Rozprawy doktorskie na temat „SOIL REINFORCED”

The modern forms of reinforced soil walls were introduced by Henri Vidal. Since then design theories have been developed alongside an increasing database of full scale, small scale and centrifuge model tests. However, very little data is available on the mechanisms of deformation for a wrap-around wall. In order to understand these mechanisms, reinforced soil walls were tested under different conditions, by varying reinforcement stiffness, backfill material, external loading and type of construction. Seven centrifuge model tests on reinforced soil models were carried out with three different types of model reinforcements and a choice of two granular backfill materials. The external loading was imposed by a strip surcharge of 100 kPa, to represent the worst load experienced on a highway or railroad. This research programme includes the development of testing methods to obtain stress-strain behaviour of the model reinforcement using fixed or roller clamps, and improvement of the construction of the Cambridge strip load cells for measuring the tension along the model geosynthetic reinforcement, and in particular to the most sensitive, weakest reinforcement. Strip load cells have successfully yielded experimental data of reinforcement tension for all the geomaterials used. The tension measurement along the reinforcement confirms that the facing of a geosynthetic wrap-around reinforced soil wall does not serve a major structural function. Boundary relaxation occurs requiring the reinforcement simply to retain the fill. The deformation of the reinforced soil walls was identified by a simple displacement mechanism which included constant shear strain and dilation in the deforming zone. A non-dimensional horizontal deflection chart was derived based on this assumption. The prediction of the front wall deformation of centrifuge model walls using such a non-dimensional chart indicated that this would offer a useful serviceability design method to designers.

COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
A utilização de pneus usados é uma técnica interessante para reforço de solos, sob o aspecto ambiental. Os pneus usados constituem uma matéria-prima abundante e de custo reduzido. A técnica de utilização de pneus em obras geotécnicas vem sendo difundida no Brasil desde meados dos anos 90, com a construção do muro experimental de solopneus da PUC-Rio, em colaboração com a Fundação Geo-Rio e a Universidade de Ottawa (Canadá). O presente trabalho tem por objetivo apresentar a metodologia para avaliação da resistência ao arrancamento de malhas de pneus. Os pneus podem ser dispostos em um plano horizontal e amarrados entre si, formando uma malha de reforço. Podem ser utilizados pneus inteiros ou com uma das bandas laterais cortadas. A sobrecarga atuando no reforço provém do confinamento provocado pela altura do aterro de solo, construído sobre a malha de pneus. Os ensaios de arrancamento dos pneus no campo utilizaram uma estrutura metálica de reação, atirantada, a qual foi desenvolvida especificamente para o programa experimental sobre reforço de solos. Os resultados permitiram idealizar um mecanismo de ruptura envolvido no processo de arrancamento das malhas de pneus, bem como a verificação das características de resistência e deformabilidade deste tipo de reforço.
The use of scrap tires as soil reinforcement is an environmentally interesting technique. Scrap tires are an abundant and low cost waste material. The technique for using tires in geotechnical construction is becoming popular in Brazil since the construction of an experimental gravity wall made with soil and tires in 1995. This wall was part of a research project by carried out by PUC-Rio in collaboration with Geo-Rio and University of Ottawa. The objective of this work is to present a methodology to evaluate the pull-out behaviour of tire meshes. The tires can be placed in a horizontal plane and tied with rope or wire, forming a reinforcement mesh. The surcharge on these meshes comes from the confinement due to the height of a soil embankment built on the mesh. Field pull-out tests were performed on these reinforcement meshes, using a metallic reaction structure, which was developed specifically for this experimental research. The results allowed the idealization of a shearing mechanism based on the pull-out of tire meshes, as well as the verification of the strength and deformability characteristics of the reinforcement.

COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
A utilização de materiais geossintéticos como reforço em obras geotécnicas vem crescendo bastante nas últimas décadas. A geogrelha, cuja função primária é o reforço de solos, é um entre os diversos tipos de geossintéticos, que vêm sendo utilizados. Diversas são as formas de interação da geogrelha com o solo em um maciço reforçado e o entendimento dos mecanismos que se desenvolvem nestas interações é essencial, pois só a partir daí pode-se obter parâmetros confiáveis para projeto. Pesquisas vêm sendo realizadas por diversos autores, mas muitos aspectos ainda devem ser estudados para que se tenha uma melhor compreensão do comportamento de solos reforçados com geogrelhas. A utilização de uma ferramenta numérica pode ser uma alternativa para que consigamos dar um passo adiante no entendimento da técnica de solo reforçado. Então, modelagens numéricas de ensaios triaxiais e de cisalhamento direto em solos reforçados e não reforçados foram realizadas com a utilização do programa Plaxis. Foram analisadas a influência do reforço no aumento da rigidez e resistência do solo e a resistência de interface solo-reforço. Para calibrar o programa e validar as análises numéricas, foram realizadas retro-análises dos ensaios realizados por Sieira (2003), onde se definiram aspectos importantes para modelar os ensaios, tal como, a melhor forma de impor as condições de contorno. Os resultados obtidos nas análises numéricas dos ensaios triaxiais sugerem que o programa Plaxis permite de forma razoável a reprodução dos ensaios reforçados, sendo possível prever o ganho de resistência do solo com a inclusão do reforço. Uma análise alternativa, onde se aplica um incremento de tensão confinante representativo da influência do reforço, foi também realizada. As análises numéricas dos ensaios de cisalhamento direto em solo arenoso não reforçado permitiram verificar a rotação do eixo das direções das tensões principais quando é aplicado carregamento cisalhante e a presença de uma zona central de cisalhamento (zona de cisalhamento). A resistência de interface sologeogrelha não foi bem reproduzida, indicando que o Plaxis não permite este tipo de avaliação. Quando os reforços encontravam-se inclinados, verificou-se a maior eficiência do reforço rígido e fazendo ângulo de 60º com a superfície de ruptura.
The use of geosynthetic materials as reinforcement in geotechnical engineering works is significantly increasing over the past decades. Geogrid, whose primary functions is reinforcing the soil mass, is one of the geosynthetics that has been used. In a reinforced soil structure, there are different types of interaction between soil and geogrid. To be possible to obtain reliable design parameters is essential to know the mobilized mechanisms in the interaction. This situation has been investigated by many researchers, but there are still many aspects to be better understood about geogrid reinforced soil behavior. In this research, numerical tools have been used to improve our knowledge about reinforced soil techniques. Numerical modeling of triaxial and direct shear tests on reinforced and non reinforced soils were carried out using software Plaxis. It was verified the resistance and stiffness increase of the soil due to geogrid inclusion and the interface soil-reinforcement resistance parameters. To calibrate the software and to validate the numerical analyses, back-analyses of the tests carried out by Sieira (2003) were done. These results helped to define important aspects to the tests modeling such as geometry and tests boundary conditions. The numerical analyses of the triaxial tests suggest that the software Plaxis reasonably allow an adequate reproduction of the reinforced soil tests. It was possible to foresee the increase of soil resistance because of reinforcement inclusion. In addition, an alternative analysis, where one applies a confining stress that reproduces the reinforcement influence, it was done. Numerical analyses of non reinforced direct shear tests had numerically evidenced the rotation of the axis of the principal stresses directions and the presence of a central zone of shear (shear zone). The soil- geogrid interface resistance was not well reproduced, indicating that Plaxis does not allow this type of evaluation. To inclined reinforcement relative to failure plane, it was verified the maximum gain of resistance is achieved with inclined reinforcement at 60º and when rigid geogrids are used.

