No description available.

No description available.

Calcium bentonite deposits of the Glendon and Bucatunna formations of the Oligocene Vicksburg Group located in Smith County, Mississippi were examined to determine the depositional environment, diagenetic history and origin of the bentonite. Traditionally, calcium bentonite was considered to be the product of the weathering of volcanic ash deposits. The hypothesis tested is that the bentonite deposits are not a result of weathered volcanic ash, but are a result of weathered marl. Core samples were drilled from the Chisholm bentonite mine in Smith County and were studied using X-ray diffraction, scanning electron microscopy, and petrographic microscopy. Abundant bacteria along with nanometer-scale organic textures were found throughout and are consistently associated with bentonite, illite, and smectite. No evidence of volcanic ash was found. It appears that the calcium bentonite clays in the Glendon and Bucatunna formations of Smith County, Mississippi formed from weathering, including bacterial activity, of glauconite-bearing marl.

As argilas são rochas constituídas por argilominerais e por minerais acessórios, cuja estrutura cristalina permite a adsorção de cátions e ânions conferindo-lhes propriedades físico-químicas particulares. Quimicamente os argilomineriais são formados essencialmente por silicatos hidratados de alumínio, ferro e magnésio. As bentonitas apresentam mais de 140 usos industriais, com variações particulares, seja devido ao emprego tecnológico desta argila, seja devido à origem geológica ou à composição mineralógica desta, por isso, sendo consideradas tipos especiais de argilas industriais. O termo bentonita é usado para designar uma argila com alto teor de argila esmectítica. O maior produtor mundial de bentonita são os Estados Unidos representando cerca de um terço do total da produção mundial. No Brasil, os mais importantes jazimentos de bentonitas encontram-se na Paraíba, nos municípios de Boa Vista, Cubati e Pedra Lavrada. A bentonita bruta da Paraíba é lavrada por empresas mineradoras e comercializada em grandes quantidades no próprio Estado, sendo estas destinadas a empresas que as beneficiam, ativam e posteriormente vendem para os demais mercados nacionais. Os preços da bentonita variam em função da qualidade do produto, da pureza, da função ou aplicação, e do tipo do beneficiamento e ativação a que foi submetido o minério. Considerando a expectativa de crescimento desse setor para os próximos anos, este estudo tem como objetivo complementar e atualizar dados tecnológicos existentes na literatura sobre as bentonitas do Estado da Paraíba, contribuindo com estudos tecnológicos das bentonitas da Paraíba realizados em 1976 pelo professor Dr. Pérsio de Souza Santos. Pretende-se evidenciar como estão as propriedades e os usos de 5 argilas da mina Lages após 35 anos de estudos. Para o desenvolvimento deste trabalho utilizaram-se 5 tipos diferentes de bentonitas cedidas pela empresa BENTONISA - Bentonita do Nordeste S.A. Para estas foram realizadas as caracterizações físico-químicas e mineralógicas. Através da análise dos resultados obtidos foi possível realizar algumas indicações para os usos potenciais destes materiais. / The clays are composed of clay minerals and accessory minerals, whose crystal structure allows the adsorption of cations giving them particular physical and chemical properties. Chemically, the argilomineriais are formed mainly of hydrated silicates of aluminum, iron and magnesium. The bentonites are special types of industrial clays because submitting more than 140 industrial uses, with particular variations, whether due to technological employment of clay, is due to the geological origin and the mineralogy of this clay. The term bentonite is used to designate a high clay content of montmorillonite. The world\'s largest producer of bentonite is the United States represents about one-third of total world production. In Brazil, the most important bentonite clay bentonite deposits are found in Paraiba, in the municipalities of Boa Vista, Cubati and Pedra Lavrada. The crude bentonite Paraíba is wrought by mining companies and sold in large quantities within the State, which are aimed at companies that benefit, activate and subsequently sold to other markets. Prices vary depending on the bentonite product quality, purity, function or application, and the type of processing and activation in the ore that was submitted. Considering the expected growth of this sector in the coming years, this study aims to complement existing technology and update data in the literature on bentonite clays of Paraíba State, contributing to technological studies of bentonites from Paraíba conducted in 1976 by Professor Dr. Pérsio de Souza Santos. It is intended to highlight are the properties and uses of these materials after 35 years of studies. To develop this work, we used five types of bentonite clays supplied by the company BENTONISA-Bentonita do Nordeste S.A., For these were the physical and mineralogical characterization. By analyzing the results we achieve some indication for the potential uses of these materials.

