compacted clay will experience compressive strains at the macroscopic level if the total vertical pressure exceeds the modified swell pressure of the compacted specimen. Alterations in the wetting induced volumetric response of compacted clays from modifications in swell pressure upon exposure to salt solutions needs to be examined. Earlier researchers had re-plotted the compressibility data for sodium- montmorillonite clays remolded with sodium chloride solutions using the osmotic suction of the remolding fluids as a stress state variable in a three-dimensional space. Along a plane in which osmotic pressure (π) is constant, the coefficient of volume compressibility (mv) was obtained. Along a plane in which the effective stress [(σ - uw)] is constant, the slope defined the osmotic coefficient of volume compressibility (mπ). The above concept is useful to predict the osmotic consolidation strains of clay specimens upon exposure to salinization paths at constant effective stress. Salt diffusion into soil water in response to osmotic suction gradients may alter the exchangeable cation composition of saturated clay specimens. Alterations in exchangeable cation composition alters the diffuse ion layer thickness of clay particles which in turn may impact the osmotic swelling strains developed by saturated saline clay specimens upon exposure to desalinization path and osmotic consolidation strains developed by saturated desalinated clay specimens upon exposure to salinization path. Saturated saline specimens refer to saturated clay specimens that are exposed to salinization (saturated specimens are inundated with salt solution) path. Saturated desalinated specimens are obtained by exposing saturated saline specimens to desalinization (inundated with distilled water) path. Osmotic swelling refers to the swelling strains developed by saturated saline specimens on exposure to desalinization path. These strains result from outward migration of salts in response to osmotic suction gradients. The influence of cation exchange reactions on the osmotic swelling strains developed by saturated saline clay specimens upon exposure to desalinization path and osmotic consolidation strains developed by saturated desalinated clay specimens upon exposure to salinization path needs examination. The swelling magnitudes of compacted specimens are influenced by variations in dry density, water content and consolidation pressure. However, the effect of variation in compaction dry density and water content on the osmotic swell behaviour of saturated saline specimen exposed to desalinization path and osmotic consolidation behaviour of saturated desalinated specimen exposed to salinization path is not known and needs examination. Based on the statement of the problem, the following objectives emerge: • To examine the influence of dissipation of matric suction and osmotic suction difference on the swelling behaviour of compacted expansive clays exposed to osmotic suction gradients (salinization path). • To examine the influence of direction of salt diffusion during dissipation of osmotic suction gradients on the swell behaviour of compacted expansive clays. • To examine alterations in the wetting induced volumetric strain response of compacted clays from modifications in swell pressure upon exposure to salt solutions at range of total vertical pressures. • To predict the osmotic consolidation strains of saturated clay specimens upon exposure to salinization paths at constant effective stress. • To examine the influence of cation exchange reactions on the osmotic swelling strains developed by saturated saline clay specimens upon exposure to desalinization path and osmotic consolidation strains developed by saturated desalinated clay specimens upon exposure to salinization path. • To examine, effect of variation in compaction dry density and water content on the osmotic swell behaviour of saturated saline specimen exposed to desalinization path and osmotic consolidation behaviour of saturated desalinated specimen exposed to salinization path. The organization of the thesis is as follows: After the first introductory chapter, a detailed review of literature is performed towards highlighting the need to examine the influence of dissipation of osmotic suction gradients on the swell-compression behaviour of compacted expansive clays in Chapter 2. Chapter 3 presents a detailed experimental program of the study. Chapter 4 examines the influence of dissipation of matric suction and osmotic suction difference on the swelling behaviour of compacted expansive clays exposed to salinization path. The chapter also examines the influence of direction of salt diffusion durin dissipation of osmotic suction gradients on the swell behaviour of compacted expansive clays. Black cotton soil from Karnataka State was used as the expansive clay specimen to examine these objectives. Inundating compacted expansive clay specimens with (0.1 M to 4 M) sodium chloride solutions at a total vertical pressure of 6.25 kPa in oedometer cells exposed the clay specimens to salinization paths. Measurements of changes in swelling strains, matric suction (measured by filter paper method) and pore water chemistry with time provided insight into the relative influence of matric suction and salt diffusion on the kinetics of swell. Examining the time-axial deformation behaviour of compacted specimens exposed to salinization paths in the post-primary swell region delineated the influence of osmotic suction dissipation on the volume change behaviour of compacted expansive clays. The influence of direction of salt diffusion in response to osmotic suction gradients on the swelling behaviour of compacted expansive clay was examined in the following manner. Salt diffusion from external reservoir to soil water (salinization path) was accomplished by inundating compacted clay specimens with 0.4 M and 4 M sodium chloride solutions in oedometer cells at 6.25 kPa. Salt diffusion from soil water to external reservoir (desalinization path) was accomplished by inundating salt-amended