Soil based construction materials (SBCMs) are formed of a mixture of gravel, sand and clay which, when mixed with water, may be used for construction. They can be an environmentally-friendly alternative to more traditional construction materials such as concrete and fired brick. SBCMs commonly incorporate foreign material into the soil to enhance the material properties. Many guides on SBCM construction advocate the use of cement as a stabiliser to strengthen the material, which detracts from the environmental credentials that earthen construction materials possess. Alternatives methods to strengthen SBCMs are therefore needed. In this thesis, waste wool fibres from a carpet manufacture are investigated as a potential alternative fibrous reinforcement in rammed earth (RE), and its effect on the behaviour of stabilised and unstabilised RE is assessed. Compressive tests, shear tests and splitting tests are performed to study the effect of fibrous (wool) and chemical (cement) stabilisation on RE, and recommendations on further use of these materials are made. Tests are also performed to investigate the shrinkage of different clays (bentonite and kaolinite) used in RE when mixed with sand or wool, in order to determine the effects of these materials on shrinkage behaviour. Finally, advice is provided regarding the use of fibrous reinforcement in SBCMs, which is applicable to both the SBCM industry and research, and new and pre-existing research areas are identified to prompt further study.

Thesis (Ph. D.)--University of Missouri-Columbia, 2007.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Typescript. Vita. Title from title screen of research.pdf file (viewed on March 6, 2009) Includes bibliographical references.

Fibres are mixed with soils to enhance their strength and hydraulic characteristics. Fibre-mixed soils are often known as the fibre-reinforced soils. In the past, both systematically and randomly reinforced soils have been used widely in civil and geotechnical structures. Randomly reinforced-soils using fibres exhibit advantages over systematically reinforced-soils because systematic reinforcements may result in weak planes within the soil mass. Randomly distributed reinforcements are also easier to apply and maintain for some applications. Previous researchers have studied the strength, compaction and compressibility behaviour of fibre-reinforced soil. Study on characteristics of fibre-reinforced soils when saturated, however, is limited to piping resistance improvement. One of the main reasons for collapse of some of the hydraulic structures is soil piping that takes place on the downstream side as a result of upward seepage. Fibre-reinforced soils can be a solution in sustainable watershed management as they can be used in irrigation and drainage projects, such as river levees, contour bunds, temporary canal diversion works, temporary check dams, soil structures, stream restoration, etc., for seepage and permeability control. This study focuses on permeability characteristics of fibre-reinforced soil. Permeability characteristics can vary depending on soil, fibre and methods used. Materials used in this study are Perth sandy soil, and locally available jute and waste tyre fibres. These materials were chosen because they are abundantly available in Perth area and surroundings. As for the waste tyre fibre, it was also chosen as a green approach to use waste materials in structures and solve their disposal problems. Fibre content varied from 0 to 10% with 1% intervals for tyre fibres and from 0 to 1.5% with 0.25% intervals for jute fibres. Fibre length varied from 5 to 25 mm with 5 mm intervals for jute fibres. Fibre length was constant in all experiments for tyre fibres as they come in a mixture of different lengths and studying the effect of length of permeability characteristics was not possible. Experimental tests were conducted on fibre-reinforced specimens in a constant-head permeameter. Experimental results suggest that the coefficient of permeability increases with an increase in fibre content for both fibre types (up to 100% for jute fibres and up to about 40% for tyre fibres). Also, it is observed that the coefficient of permeability increases with an increase in fibre length for jute fibres, as a general trend. As expected, water content increases and dry and saturated unit weights decrease with inclusion of higher fibre contents and longer fibres as a general trend. Fibre-reinforced soil specimens and the water discharge were modelled numerically using the commercial software SEEP/W in order to study the effects of fibre inclusion on permeability characteristics. The findings from the developed numerical model agree well with the experimental observations.

