A geocélula foi desenvolvida, inicialmente, com o intuito de melhorar a capacidade de carga do solo. Contudo, este geossintético também é empregado para compor muro de arrimo de gravidade, como sistema de faceamento de estruturas reforçadas, como proteção de taludes contra erosão e como revestimento de canais. Na melhora da capacidade de carga de solos, a geocélula pode ser usada no reforço de fundações, de vias rodoviárias e ferroviárias, e em aterros sobre solos moles. Na literatura existem poucos modelos de previsão da capacidade de carga de solos reforçados com geocélulas, contudo, com limitações em sua aplicabilidade. Neste aspecto, o presente trabalho apresenta um novo método de previsão considerando os mecanismos de desenvolvimento da resistência tanto do solo de fundação como da geocélula, sendo estes os efeitos laje e do confinamento. Este novo método de cálculo é verificado com resultados de ensaios de placa de laboratório conduzidos por diversos autores e por simulações numéricas computacionais, sendo, também, comparado qualitativamente e quantitativamente com os demais métodos de cálculo. Os resultados indicaram que os valores calculados pelo presente modelo foram mais próximos daqueles obtidos pelos ensaios e pelas simulações, em comparação com os demais métodos. O presente modelo se adequou de forma satisfatória para diferentes características da geocélula (geometria e material de constituição), do solo de fundação e de preenchimento (diferentes tipos de areia e argila) e da geometria do carregamento (placas circular, retangular e corrida). Por fim, o método foi aplicado em reforço de fundações e de solos moles e verificado de forma satisfatória com o uso de modelos numéricos. / The geocell was initially designed to improve the soil bearing capacity. However, this geosynthetic also can be used as a retaining wall, facing for reinforced soil structures, slope protection against erosion and channel lining. In the soil bearing capacity improvement the geocell can be applied as reinforcement of foundation, soft soil embankments and roads and railroads. In the literature there are few methods for predicting bearing capacity of geocell-reinforced soil, however with disabilities that limit their applicability. In this regard, a new method for predicting the bearing capacity of geocell-reinforced soils is presented herein, taking into account the soil foundation resistance and the geocell reinforcement mechanisms, namely, stress dispersion effect and confinement effect. The present method is verified with the results of laboratory plate load experiments by several authors and numerical simulations, and compared with other calculation methods. The results indicated that the calculated results obtained from this method were very close to experimental and numerical results, better than other methods. This method also proved to be a good approach for different geocell characteristics (geometry and constitution material), for foundation soil and geocell infill (different types of sand and clay) and for loading shape (circular, rectangular and strip). In the last Chapter, the method has been applied in foundation and soft soil improvement and satisfactory verified by numerical simulations.

The mechanism of soil-reinforcement interaction for a reinforced embankment on soft clay has been explored by conducting a parametric study using a coupled non-linear elastoplastic finite element program. One of the major issues in the design of a reinforced embankment on soft clay is the magnitude of tension that can be mobilized in the geosynthetic reinforcement. Previous research using geotechnical centrifuge modelling and present research using finite element modelling has confirmed that the tension mobilized in the reinforcement is only of the order of active lateral thrust in the embankment. The parametric study has revealed that the soil-reinforcement interaction mechanism depends on the ratio of embankment height to the depth of the clay layer. The embankment behaves similar to a rigid footing in case of deep clay deposit. In this case, the failure mechanism is similar to a slip circle and there is very little contribution from the clay-reinforcement interface towards the mobilization of reinforcement tension. However, if the depth of clay deposit is small, the soil-reinforcement interaction mode is similar to direct shear failure and slip surface is located close to the clay-reinforcement interface. In this case, the contribution of clay-reinforcement interface towards the tension mobilized in the reinforcement is higher and therefore, the contribution of the reinforcement towards overall stability of the embankment is greater. Based on the results of the parametric study a novel serviceability criterion is proposed that aims to limit the lateral deformation of the clay foundation at the toe of the embankment by limiting the allowable mobilized tension in the reinforcement. A simple procedure for the evaluation of the efficiency of soil-reinforcement interface for reinforced embankments on soft clays is also proposed. The validity of the proposed serviceability criterion and the design charts was successfully tested using two field case studies. Sackville test embankment constructed to failure in 1989 and a levee test section that remained serviceable after construction in 1987 at Plaquemine, Louisiana were able to confirm the validity of the serviceability criterion proposed in the present study.