specimens with distilled water in oedometer cells at 6.25 kPa. Salt-amended specimens refer to expansive clay specimens remolded with 0.4 M/4 M sodium chloride solution at desired moisture content and compacted to the design density. Experimental results illustrated that compacted specimens dissipated matric suction by absorption of distilled water and sodium chloride solutions. The initial osmotic suction difference was dissipated by inward diffusion of salts; salt solutions absorbed to dissipate matric suction also contributed to dissipation of osmotic suction difference. The compacted clay specimens swelled on inundation with sodium chloride solutions as dissipation of matric suction and the attendant growth of diffuse ion layer repulsion dominated compacted clay behaviour exposed to salinization paths. However exposure to salinization path reduced swell magnitudes of compacted clay specimens from reductions in diffuse ion layer thickness. The time-swell plots of the compacted clay specimens exposed to salinization path categorized into initial, primary and secondary swell regions. Rates of primary swell were 5 to 21 times larger than rates of secondary swell. Experimental data suggested that primary swell develops relatively rapidly as it is linked to rate of matric suction dissipation. Secondary swell developed more slowly as it is controlled by diffusion of salts and adsorption-desorption reactions. Increase in dissolved salts concentration in soil water during primary swell occurs from salt solution absorbed in response to matric suction and salt diffused in response to osmotic suction difference. Comparatively, increase in dissolved salts concentration in soil water during secondary swell occurs from diffusion of salts in response to osmotic suction gradients. Exposure of salt-amended clays to desalinization path caused outward diffusion of salts to dissipate osmotic suction difference and absorption of distilled water to quench the matric suction of the salt-amended specimens. The salt-amended specimens developed greater swell potentials than compacted specimens inundated with distilled water owing to reduction in dissolved salt concentration of soil water and replacement of native exchangeable calcium and magnesium ions by sodium ions. The time-swell behaviour of salt-amended specimens exposed to desalinization path categorize into four regions: small initial swell region followed by large primary swell and small secondary swell regions and lastly a large tertiary swell region. Complete dissipation of matric suction coincides with end of primary swell and both processes terminate in 120-240 minutes after inundation for salt-amended specimens exposed to desalinization paths. Further, only small fraction (16 to 18 %) of possible salt extrusion occurs at the end of primary swell and bulk of salt extrusion occurs during secondary and tertiary swell. Secondary swell developed at a slower rate than primary swell, as the rate of osmotic suction dissipation during secondary swell was smaller than rate of matric suction dissipation during primary swell. Likewise, tertiary swell developed at similar or faster rate than primary swell, as rate of osmotic suction dissipation during tertiary swell is similar or quicker than rate of matric suction dissipation during primary swell for the salt-amended clays. Analysis of the laboratory results showed that greater magnitude of outward salt diffusion mobilizes larger magnitudes of secondary + tertiary swell in response to dissipation of osmotic suction difference in case of the salt-amended clay specimens. Comparison of swelling behaviour of specimens exposed to salinization and desalinization paths revealed that the direction of salt diffusion impacts their swelling behaviour. Inward salt diffusion during salinization path reduces the swell magnitude of the compacted specimens. Bulk of the swell occurs during primary swell. Outward salt diffusion during desalinization path imparts a larger swell magnitude to the salt-amended specimens in comparison to the compacted specimen inundated with distilled water. Bulk of the swell occurs during secondary + tertiary swell. Dissipation of matric suction was rapid and coincided with the end of primary swell during salinization and desalinization paths. Bulk diffusion of salts during secondary and tertiary swell was a relatively slow process. Chapter 5 examines alterations in the wetting induced volumetric response of compacted clays from modifications in swell pressure upon exposure to salt solutions at range of total vertical pressures (6.25 kPa to 200 kPa). The chapter delineates the manner in which dissipation of matric suction (arising due to unsaturated status of compacted clay) and osmotic suction difference (arising due to chemical concentration gradients between soil water and chemical reservoir) impacts the DDL repulsion pressure/swell pressure and wetting-induced volume change behaviour of compacted expansive clays as a function of total vertical pressures (6.25 kPa to 200 kPa). Alterations in the diffuse double layer repulsion pressure of compacted clays from salt diffusion are calculated based on Gouy- Chapman diffuse double theory. The diffuse double layer repulsion pressures of compacted clays exposed to salinization paths are compared with the oedometer swell pressures. The impact of modifications in swell pressure from salt diffusion on the nature of wetting-induced volumetric strains (swell/compression) experienced by the compacted expansive clay specimens exposed to salinization paths is also examined. The nature of wetting-induced volume change behaviour is analyzed in context of the total vertical pressure to swell pressure ratio of specimens exposed to salinization paths. Salinization experiments are performed in conventional oedometers with the chemical boundary conditions imposed in an “open air” fashion. In the salinization experiments, salt solutions in the oedometer reservoir were in contact with the soil water through wet porous stones. Experimental results revealed that dissipation of