The use of tensile reinforcement to increase the tensile strength and shear strength of soils has lead to many new applications of reinforced soil. The use of such reinforcing in embankments and foundations over weak soils is one of the most recent applications of this technology. The studies conducted were concerned with the development of and application of analytical techniques to reinforced soil foundations and embankments over weak soils. A finite element computer program was modified for application to reinforced soil structures, including consolidation behavior of the foundation soil. Plane strain and axisymmetric versions of the program were developed and a membrane element developed which has radial stiffness but no flexural stiffness. The applicability of the program was verified by comparing analytical results to case histories of reinforced embankments and to model studies of reinforced foundations. A simplified procedure for computing the bearing capacity of reinforced sand over weak clay was developed which is more general than those previously available. Good agreement with available experimental results was obtained, providing preliminary verification of the procedure. Extensive analyses were made of a reinforced embankment successfully constructed with no sign of distress, and of two reinforced embankments constructed to failure. These analyses showed that good agreement can be obtained between measured and calculated reinforcement forces, settlements, and pore pressures for both working and failure conditions. The analyses further show that the use of the finite element method and limit equilibrium analyses provide an effective approach for the design of reinforced embankments on weak foundations.
Ph. D.
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Soil reinforced retaining wall structures are materiallymore efficientthan competing construction solutions such as gravity and cantilever walls. Nevertheless, the behaviour and interactions between the com ponent materials are com plex and not fully understood. Current design methods are typically limited to simple cases with respect to material properties, geometry, and boundary conditions. Advanced numerical models using finite element and/or finite difference methods offer the possibilityto extend the understanding ofthese systems and to predictwall performance under operational conditions. In this Thesis, numerical models were developed and shown to give satisfactory predictions ofwall behavior when compared with results of instrumented physical structures. The verified models were useful for sensitivity analyses using a range ofwall geometries and boundaryconditions, material parameters and different constitutive models. As examples ofthe obtained results, the compressibility ofthe precast panel bearing pads significantly modified the axial vertical facing load but has no significant effect on the tension developed in the soil reinforcement layers. Also, the stiffness ofthe foundation soil has greater effect on the tension developed in soil steel reinforcing elements than for polymeric reinforcement layers.lt has been possible to perform sensitivity analysis using parameters that define soil-structure interactions. Such interactions have been analyzed using different commercial software programs and bydefining them with elements from the continuum media using 2D and 3D models. Laboratory reinforcement pullout tests using steelladder and polymeric strips were performed as part of the Thesis. Those parameters that have the greatest influence on soil-reinforcement interaction are identified, quantified, and compared to default-design wlues anda range ofvalues used to calibrate numerical models. From the results of2D and 3D numerical models suitable correlations have been obtained to allow 2D models to be used in plane strain reinforced soil walls with discontinuous soil reinforcement elements in the running walllength ofthese structures. With a proper sustainability assessment it has been possible to make quantitative comparisons between reinforced soil wall structures and other alternativés performing the same function (such as gravity and cantilever walls) construcfed to different heights. Using a modelbased on the multi-attributeutilitytheoryand wlue analysis decision-making, the best solutions with least negative impact were identified in an example set of alternative earth retaining wall options from a sustainable perspective. The results include possible scenarios based on the relative importance ofthe three pillars ofsustainability(i.e., environmental, economic, and sociallfunctional) as judged bydifferentstakeholders. Reinforced soil walls turned outto be the best choice in most cases analyzed, based on a quantitative end score. The models and analysis methodologies developed as part ofthis Thesis work have improved understanding ofthe behavior ofthese structures, and offered possibilities to improve and optimize designs in the future.
Els murs de contenció amb sòl reforçat són estructures materialment més eficients que altres solucions constructives alternatives, com ara els murs de gravetat o en voladís. No obstant això, el seu comportament i les interaccions entre els materials que componen aquestes estructures són complexos i no entesos completament. Els mètodes de disseny actuals solen estar limitats a casos senzills respecte a les propietats dels materials, la geometria i les condicions de contorn. Models numèrics avançats utilitzant elements finits i/o diferències finites ofereixen la possibilitat d'ampliar la comprensió d’aquests sistemes estructurals i de predir el comportament de l'estructura en condicions de servei. En aquesta Tesi s'han desenvolupat models numèrics que han demostrat donar prediccions satisfactòries del comportament d’aquest tipus de murs quan es comparen amb resultats obtinguts d'estructures físiques instrumentades. Aquests models verificats han estat útils per a poder fer anàlisis de sensibilitat segons diferents geometries del parament i condicions de contorn, paràmetres dels materials i diferents models constitutius. Com a exemple dels resultats obtinguts, s’ha determinat que la capacitat de compressió de les peces de recolzament dels panells prefabricats modifica de manera significativa la càrrega desenvolupada vertical axial en el parament, però no té un efecte significatiu en la tensió desenvolupada a les capes de reforç del sòl. O també, que la rigidesa del sòl de fonamentació té un efecte més gran sobre la tensió desenvolupada en elements de reforç metàl·lics que en polimèrics. Ha estat possible dur a terme anàlisis de sensibilitat utilitzant els paràmetres que defineixen les interaccions sòl-estructura. Aquestes interaccions han estat analitzades utilitzant diferents programes comercials numèrics i definint-les amb elements del medi continu tant en models 2D com en 3D. Com a part de la Tesi, s'han de dut a terme assaigs de laboratori d'extracció de reforços tipus malla metàl·lica i banda polimèrica. Els paràmetres que tenen una influència principal en la interacció sòl-reforç han sigut identificats, quantificats i comparats tant amb els valors per defecte de disseny com amb valors reportats a la literatura utilitzats per a calibrar models analítics, permetent el calibratge dels models numèrics generats. Dels resultats dels models 2D i 3D s’han obtingut correlacions que permeten concloure que els models 2D en deformació plana són adequats per a representar el funcionament de les estructures de sòl reforçat amb elements de reforç discontinus a la direcció del parament. Mitjançant una avaluació adequada de la sostenibilitat ha estat possible fer comparacions quantitatives entre estructures de sòl reforçat i altres alternatives constructives que compleixen la mateixa funció (com els murs de gravetat o en voladís) construïdes a diferents altures. Mitjançant un model basat en la teoria de la utilitat multiatribut i d’anàlisi de valor per a la presa de decisions, es van identificar els processos més representatius i de major impacte des d’un punt de vista sostenible. Els resultats obtinguts inclouen un ajust basat en possibles escenaris de presa de decisió per la importància relativa dels tres pilars de la sostenibilitat (ambiental, econòmic, i social/funcional). L'alternativa de sòl reforçat va resultar ser la millor, obtenint una puntuació més alta en gran part dels escenaris de presa de decisió considerats. En base a una puntuació quantitativa final, els murs de sòl reforçat van resultar ser la millor opció en la majoria dels casos analitzats. Els models i metodologies d'anàlisi desenvolupades com a part de aquest treball de Tesi han millorat la comprensió del comportament d’aquestes estructures, i ofereixen possibilitats per a millorar i optimitzar els seus dissenys en el futur
Los muros de contención con suelo reforzado son estructuras materialmente más eficientes que otras soluciones constructivas alternativas, tales como los muros de gravedad o en voladizo. Sin embargo, su comportamiento y las interacciones entre los materiales que componen estas estructuras son complejos y no completamente comprendidos. Los métodos de diseño actuales suelen estar limitados a casos sencillos con respecto a las propiedades de los materiales, la geometría y las condiciones de contorno. Modelos numéricos avanzados utilizando elementos finitos y/o diferencias finitas ofrecen la posibilidad de ampliar la comprensión de estos sistemas y de predecir el comportamiento de la estructura en condiciones de servicio. En esta Tesis se han desarrollado modelos numéricos que han demostrado dar predicciones satisfactorias del comportamiento de este tipo de muros cuando se comparan con resultados obtenidos de estructuras físicas instrumentadas. Estos modelos verificados han sido útiles para análisis de sensibilidad según diferentes geometrías del paramento y condiciones de contorno, parámetros de los materiales y diferentes modelos constitutivos. Como ejemplo de los resultados obtenidos, la capacidad de compresión de las piezas de apoyo de los paneles prefabricados modifica de manera significativa la carga vertical axial desarrollada en el paramento, pero no tiene un efecto significativo en la tensión desarrollada en las capas de refuerzo del suelo. O también, que la rigidez del suelo de cimentación tiene un mayor efecto sobre la tensión desarrollada en elementos de refuerzo metálicos que en poliméricos. Ha sido posible llevar a cabo análisis de sensibilidad utilizando los parámetros que definen las interacciones suelo-estructura. Tales interacciones han sido analizadas utilizando diferentes programas numéricos comerciales y definiéndolas con elementos del medio continuo tanto en modelos 2D como 3D. Como parte de la Tesis, se han llevado a cabo ensayos de laboratorio de extracción de refuerzos tipo malla metálica y banda polimérica. Los parámetros que tienen una mayor influencia en la interacción suelo-refuerzo han sido identificados, cuantificados y comparados tanto con los valores por defecto de diseño como con valores reportados en la literatura usados para calibrar modelos analíticos, permitiendo la calibración numérica de los modelos generados. De los resultados de los modelos 2D y 3D se han obtenido correlaciones que permiten concluir que los modelos 2D en deformación plana son adecuados para representar el funcionamiento de las estructuras de suelo reforzado con elementos de refuerzo discontinuos en la dirección del paramento. Con una evaluación adecuada sostenibilidad ha sido posible hacer comparaciones cuantitativas entre estructuras de suelo reforzado y otras alternativas constructivas que cumplen la misma función (tales como los muros de gravedad o en voladizo) construidas a diferentes alturas. Mediante un modelo basado en la teoría de la utilidad multiatributo y análisis de valor para la toma de decisiones, se identificaron los procesos más representativos y de mayor impacto desde un punto de vista sostenible. Los resultados obtenidos incluyen un ajuste basado en posibles escenarios de toma de decisión por la importancia relativa de los tres pilares de la sostenibilidad (ambiental, económico, y social/funcional). La alternativa de suelo reforzado resultó ser la mejor, obteniendo una mayor puntuación en gran parte de los escenarios de toma de decisión considerados. En base a una puntuación final cuantitativa, los muros de suelo reforzado resultaron ser la mejor opción en la mayoría de los casos analizados. Los modelos y metodologías de análisis desarrolladas como parte de este trabajo de Tesis han mejorado la comprensión del comportamiento de estas estructuras, y ofrecen posibilidades para mejorar y optimizar sus diseños en el futuro

