Abstract Soils are particulate materials, which often stand out for their low shear strength. In most cases, this aspect justifies adapting the geotechnical project for this characteristic, which can be even more problematic in the case of soft sands, since it often occurs in superficial layers in various parts of the metropolitan region of Fortaleza. Therefore, the soil improvement procedure with the addition of small cement fractions can be crucial. The content to be adopted should be such as to bring a more economically viable alternative to the geotechnical design of a shallow foundation, for example. The present research aims to propose a modified Mohr-Coulomb envelope for artificially cemented soils. The proposal is based on the development of two functions that relate shear strength parameters (cohesion and friction angle) with the cement content. In order to assess the proposed functions, triaxial shear tests were performed on the sand with different cement contents. The adjustments presented consistent results. In addition, the proposed envelope was validated using published results encountered in literature.

Abstract Fibre reinforcement is considered a good alternative for improving the geotechnical properties of soil. However, studies that investigate its behaviour, accounting for the unsaturated condition, and the hydraulic behaviour of soil mixtures with fibre, are limited. Therefore, the current study evaluates the impact of the inclusion of polypropylene fibres on the hydraulic behaviour of soil through geotechnical characterisation, scanning electron microscopy (SEM), macroporosity and microporosity tests, and filter paper tests. The soil-water characteristic curve (SWCC) of different mixtures of fibre-reinforced soil was adjusted by the models enshrined in the literature, using polypropylene fibres of length 6 mm, diameter 18 μm, and fibre contents 0.25% (SF025), 0.75% (SF075), 1.0% (SF100), and 1.25% (SF125) relative to the dry weight of the soil. The results indicated a transition from unimodal to bimodal shape in the SWCC for the polypropylene fibre-reinforcement, suggesting that their inclusion altered the soil structure. The same bimodal behaviour of SWCC was observed in all reinforced samples that produced similar values of air-entry suction and residual volumetric water content, but with increased water retention for the same level of suction for higher fibre content. The results of the tension table test indicated an increase in the volume of macropores with an increase in fibre content and a decrease in micropore volumes. These results agree with the compaction tests, which showed a decrease in the dry maximum density with an increased fibre content, whereas the optimum water content increased.

RESUMO Os aterros sanitários são obras construídas para o confinamento seguro dos resíduos sólidos e, entre seus elementos de projeto, destaca-se a camada de impermeabilização da cobertura final, frequentemente construída com solo argiloso, que deve, entre outras funções, minimizar ao máximo a infiltração de águas pluviais para o interior do aterro e o fluxo de gases com o meio ambiente. As características físicas, químicas e mineralógicas dos materiais dessa camada devem ser analisadas para a avaliar seu potencial de utilização. O presente trabalho teve como objetivo avaliar o desempenho de argilas expansivas, sujeitas à variação de umidade, como material impermeabilizante de cobertura de aterros sanitários, sendo caracterizadas duas amostras por meio de ensaios geotécnicos. As características foram compatíveis com os requisitos exigidos nas normas consultadas. A parte superior de uma camada de argila compactada foi reproduzida com uma das amostras em um modelo experimental, sujeita à secagem, com observação da formação de trincas e medições do teor de umidade ao longo do tempo e profundidade. A formação de trincas na superfície se iniciou para teores de umidade acima do limite de plasticidade. A aplicação de uma carga hidráulica na superfície após a etapa de secagem resultou em um fechamento das trincas em razão da expansão da argila, indicando eficiência na restrição de entrada de águas pluviais. No entanto, o uso de material expansivo para esse fim deve ser investigado quanto ao seu desempenho em campo, tanto na fase de construção, durante a compactação, quanto de operação, quando estará sujeito às variações climáticas.

ABSTRACT Solid waste landfills are works built to contain solid urban waste, being the most used final disposal method in Brazil. One of the most important components of the project is the final cover, the low hydraulic conductivity layer, with clayey materials, which has the function of minimizing the infiltration of rainwater into the landfill and the entry and exit of gases. The physical, chemical and mineralogical characteristics of clayey materials must be analyzed for potential use as a cover layer. The present work aimed to evaluate the use of clays, with expansive characteristics, subject to water content variations, as cover material in landfills, being characterized two clay samples through geotechnical tests. The characterization indicated samples with characteristics compatible with the requirements demanded by the consulted standards. One of them was used in a laboratory model and reproduced the upper part of a layer of compacted clay, subject to drying on the surface, with observation of the formation of cracks, and with measurements of the water content over time and depth. Cracks on the clay surface occurred during the drying process, starting for water contents above the limit of plasticity of the clay. The application of a hydraulic head on the surface, after the drying step, resulted in cracks closure, due to the expansion of the clay, indicating efficiency in the restriction of rainwater entry. However, the use of expansive material for this purpose should be investigated regarding its performance in the field, both in the construction phase, during compaction, and in operation, subject to climatic variations.

