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Thesis (Ph.D.) -- University of Texas at Arlington, 2008.

Swelling of a polymer gel is a kinetic process coupling mass transport and mechanical deformation. A comparison between a nonlinear theory for polymer gels and the classical theory of linear poroelasticity is presented. It is shown that the two theories are consistent within the linear regime under the condition of a small perturbation from an isotropically swollen state of the gel. The relationships between the material properties in the linear theory and those in the nonlinear theory are established by a linearization procedure. Both linear and nonlinear solutions are presented for swelling kinetics of substrate-constrained and freestanding hydrogel layers. A new procedure is suggested to fit the experimental data with the nonlinear theory. A nonlinear, transient finite element formulation is presented for initial boundary value problems associated with swelling and deformation of hydrogels, based on nonlinear continuum theories for hydrogels with compressible and incompressible constituents. The incompressible instantaneous response of the aggregate imposes a constraint to the finite element discretization in order to satisfy the LBB condition for numerical stability of the mixed method. Three problems of practical interests are considered: constrained swelling, flat-punch indentation, and fracture of hydrogels. Constrained swelling may lead to instantaneous surface instability. Indentation relaxation of hydrogels is simulated beyond the linear regime under plane strain conditions, and is compared with two elastic limits for the instantaneous and equilibrium states. The effects of Poisson’s ratio and loading rate are discussed. On the study of hydrogel fracture, a method for calculating the transient energy release rate for crack growth in hydrogels, based on a modified path-independent J-integral, is presented. The transient energy release rate takes into account the energy dissipation due to diffusion. Numerical simulations are performed for a stationary center crack loaded in mode I, with both immersed and non-immersed chemical boundary conditions. Both sharp crack and blunted notch crack models are analyzed over a wide range of applied remote tensile strains. Comparisons to linear elastic fracture mechanics are presented. A critical condition is proposed for crack growth in hydrogels based on the transient energy release rate. The applicability of this growth condition for simulating concomitant crack propagation and solvent diffusion in hydrogels is discussed. / text

Current design guidelines for reinforced soil walls and slopes recommend the use of granular soils such as gravels and sands as select fills. Cost savings could potentially be realized by using on-site clays and silts. Some clays are swelling and silts are frost susceptible. When considering the use of swelling clays and frost susceptible silts as fills, environmental loading due to swelling-shrinkage and freeze-thaw effects from environmental changes could become a design issue. To examine the hypothesis that consideration of environmental loading during design will produce improvements in the performance of geosynthetic-reinforced soil structures that use clays or silts as fill materials, experimental and numerical studies were undertaken. Geosynthetic-reinforced clay specimens were subjected to wetting and drying in a model test apparatus developed and commissioned for this study. In separate test set-up, reinforced silt specimens were subjected to freezing and thawing. Tests on unreinforced specimens were also performed in otherwise identical conditions for comparison purposes. Movements of the specimens, soil strains, reinforcement strains, soil suctions and soil temperatures were monitored during the application of environmental loading in addition to mechanical loading from external stresses. The results of the laboratory model tests showed that reinforcements reduced horizontal displacements of the clay specimens during wetting and drying. The same is true for the case of silt during freezing and thawing. The environmental loading induced strains, and therefore stresses in the reinforcements. The measured geogrid strain during the wetting-drying of reinforced clay specimen was up to 0.75%. Similarly, the measured geogrid strain in the reinforced silt specimen during freezing-thawing cycles was up to 0.57%. The strains were greater than the strains generated by mechanical loading for the range of applied stresses used in this study. Numerical models were developed to simulate wetting only induced swelling of reinforced clays and freezing only induced expansion of reinforced silts specimens. They were used to simulate the results of laboratory model tests. The performance of geosynthetic-reinforced soil slopes with swelling clay fills and frost susceptible silt fills was evaluated. Parametric studies were performed to determine important parameters affecting the performance of reinforced clay and silt slopes.