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Atualmente, muitos projetistas utilizam diferentes métodos para o projeto de muros de solo reforçado com geossintéticos. Uma avaliação desses diversos métodos pode ser realizada pela comparação com os resultados obtidos do monitoramento de casos reais e suas respectivas retro- análises, sendo este o objetivo desse trabalho. Na presente pesquisa, três casos reais bem documentados de muros de solo reforçado (MSR) com geossintéticos, construídos no Brasil, foram selecionados para análise. O monitoramento destas estruturas registra a força de tração em cada camada de reforço, ao final da construção. A magnitude de força máxima de tração, medida nos reforços foi comparada com os resultados previstos pelos diferentes métodos de projeto. Além disso, foram realizadas simulações numéricas para avaliar o desenvolvimento de forças de tração nos reforços e comparar os resultados medidos com os previstos pelas simulações. Estas comparações indicam que, em dois dos três casos avaliados, os métodos baseados em equilíbrio limite subestimaram os valores de força de tração, principalmente nas camadas superiores. Isto vale para MSR compactados com equipamentos de alta energia. O método analítico sob condições de trabalho, proposto por Ehrlich e Mitchell (1994), prevê resultados superiores aos registrados em campo, ou seja, a favor de segurança, para os três casos avaliados. A simulação numérica consegue obter ordens de grandeza das forças de tração máxima próxima aos resultados de campo. A formulação de Ehrlich e Mitchell (1994) para o cálculo da tensão vertical induzida durante a compactação, em conjunto com a modelagem por MEF, aponta resultados coerentes para os três muros.
Currently, several different methods for designing geosynthetic reinforced soil walls are available in the literature. An evaluation of these methods can be carried on by a direct comparison with the observed response of instrumented walls in the field. This comparison is the main objective of this research work. Three case histories of geosynthetic reinforced soil wall, constructed in Brazil, were selected for this research. The monitored response of these structures registered the tension in each reinforcement layer during construction. The maximum values of reinforcement tension have been compared with the computed values from different design methods. Moreover, predicted tension values from numerical simulations were also compared to the measured values in each reinforcement layer in the instrumented field walls. These comparisons indicate that, in two of the three evaluated cases, the design methods based on limit equilibrium underestimated the maximum tension. This was noted to be particularly significant in the upper layers of reinforced walls compacted under high energy levels. The analytical method based on work conditions proposed by Ehrlich and Mitchell (1994) resulted in tension values higher than those registered in the field instrumentation, for the three selected cases. Numerical simulations predicted maximum tension in reinforcements with similar values than those from the field instrumentation. The Ehrlich and Mitchell (1994) formulation for predicting the vertical tension induced by compaction resulted coherent with computed values from numerical finite element method for the three walls evaluated herein.

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
Este estudo apresenta o comportamento de um solo argiloso reforçado e não reforçado com fibras de coco verde (resíduo proveniente do consumo da água de coco), através da realização de ensaios de caracterização e ensaios mecânicos de compactação e de ensaios triaxiais isotropicamente drenados. A fibra de coco utilizada foi obtida por processo mecânico na empresa ECOFIBRA, que possui uma parceria com a Companhia de Limpeza Urbana da cidade do Rio de Janeiro (COMLURB) em projeto piloto de coleta seletiva das cascas de coco verde. O material recebido foi estudado de duas maneiras, as fibras foram inseridas ao solo moídas e cortadas (no comprimento aproximado de 2cm). O solo argiloso, de origem coluvionar, foi retirado do campo experimental da PUC-Rio. Busca-se estabelecer padrões de comportamento que possam explicar a influência da adição da fibra de coco verde, relacionando-a com os parâmetros de resistência ao cisalhamento do solo e dos compósitos. Os ensaios foram realizados em amostras compactadas na densidade máxima e umidade ótima, com teores de fibra moída de 0,5 por cento e 1 por cento e teores de fibra cortada de 0,5 por cento, 0,75 por cento, 1 por cento, 1,25 por cento e 1,5 por cento, em relação ao peso seco do solo. Observa-se um incremento na resistência ao cisalhamento das misturas solo-fibra, uma vez que se observa um discreto aumento do ângulo de atrito e em um expressivo aumento da coesão das misturas reforçadas, em comparação aos dados obtidos para o solo puro. Os resultados se mostraram satisfatórios para aplicação do solo reforçado com fibras de coco em camadas de aterros temporários submetidos a carregamentos estáticos, dando assim uma destinação mais sustentável a este resíduo, atendendo às questões ambientais e sócio-econômicas.
This study presents the behavior of reinforced and unreinforced clay soil with green coconut fibers (waste from consumption of coconut water), by conducting tests for the characterization and mechanical compaction tests and isotropically drained triaxial tests. The coconut fiber used is obtained by a mechanical process in ECOFIBRA company, which has a partnership with the Urban Cleaning Company of the city of Rio de Janeiro (COMLURB) in a pilot project about separate collection of green coconut shells. The received material was studied in two ways; the fibers were inserted into the milled and cut (in the approximate length of 2 cm). The clay soil, with colluvium origin, was removed from the experimental field of PUC-Rio. Seeks to establish patterns of behavior that might explain the influence of the addition of green coconut fiber, relating it to the parameters of shear strength and deformation of soil and composites. The tests were performed on samples compressed at maximum density and optimum moisture content in the milled fiber of 0.5 percent and 1percent fiber content and the cut of 0.5 per cent, 0.75 per cent, 1 per cent, 1.25 per cent and 1.5 per cent on dry weight of the soil. Observed na increase in shear strength of the soil-fiber mixtures, since it was observed a modest increase in friction angle and a significant increase in the cohesion of reinforced mixtures, ompared to the data obtained for the pure soil. The results ere satisfactory for application of soil einforced with coconut fiber layers temporary landfills subjected to static loads, thus giving a more sustainable destination to this residue, given the environmental and socio-economic.