As argilas são rochas constituídas por argilominerais e por minerais acessórios, cuja estrutura cristalina permite a adsorção de cátions e ânions conferindo-lhes propriedades físico-químicas particulares. Quimicamente os argilomineriais são formados essencialmente por silicatos hidratados de alumínio, ferro e magnésio. As bentonitas apresentam mais de 140 usos industriais, com variações particulares, seja devido ao emprego tecnológico desta argila, seja devido à origem geológica ou à composição mineralógica desta, por isso, sendo consideradas tipos especiais de argilas industriais. O termo bentonita é usado para designar uma argila com alto teor de argila esmectítica. O maior produtor mundial de bentonita são os Estados Unidos representando cerca de um terço do total da produção mundial. No Brasil, os mais importantes jazimentos de bentonitas encontram-se na Paraíba, nos municípios de Boa Vista, Cubati e Pedra Lavrada. A bentonita bruta da Paraíba é lavrada por empresas mineradoras e comercializada em grandes quantidades no próprio Estado, sendo estas destinadas a empresas que as beneficiam, ativam e posteriormente vendem para os demais mercados nacionais. Os preços da bentonita variam em função da qualidade do produto, da pureza, da função ou aplicação, e do tipo do beneficiamento e ativação a que foi submetido o minério. Considerando a expectativa de crescimento desse setor para os próximos anos, este estudo tem como objetivo complementar e atualizar dados tecnológicos existentes na literatura sobre as bentonitas do Estado da Paraíba, contribuindo com estudos tecnológicos das bentonitas da Paraíba realizados em 1976 pelo professor Dr. Pérsio de Souza Santos. Pretende-se evidenciar como estão as propriedades e os usos de 5 argilas da mina Lages após 35 anos de estudos. Para o desenvolvimento deste trabalho utilizaram-se 5 tipos diferentes de bentonitas cedidas pela empresa BENTONISA - Bentonita do Nordeste S.A. Para estas foram realizadas as caracterizações físico-químicas e mineralógicas. Através da análise dos resultados obtidos foi possível realizar algumas indicações para os usos potenciais destes materiais. / The clays are composed of clay minerals and accessory minerals, whose crystal structure allows the adsorption of cations giving them particular physical and chemical properties. Chemically, the argilomineriais are formed mainly of hydrated silicates of aluminum, iron and magnesium. The bentonites are special types of industrial clays because submitting more than 140 industrial uses, with particular variations, whether due to technological employment of clay, is due to the geological origin and the mineralogy of this clay. The term bentonite is used to designate a high clay content of montmorillonite. The world\'s largest producer of bentonite is the United States represents about one-third of total world production. In Brazil, the most important bentonite clay bentonite deposits are found in Paraiba, in the municipalities of Boa Vista, Cubati and Pedra Lavrada. The crude bentonite Paraíba is wrought by mining companies and sold in large quantities within the State, which are aimed at companies that benefit, activate and subsequently sold to other markets. Prices vary depending on the bentonite product quality, purity, function or application, and the type of processing and activation in the ore that was submitted. Considering the expected growth of this sector in the coming years, this study aims to complement existing technology and update data in the literature on bentonite clays of Paraíba State, contributing to technological studies of bentonites from Paraíba conducted in 1976 by Professor Dr. Pérsio de Souza Santos. It is intended to highlight are the properties and uses of these materials after 35 years of studies. To develop this work, we used five types of bentonite clays supplied by the company BENTONISA-Bentonita do Nordeste S.A., For these were the physical and mineralogical characterization. By analyzing the results we achieve some indication for the potential uses of these materials.