The mechanism of soil-reinforcement interaction for a reinforced embankment on soft clay has been explored by conducting a parametric study using a coupled non-linear elastoplastic finite element program. One of the major issues in the design of a reinforced embankment on soft clay is the magnitude of tension that can be mobilized in the geosynthetic reinforcement. Previous research using geotechnical centrifuge modelling and present research using finite element modelling has confirmed that the tension mobilized in the reinforcement is only of the order of active lateral thrust in the embankment. The parametric study has revealed that the soil-reinforcement interaction mechanism depends on the ratio of embankment height to the depth of the clay layer. The embankment behaves similar to a rigid footing in case of deep clay deposit. In this case, the failure mechanism is similar to a slip circle and there is very little contribution from the clay-reinforcement interface towards the mobilization of reinforcement tension. However, if the depth of clay deposit is small, the soil-reinforcement interaction mode is similar to direct shear failure and slip surface is located close to the clay-reinforcement interface. In this case, the contribution of clay-reinforcement interface towards the tension mobilized in the reinforcement is higher and therefore, the contribution of the reinforcement towards overall stability of the embankment is greater. Based on the results of the parametric study a novel serviceability criterion is proposed that aims to limit the lateral deformation of the clay foundation at the toe of the embankment by limiting the allowable mobilized tension in the reinforcement. A simple procedure for the evaluation of the efficiency of soil-reinforcement interface for reinforced embankments on soft clays is also proposed. The validity of the proposed serviceability criterion and the design charts was successfully tested using two field case studies. Sackville test embankment constructed to failure in 1989 and a levee test section that remained serviceable after construction in 1987 at Plaquemine, Louisiana were able to confirm the validity of the serviceability criterion proposed in the present study.

A geocélula foi desenvolvida, inicialmente, com o intuito de melhorar a capacidade de carga do solo. Contudo, este geossintético também é empregado para compor muro de arrimo de gravidade, como sistema de faceamento de estruturas reforçadas, como proteção de taludes contra erosão e como revestimento de canais. Na melhora da capacidade de carga de solos, a geocélula pode ser usada no reforço de fundações, de vias rodoviárias e ferroviárias, e em aterros sobre solos moles. Na literatura existem poucos modelos de previsão da capacidade de carga de solos reforçados com geocélulas, contudo, com limitações em sua aplicabilidade. Neste aspecto, o presente trabalho apresenta um novo método de previsão considerando os mecanismos de desenvolvimento da resistência tanto do solo de fundação como da geocélula, sendo estes os efeitos laje e do confinamento. Este novo método de cálculo é verificado com resultados de ensaios de placa de laboratório conduzidos por diversos autores e por simulações numéricas computacionais, sendo, também, comparado qualitativamente e quantitativamente com os demais métodos de cálculo. Os resultados indicaram que os valores calculados pelo presente modelo foram mais próximos daqueles obtidos pelos ensaios e pelas simulações, em comparação com os demais métodos. O presente modelo se adequou de forma satisfatória para diferentes características da geocélula (geometria e material de constituição), do solo de fundação e de preenchimento (diferentes tipos de areia e argila) e da geometria do carregamento (placas circular, retangular e corrida). Por fim, o método foi aplicado em reforço de fundações e de solos moles e verificado de forma satisfatória com o uso de modelos numéricos. / The geocell was initially designed to improve the soil bearing capacity. However, this geosynthetic also can be used as a retaining wall, facing for reinforced soil structures, slope protection against erosion and channel lining. In the soil bearing capacity improvement the geocell can be applied as reinforcement of foundation, soft soil embankments and roads and railroads. In the literature there are few methods for predicting bearing capacity of geocell-reinforced soil, however with disabilities that limit their applicability. In this regard, a new method for predicting the bearing capacity of geocell-reinforced soils is presented herein, taking into account the soil foundation resistance and the geocell reinforcement mechanisms, namely, stress dispersion effect and confinement effect. The present method is verified with the results of laboratory plate load experiments by several authors and numerical simulations, and compared with other calculation methods. The results indicated that the calculated results obtained from this method were very close to experimental and numerical results, better than other methods. This method also proved to be a good approach for different geocell characteristics (geometry and constitution material), for foundation soil and geocell infill (different types of sand and clay) and for loading shape (circular, rectangular and strip). In the last Chapter, the method has been applied in foundation and soft soil improvement and satisfactory verified by numerical simulations.