The application of geosynthetic reinforcements in civil/geotechnical engineering projects (retaining walls, foundations, pavements, dams, slopes, etc.) has gained much popularity during the past few decades due to several benefits, including cost-effectiveness, environmentally friendly and sustainability. A detailed literature review as presented in this thesis has indicated that when a slope is reinforced with the geosynthetic layer(s), it improves the overall stability of the slope with or without loaded footing on the slope crest. However, studies on the performance of strip footings embedded in the slopes are very limited, and, especially for the geosynthetic-reinforced slopes, there is no work when the slope is reinforced with geosynthetic layers with or without wraparound ends. Also, there is no available literature on the design charts for low-height slopes, without footing/surcharge loads on the crest, which are usually constructed for the landscape developments in many countries. Furthermore, the literature has no information on the stability charts for reinforced sand slopes carrying embedded strip footing subjected to loads. This thesis work is based on the laboratory experiments and numerical simulations. The laboratory model tests were conducted on a sand slope supporting an embedded strip footing (width B = 75 mm ) in a rigid test tank (internal dimensions of 1250 mm × 445 mm in plan and 800 mm in height). The slope was reinforced with a single and multilayer geotextile with and without wraparound ends as different test trials. The model tests were conducted to evaluate the effect of the footing embedment depth D, footing edge distance e , number of geotextile layers N , and wraparound end of geotextile on the behaviour of the embedded footing. The footing was subjected to incremental loads to observe the corresponding stabilised settlements until it failed. The slope angle and relative density of the sand were maintained at constant values, β = 35 and Dr = 70%, respectively, throughout the laboratory experiments. For the case of the single geotextile layer with no wraparound ends, the geotextile was installed at the depth ratio u / B = 0.5 below the base of the footing which was first fixed at the edge distance ratio e / B = 1, while the depth ratio (D/ B)was varied from 0 to 1.5. After that, the footing was maintained at a constant depth ratio D/ B = 1 while the edge distance ratio (e / B) was varied from 0 to 3. In the case of the multilayer geotextile (N = 2, 3) , with no wraparound ends and single layer geotextile with wraparound ends, the top geotextile layer was placed at the depth ratio u / H = 0.5 below the base of the footing and the subsequent layers were positioned at a constant vertical spacing(h) to footing width ratio h / B = 0.5 from the top layer. The footing edge distance ratio was kept constant as e / B = 1 while depth ratio (D/ B) was varied from 0 to 1. The numerical models for the laboratory experiments were developed using the Plaxis 2D, a finite element package. The numerical analysis utilised the Mohr-Coulomb criterion to model the slope soil, the geogrid option to model the geotextile layer(s), the gravity force to simulate the initial stress condition within the slope and prescribed footing load option to simulate the applied footing loads accompanied by iterative analysis until failure occurred. The developed numerical after validation has been used for a detailed parametric study in order develop design charts for the stability of slopes with embedded footing. Additionally, the stability (factor of safety) analysis of a geotextile-reinforced low-height sandy slope, without footing or surcharge loads, was carried out using the limit equilibrium method available in Slope/W package. The experimental results indicate that the bearing capacity of the footing increases with increasing D/ B , e / B and N . The benefits derived from reinforcing the slope with geotextile layers have been evaluated using a non-dimensional parameter, called the ultimate bearing capacity ratio BCRu , defined as the ratio of ultimate bearing capacity of the reinforced case to that of unreinforced case. In the case of the single layer geotextile without wraparound ends, the maximum value of BCRu ≈ 2.5 − 3 is observed for D/ B = 0 and e / B = 0 , while the minimum value of BCRu ≈1.5 has been obtained for D/ B =1and e / B = 3 . The BCRu for the multilayer geotextile with no wraparound ends improves with an increase in N but reduces with an increase in D/ B . The minimum BCRu , BCRu (min) ≈ 2 , is observed for N =1 and D/ B =1, while the maximum BCRu , BCRu (max) ≈ 6 is attained when the footing is placed at D/ B = 0 and N = 3 . The installation of the single layer geotextile with wraparound ends brings an additional improvement in the bearing capacity of the footing compared to the case of no wraparound ends. The results obtained from the numerical simulations, on the load-settlement analysis of the embedded footing, closely agree with the experimental data, particularly for low settlements. The results from the numerical slope analysis show that the factor of safety (F) of the unreinforced sandy slope with an embedded footing increases with an increase in the footing edge distance ratio (e / B) , footing depth ratio (D/ B) and soil relative density(Dr ) , but it decreases with an increase in the slope angle (β ) and applied pressure on the footing(q) . For the surface footing (D/ B = 0) , F increases to a critical value at e / B = 3 then remains constant for e / B > 3. Though in the experimental study, only Dr = 70% was used, in the numerical simulations, = 50% r D and = 90% r D have also been considered. The study shows that with respect to increase in Dr , F significantly improves until Dr = 70%; after that, further increase in reduces the rate of increase in F . For the low-height sandy slopes, placing a single geosynthetic reinforcement layer at the depth ratio u / H = 0.5 in the 40° slope results in a stable slope with a maximum factor of safety Fr (max) = 1.61 , but this depth is not appropriate to stabilize the 50° and 60° slopes. The study shows that three geosynthetic layers are generally not be required as the two-reinforcement layers are adequate to attain the minimum factor of safety as usually recommended in most standards on stability of slopes. This thesis has many graphical presentations, which can be used as the design charts by the practising engineers.

Geosynthetic Reinforced Soil (GRS) is a promising technology that can be implemented in walls, culverts, rock fall barriers, and bridge abutments. Its use in walls and abutments is similar to Mechanically Stabilized Earth Walls (MSEW) reinforced with geosynthetics. Both GRS and MSEW are reinforced soil technologies that use reinforcement to provide tensile capacity within soil masses. However, the soil theories behind each method and the design methodologies associated with GRS and MSEW technologies are quite different. Therefore, a study was undertaken to compare the required tensile strength predicted by these various reinforced soil design methodologies. For the purposes of this study, the required ultimate tensile strength was defined as the ultimate tensile strength needed in the reinforcement after all applicable factors of safety, load factors, and reduction factors were applied. The investigation explored both MSEW and GRS. GRS has been made an FHWA "Every Day Counts" initiative. Due to the push to implement GRS technology, it is critical to understand how GRS design methods differs from classic MSEW design methods, specifically in the prediction of ultimate tensile strength required. A parametric study was performed comparing five different reinforced soil analysis methods. Two are current MSEW design methods and one was a proposed revision to an existing MSEW design method. The final two were GRS design methods. These design methods are among the most current and/or widely used design references in the United States regarding reinforced soil technology. There are significant differences between the methods in the governing soil theory particularly between GRS and MSEW design methods. The goal of the study was to understand which design parameters had the most influence on calculated values of the required ultimate tensile strength and nominal "unfactored" tensile strength. A base case was established and a reasonable set of parameter variations was determined. Two loading conditions were imposed, a roadway loading scenario and a bridge loading scenario. Based on parametric study findings, conclusions were drawn about which design parameters had the most influence for different design methods. Additionally, the difference in overall predicted required tensile strength was assessed between the various methods. Finally, the underlying soil theory and assumptions employed by the different methods and their influence on predicted required tensile strength values was interpreted.
Master of Science

This thesis describes a study into the action of geotextiles in providing combined drainage and reinforcement to cohesive soil and the identification of the interaction of different geotextiles with a cohesive soil. The study involved both experimental and analytical investigations. Fine grained cohesive soil is a complex material. The introduction of geosynthetics providing both drainage and a reinforcement function produce a marked increase in the shear strength characteristics of the clay material. A number of consolidated undrained and consolidated drained triaxial compression tests and Rowe cell consolidation tests were conducted. The objective of the tests was to identify the separate effects (improvement) on the shear strength properties of the cohesive soil (kaolin) provided by the drainage function and separately that provided by the reinforcing function of a number of geotextiles. An Electron Scanning Microscope study was used to investigate the interaction between the cohesive soil and the geosynthetic materials. The study provided qualitative information concerning the relative improvement of the physical properties of a fine grained cohesive soil when used in construction with range of geosynthetic materials. Analysis of the results of the research suggest that geotextile products could offer significant technical, practical and economic advantages when constructed with poor quality soils. The combined function of drainage and reinforcement which could be developed by some geosynthetic materials could be substantial. Combining the functions of drainage and reinforcement in a single material requires the resulting geosynthetic to have special properties. The form of a geocomposite drainage and reinforcement material with these properties is proposed