Austin, Texas consists of highly expansive soils that have caused failures in many structures. Minimizing the detrimental effects of expansive soils on structures requires that the swelling of these soil(s) is quantified accurately, efficiently, and timely. A testing procedure was developed to directly measure soil swelling using centrifuge technology by Plaisted, 2009. This testing procedure was developed in order to reduce the test duration while generating more swelling data relative to conventional tests that directly measure swell. However, the new procedure was incapable of obtaining in-flight swell data, resulting in the need to develop a procedure to directly measure swell during centrifugation. The objectives of this study were to update the testing procedure developed by Plaisted, 2009 by incorporating the use of an in-flight Data Acquisition System (DAS) that would produce accurate and repeatable results; and use the updated testing procedure to quantify the effects of compaction conditions on swelling for three expansive soils in the Austin area (Eagle Ford Shale, Houston Black Clay, and Taylor Clay). A DAS consisting of linear position sensors, analog to digital converters, JeeNode Arduinos, and an accelerometer was developed and installed within the centrifuge. Specimens were compacted at various water contents, and densities, and subjected to different g-levels. The effects of g-level, compaction water content, compaction dry unit weight, and soil type were determined by comparing the 34 hour swell percentages for the compacted specimens. The results of this study showed that in-flight monitoring of clay swelling could be successfully implemented in a comparatively small centrifuge, and that the data collected from the DAS was accurate and repeatable. Swelling of tested soils was found to be sensitive to changes in water content around optimum, with specimens compacted wet of optimum swelling less than specimens compacted dry of optimum. A 6% increase in relative compaction was found to negligibly affect the swelling. Finally, variations in confinement and compaction conditions were found to have a greater effect on swelling for soils that are more expansive in nature compared to soils less expansive in nature. / text

The fully softened shear strength was defined by Skempton (1970) as the peak drained shear strength of a clay in a normally consolidated state. All the experience available on the applicability of the fully softened shear strength for slopes is based on back-analyses. Back-analyses of first-time failures in cuts in stiff-fissured clays and embankments constructed of fat clays have shown that, over a long period of time, the shear strength gets reduced from what is measured in the laboratory using undisturbed samples to the fully softened shear strength. These back-analyses require knowledge or assumption of pore pressures in the slope, which will have a significant influence on the shear strength obtained. Karl Terzaghi, in 1936, was the first person that qualitatively explained the behavior of cut slopes in stiff-fissured clays. According to Terzaghi (1936), a softening process is initiated by the water percolating into the fissures causing swelling and decreasing the overall shear strength of the clay mass. Investigations presented later by Skempton and his colleagues showed that the controlling shear strength for cuts in stiff-fissured clays was equal to the fully softened shear strength and recommended this shear strength to be used for design (Skempton 1970; Chandler and Skempton 1974; Chandler 1974; Skempton 1977). Skempton (1977) concluded that displacements caused by progressive failure decrease the shear strength of stiff clays toward the fully softened shear strength. At first, it was believed that only stiff-fissured clays were subjected to softening and that intact clays should be designed using the peak shear strength measured using undisturbed samples (Skempton and Brown 1961; Skempton 1964, 1970). Recent publications have showed that the likelihood of a clay experiencing softening is more dependent on the plasticity of the clay rather than the fissures (Bjerrum 1967; Chandler 1984a; Mesri and Abdel-Ghaffar 1993). Fat clays, when compared to lean clays, tend to be more brittle. This means that fat clays have a more pronounced decrease in shear strength after the peak