This paper presents results of a comprehensive investigation undertaken to quantify the efficiency of using reinforcement layers in order to enhance the bearing capacity of soils that are characterised by the existence of localised soft pockets. Small-scale model experiments using two dimensional tank were conducted with beds created from well graded sand with mean particle size of 300 μm but prepared with different dry densities. A relatively softer material was embedded at predetermined locations within the sand beds so as to represent localised soft pockets. Various arrangements of soil reinforcement were tested and compared against comparable tests but without reinforcement. In total 42 tests were carried out in order to study the effect of the width and depth of the soft pocket, the depth of one reinforcing layer and the length and number of reinforcing layers on the soil bearing capacity. The results show clearly that the ultimate bearing capacity reduces by up to 70% due to the presence of a soft pocket. It was also noted that the proximity of the soft pocket also influenced the bearing capacity. Reinforcing the soil with a single layer or increasing the length of reinforcement is not as effective as was anticipated based on previous studies. However, bearing capacity increased significantly (up to 4 times) to that of unreinforced sand when four layers of reinforcement were embedded. The results suggest that rupture of the bottom reinforcement layer is imminent in heavily reinforced sand beds overlying soft pockets and therefore its tensile strength is critical for successful reinforcement.

Este trabalho aborda o comportamento de dois solos (uma argila e uma areia), reforçados com fibras plásticas de polipropileno. Os solos foram compactados no teor de umidade ótimo e peso específico seco máximo e foram misturados com fibras de diferentes teores e comprimentos. Os resultados dos ensaios de compressão simples foram usados para selecionar os teores e comprimentos ótimos de fibras. Os resultados mostraram que a resistência do solo arenoso cresceu com o aumento do teor e comprimento das fibras e o solo argiloso apresentou acréscimo de resistência, com o aumento do teor até o comprimento de fibra de 10 mm. As curvas tensão-deformação dos ensaios triaxiais, para solos com e sem reforço foram similares, com uma resistência de pico definida e pequena redução de queda de tensão pós pico. As amostras de solo arenoso apresentaram considerável aumento de resistência, com o aumento do teor e comprimento das fibras. Pequenos painéis, fabricados com o solo argiloso (300 x 300 x 100) mm, mostraram que a presença da fibra pode reduzir a magnitude das trincas quando comparados com o solo sem reforço. / This work presents the behavior of two soils (clay and sandy) reinforced with polypropylene plastic fibers. The soils were compacted at the optimum moisture content and maximum dry unit weight and were mixed with fibers of different lengths and contents. Unconfined compressive tests results were used to select the optimum fiber length and content. The results showed that the granular soil strength increased with increasing fiber length and content. The cohesive soil, on the other hand, showed strength up to fiber length of 10 mm. Stress - strain curves from triaxial tests for both reinforced and unreinforced cohesive soil were similar with a defined peak strength and small post peak reduction. Granular soil samples presented considerable strength increases with the increases of length and fiber content. Small panels fabricated with the reinforced cohesive soil (300 x 300 x 100) mm, showed that the presence of fiber can reduce crack magnitude when compared with the unreinforced soil.

Este trabalho apresenta resultados de ensaios de fluência de geotêxteis não tecidos executados em ensaios confinados. No equipamento utilizado, o reforço é confinado entre camadas de solo, permitindo que ambos os materiais tenham liberdade para apresentar deformações ao longo do tempo. Nesses ensaios, uma tensão vertical é aplicada ao solo que por sua vez solicita o reforço. Os ensaios foram realizados com três geotêxteis não tecidos, sendo dois de polipropileno e um de poliéster, e quatro tipos de solo confinante: três materiais granulares e uma argila silto-arenosa. Além disso, também foram executados ensaios de fluência não confinada para permitir comparação com os ensaios confinados. Os resultados indicaram que houve grande contribuição do confinamento na redução das deformações por fluência dos materiais ensaiados. Também foi avaliada a influência de alguns fatores na fluência confinada dos geotêxteis não tecidos, tais como: tipo de solo, tipo de geotêxtil e gramatura do reforço. Tais resultados são interessantes para avaliar o potencial de fluência do composto solo-geotêxtil que, normalmente, é baseado somente em ensaios no elemento isolado de reforço / This work presents results of creep tests on no woven geotextiles tested in confined lab tests. In the used equipment, the reinforcement is confined between two soil layers, allowing both materials to have freedom to deform with time. In those tests, a vertical stress is applied to the soil that transfers load to the reinforcement. The tests were performed using three no woven geotextiles, two of polypropylene and one of polyester, and four types of confining soil: three granular materials and sandy silty clay. Besides, unconfined creep tests were carried out to allow comparison with the confined tests. The results indicated that there was great contribution of the confinement in the reduction of the creep deformations of the tested materials. Also the influence of some factors was evaluated in the confined creep of the no woven geotextiles, such as: soil type, type of geotextile and mass per unit area of the reinforcement. Such results allow the evaluation of the potential of creep of the system soil-geotextile