initial osmotic suction difference between soil water and oedometer reservoir via salt migration impacted the diffuse double layer repulsion pressure and the wetting-induced volume change behaviour of compacted clays. Osmotic suction varies directly; while, the diffuse double layer thickness inversely varies with dissolved salt concentration of soil water. Consequently, inundation with sodium chloride solutions increase the initial osmotic suction difference at the expense of the diffuse double layer repulsion pressures developed by the compacted clay specimens. Salt diffusion in response to dissipation of osmotic suction difference reduced the theoretical (DDL repulsion pressure) and experimental swell pressures of compacted clays inundated with sodium chloride solutions. The theoretical swell pressures however greatly differed from the experimental swell pressures. The total vertical pressure to modified experimental swell pressure ratio determined the nature of axial strains (swell or compression) experienced by compacted clays on exposure to osmotic suction gradients. When the total vertical pressure to modified swell pressure ratio less than unity, the compacted clay specimens experienced net swelling on inundation with sodium chloride solutions. Conversely, when the total vertical pressure to modified swell pressure ratio exceeded unity, the compacted clay experienced net compression on inundation with sodium chloride solutions. When the total vertical pressure to modified swell pressure ratio was unity, the compacted clay did experience any net axial strains on inundating with sodium chloride solution. The ingress of sodium chloride solutions in response to matric suction saturated the void spaces of the compacted specimens prior to commencement of compression. As a result, compression strains experienced by the compacted specimens on exposure to salt solutions were mainly contributed by osmotic consolidation strains. The amount of salt diffused into soil water had direct bearing on the magnitude of osmotic consolidation strains experienced by the compacted specimens at given total vertical pressure value. The time-rates of primary consolidation are approximately 20 to 100 times quicker than rates of osmotic consolidation. The much slower rates of osmotic consolidation arise, as this process is mainly diffusion controlled in comparison to primary consolidation that is mainly dependent on the soil’s permeability to water flow under load-imposed hydraulic gradients. Primary consolidation strains exceed the osmotic consolidation strains at total vertical pressures of 100 kPa and 200 kPa on exposing the compacted specimen to 1 M sodium chloride solution. The osmotic consolidation strain exceeds the primary consolidation strain on exposing the compacted specimen to 4 M sodium chloride solution at total vertical pressure of 200 kPa. Chapter 6 develops a method to predict the osmotic consolidation strains of saturated clay specimens upon exposure to salinization paths at constant effective stress, examines the influence of cation exchange reactions on the osmotic swelling strains developed by saturated saline clay specimens upon exposure to desalinization path and osmotic consolidation strains developed by saturated desalinated clay specimens upon exposure to salinization path and effect of variation in compaction dry density and water content on the osmotic swell behaviour of saturated saline specimen exposed to desalinization path and osmotic consolidation behaviour of saturated desalinated specimen exposed to salinization path Experimental results illustrated that for a given osmotic suction difference (∆π), larger osmotic consolidation strains are predicted at the lower range of consolidation pressures (25-100 kPa), than at the higher range of consolidation pressures (200-400 kPa) as physico-chemical effects dominated the deformation behaviour at the lower stresses, while; mechanical effects (frictional effects, particle interference) became important at higher range of stresses due to proximity of particles and particle groups. Comparatively, at constant consolidation pressure, the magnitudes of osmotic consolidation strains developed by the saturated clay specimens depend on the magnitude of osmotic suction difference (∆π) imposed on the specimens. The slope of the axial strain versus osmotic suction curve defined the coefficient of osmotic compressibility (mπ). Likewise, slope of the axial strain versus effective stresses plot defined the mv values for the specimens. The mπ values are 10 to 20 times smaller than the mv values indicating that the saturated clay specimens experience smaller osmotic consolidation strains from unit increase in osmotic pressure than consolidation strains from unit increase in consolidation pressure. The predicted osmotic consolidation strains were 1.9 to 2.9 times larger than the experimentally determined values. The experimental values were lower as the saturated clay specimens did not compress sufficiently enough on exposure to salinization at concerned effective stress as the well developed diffuse ion layer of the saturated clay specimen inhibited (osmotic) consolidation of the clay specimen. Ion-exchange reaction has a profound influence on the osmotic swelling developed by the saturated saline specimens and osmotic consolidation strains developed by saturated desalinated specimens upon exposure to osmotic suction gradients. Saturated saline specimens are obtained by salinization of the distilled water aturated specimen with sodium chloride solution at desired vertical stress. During salinization ion exchange occurs between sodium ions of inundating fluid and native divalent exchangeable cations of the clay surface. Upon desalinization in distilled water environment, the saturated saline specimen developed 9.2 % osmotic swelling strain at consolidation pressure of 200 kPa over period of 2560 hours. Comparatively, the unsaturated compacted specimen developed much smaller swelling strain of 0.32 % over period of 26 hours upon inundation with distilled water