shear strength is achieved and for this reason are more susceptible to progressive failure. First-time failures in stiff clays usually occur a long period of time after construction. For this reason, steady state seepage was used in the back-analyses of the case histories presented by Skempton and his colleagues. They found that a pore pressure ratio of 0.3 was applicable to first-time failures in cuts in stiff-fissured clays (James 1970; Vaughan and Walbancke 1973; Chandler 1974; Skempton 1977). Investigations presented by Professor Steve Wright and his colleagues of the University of Texas at Austin showed, based on back-analyses, that the fully softened shear strength is also the controlling shear strength of compacted embankments constructed of highly plastic clays (Green and Wright 1986; Kayyal and Wright 1991; Wright 2005; Wright et al. 2007). Steve Wright and his colleagues concluded that weathering, expressed in cycles of wetting and drying, was the main mechanism decreasing the shear strength of compacted clay embankments toward the fully softened shear strength. Failures in this type of projects were found to be shallow (less than 10 ft deep) and to occur numerous years after construction (USACE 1983; Stauffer and Wright 1984; Kayyal and Wright 1991; Wright et al. 2007). A pore pressure ratio ranging from 0.4 to 0.6 was found to be applicable for the case histories analyzed by Wright and his colleagues. Day and Axten (1989) recommended the use of the infinite slope method with seepage parallel to the slope face for slope stability analyses. This same recommendation was presented by Lade (2010). A seepage parallel to the slope face corresponds to a pore pressure ratio ranging from 0.4 to 0.5 for slopes with ratios of 2H:1V to 5H:1V. Failures on compacted clay embankments related to softening have been reported in Texas (Stauffer and Wright 1984; Kayyal and Wright 1991; Wright 2005; Wright et al. 2007), and Mississippi (USACE 1983). According to McCook (2012), softening of this type of structures also occur in Louisiana To perform slope stability analyses using fully softened shear strength parameter, the type of soils, type of projects, and depths where this shear strength is applicable, and the pore pressures and factor of safety to be used in design should be determined. As stated above, the fully softened shear strength has been found to be the controlling shear strength of cuts in stiff clays and compacted embankments constructed of highly plastic clays. Steady state seepage conditions should be used to design cuts in stiff clays, and a pore pressure ratio ranging from 0.4 to 0.6 or a phreatic surface at the surface of the slope should be used to design compacted embankments made of fat clays. In cuts in stiff clays, both shallow and deep failures related to fully softened shear strength have been observed. For this type of project, the recommended methodology for design is to assign a curved fully softened failure envelope to the whole slope, search for the critical failure surface, and obtain the factor of safety. This approach will provide the correct factor of safety but the critical surface obtained might not be what is expected to occur in situ. Pore pressures corresponding to steady state seepage should be used for design. It should be emphasized that the recommendation to use fully softened shear strength in first-time failures in stiff clays is based on the back-analyses of case histories. Research is required to better understand progressive failure and its influence on the shear strength mobilized in situ. In compacted embankments constructed of fat clays, only shallow failures related to fully softened shear strength have been observed. For this type of projects, the recommended methodology for design is to assign a curved fully softened failure envelope to the whole embankment, search for the critical failure surface, and obtain the factor of safety. If for any reason deep failures are to be considered in designing compacted embankments constructed of fat clays, based on the fact that failures in this type of projects are usually shallow, the first 10 ft below the surface of the slope should be assumed to have a shear strength equal to the fully softened shear strength. Pore pressures should be calculated based on a water table coincident with the slope face. The fully softened shear