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Avaliação experimental da interação solo coesivo-fita polimérica sob condições de teor de umidade variáveis. / Experimental evaluation of the effect of soil moisture content on cohesive soil-geosynthetic strap interaction.Patrícia Del Gaudio Orlando 20 March 2015 (has links)
Em geral, as recomendações normativas sugerem a utilização de materiais granulares para a construção de estruturas em solo reforçado, principalmente devido à sua elevada resistência ao cisalhamento e boa capacidade de drenagem. No entanto, nem sempre há disponibilidade deste tipo de material no entorno das obras, tornando o uso dos solos finos imperativo para a viabilização desta solução. No Brasil, solos residuais finos são encontrados em abundância e, muitas vezes, apresentam excelentes parâmetros de resistência ao cisalhamento e baixa compressibilidade. Contudo, o seu uso pode induzir poro-pressões indesejáveis durante a construção ou cisalhamento do aterro reforçado. Por outro lado, as elevadas sucções matriciais que podem persistir em seu interior geram um aumento na estabilidade dos maciços reforçados. Neste contexto, este trabalho apresenta os resultados experimentais e discute o efeito da variação climática (umedecimento e secagem) na resistência de interface solo coesivo-fita polimérica de uma estrutura de contenção em solo reforçado. Os ensaios foram realizados com amostras compactadas de um solo residual de gnaisse típico da cidade de São Paulo e uma fita polimérica de alta aderência. Os corpos de prova foram submetidos a ensaios de cisalhamento direto e de arrancamento sob três diferentes níveis de tensão normal e de sucção, além da condição inundada. Ensaios triaxiais saturados (CU) e não saturados (CW) foram realizados para a determinação da envoltória de resistência tridimensional do solo, avaliação da eficiência da interação solo-reforço e para a verificação do comportamento da água intersticial durante o cisalhamento. Os resultados indicam que o solo coesivo em questão apresenta excelentes parâmetros de resistência ao cisalhamento, elevada capacidade de se manter sob pressões negativas da água intersticial e uma eficiente interação com as fitas poliméricas, o que possibilitaria a execução de estruturas estáveis quanto ao arrancamento dos reforços. Além disso, sugerem um crescimento não linear da máxima resistência de interface com o aumento da sucção matricial do solo e uma tendência de redução dos coeficientes de atrito aparente solo-reforço (f*) com o umedecimento das amostras. Porém, mostraram que a sucção matricial exerce pouca influência na resistência residual da interface solo reforço. / Current specifications for reinforced soil structures generally require the use of granular backfill due to their high strength, well drainage capacity and low volume change potential. However, in cases where granular fills are not easily and readily available, poorly draining soils should be used to enable the implementation of a mechanically stabilized earth wall (MSEW). In Brazil, the fine-grained residual soils that cover large areas of its territory frequently present high shear strengths and low compressibility. However, the use of cohesive soils can cause unwanted effects in structure stability due to the water content variations of the backfill soil, and the potential development of pore-water pressures or loss of strength. On the other hand, matric suctions may increase the soil-geosynthetic interface shear strength. In this context, this study presents the experimental results and discusses the effects of seasonal climatic variations (wetting and drying) on shear strength of soil-geosynthetic straps interfaces under unsaturated conditions. For the laboratory investigation, a compacted residual soil of gneiss composed of 80% silty sand passed through a 0.075mm sieve, sourced from São Paulo city, and a high-tenacity polyester strap were used. Direct shear and pullout tests were conducted with three different net normal stresses and levels of matric suction, besides the inundated condition. Triaxial tests under saturated (CU) and unsaturated (CW) conditions with suction measurement using a high capacity tensiometer were performed in order to evaluate the shear strength parameters of the unsaturated soil, the interface efficiency of the soil-geosynthetic strap and the pore water pressure variations during shear. The results indicate that the cohesive soil used in this study has excellent shear strength parameters, a high capacity to maintain negative pore water pressures and presents an efficient interaction with the geosynthetics straps, which would allow the implementation of a stable MSEW for failure by pullout. Furthermore they reveal that the peak shear strength of the soil-geosynthetic strap interface increases nonlinearly with the soil suction, while the apparent friction factor (f*) decreases with the increase in molding moisture contents. On the other hand, the effect of suction on the post-peak shear strength of the interface was negligible.
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Analysis of steep sided landfill lining systemsFowmes, Gary John January 2007 (has links)
The EC Landfill Directive (1999), which is enforced in England and Wales through the Landfill (England and Wales) Regulations (2002), has increased the technical challenge associated with the design and construction of landfill containment systems, in particular those on steep side slopes. Increased numbers of lining system components, varied configurations, and complex loading scenarios require advanced analysis tools to facilitate design. This project involved the development of advanced numerical modelling techniques, based on the FLAC finite difference modelling code. The analysis toolbox can be used to predict the behaviour of multilayered geosynthetic and soil lining systems, during and after staged construction. The model can include non-linear interface and geosynthetic axial properties, represent complex loading, including downdrag from the waste mass, whilst retaining the flexibility to represent varied geometries and include engineered support structures. Whilst numerical modelling is becoming increasingly commonplace in commercial design, there is little evidence of the validation of numerical models with field or experimental data. Validation of the analysis toolbox described in this document was conducted by back analysis of published data, modelling of landfill failure mechanisms, and comparisons to large scale laboratory testing. Design of field scale instrumentation has also been carried out as part of this project. The influence of interface shear strength variability has been assessed through the compilation of a comprehensive database, and the effect of this variability on lining system behaviour assessed through reliability based analyses. This has shown probability of failures may be higher than proposed limiting values when adopting traditional accepted factors of safety. A key area of interest identified during the project was the requirement for support, potentially through reinforcement, of the geological barrier. The inclusion of randomly reinforced fibres in bentonite enhanced soil has shown the potential for increased strength, without adverse effects on hydraulic barrier performance. ii Additionally, the influence of geomembrane seams on lining system integrity has been investigated, showing that fusion welded seams can result in stress concentration and extruded seams can cause significant stress concentration.
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