at consolidation pressure of 200 kPa. The 100-fold larger duration needed by saturated saline specimen to develop larger osmotic swelling strain arose from diffusion controlled outward migration of salts from soil water to distilled water reservoir. The saturated saline specimen exhibited 29-fold larger swell magnitude than the compacted clay specimen at same consolidation pressure as the combined effects of reduction in dissolved salt concentration (from outward diffusion of salts) and enhanced exchangeable sodium concentration increased the diffuse ion layer thickness around clay particles to an extent that the saline specimens swelled by 9 % at 200 kPa. Experimental results also indicated that after ion-exchange equilibrium was established, subjecting saturated saline specimens to cycles of desalinization yielded similar magnitudes of osmotic swelling strains. Likewise saturated desalinated specimen subjected to cycles of salinization yielded similar magnitudes of osmotic consolidation strains. Also the magnitudes of osmotic swelling and osmotic consolidation strains exhibited by the saturated saline and saturated desalinated specimens were of similar magnitudes. Variations in compaction density of the compacted clay specimens had bearing on the osmotic swelling developed by the saturated saline specimens and osmotic consolidation strains developed by the saturated desalinated specimens in response to dissipation of osmotic suction gradients. Desalinization caused the 1.42 Mg/m3series saturated saline specimen to experience 2 fold larger swelling strain than the 1.28 Mg/m3 series saline specimen from outward salt diffusion in response to dissipation of osmotic suction gradient. Similarly, salinization caused the 1.42 Mg/m3 series saturated desalinated specimen to experience 1.46 fold larger osmotic consolidation strain from inward salt diffusion than the 1.28 Mg/m3 desalinated specimen. The much larger swell potential exhibited by the 1.42 Mg/m3saline specimen than the 1.28 Mg/m3 series saline specimen indicates that the influence of compaction dry density persists even after saturation and alterations in exchangeable cation composition of the compacted clay specimens. Experimental results demonstrated that variations in compaction water do not have a bearing on the osmotic swelling and osmotic consolidation strains subsequently developed by the saturated saline and desalinated specimens. Chapter 7 summarizes the main findings of this study.

<p>Disturbances introduced in wall-bounded flows can grow and lead to transition from laminar to turbulent flow. In order to reduce losses or enhance mixing in energy systems, a fundamental understanding of the flow stability and transition mechanism is important. In the present thesis, the stability, transition mechanism and early turbulent evolution of wall-bounded flows are studied. The stability is investigated by means of linear stability equations and the transition mechanism and turbulence are studied using direct numerical simulations. Three base flows are considered, the Falkner-Skan boundary layer, boundary layers subjected to wall suction and the Blasius wall jet. The stability with respect to the exponential growth of waves and the algebraic growth of optimal streaks is studied for the Falkner-Skan boundary layer. For the algebraic growth, the optimal initial location, where the optimal disturbance is introduced in the boundary layer, is found to move downstream with decreased pressure gradient. A unified transition prediction method incorporating the influences of pressure gradient and free-stream turbulence is suggested. The algebraic growth of streaks in boundary layers subjected to wall suction is calculated. It is found that the spatial analysis gives larger optimal growth than temporal theory. Furthermore, it is found that the optimal growth is larger if the suction begins a distance downstream of the leading edge. Thresholds for transition of periodic and localized disturbances as well as the spreading of turbulent spots in the asymptotic suction boundary layer are investigated for Reynolds number Re=500, 800 and 1200 based on the displacement thickness and the free-stream velocity. It is found that the threshold amplitude scales like Re^-1.05 for transition initiated by streamwise vortices and random noise, like Re^-1.3 for oblique transition and like Re^-1.5 for the localized disturbance. The turbulent spot is found to take a bullet-shaped form that becomes more distinct and increases its spreading rate for higher Reynolds number. The Blasius wall jet is matched to the measured flow in an experimental wall-jet facility. Both the linear and nonlinear regime of introduced waves and streaks are investigated and compared to measurements. It is demonstrated that the streaks play an important role in the breakdown process where they suppress pairing and enhance breakdown to turbulence. Furthermore, statistics from the early turbulent regime are analyzed and reveal a reasonable self-similar behavior, which is most pronounced with inner scaling in the near-wall region.</p>

Concern with global climate change has led to the interest in the use of natural refrigerants, such as carbon dioxide, as replacements in heat pump systems. When operating in a transcritical cycle, carbon dioxide heat pumps are well suited for use in high temperature water heating heat pumps. In this work, four systems are analyzed: with and without the use of a suction line heat exchanger, and two water heating schemes. These two schemes involve the heating of water to its desired temperature at a low water flow rate in a single pass through the heat pump, and the heating of water at a high water flow rate, but requiring multiple passes. The performance and resulting heat exchanger size of these four systems is analyzed through the development of an overall system model. This system model uses component-level models that were developed based upon heat exchanger geometry and subsequently validated through experimental testing on a test facility developed for this purpose.