strength should not be used in the foundation soil. If any softening occurred in the foundation soil, this should be reflected in the shear strength measured using undisturbed samples. Softening of the foundation soil is not expected to occur after the embankment is constructed. The consequences of shallow and a deep failures are usually not the same. For this reason, is reasonable that the same factor of safety should not be required for both cases. A shallow failure may be considered by some agencies solely as a maintenance issue. The factor of safety should be based on the uncertainties in the parameters being used for design and the consequences of failure of the structure (Duncan and Wright 2005). The parameters that have more impact on the factor of safety obtained for slope stability are shear strength and pore pressures. The fully softened shear strength is the lowest shear strength expected to be mobilized in first-time slides. This shear strength, coupled with a conservative assumption of pore pressure gives a low uncertainty in the parameters that have the most influence in the factor of safety. For shallow failures, the consequences of failure are very low. For this reason, if the fully softened shear strength is used, coupled with a water table corresponding to the worst case scenario possible, a factor of safety as low as 1.25 can be used. For deep failures, the consequences of failure will vary depending on the structure. The pore pressure for this type of analyses should be based on the worst seepage condition expected throughout the life of the project. In this case, for structures with low to mid consequences of failure, a factor of safety of 1.35 can be used. For structures with a high consequence of failure, a factor of safety of 1.50 can be used. These factors of safety are based on the recommendations presented by Duncan and Wright (2005) for factors of safety based on uncertainties in the parameters and consequences of failures. The fully softened shear strength should be measured using normally consolidated remolded specimens as recommended by Skempton (1977). Soil samples should be hydrated for two days using distilled or site-specific water. The soil sample should then be washed or pushed through a No. 40 (425 µm) sieve. To achieve the desired water content, the soil sample cab be air-dried or more water should be added. Water contents equal to or higher than the liquid limit should be used to prepare test specimens for fully softened shear strength measurements. The direct shear device is recommended for fully softened shear strength measurements. The Bromhead ring shear device does not provide accurate values of fully softened shear strength. The triaxial device requires more time and effort to measure the fully softened shear strength and provides about the same fully softened shear strength as the direct shear device. The fully softened shear strength failure envelope can be estimated using the correlation presented in Figure 6.59 for the parameters required for Equation 4.1. This correlation is only intended to be used in preliminary design or if better information is not available. Laboratory determination of fully softened shear strength is always recommended for final designs. If this is not possible, the confidence limits presented in Figure 6.59 should be used to determine the fully softened shear strength parameters. / Ph. D.

Authigenic clays are potential proxies for paleoclimate change when formed under saline conditions. Between 1.9 -1.7 mya, Olduvai was a closed-hydrologic basin into which Al- and Fe- rich detrital clays were transported from surrounding soils. Authigenic Mg-rich smectite formed within the basin due to chemical alteration in alkaline and saline conditions. 40 samples were chosen from a stratigraphic section in the center of the paleolake and analyzed to characterize the geochemical facies of the material using XRD, EMPA, and FTIR. ~70% of samples were Mg-rich with clay d060 XRD peaks between 1.506-1.523Å. EMPA indicated (Al2O3 + Fe2O3)/MgO ratios ranged from 0.2-4.8, 21 had ratios >1.0, indicating higher (Al2O3 + Fe2O3) content. These clay data correlated with bulk XRF data, indicating diagenetic controls on bulk composition. Therefore, bulk geochemistry can potentially indicate paleoclimate change when influenced by Mg-rich phyllosilicate formation.