The removal of milk fouling deposits often requires the diffusion of electrolyte solutions such as sodium hydroxide through a gel. Very often more than one single anion and one single cation are involved and thus the modelling of such diffusion requires a multicomponent description. Diffusion of electrolyte solutions through gels can be modelled using the Maxwell-Stefan equation. The driving forces for diffusion are the chemical potential gradients of ionic species and the diffusion potential, i.e., the electrostatic potential induced by diffusion of the ions. A model based on the Maxwell-Stefan equation was applied to electrolyte solutions and electrolyte solutions with a gel. When modelling the diffusion of electrolyte solutions, the resulting equations were found to be a partial differential algebraic equation system with a differentiation index of two. The identification of this characteristic of the system enabled a solution method using the method of lines to be developed. When modelling the diffusion of electrolyte solutions through a gel an explicit expression for diffusion potential was developed and hence the diffusion equations were solved. Numerical solutions were presented for a number of case studies and comparisons were made with solutions from literature and between different electrolyte systems. It was found that the results of diffusion of electrolytes were in good agreement with those of experiments and literature. In the case of diffusion of electrolytes through a gel, swelling of the gel was predicted. The model can be improved by adding thermodynamic factors and can be easily extended to multiple ion systems.

Current design guidelines for reinforced soil walls and slopes recommend the use of granular soils such as gravels and sands as select fills. Cost savings could potentially be realized by using on-site clays and silts. Some clays are swelling and silts are frost susceptible. When considering the use of swelling clays and frost susceptible silts as fills, environmental loading due to swelling-shrinkage and freeze-thaw effects from environmental changes could become a design issue. To examine the hypothesis that consideration of environmental loading during design will produce improvements in the performance of geosynthetic-reinforced soil structures that use clays or silts as fill materials, experimental and numerical studies were undertaken. Geosynthetic-reinforced clay specimens were subjected to wetting and drying in a model test apparatus developed and commissioned for this study. In separate test set-up, reinforced silt specimens were subjected to freezing and thawing. Tests on unreinforced specimens were also performed in otherwise identical conditions for comparison purposes. Movements of the specimens, soil strains, reinforcement strains, soil suctions and soil temperatures were monitored during the application of environmental loading in addition to mechanical loading from external stresses. The results of the laboratory model tests showed that reinforcements reduced horizontal displacements of the clay specimens during wetting and drying. The same is true for the case of silt during freezing and thawing. The environmental loading induced strains, and therefore stresses in the reinforcements. The measured geogrid strain during the wetting-drying of reinforced clay specimen was up to 0.75%. Similarly, the measured geogrid strain in the reinforced silt specimen during freezing-thawing cycles was up to 0.57%. The strains were greater than the strains generated by mechanical loading for the range of applied stresses used in this study. Numerical models were developed to simulate wetting only induced swelling of reinforced clays and freezing only induced expansion of reinforced silts specimens. They were used to simulate the results of laboratory model tests. The performance of geosynthetic-reinforced soil slopes with swelling clay fills and frost susceptible silt fills was evaluated. Parametric studies were performed to determine important parameters affecting the performance of reinforced clay and silt slopes.

Bentonite is a smectite type clay mineral and swells in water. In this thesis, the effect of acetone, methyl-ethyl ketone, n-hexane on the properties of bentonite was determined by thermal analysis and water absorption tests. The tests indicated no significant change with treating bentonite with organic liquids. Because of the swelling property, only small amount of bentonite can be suspended in water. This may limit certain applications of bentonite. In this thesis, feasibility of suspending large quantities of bentonite in a non-aqueous media was studied. The concentrations for a pumpable high solid bentonite slurry were determined. As aqueous slurry showed pumpable properties up to 30-35 pounds/barrel, this concentration was as high as 125-150 pounds/barrel for acetone, 175-200 pounds/barrel for methyl-ethyl ketone and 325-350 pounds/barrel for n-hexane. Bentonite deposite has a complicated composition, containing free silica minerals, such as quartz, cristobalite, and opal / silicate minerals, such as feldspar, mica, and zeolite / carbonates or sulfates of alkaline earth metals, such as calcite, dolomite, and gypsum / and, in addition, iron compounds and humus. As mined it is primarily broken and dried and then pulverized by means of an attrition grinding machine. In this study dispersion of raw bentonite by high shear blending and shaking forces in the presence of acetone, methyl-ethyl ketone and n-hexane and eliminating the non-clay impurities by screening were studied. Many attempts have been made to provide a bentonite composition retaining the full swelling properties of the bentonite by the addition of non-aqueous liquids for obtaining a flexible waterproofing sheet. In this research the possible method for deposition of bentonite in a sponge by saturating the sponge with bentonite using organic liquids was investigated.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第13789号 / 工博第2893号 / 新制||工||1427(附属図書館) / 26005 / UT51-2008-C705 / 京都大学大学院工学研究科材料化学専攻 / (主査)教授 瀧川 敏算, 教授 木村 俊作, 教授 田中 文彦 / 学位規則第4条第1項該当