Confidence in the design of reinforced retaining structures is based on a limited body of experimental field data from performance monitoring of a relatively small number of case studies. In order to improve upon that confidence in design, this research addresses the back-analysis of the only field study involving a reinforced steep slope with independent measurements of tensile force and strain, which was first described by Fannin & Hermann (1990). Knowing the mobilized strength in the reinforcement, a back-analysis was performed using widely accepted design practice, with the purpose of establishing the mobilized angle of friction within the backfill soil of the structure. The mobilized friction angle was compared with the findings of laboratory shear strength tests in direct shear, triaxial and plane-strain conditions. The comparison provides further evidence in support of the expectation that plane-strain conditions prevail within the reinforced steep slope, and the recommendation in the British code of practice to use the peak friction angle for design. Additionally, visual inspection and index testing on exhumed geogrid samples from the structure described by Fannin & Hermann (1990) established that the geogrid has experienced no major physical damage, nor any significant degradation associated with durability of the polymer material. Moreover, rapid loading creep tests data show excellent agreement between exhumed and typical values, implying no significant durability degradation in the geogrid of the Skedsmo structure. Accordingly, isochronous load-strain-time data can be used with confidence for predicting the long-term strain of geogrid reinforced soil structures.
Applied Science, Faculty of
Civil Engineering, Department of
Graduate

HUESKER SYNTHETIC GMBH
No presente trabalho foi estudado o comportamento de um muro de solo reforçado com 5m de altura e 1700m de extensão, construído como parte do dique que compõe o Depósito de Resíduos de Bauxita 7 da ALCOA Alumínio S.A. em Poços de Caldas, MG. Neste muro foram empregados um solo residual siltoargiloso obtido no local e geogrelhas. O muro foi instrumentado para medição de deslocamentos horizontais e verticais durante a construção. Na mesma área, também foi construído um aterro experimental de 2,6m de altura que permitiu a realização de 16 ensaios de arrancamento de grandes dimensões. Foram realizados ensaios de laboratório para definir os parâmetros de resistência e deformabilidade do solo. Os parâmetros obtidos foram empregados em simulações numéricas da construção do muro e dos ensaios de arrancamento pelo Método dos Elementos Finitos, utilizando-se o programa PLAXIS 2D v.8. Os resultados obtidos demonstraram que os deslocamentos ocorridos durante a construção do muro são comparáveis a valores reportados por outros autores. As previsões numéricas da construção do muro e dos ensaios de arrancamento apresentaram boa concordância com os resultados medido em campo. Constatou- se que a resistência ao arrancamento obtida foi superior às previsões baseadas em formulações tradicionais da literatura.
The behavior of a 5m high and 1700m long reinforced soil wall was studied in this work. The wall constitutes the upper part of a dike constructed in Poços de Caldas-MG, Brazil, by Alcoa Aluminum S.A. to contain Bauxite residues. The wall was constructed using geogrids and a residual silty-clay. Two wall sections were instrumented. Horizontal and vertical displacements were monitored during construction. An 2.6m high experimental fill was constructed to conduct 16 large-scale pullout tests. Soil laboratory tests were conducted to define the strength and deformability parameters. The construction of the wall and the pullout tests were simulated using the PLAXIS 2D v.8 Finite Element Method code. The numeric predictions agree well with the field results. The measured horizontal displacements show good agreement with results reported by other authors and the pullout resistance was found to be greater than the values estimated by traditional methods.

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE EXCELENCIA ACADEMICA
Este estudo apresenta o comportamento de solos reforçados com adição de pérolas de EPS (Poliestireno Expandido) através de estudo experimental. Os solos utilizados foram: um solo argiloso de origem coluvionar, uma areia limpa, mal graduada e bentonita. Foram realizados ensaios de caracterização física e de caracterização mecânica, como ensaios de compactação Proctor Normal, ensaios triaxiais consolidados isotropicamente drenados (CID) e ensaios de cisalhamento direto para buscar estabelecer padrões de comportamento que possam explicar a influência da adição de pérolas de EPS, relacionando-a com os parâmetros de resistência ao cisalhamento. Os ensaios triaxiais CID foram realizados em amostras de solo argiloso compactadas na densidade máxima seca e umidade ótima, com teores de pérolas de EPS de 0 por cento, 0,25 por cento, 0,50 por cento, 0,75 por cento e 1 por cento, em relação ao peso seco do solo e os ensaios triaxiais CID em amostras de areia foram realizados para uma densidade relativa de 50 por cento e umidade de 10 por cento, com teores de pérolas de EPS de 0 por cento, 0,50 por cento e 0,75 por cento, em relação ao peso seco do solo. Os ensaios de cisalhamento direto com bentonita foram realizados com teores de pérolas de EPS de 0 por cento, 0,50 por cento e 0,75 por cento, em relação ao peso seco do solo. Os resultados mostraram que o tipo de solo, o teor de pérolas de EPS e o nível de tensão confinante influenciam positivamente o comportamento mecânico final dos compósitos com relação aos parâmetros de resistência, porém não há uma tendência de comportamento bem definida ao analisar cada fator independentemente. Portanto, o uso de pérolas de EPS em obras geotécnicas de carregamento estático contribuiria com o menor consumo de material natural e a consequente redução dos custos de transporte e volume de material mobilizado.
This study presents the behavior of soils reinforced with EPS (Expanded Polystyrene) beads through experimental study. The soils used were a coluvionar soil, a clean and barely graduated sand and bentonite. Physical characterization, Standard Proctor, consolidated drained triaxial and direct shear tests were performed to establish patterns of behavior that may explain the influence of the addition of expanded polystyrene beads, linking it with shear strength parameters. The CID triaxial was performed on samples of clayey soil compacted within the maximum dry density and optimum moisture content with expanded polystyrene beads ratios of 0 percent, 0.25 percent, 0.50 percent, 0.75 percent and 1 percent by dry weight of soil. CID triaxial tests on sand samples were made to a relative density of 50 per cent and 10 per cent of moisture content, with EPS beads ratios of 0 percent, 0.50 percent and 0.75 percent by dry weight of soil. The direct shear tests with bentonite were made with EPS beads ratios of 0 percent, 0.50 percent and 0.75 percent by dry weight of soil. The results showed that the kind of soil, the EPS content and level of confining stress level influence positively on the final mechanical behavior of the composites with respect to strength parameters, but there is no well-defined pattern of behavior to examine each factor independently. Therefore, the use of EPS beads in geotechnical works, contribute to lower consumption of natural material and the consequent reduction in transport costs and volume of mobilized material.

Geosynthetic Reinforced Soil (GRS) structures brought significant improvement in the engineering behavior of soil structures and spread to countries throughout the world in recent decades. GRS structures use simpler construction techniques, tolerate more differential settlement, exhibit better seismic performance, and provide greater ductility and safety than conventional soil structures.