Simple unpaved roads consist of a layer of coarse granular material placed directly onto the surface of weak or compressible ground. It is thought that the construction of such roads can be considerably improved by the incorporation of a geogrid at the base of the granular fill layer. Geogrids are a type of geotextile, distinguished by their relatively large aperture size. Laying out a geogrid on the surface of the ground before placing the fill layer may in many cases allow a reduced thickness of fill material to be used, and may also substantially increase the load required to cause a complete failure of the system. No generally accepted design method exists for the construction of reinforced unpaved roads, due to the complex mechanisms which govern deformations in the system. The primary aim of this dissertation was to investigate the performance, in such a construction, of a particular geogrid, namely Tensar, manufactured by Netlon Ltd. A detailed model study into failure mechanisms was undertaken using laboratory apparatus constructed to conduct work at 1/4 full scale. Simple plane-strain, monotonic footing tests were carried out on systems consisting of a fill layer compacted onto a consolidated clay subgrade, both with and without the incorporation of a model grid at their interface. The testing technique included a comprehensive study of photographs taken of marker movements in the clay through the transparent sides of the test-box during tests. The relevant failure mechanisms associated with reinforced and unreinforced systems were established. In addition the significance of shear stresses acting at the subgrade surface was recognised and a concept whereby the appropriate subgrade bearing capacity factor is related to these shear stresses was developed. The modelling techniques adopted in this work obviated the need for a centrifuge.

The purpose of this study is to obtain an insight into the mechanisms by which a geosynthetic membrane influences the performance of a plane strain and an axisymmetric two-layer soil system, where the reinforcement is incorporated either into a layer of fill, or at the interface of a layer of fill overlying clay subgrade. New axisymmetric membrane and interface element formulations are developed and incorporated in to an existing large strain finite element code. A linear elastic model of behaviour is used for the membrane material and an elastic-perfectly frictional model, based on the Mohr-Coulomb yield function, is implemented for the interface. These new formulations both take account of large global displacement and rotation effects, although the interface element is constrained to small relative displacements, and are checked against small and large strain closed form test problems. The finite element equations are based on an Updated Lagrangian description of deformation. Plane strain finite element investigations into the significance of the resolution and relative size of the finite element mesh, and the differences between large and small strain analyses, are undertaken. For typical unreinforced and reinforced plane strain and axisymmetric two- layer soil systems a detailed analysis is presented of the soil displacements, strains, stresses, principal stress directions, mobilised fill friction angles and the stresses on the underside of the footing. A series of plane strain and some axisymmetric parametric studies of the various material properties is conducted, to assess the influences and relative importance of those variables to the performance of the two-layer soil system under monotonic loading. The study considers various reinforcement lengths and stiffnesses, fill depths and strengths, and different clay strengths. The mechanisms of reinforcement are identified through careful examination of the footing load-displacement response, the reinforcement tension and the stresses and displacements at the interfaces with the surrounding soil. A comparative study is also undertaken between the results obtained by the finite element model and those predicted by a plane strain and axisymmetric limit equilibrium design method. The effects of including a low friction membrane within an oil storage tank base, as secondary containment against oil leakage, are investigated by a series of axisymmetric finite element analyses.

A series of finite element predictions of the behaviour of a reinforced unpaved road consisting of a layer of fill compacted on top of a clay subgrade with rough, thin reinforcement placed at the interface, is described in this thesis. These numerical solutions are obtained using a large strain finite element formulation that is based on the displacement method, and are restricted to the case of plane strain, monotonic loading. Separate elements are used to model the soil and reinforcement. In the finite element formulation, an Eulerian description of deformation is adopted and the Jaumann stress rate is used in the soil constitutive equations. Elastic perfectly-plastic soil models are used which are based on the von Mises yield function for cohesive soil and the Matsuoka criterion for frictional material. Emphasis is placed on obtaining new closed form solutions to parts of calculations that are performed numerically in many existing finite element formulations. The solution algorithm is based on a "Modified Euler Scheme". The computer implementation of the formulation is checked against an extensive series of test problems with known closed form solutions. These include the analysis of finite deformation of a single element of material and the calculation of small strain collapse loads. Finite cavity expansion is also studied. This numerical formulation is used to perform back analyses of a series of reinforced unpaved road model tests. The reinforcement tensions, and the stresses at the interface with the surrounding soil, are calculated using the numerical model and discussed with a view to identifying the mechanisms of reinforcement. Two existing analytical design models of the reinforced unpaved road are described and critically reviewed in the light of the finite element results.