Cette thèse s’inscrit dans la démarche de caractérisation mécanique des tissus mous du vivant in situ et in vivo par un dispositif de succion utilisable en salle opératoire. L’objectif est de fournir au chirurgien un outil simple, efficace, et si possible de coût réduit, pour estimer les propriétés mécaniques spécifiques au patient et en temps réel afin guider leur décisions. Malheureusement, les structures biologiques sont souvent hétérogènes due à leur composition (peau, muqueuse, fibres musculaires, matière adipeuse, fascias, vascularisation, …). En particulier, ces structures biologiques présentent un gradient de propriétés mécanique dans la profondeur. Il s’agit donc de répondre à un problème complexe, d’autant plus qu’il est nécessaire de proposer une méthode non destructive adaptée à une mesure in situ et in vivo en salle opératoire.Parmi les procédés de caractérisation mécanique rencontrés, les méthodes basées sur la succion sont courantes. Ce procédé de mesure consiste à aspirer un volume de tissu mou à travers une ouverture en mesurant simultanément la pression et la hauteur de tissu dans l’enceinte. Une procédure d’identification inverse est ensuite mise en place pour identifier les propriétés mécaniques du tissu. Cette mesure de hauteur étant généralement effectuée à l’aide d’une caméra, le design des systèmes rencontrés reste cependant délicat, en particulier pour respecter les contraintes d’encombrement et de stérilisation des systèmes.Au cours de ce travail, la méthode d’aspiration a été revisitée en remplaçant la mesure de hauteur par une mesure de volume. L’extrémité du dispositif d’aspiration se réduit maintenant à un simple tube : le système fourni est donc facilement stérilisable, le diamètre et la géométrie de l’ouverture peuvent être choisis en fonction des objectifs des mesures à effectuer. Il semble donc difficile d’imaginer un système plus simple, d’encombrement plus réduit et de coût inférieur à celui-ci.Plusieurs problématiques ont été étudiées autour de ce nouveau système :les précisions de mesures obtenues par volume ou, plus classiquement, par caméra ont été confrontées. Au bilan, la mesure de volume présente un ratio signal/bruit similaire ou inférieur aux mesures de volume obtenues par caméra. L’impact de différents paramètres expérimentaux a été évalué et quantifié, permettant d’optimiser la qualité des mesures.les résultats d’identification inverse ont été validés sur des échantillons en silicone. Leur matériau constitutif a été caractérisé pour référence en traction uniaxiale et par bulge test. Les modules de Young obtenus par identification inverse sur le test d’aspiration (calcul itératif par Elements Finis) montrent une sur-estimation de 7% au maximum avec les résultats des tests de référence. Ce résultat est une amélioration significative par rapport aux sur-estimations de 30% rencontrées dans la littérature.les caractéristiques du système ont été mises à profit pour mesurer directement l’épaisseur et les propriétés mécaniques de couches superficielles de tissus multicouches sans autre système de mesure. La preuve de concept a été effectuée expérimentalement sur un échantillon artificiel constitué de deux silicones différents. Au bilan, l’épaisseur de la couche supérieure a été identifiée avec une erreur inférieure à 4% , les modules de Young des deux matériaux avec une erreur inférieure à 8%. Ces résultats sont jugés très encourageants pour une future application de la méthode à des tissus du vivant.une méthode d’identification inverse des propriétés mécaniques en temps réelle a été développée. Cette procédure est basée sur une réduction de modèle et fournit également des indications sur la sensibilité de l’identification aux différents paramètres expérimentaux. L’utilisation de cette méthode d’inversion a montré une erreur d’identification de 10 et 12% par rapport aux valeurs de références sur les spécimens constitués de deux couches de silicones. / In-vivo characterization of biological soft tissues is a key step toward patient-specific biomechanical simulation and planning of intra-operative assisted surgery. These tissues’ structures are usually highly heterogeneous due to the variety of their constituents (skin, mucosa, muscle fibers, fat, fascia, vascularization, etc.). In particular, their local mechanical properties may change with depth.Among various characterization techniques, aspiration method is a standard due to its simplicity: tissue is aspirated through a hole while measuring the negative pressure and the associated apex height. An inverse problem is then solved to identify the material mechanical properties. In the literature, the apex height was usually measured using a camera, which induced design difficulties, in particular regarding the required sterilization process for in-vivo measurements.This thesis aims at developing new practical aspiration techniques and inverse analyze techniques to deal with these challenges.First, the aspiration method is revisited, replacing the apex height optical measurement by the measurement of the aspirated tissue volume. In the proposed method the system head was reduced to a simple tube: sterilization becomes easy and the aspiration aperture diameter can be changed according to experimental requirements. The proposed system is thus probably among the simplest, lightest and most inexpensive devices one could achieve.Then, many studies are developed: (i) a comparison of this volume-based method with classical techniques based on