Expansion or swelling behavior of expansive soil has always created problems in the field of geotechnical engineering. When any construction has been carried out on expansive soil without pre-knowledge of their properties under various environmental conditions, the damage is severe. One of the methods to find out swelling potential of expansive soil is the expansive index (EI). The present study investigates the reduction of EI for the two commercially available expansive soils i.e., kaolinite and bentonite when mixed with Ottawa sand and Class C fly ash. The percentages of Ottawa sand and Class C fly ash mixed with kaolinite and bentonite were 0 to 50% by weight. The results show that there is a significant reduction in the swelling properties of expansive soil with the addition of Ottawa sand and Class C fly ash. The reduction in expansive index ranged approximately from 10 to 50% and 4 to 49% for kaolinite and bentonite, respectively. Also the maximum swelling pressure of kaolinite and bentonite soil decreased approximately 93% and 64%, respectively with the addition of various percentages of Ottawa sand and Class C fly ash. These results help to identify the swelling potential and swelling pressure of expansive soil with different percentages of sand and fly ash which will be beneficial to the geotechnical engineer. Standard index properties test such as liquid limit, plastic limit and shrinkage limit test was conducted to see the characteristic of expansive soil when mixed with less expansive sand and Class C fly ash. Also, for these expansive soils one dimensional (1-D) consolidation characteristics was studied with sand and Class C fly ash mixtures and the results were compared with pure kaolinite and bentonite soil. Pre-consolidation (Pc) behavior, compression index (Cc) and recompression or swelling index (Cs) properties were also studied for the different percentages of sand and Class C fly ash with expansive soil.