The Federal Highway Administration (FHWA) conducted performance tests that validated their guidance for soil reinforced with geosynthetic sheets. In contrast, this thesis investigates capacity and deformation of soil reinforced with geosynthetic strips. While comparing strip-GRS with sheet-GRS, this research focuses on the mechanics of coherence, providing both the analysis and the laboratory tests for validation. The meaning of “coherence” as granular stability is taken from the 1987 report by Mitchell and Villet that pioneered reinforced soil in America, but its meaning is also associated with “jammed,” a word now commonly used among practitioners of the discrete element method.

The strip-GRS research of this dissertation is part of a larger effort of this university to derive analytical methods for reinforced soil structures where only empirical methods had been available previously. Fortuitously, the results of this completed research are now relevant to a discussion that began at the international congress (19^th ICSMGE) in September 2017. In that discussion, which hopes to extrapolate to standard practice from a few field measurements, the industry glimpses the feasibility and benefits of soil structures reinforced with geosynthetic strips.

Soil reinforcement with discrete flexible fibres has always been an issue for further research. In Geotechnical engineering field, the research on sandy soil has considerably been more than the clayey one. The main reason for this lack can be expressed as the complexity of clayey material due to their cohesion and interaction between clay and reinforcement.The present research aims to show possibility of discrete fibre usage in clay. For this purpose, selection of material has been conducted with special care to make the project outcome applicable to industry projects. The fibre which was used for this research prepared by BASF Company in Western Australia and currently is used in fibre reinforced concrete for infrastructure projects. Kaolin has been used as soil part and provided by Prestige Company.Experimental approach was applied to investigate the effect of different parameters on composite soil strength. These tests cover the variety range of soil mechanics tests from compaction tests to triaxial compression tests. The results from all the tests were presented in the thesis.A theoretical model was also developed for clayey material for the first time with the use of modified cam clay model to predict the behaviour of samples precisely. This model is based on the rule of mixture and considers the effect of soil and fibre separately. The model was validated with the results from CD triaxial test.

Recent developments in constructions have heightened the need for protecting existing buried infrastructure. New roads and buildings may be constructed over already existing buried infrastructures e.g. buried utility pipes, leading to excessive loads threatening their stability and longevity. Additionally applied loads over water mains led to catastrophic damage, which result in severe damage to the infrastructure surrounding these mains. Therefore, providing protection to these existing buried infrastructure against increased loads due to new constructions is important and necessary. In this research, a solution was proposed and assessed, where the protection concept would be achieved through the inclusion process of geogrid-reinforcing layers in the soil cover above the buried infrastructure. The controlling parameters for the inclusion of geogrid-reinforcing layers was assessed experimentally and numerically. Twenty-three laboratory tests were conducted on buried flexible and rigid pipes under unreinforced and geogrid-reinforced sand beds. All the investigated systems were subjected to incrementally increasing cyclic loading, where the contribution of varying the burial depth of the pipe and the number of the geogrid-reinforcing layers on the overall behaviour of the systems was investigated. To further investigate the contribution of the controlling parameters in the pipe-soil systems performance, thirty-five numerical models were performed using Abaqus software. The contribution of increasing the amplitude of the applied cyclic loading, the number of the geogrid-reinforcing layers, the burial depth of the pipe and the unit-weight of the backfill soil was investigated numerically. The inclusion of the geogrid-reinforcing layers in the investigated pipe-soil systems had a significant influence on decreasing the transferred pressure to the crown of the pipe, generated strains along its crown, invert and spring-line, and its deformation, where reinforcing-layers sustained tensile strains. Concerning rigid pipes, the inclusion of the reinforcing-layers controlled the rebound that occurred in their invert deformation. With respect to the numerical investigation, increasing the number of the reinforcing-layers, the burial depth of the pipe and the unit-weight of the backfill soil had positive effect in decreasing the generated deformations, stresses and strains in the system, until reaching an optimum value for each parameter. Increasing the amplitude of the applied loading profile resulted in remarkable increase in the deformations, stresses and strains generated in the system. Moreover, the location of the maximum tensile strain generated in the soil was varied, as well as the reinforcing-layer, which suffered the maximum tensile strain.
Government of Egypt

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.

The phenomenon known as the ‘arching effect’ occurs when a portion of granular mass yields relative to an adjacent stationary region. The movement is resisted by shearing stresses which act to reduce the pressure on the yielding support and increase the pressure on the adjacent stationary supporting zones. Arching is widely observed in both natural and man-made structures such as piled embankments, tunnelling, and above mine works and sinkholes. In this research the arching effect is recreated in the increased gravity environment of a geotechnical centrifuge where the pressure distribution across both the yielding and supporting soil masses is measured and the resulting soil displacements observed. A motor driven ‘trapdoor’ apparatus was built inside a plane strain container to model the yielding support. Both the trapdoor and an adjacent support were instrumented to measure the force (and derived pressure) distribution. Soil and trapdoor displacements are determined by analysis of digital images taken in-flight through a Perspex wall of the container. One method of increasing soil shear strength and its resistance to deformation is the reinforcement of soil with randomly distributed discrete fibres. The degree of improvement has been shown to be directly related to the fibre content in the soil, the fibre aspect ratio, orientation and mechanical properties. In this research the effect of fibre reinforcement on the arching process and resulting deformation is examined by variation of fibre parameters such as fibre aspect ratio and volumetric content of fibre. The influence of fibre and model scale effects were investigated by conducting a modelling of models exercise whereby trapdoor scale and effective stress were varied whilst maintaining a constant cover depth to structure width ratio, and compaction effort. The results were compared directly with those obtained for unreinforced soil trapdoor tests in order to determine the extent of improvement offered by fibre-reinforcement.

Since the last three decades, several studies have been conducted related to improvement in bearing capacity of pavements, embankments, and shallow foundations resting on geosynthetic reinforced soil. Most of the work has been carried out on single layer soil e.g., sand or clay layer only. Very few studies are available on a double layer soil system; but no study is available on the local soil of Carbondale, Illinois. The present study investigates the physical and engineering properties of a local soil and commonly available sand and improvement in the bearing capacity of a local soil for a rectangular footing by replacing top of the local soil with sand layer and placing geogrids at different depths. Seven tests on the model footing were performed to establish the load versus settlement curves of unreinforced and reinforced soil supporting a rectangular foundation. The improvement in bearing capacity is compared with the bearing capacity of the local soil and double layer unreinforced soil system. The test results focus on the improvement in bearing capacity of local soil and double layer unreinforced soil system in non-dimensional form i.e., BCR (Bearing Capacity Ratio). The results obtained from the present study show that bearing capacity increases significantly with the increasing number of geogrid layers. The bearing capacity for double layer soil increases, by placing three inch sand layer at the top of local soil, was not significant. The bearing capacity of the local soil increased at an average of 7% with three inches sand layer. The bearing capacity for the double layer soil increases with an average of 16.67% using one geogrid layer at interface of soils (i.e., local soil and sand) with u/B equal to 0.67. The bearing capacity for the double layer soil increases with an average of 33.33% while using one geogrid in middle of sand layer having u/B equal to 0.33. The improvement in bearing capacity for double layer soil maintaining u/B equal to 0.33 and h/B equal to 0.33; for two, three and four number geogrid layer were 44.44%, 61.11%, 72.22%, respectively. The results obtained from this research work may be useful for the specific condition or similar type of soil available anywhere to improve the bearing capacity of soil for foundation and pavement design.