optical measurements, (ii) the validation of the volume-based aspiration device and inverse identification on soft homogeneous synthetic materials, (iii) the development of a method for in-vivo identification of multi-layered soft tissues and its validation on two-layer synthetic samples, and (iv) a method for real-time inverse mechanical identification of constitutive materials using the aspiration results.The experimental signal-to-noise ratio in raw volume measurements obtained either optically or by the volume-based method were compared. The effects on the accuracy of various experimental parameters were investigated and quantified: the volume measurement was proved to present the same order or even better accuracy compared to optical measurements.To validate the inverse identifications using the volume-based aspiration method, silicone samples were then made and characterized using (1) aspiration, and, as references, two standard tests such as (2) uniaxial and (3) equibiaxial extension tests. Performing a Finite Element (FE) inverse identification on the experimental results provided Young’s moduli similar to classical tests with about 7% maximum overestimation for the silicones. This underlines a significant improvement of the measurement method accuracy compared to the literature (about 30% relative overestimation).In the proposed device, the aspiration aperture diameter can be easily changed. This feature was used to develop a new method to characterize the mechanical properties as well as the superficial layers’ thicknesses in multi-layer soft tissues. A proof of concept was experimentally validated on two-layer artificial soft silicone specimens. As a conclusion, the superficial layer thicknesses and the materials Young’s moduli were identified with a maximum error of 4 and 8%, respectively. Such results thus provide encouraging perspectives for the in-vivo characterization of two-layer anatomical structures such as skin and sub-dermal tissues.Eventually, a Design Of Experiment (DOE) method was applied to drastically decrease the computation time involved during the inverse identification step, which is a prerequisite for any use in a clinical routine. The identifications using the DOE method were compared with the reference characteristics of the investigated silicones and maximum errors of 10 and 12% were obtained for the homogeneous and two-layer samples, respectively.

Este trabalho analisa os efeitos das trajetórias de umedecimento e secagem no módulo de resiliência e cisalhamento direto quanto à resistência e deformabilidade elástica de solos compactados através de ensaios triaxiais de carga cíclica e ensaios de cisalhamento direto. O solo estudado é oriundo de jazida localizada próximo à BR116/RS, no município de Guaíba, sendo usualmente utilizado como material para execução de aterros rodoviários. As curvas de retenção do solo foram obtidas pelo método de papel filtro para solos compactados com variação de teor de umidade ótima de ±2%. Os estudos de módulo de resiliência e de resistência ao cisalhamento foram analisados nestas condições e demonstraram que o efeito do teor de umidade é significativo nas trajetórias de secagem e umedecimento. As curvas de retenção mostraram diferentes formas de acordo com a umidade de compactação e apresentaram histerese após a amostra ser submetida à trajetória de secagem. Observou-se que os solos compactados no ramo seco apresentaram valores mais elevados de módulo de resiliência e de resistência ao cisalhamento que aqueles que se encontravam no ramo úmido da curva de compactação. Uma análise do solo compactado no ramo seco e umedecido posteriormente até o ramo úmido teve comportamento semelhante aos moldados neste ramo. Por outro lado, na trajetória de secagem dos solos compactados no ramo úmido observou-se um aumento na resistência. Os modelos de desempenho para módulo de resiliência apresentaram boas correlações e para os que utilizam a sucção, observa-se um comportamento diferente com relação aos que não utilizam e com relação às constantes de cada modelo. / This paper analyzes the effects of wetting and drying paths in resilient modulus and shear strength for resistance and elastic deformability of compacted soils through triaxial cyclic load tests and direct shear tests. The soil studied is derived from BR116/RS near the Guaiba’s city, usually being used for subgrade. The retention curves of the soil were obtained by the filter paper method, with optimum moisture content varying a range of ± 2%. The studies of resilient modulus and shear strength were analyzed in these conditions and showed that the effect of moisture content is significant in the drying and wetting trajectories. The retention curves showed different forms according to the moisture content in the compaction, showed hysteresis after the specimen is subjected to the drying trajectory. It was observed that the soils compacted and tested in the dry branch had higher resilient modulus and shear strength than those compacted in the wet branch. An analysis of the soil compacted in the dry branch and subsequently dampened up to the wet branch had similar behavior to the soil molded ah this branch. On the other hand, in the trajectory of drying of the compacted soil at wet branch there is an increase in resistance. Performance models for resilient modulus showed good correlations and those using suction, observe a different behavior with respect to that use and not with respect to the constants of each model.