Neste trabalho foi realizado um estudo das interações entre o corante catiônico azul de metileno com partículas de argilas em suspensão aquosa, visando detectar processos de migração de moléculas de corante entre partículas de argila. Até o momento as interações entre moléculas de corante e partículas de argila vem sendo descritas tendo-se em conta dois processos, um deles devido a adsorção de moléculas de corante nas superfícies externas e migração do corante para a região interlamelar, e outro devido as interações partícula-partícula, onde as interações entre as partículas de argila levam a formação de aglomerados de partículas, com o corante aprisionado nas regiões internas formadas. Há fortes indícios da ocorrência da migração de moléculas de corante entre partículas de argila, porém não houve detecção direta deste processo. No presente trabalho, foi idealizada uma metodologia que permitiu detectar variações espectrais, as quais podem ser atribuídas ao processo de migração de corante entre partículas de argila. A metodologia empregada consistiu na adição de suspensão de argila à suspensão argila-corante. Foram realizadas medidas espectrofotométricas na região do visível, em função do tempo, a partir do instante em que as suspensões são misturadas. Os espectros determinados para as amostras foram comparadas com os espectros determinados para a amostra de referência, a qual foi preparada pela adição de água a suspensão corante argila. Os resultados mostraram que as amostras e a referência apresentam comportamento espectral distinto, este comportamento pode ser atribuídos a migração de moléculas de corante entre partículas de argila. De forma geral, verificou-se que a migração do corante entre partículas ocorre preferencialmente para as partículas da argila SWy-1, pois esta argila apresenta a região interlamelar disponível para a adsorção das moléculas de AM, onde ocorre a protonação da molécula do corante, tornado-a mais estável. Os experimentos utilizando membrana de diálise mostraram que quando as suspensões estão isoladas pela membrana a migração das moléculas de corante entre partículas de argila não ocorre, é necessário uma interação ou contato entre as partículas para que a migração ocorra. / In the present work, studies on the interaction between the cationic dye methylene blue and clay particles in aqueous suspension are presented, aiming to detect migration processes of dyes molecules between clay particles. Up to now, the interaction between dye molecules and clay particles is described considering mainly two processes, one due to the adsorption of the dye molecules onto the outer surfaces of the clay particles, and subsequent migration toward the inner surfaces of the clay tactoids. The other process involves particle-particle interaction; the interaction between clay particles promotes particle agglomeration, with dye molecules being trapped in the internal sites formed between particles. There are strong evidences that dye molecules can exchange between dye coated particles, and in the present study a methodology was idealized to detect spectral changes, which could be attributed to migration of dye molecules between clay particles. According to the methodology used, clay particles were added to a dye-clay suspension and spectrophotometric measurements in the visible region was taken after different time intervals. The results were compared with reference spectra, determined for samples prepared adding water to the clay-dye suspension. The results showed that the spectral behavior of the samples and the reference were different, and this behavior can be attributed to the migration of adsorbed dye molecules between clay particles. It was observed that migration occurs preferentially in a direction towards the SWy-1 clay particles. The clay SWy-1 has interlamellar surfaces available to the dye adsorption. In the interlamellar region there are acids sites, where the dyes molecules are protonated. The protonation of dye molecules stabilize the adsorbed molecules. The experiments using dialysis membrane showed that when the particles are isolated by a membrane, the migration between clay particles do not occur, indicating that a close contact or interaction between the clay particles is necessary to the migration occur.

This dissertation describes the development of a new multi-directional direct simple shear testing device, the Texas A&M Multi-directional Direct Simple Shear (TAMU-MDSS), for testing marine soil samples under conditions, which simulate, at the element level, the state of stress acting within a submarine slope under dynamic loading. Prototype testing and an experimental program to characterize the response of marine clays to complex loading conditions are presented. The work is divided into four major components: 1) Equipment Development: Design and construction of a prototype multi-directional direct simple shear testing device (TAMU-MDSS) that addresses the limitations of previous devices. 2) Support systems: selection of control software, development of data acquisition system and design of back pressure systems for direct pore pressure measurements. 3) Prototype Testing: performance of the TAMU MDSS system and testing of strain-control and stress-control capabilities. 4) Experimental Testing: characterize the response of marine clays to monotonic, dynamic and random loads. The two-directional monotonic, cyclic, circular and figure-8 tests demonstrated the undrained shear strength increases with increasing initial shear stress, (i.e, slope), for shearing in the same direction (equivalent to downhill). The strength decreases for shearing in the direction opposite to the initial stress (shearing uphill). The response is as brittle for shearing in the same direction as the shear stress applied during consolidation initial shear stress and ductile for shearing opposite to initial shear stress. These findings have important implications for the stability of the slope, predicting that forces acting downward in the slope direction will need to mobilize less strain to reach peak strength and initiate failure. This information provides insight into the behavior of marine soils under complex loading conditions, and provides high quality laboratory data for use in constitutive and finite element model development for analysis of submarine slopes.