La sécheresse, accentuée par le réchauffement climatique actuel et à venir, induit des phénomènes de retrait et de gonflement dans de nombreux sols argileux. Ces phénomènes se traduisent principalement par deux conséquences majeures : la modification des propriétés physiques du sol qui influe directement sur l’agriculture et les déformations induisant souvent des tassements différentiels aux niveaux des structures et des ouvrages. Jusqu’à aujourd’hui, ces phénomènes ont été étudiés principalement à l’échelle mésoscopique (échelle « classique » de laboratoire) et macroscopique (échelle de l’ouvrage). Des recherches ont été menées à l’échelle microscopique mais dans des contextes particuliers (argiles destinées au stockage des déchets radioactifs). Le travail de recherche présenté dans ce mémoire de thèse constitue par conséquent une des premières études sur des argiles naturelles, prélevées in situ sur des sites affectés par le retrait-gonflement : la montmorillonite grecque et l’argile verte de Romainville. Ces deux argiles ont été soumises à des cycles d’humidification-séchage dans le Microscope Electronique à Balayage Environnemental (MEBE) afin de quantifier le retrait-gonflement et d’en étudier la cinétique. Un protocole expérimental a été établi, basé sur l’application de l’humidification et du séchage par paliers avec des temps d’équilibre et une fréquence d’application réguliers. Ces essais ont été menés dans le but d’analyser : l’influence de la composition minéralogique, l’étude de l’effet d’échelle et l’influence du type de pilotage (pression ou température). En parallèle à ces essais, des expérimentations ont été menées à l’échelle mésoscopique afin d’établir d’éventuels liens entre les deux échelles. Ils ont consisté en l’étude de l’évolution de la microstructure, de la microporosité et de l’établissement des courbes de rétention. Les observations effectuées à ces deux échelles ont mené à la mise au point de deux méthodes, volontairement simplifiées pour des facilités de mise en œuvre et d’une investigation rapide (études préliminaires, bureaux d’étude). Ces deux méthodes sont, l’une analytique, l’autre numérique, permettant la transition vers l’échelle macroscopique et pour pouvoir estimer le retrait et le gonflement possibles sur un site donné. L’analyse des résultats des essais effectués à l’échelle microscopique (essais MEBE) conduit aux remarques suivantes : la majeure partie des déformations se produit aux fortes humidités relatives ; les déformations mesurées à l’échelle microscopique sont similaires à celles mesurées à l’échelle mésoscopique ; la cinétique de gonflement et de retrait est marquée par plusieurs phases distinctes selon l’argile considérée ; la composition minéralogique, la taille des agrégats et le type de pilotage présentent une influence au niveau de l’amplitude du retrait-gonflement et de la cinétique. L’analyse des résultats des essais effectués à l’échelle mésoscopique (essais de laboratoire) conduit aux remarques suivantes : la limite de retrait (Wr) correspond à une teneur en eau de 13 % et un indice des vides de 0,52 ; aux fortes et moyennes succions, le sol présente une microstructure compacte avec une macroporosité augmentant avec la succion ; aux faibles succions, la microstructure compacte évolue de contours nets et saillants des agrégats à des contours plus doux et réguliers ; des microorganismes ont été observés, engendrant une porosité à la surface très importante, pouvant entraîner un vieillissement du sol et la création de chemins préférentiels pour la pénétration de l’eau ; avec la diminution de la succion, une diminution de la surface spécifique externe et du volume microporeux est observée ; l’humidification et le séchage des échantillons ne semblent pas induire pas de conséquences irréversibles sur la microstructure. / The drought, emphasised by the current global warming and to come, leads phenomena of shrinkage and swelling of many clayey soils. These phenomena are mainly translated by two major consequences: the modification of the physical properties of the soil which influences directly the agriculture and the deformations leading often differential compaction at the levels of the structures and the buildings. Until today, these phenomena were mainly studied at the mesoscopic level (laboratory classical level) and macroscopic level (buildings scale). Research was led to the microscopic level but in particular contexts (clays intended for the confinement of the radioactive waste). The research work presented in this thesis manuscript constitutes consequently one of the first studies on natural clays, taken in situ from sites affected by the swelling-shrinkage: the Greek montmorillonite and the clay of Romainville. These two clays were subjected to wetting-drying cycles in the Environmental Scanning Electron Microscope (ESEM) in order to quantify the swelling-shrinkage and to study kinetics. An experimental protocol was established, based on the application of the wetting and the drying by stages with regular time of stabilisation and frequency of application. These tests were led in order to analyse: the influence of the mineralogical composition, the study of the effect of scale and the influence of the type of piloting (pressure or temperature). In parallel to these tests, some experiments were led to the mesoscopic level to establish possible links between both levels. They consisted of the study of the evolution of the microstructure, the microporosity and the establishment of the retention curves. The observations made in these two levels led to the development of two methods, voluntarily simplified for ease of implementation and of a fast investigation (preliminary studies, engineering consulting firms). These two methods are, the one analytics, the other numerical, allowing the transition towards the macroscopic level and to be able to estimate the possible shrinkage and the swelling on a given site. The analysis of the results of the tests made in the microscopic level (ESEM tests) leads to the following remarks: the major part of the strains occurs in the high relative humidities; the strains measured in the microscopic level are similar to those measured in the mesoscopic level; the kinetics of swelling and shrinkage are marked by several different phases according to the considered clay; the mineralogical composition, the size of the aggregates and the type of piloting present an influence at the level of the amplitude of the shrinkage - swelling and the kinetics. The analysis of the results of the tests made in the mesoscopic level (laboratory tests) leads to the following remarks: the shrinkage limit (Wr) corresponds to a 13 % moisture content and a void index of 0,52; in the high and medium suctions, the soil presents a compact microstructure with a macroporosity increasing with the suction; in the low suctions, the compact microstructure evolves of sharp outlines of the aggregates in rounder outlines; microorganisms were observed, engendering a very important porosity on the surface, being able to pull an ageing of the ground and the creation of preferential paths for the penetration of the water; with the decrease of the suction, the decrease of the external specific surface and of the microporous volume is observed; the wetting and the drying of samples do not seem to lead no irreversible consequences on the microstructure.