Ce travail de thèse est consacré à l'étude des milieux granulaires humides. On étudie principalement le cas de faibles teneurs en eau. L'influence du phénomène de capillarité sur la rétention d'eau et sur le comportement mécanique du milieu est analysée. A chaque état d'équilibre, la distribution d'eau dans le milieu granulaire est obtenue en appliquant une succion homogène dans un volume élémentaire représentatif. La méthode multi-échelles utilisée se nourrit d'expérimentations/modélisation à l'échelle des interactions entre les grains, et produit des simulations en éléments discrets du comportement macroscopique qui sont comparées aux résultats d'expérimentation. A l'échelle des interactions capillaires, une étude expérimentale du pont liquide pilotée en succion permet la validation d'un modèle basé sur l'approximation toroïdale du profil du pont liquide. A l'échelle macroscopique, les courbes de rétention d'eau simulées sont proches des courbes de rétention d'eau expérimentales réalisées sur des milieux modèles composés de billes de verre. Enfin, le comportement mécanique macroscopique est simulé. On note une fragilisation du matériau en fonction de la succion dans le domaines des faibles teneurs en eau qui s'explique par une diminution de la densité des ponts liquides. La prise en compte d'une rugosité des grains permet une meilleure description de la transition entre un état humide et un état sec. L'analyse des contraintes montre la pertinence du tenseur des contraintes associé aux interactions attractives dans l'étude de l'évolution de la contrainte à la rupture (compression simple) et de la compressibilité (compression oedométrique) en fonction de la succion. / This work deals with study of humid granular media. Weak water percent media are mainly studied. The influence of capillarity on water retention and mechanical behaviour is analyzed. At each state of equilibrium, water distribution is obtained by applying a homogeneous suction in the entire elementary representative volume. The multi-scale approach used, is based on experimental/modelling at the local scale (interaction between grains) and produce discrete elements simulation of the macroscopic behaviour which are compared to experimental results. At the scale of the interactions, an experimental study of the liquid bridge piloted by suction validates a model based on the toroidal approximation of the liquid bridge shape. At the macroscopic scale, simulated water retention curves are near of experimental water retention curves made on a model sample composed of glass beads. Then, the mechanical behaviour is simulated. We notice a loss of cohesi on in function of suction because of a reduction of the liquid bridge density. The introduction of a roughness allows a best representation of the transition between the non saturation state and the dry state. The analysis of the stress reveal the pertinence of the stress tensor associated with attractives interactions in the evolution of rupture stress (simple compression) and compressibility (oedometric compression) in function of suction.

Esta tese apresenta um estudo de solos colapsíveis utilizando provas de carga em placas executados com inundação da cava. Durante o ensaio a sucção foi monitorada com tensiômetros instalados em cinco profundidades distintas. A inundação da cava foi também monitorada pelo uso da técnica de reflectometria no domínio do tempo. Desta forma pode-se acompanhar a evolução da frente de infiltração e da sucção durante todas as fases do ensaio. Foi introduzido também o uso da tomografia computadorizada para registrar as alterações causadas no solo pelo carregamento e posterior inundação. O acompanhamento da frente de infiltração durante o ensaio foi importante para conhecer a profundidade de influência do colapso no maciço do solo. De posse dos valores de sucção, foi possível a utilização de modelos para solo não saturado para verificar a sua aplicabilidade na previsão de comportamento de estruturas de fundação. A tomografia computadorizada forneceu informações a respeito da distribuição de massa específica do solo antes e depois do carregamento, permitindo concluir que a região mais afetada pelo colapso se restringe a 0,25 D. / This thesis presents a soil collapse study using plate load tests performed with soaking the test pit. During the test suction was monitored by tensiometers embedded at five different depths. Thus, it was possible to follow the wetting front and suction evolution all over the tests stages. lt was also introduced the computerized tomography technique to record the soil changing caused by loading and wetting. Monitoring the wetting front during the test was important to know the influence depth of collapse at soil mass. Having the suction values it was possible to use behaviour models of unsaturated soils to verity their applicability on predicting foundations structure settlements. The computerized tomography yields informations about soil unit weight distribution before and after loading, allowing concludes that collapse most affected region is restrained up to 0.25 D.