RESUMO Para adequar-se à realidade da sociedade contemporânea, a organização de todo e qualquer processo produtivo deverá prevê planos de gerenciamento de resíduos, que buscam encontrar alternativas técnicas, econômicas e ambientalmente viáveis para os subprodutos advindos de sua operação. Sob esta premissa as empresas Energia Pecém e Eneva, que gerenciam as Usinas Termelétricas Porto Pecém I e II, firmaram parceria com a Universidade Federal do Ceará (UFC), visando o desenvolvimento de projeto científico que objetivava dar destinos adequados aos resíduos advindos da queima do carvão mineral nas UTE’s. O resultado foi o desenvolvimento de diversos trabalhos que avaliaram alternativas para o emprego das cinzas. O presente estudo verificou a possibilidade de empregar as cinzas em camadas de barreiras impermeabilizantes de fundo de aterros (liners). Foram realizados diversos ensaios geotécnicos com o intuito de caracterizar o material e verificar se o mesmo possui as propriedades necessárias a utilização proposta, como por exemplo, a condutividade hidráulica, que para este fim deverá ser inferior a 10-7 cm/s. Entretanto, observou-se variabilidade significativa nos valores dos parâmetros estudados, o que levou a necessidade de analisar o uso de um material composto, misturas de solo (areia argilosa) e cinza composta em diferentes proporções, que apresentou resultados mais consistentes, atingindo valores de condutividade hidráulica próximos aos exigidos para uso como liner. Dentre as misturas de solo e cinza analisadas, mistura denominada S70C30 (70% de massa de solo e 30% em massa de cinza), apresentou um coeficiente de permeabilidade saturada de 4,26x10-7 cm/s que juntamente com outras características geotécnicas, mostrou-se adequada para o uso proposto.

ABSTRACT In order to adapt to the reality of contemporary society, the organization of any and all productive processes should include waste management plans, which seek to find technical, economic and environmentally viable alternatives to the by-products arising from its operation. Under this premise the companies Energia Pecém and Eneva, which manage the Porto Pecém I and II thermoelectric plants, entered into a partnership with the Federal University of Ceará, aiming at the development of a scientific project that aimed to provide adequate destinations for the residues arising from the burning of coal in the thermoelectric plants. The result was the development of several works that evaluated alternatives for the use of ashes. The present study verified the possibility of using the ashes in layers of waterproofing barriers of landfills (liners). Several geotechnical tests were carried out in order to characterize the material and verify if it has the necessary properties for the proposed use, such as hydraulic conductivity, which for this purpose should be less than 10-7 cm/s. However, significant variability was observed in the values of the studied parameters, which led to the need to analyze the use of a composite material, mixtures of soil (clayey sand) and composite ash in different proportions, which presented more consistent results, reaching hydraulic conductivity values close to those required for use as a liner. Among the mixtures of soil and ash analyzed, a mixture called S70C30 (70% soil mass and 30% ash mass) had a saturated permeability coefficient of 4.26x10-7 cm/s which together with other geotechnical characteristics, was adequate for the proposed use.

RESUMO O elevado volume de cinzas de carvão mineral acumulado nas bacias de armazenamento da Usina Termoelétrica Energia Pecém resultou em uma demanda por pesquisas que propusessem diferentes formas de utilização desse resíduo, de modo a dar um destino final para este material. O uso das cinzas na forma de coberturas secas de depósitos de resíduos se mostrou uma alternativa viável, devido à existência de estudos relacionados ao tema e à possibilidade de absorção de quantia significativa do volume de resíduos produzido. O estudo apresentado corresponde à segunda etapa de uma pesquisa que verificou a viabilidade da aplicação de cinzas de carvão em sistemas de cobertura de aterros sanitários de resíduos sólidos urbanos. Com base nos resultados de uma modelagem numérica preliminar, foram executadas três colunas de solo, que representaram três modelos de cobertura: Coluna A – Uma camada superior de solo natural (30 cm) e uma camada de material impermeabilizante com a mistura de solo e cinzas MS70C30 (30 cm, com 70% de solo e 30% de cinzas); Coluna B - Uma camada de solo natural (30 cm) e uma camada de material impermeabilizante com cinza composta (30 cm); e Coluna C – Camada única de solo natural (30 cm), representando a cobertura encontrada no Aterro Sanitário do Município de Caucaia. A Coluna A foi instrumentada com três sensores de umidade. Foram realizados dois ensaios de infiltração em cada coluna, avaliando-se os volumes percolados em cada sistema e os perfis de saturação da coluna instrumentada (Coluna A). Ao se avaliar volume percolado em cada ensaio, verificou-se que a mistura MS70C30 (Coluna A) mostrou o melhor desempenho, resultando em um volume percolado muito inferior em relação aos outros dois modelos. O material também manteve as condições de saturação elevadas, acima de 90% ao longo de quase todo os ensaios, condição necessária para reduzir a fuga de biogás do interior do sistema.

ABSTRACT The significant amount of coal ashes stored in Energia Pecém Thermoelectric Plant adjacent yards required researches that propose ways of applying this waste, allowing their correct final disposal. Application of this material in dry covers systems proved to be a viable alternative, due the former experience in other works and the possibility of absorbing a large amount of the ashes produced. This work corresponds to second part of a research that studed the application of coal ashes in engineered sanitary landfills dry cover systems. Considering data of a preliminar numerical modelling analysis, three soil columns was builded, which represented three different dry cover systems: Column A – A natural soil layer (30 cm) and a waterproof layer composed of the soil and ashes mixture M70C30 below (30 cm, composed by 70% soil and 30% ashes); Column B – A natural soil layer (30 cm) and a waterproof layer composed of ashes (30 cm) and Column C – A single layer composed of natural soil (30 cm) reproducing the dry cover adopted in Caucaia Municipal Sanitary Landfill. The Column A was instrumented with three moisture sensors. For each column were executed two infiltration tests, measuring the percolated water volume. Furthermore, the saturation profile of the instrumented column (Column A) was obtained in the two tests. The resulting data of the experimental model demonstrated that de system with the MS70C30 mixture in the waterproof layer presented the best performance when analysing the reduction of water flux. The percolated water volume measured in this case was much lower than that obtained for the other two columns. The same material managed high levels of saturation, over 90% during almost the entire duration of tests, necessary condition to reduce biogas diffusivity in the system.