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.

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.

Previous experimental studies of soil-reinforcement interaction have generally concentrated on the effect of reinforcement working in axial tension; this study looks at reinforcement working in bending and shear. The experimental programme was carried out in a large scale direct shear apparatus able to contain a cubic soil sample of side 1m. A previous study showed that the apparatus required improvements to its boundaries. Modifications to the apparatus resulted in a significant improvement in the performance of the apparatus. The data being comparable with those from direct shearboxes with similar symmetrical boundary conditions. The effect of reinforcement in shear and bending was studied by varying the reinforcement cross section reinforcement orientation, method of installation, and the relative soil- reinforcement stiffness and strength. All tests were carried out on a well graded and uniform quartz sand. The reinforcement was typically mild steel circular bar. Data from tests on instrumented reinforcement bars allowed the distribution of lateral loading to be observed. This led to the development of a mathematical model for predicting the shear force available from reinforcement in soil. A comparison of this model with the test data and from data in the literature revealed it to provide an accurate upper estimate of reinforcement shear force are much greater than those required for axial force. The conclusions in this dissertation address much of the ambiguity over the use of soil reinforcement in shear and bending for soil nailing and dowelling design.

The research described in this dissertation follows on from the study made by Jewell (1980)into the effects of tensile reinforcement on the mechanical behaviour of sand. For this study Jewell used the direct shear test with reinforcement placed about the central plane as shown in fig. 1.1. The direct shear test was chosen for the following reasons. (1) The reinforcement variables could be better controlled and examined in a unit cell test than in modular field studies of soil reinforcement systems. (2) The pattern of deformation is similar to that experienced by soil in which a rupture band develops, with the principal axes of stress, strain and strain increment free to rotate as is the case in model and field structures. (3) The overall shear strength of the sample is measured directly at the boundaries of the apparatus. The direct shear tests were monitored by boundary measurements and internal measurements using a radiographic technique. The findings are outlined below with reference made to relevant observations by other researchers. 1) The optimum orientation for a relatively flexible steel grid was found to be approximately along the direction of principal tensile strains in the unreinforced sand, see fig.1.2. This indicated that the reinforcement functioned by limiting tensile strains in the sand. McGown et al. (1978) obtained a similar result for plane strain cell tests on sand containing a single layer of flexible reinforcement. However in both studies the reinforcement was observed to waken the sand. Jewell recognized weakening to occur when the steel grid was placed along the direction of principal compressive strains in the unreinforced sand. This was attributed to a reduction in vertical effective stress. McGown et al. observed weakening of the sand when the reinforcement orientation approached the rupture band which developed in the sand alone. This was recognized to be the direction of zero-extension in the unreinforced sand. The weakening was linked to a lower bond between soil and reinforcement than soil alone. 2) Internal strains determined by Jewell showed the tensile reinforcement modified strains in the sand over a well defined zone, see fig.1.3. This resulted in a significant rotation of principal axes of strain increment, with the bond of major strains which developed across the centre of the box in the unreinforced sand being prohibited from forming. This agreed with boundary measurements, indicating the reinforcement functioned by limiting tensile strains in the sand. Consequently a less favourable mode of failure took place. The limit of rotation of principal axes of strain increment was understood to be the alignment of a direction of zero-extension in the sand with the reinforcement. These findings agree with the ideas expressed by Basset and Last (1978) on the mode of action of tensile reinforcement, which in particular was related to the effect of tensile reinforcement on the strain field in a reinforced earth wall as shown in fig.1.4. 3) For efficient use of tensile reinforcement it was demonstrated that the bond with sand should be as high as possible. This could be achieved by roughening the surface. Alternatively, the bond was improved by introducing openings or apertures in the reinforcement, changing the shape to a grid. It appeared that the bond for a suitably proportioned grid could be as high as for a fully roughened surface. 4) The longitudinal stiffness of tensile reinforcement was observed to affect the magnitude and rate of increase in strength in the direct shear tests. The rupture strain of tensile reinforcement relative to maximum tensile strains of the soil, under the same operational stress conditions, have also been observed to influence the reinforcing effect in terms of its limiting behaviour, i.e. whether brittle or ductile (McGown, et al. 1978). With regards to the performance of reinforced earth walls, Al-Hussanini and Perry (1976) observed that steel reinforced strips produced a stiffer and stronger structure than a more extensible fabric reinforcement, even though surface roughness was less. The importance of reinforcement tensile stiffness is recognized in limit equilibrium designs for tensile reinforced soil structures by limiting the available reinforcement force to the tensile strains that can develop in the soil (e.g. Jewell 1985). For highly structured non-woven and composite geotextiles, McGown et al. (1982) demonstrated that the stress-strain behaviour can be significantly affected by soil confinement. Testing wider strips in isolation was not found to replicate the effects of soil confinement. Another factor which needs to be considered when assessing the tensile property of a polymer reinforcement is creep. McGown et al. (1984) illustrated an appropriate method of interpreting creep data using isochronous curves, which enable long term laboratory test data to be extrapolated to the design life of the soil structure. 5) The strain and hence stress fields in the reinforced direct shear tests have been shown to be complex and non-uniform. However Jewell successfully modelled the variation of reinforcing effect for tensile reinforcement at different orientations by using a simple limit equilibrium analysis, see fig.1.5. The effect of the tensile reinforcement force was represented as: - an increase in the normal effective stress acting on the central plane of the box due to the normal component of the force and - a reduction in the applied shear stress due to the parallel component of the force to the central plane. Subsequently this analysis has been applied to limit equilibrium design methods for reinforcing soil retaining walls and embankments, Jewell et al. 1984, and Jewell 1982 respectively. 6) A reduction in the reinforcing effect for individual reinforcement due to the presence of other reinforcement was observed in the shear box. This loss of efficiency of individual reinforcement was termed interference. Interference between tensile reinforcement has also been studied by Guilloux et al. (1979) for the pull-out resistance from soil. However interference between reinforcement has yet to be introduced into a limit equilibrium design method.