Este trabalho apresenta resultados de provas de carga em tubulões a céu aberto, com o monitoramento do teor de umidade através do processo de tradagem, a cada metro, até uma profundidade de 9,0 m, em um maciço de solo não-saturado e colapsível, representativo da região centro-oeste do interior do Estado de São Paulo. Ao todo, realizaram-se dez provas de carga, no Campo Experimental de Fundações da EESC/USP, com e sem inundação do terreno, com carregamento do fuste, foram introduzidas placas de isopor (E.P.S) a fim de, durante a realização dos ensaios, obter separadamente as parcelas de resistência de base e por atrito lateral. A partir dos dados obtidos, procedeu-se uma análise da influência da pressão de sucção, da inundação do terreno e do intervalo de tempo entre a escavação e os outros dois, concretados logo após a etapa de escavação. Observou-se que a sucção tem um efeito importante no comportamento dos tubulões a céu aberto: com o aumento da sucção maiores se tornam as resistências de base e por atrito lateral. Consequentemente, a influência do colapso apresenta-se mais significativa com o aumento da pressão de sucção. / This work presents results of static load tests, in large diameter bored piles, with measurements of soil moisture content in an unsatured collapsible soil, considered as representative of the middle - west region of the State of São Paulo, Brazil. Ten load tests were performed at Foundation Experimental Field of the EESC/USP, with and without wetting of the pit and the with quick maintained load (QML). In the large diameter bored piles were introduction, between the base and the shaft, an layer of \"isopor\", to separate the skin friction and the base resistance, during the static load tests. The gathered data allowed an assessment of the influence the soil suction, of the soil soaking and the effect between excavation and concrete in the behaviour these isolate elements of foundation.

Analisa-se a influência da sucção matricial e da dimensão de sapatas na capacidade de carga e nos recalques de fundações rasas, assentes em areia não-saturada. Na primeira parte da pesquisa foram analisadas 14 provas de carga estática em placas metálicas rígidas assentes a 1,5 m de profundidade, com diâmetros de 0,20, 0,40 e 0,80m e em uma sapata circular de concreto com diâmetro de 1,50 m, no campo experimental de fundações da USP/São Carlos. Devido ao caráter colapsível do solo, a sucção matricial foi monitorada por meio de tensiômetros instalados no fundo da cava. Na segunda parte da pesquisa, foram realizados ensaios em centrífuga, na Universidade do Colorado em Boulder, utilizando-se placas metálicas de 30 mm, 50 mm e 100 mm, ensaiadas a 1 g, 5 g, 10 g, 15 g, 25 g, 50 g e 100 g. As placas foram assentes em maciço de areia em três condições de umidade: seca, inundada e não-inundada. A partir dos resultados obtidos, procedeu-se a análise da capacidade de carga levando-se em conta tanto o efeito da dimensão como o da sucção matricial. A influência da dimensão nos recalques também foi analisada. Ratificou-se que o aumento da sução matricial provoca um aumento substancial na capacidade de carga do sistema placa-solo e uma diminuição considerável nos recalques. Em relação à influência da dimensão no comportamento de fundações rasas, demonstrou-se que tanto a variação da capacidade de carga como a dos recalques não ocorre de forma linear e crescente como apresentado pelos métodos teóricos. Para pequenas dimensões da sapata, os valores de capacidade de carga e recalque aumentam / The influence of matric suction and size of footings in the bearing capacity and settlement of shallow foundations in unsaturated sandy soils are analyzed. Fourteen plate load tests were performed in the first part of the research. Rigid metallic plates with diameters 0,20, 0,40, 0,80 m and one concrete circular footing with 1,50 m were used in the tests. All plates and footing were positioned at 1,50 m depth. The tests were performed in the foundation experimental field of USP/São Carlos. Due to the soil collapsible character, the tests were performed with the monitoring of matric suction pressure through tensiometers installed in the bottom of the holes. Centrifuge tests were carried out at the University of Colorado at Boulder in the second part of the research. Metallic plates with 30 mm, 50 mm and 10 mm were used and the gravity levels were 1 g, 5 g, 10 g, 15 g, 25 g, 50 g e 100 g. The plates were positioned on top of a sandy soil with three moisture conditions: dry, flooded and non-flooded. Thus, the capacity will be analyzed taking into consideration both the geometry of the tested plates and the influence of the matric suction pressure. The footing size influence in the settlement was also analyzed. A substantial increase of the plate-soil system bearing capacity and a considerable decrease in the settlements, caused by matric suction increase, was confirmed. It was also demonstrated that the bearing capacity and settlements variations are not a linearly increasing function of the size as theoretical methods suggest. For small footings, the bearing capacity and settlement increase as the footing size decreases