During the past few decades, many studies have been conducted to investigate the load-settlement behaviour of geosynthetic-reinforced foundations, and researchers proposed different methods to improve the performance of geosynthetic-reinforced foundation soils as well as to develop empirical equations to estimate their bearing capacity. In the recent past, using geotextile reinforcement with wraparound ends has been recommended to strengthen the foundation soil aimed at improving the effectiveness of using geosynthetic reinforcements. However, there are still areas that received far too little attention in the past, e.g. the optimum geometric parameters in geosynthetic-reinforced sandy soils with or without using wraparound reinforcement technique. An optimal design and the effectiveness of employing geosynthetic material for strengthening the foundation soil require an extensive knowledge of the load-settlement behaviour and failure mechanism of reinforced soils. This thesis presents extensive laboratory measurements and numerical analysis conducted to (i) investigate the effect of angle of internal friction of soil on the optimum burial depth of the reinforcement and the bearing capacity of the geosynthetic-reinforced sandy soil based on numerical modelling, (ii) study the effects of reinforcement geometrical parameters, namely land width occupied by the reinforcement, and the lap length of the wrapped ends, based on numerical modelling, (iii) present experimental evaluations of the effectiveness of the wraparound reinforcement technique for improving the bearing capacity and load-settlement characteristics of sandy soils, and (Das & Sivakugan) study the strain distribution and the mobilisation of tensile modulus in geotextile reinforcement buried within the sandy soil. In the experimental phase, laboratory model strip footing tests were performed to investigate the influence of wraparound lap length and occupied land width on the load-settlement behaviour of sandy soil. In addition, an instrumentation program with pressure cells and strain gauges was designed to investigate stress and strain distribution within the sand bed. The test results show that the existence of wraparound ends of the geotextile reinforcement improves the bearing capacity of sand bed by about 70% comparing with reinforced foundation soil without wraparound ends. The strain distribution observations reveal that the theoretical solution may overestimate the tensile strength of the geotextile in the range of 30-60 % that can be due to the in-isolation methods being used by standards to measure the tensile modulus of geosynthetics. In the numerical phase, first, a numerical model was built to investigate the effect of the angle of internal friction of sand on the optimum burial depth of geosynthetic reinforcement. Numerical outputs reveal that the optimum burial depth depends significantly on the angle of internal friction of sand, and has a linear relationship with the height of the active wedge beneath the footing. In the second stage, a parametric study of the wraparound reinforcement technique was carried out to investigate the effects of geometrical parameters of wraparound reinforcement on the bearing capacity of the sandy soil. The model was used to critically analyse the reinforcing mechanisms for improved bearing capacity caused by wraparound ends. The results reveal that the efficiency of reinforced models with wraparound ends in terms of occupied land area is about 100% higher than that of without wraparound ends. The research carried out as presented in this thesis demonstrates that the wraparound geosynthetic reinforcement technique can be highly beneficial in a location of limited land width for foundation construction.

This study uses dynamic centrifuge tests and three-dimensional (3D), nonlinear finite-difference analyses to: (1) evaluate the effect of soil-cement grid reinforcement on the seismic response of a deep soft soil profile, and (2) to examine the dynamic response of structures supported by shallow foundations on soft clay reinforced by soil-cement grids. The soil profile consisted of a 23-m-thick layer of lightly over-consolidated clay, underlain and overlain by thin layers of dense sand. Centrifuge models had two separate zones for a total of four different configurations: a zone without reinforcement, a zone with a "embedded" soil-cement grid which penetrated the lower dense sand layer and had a unit cell area replacement ratio Ar = 24%, a zone with an embedded grid with Ar = 33%, and a zone with a "floating" grid in the upper half of the clay layer with Ar = 33%. Models were subjected to a series of shaking events with peak base accelerations ranging from 0.005 to 0.54g. The results of centrifuge tests indicated that the soil-cement grid significantly stiffened the site compared to the site with no reinforcement, resulting in stronger accelerations at the ground surface for the input motions used in this study. The response of soil-cement grid reinforced soft soil depends on the area replacement ratio, depth of improvement and ground motion characteristics. The recorded responses of the structures and reinforced soil profiles were used to define the dynamic moment-rotation-settlement responses of the shallow foundations across the range of imposed shaking intensities. The results from centrifuge tests indicated that the soil-cement grids were effective at controlling foundation settlements for most cases; onset of more significant foundation settlements did develop for the weakest soil-cement grid configuration under the stronger shaking intensities which produced a rocking response of the structure and caused extensive crushing of the soil-cement near the edges of the shallow foundations. Results from dynamic centrifuge tests and numerical simulations were used to develop alternative analysis methods for predicting the demands imposed on the soil-cement grids by the inertial loads from the overlying structures and the kinematic loading from the soil profile's dynamic response.
Ph. D.

碩士
國立高雄第一科技大學
營建工程所
95
The application of reinforced earth embankment in mountain areas is easily restricted by available space. It raises difficulty for allocating length of reinforcement. If we add soil nails on the back side of reinforced earth embankment, the soil nails could provide extra force as compensation for the lack of sufficient length of reinforcement embankment. This paper analyze applications of reinforced embankment system for different geometric slopes via the Limit Equilibrium Analysis computer program – ReSSA. Deduce length of reinforcement from safe factors of research result. In addition, Compound Construction Method combined soil nails and reinforcement retaining structure has been proven to be highly feasible. In order to solve the problem of mentioned above in mountain areas, this paper also uses the Compound Construction Method to design, and analysis via Finite Element Method program – PLAXIS. The geometric conditions of reinforced earth embankment include: (1) height of reinforcement earth embankment; (2) angle of reinforcement slope; (3) length of reinforcement material. Besides, this paper also has an emphasis on different weight loadings, both in static and dynamic states, on reinforced embankment. In order to build design chart of soil nail force for Reinforced Earth Embankments Reinforced by Soil Nails system as a basis. For different geometric conditions, this paper takes 7 meters, 9 meters, and 12 meters height into consideration. The result shows that the higher the embankment, the more tensile force the soil nails endures. As for the angle of embankment slope, we study it under 60 degree, 70 degree, 80 degree, and 90 degree, and find that the steeper the reinforced embankment, the more tensile force the soil nails takes. Besides, the angle of reinforcement slope influences tensile force distribution from each step of soil nails. While above one-third of embankment height, the bigger the angle of embankment slope, the more tensile force the soil nails takes; surprisingly, while below one-third of embankment height, the bigger the angle of embankment slope, the less tensile force the soil nails sustains. As for the length of reinforced materials, the longer the reinforced materials, the less the maximum tensile force of soil nails bears. Moreover, this paper studies friction angle of backfill in 25 degree, 30 degree, and 35 degree, to understand influences on stability of reinforced area from different backfill. The result shows when the friction angle of backfill is higher, reinforced earth embankment maintains higher stability and soil nails endure less tensile force. For mastering the tensile force needed from soil nails in different geometric conditions, this paper categorizes results of mechanics analysis from reinforced earth embankment connected with soil nails under static weight loadings in different geometric conditions, and establishes design chart of tensile force from soil nail to normalize the maximum tensile force.