Thèses sur le sujet « GEOGRID REINFORCED »

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.

Composite geogrids can successfully be used as a pavement-reinforcement material to increase the performance of pavement structures. This thesis presents a comprehensive study that has investigated the effectiveness of composite geogrids as subgrade reinforcement in unpaved granular pavements that are subjected to cyclic loading and constructed with local materials available in Queensland, Australia. The research outcomes suggest guidelines to design and construct unpaved granular pavements with the composite geogrid reinforcement at the base-subgrade interface. These guidelines benefit the industry by reducing construction and maintenance costs, and environmental pollution.

The study of innovative pavements is of significant importance in geotechnical engineering in Brazil, due to the continued need to increase the network of roadways. This requires optimized projects, not only for economic, but also for technical reasons. Technical solutions that use geosynthetics in asphalt overlays have been identified to minimize fatigue and reflective cracks. However, the majority of the application of this technology has ignored the possible additional structural benefits brought by the inclusion of geosynthetics as reinforcement in asphalt layers. The objective of this research is to assess the reinforcement benefits of geogrids placed within asphalt overlays on the structural performance of flexible pavements. In addition, this study investigates the tensile-strain response of geogrids under traffic conditions, induced by cyclic wheel loads generated by a new accelerated pavement testing facility (APT) that was specifically developed for this research. The APT facility consists of a large steel testing box, in which field-scale pavement layers could be constructed. Pavement materials included subgrade soil, aggregate base, hot mix asphalt concrete, asphalt emulsion and a PVA geogrid. Pavement performance was assessed by applying a cyclic wheel load pressure of 700 kPa to the pavement surface. The pavement sections investigated in this study included a geogrid-reinforced and an unreinforced asphalt overlay sections, a single new geogrid-reinforced asphalt layer, and a geogrid-reinforced asphalt overlay with reduced base course thickness. A variety of sensors were used to measure asphalt concrete strains, surface plastic and elastic displacements, and induced traffic loads. Displacements along the geogrid specimens were measured using a tell-tail system. As result, several reinforcement mechanisms of this technique could be quantified in the present study. Polymeric geogrid reinforcements were found to have considerably reduced strains developed at the bottom of asphalt layers, as well as to have reduced vertical stresses in pavement lower layers. Resistance to rutting and lateral movement induced by the geogrids were also clearly evidenced in the presented study. The measurement of displacements along the geogrid provided understanding of the distribution of strains during traffic loading. A mobilized length was identified in geogrid-reinforced sections, showing that the bonding between geogrids and asphalt layers and the stiffness of the geogrid ensured satisfactory performance of the pavement sections. The results also illustrated that the lateral restraining mechanisms effect is a governing mechanism to improve the performance of the asphalt layers by the development of shearing resistance with the geogrids. Overall, it was concluded that geogrids within asphalt overlays act as reinforcement and not merely to delay cracks, providing enhanced performance to flexible pavement structures.
O estudo de pavimentos é de grande importância na Engenharia Geotécnica brasileira devido à crescente necessidade de melhora da situação da rede rodoviária nacional. Para tanto, o desenvolvimento e a aplicação de novas técnicas são necessários, principalmente no âmbito econômico. A técnica do uso de reforços geossintéticos em capa asfáltica é identificada como uma alternativa ao aumento da vida útil do pavimento através da mitigação de trincas por fadiga e de reflexão. No entanto, a maioria das aplicações desta técnica não correlaciona os benefícios estruturais da inclusão do geossintético na capa asfáltica para a melhora do desempenho global do pavimento. O objetivo desta pesquisa é investigar os benefícios estruturais no desempenho de pavimentos flexíveis trazidos pelo reforço de geogrelhas em camadas asfálticas. Ainda neste estudo, será investigada a reposta tensão-deformação destas geogrelhas sobre as condições de tráfego através do uso de ensaios acelerados de pavimento. Um equipamento foi desenvolvido para esta pesquisa e consiste numa caixa metálica de grande porte, em que seções de pavimento em escala real podem ser construídas. O desempenho das seções de pavimento foi avaliado com a aplicação de cargas cíclicas de roda com pressão de contato de 700 kPa. Os materiais que compõem as seções de pavimento incluem solo de subleito, brita graduada simples, concreto betuminoso usinado à quente, emulsão asfáltica e geogrelha de PVA. Foram estudadas uma seção com geogrelha como reforço no recapeamento da camada asfáltica, uma seção idêntica não reforçada, uma seção com uma única capa asfáltica reforçada com geogrelha e uma seção com geogrelha no recapeamento da camada asfáltica, porém com espessura de base reduzida em relação aos demais ensaios. Sensores nas camadas do pavimento mediram tensões e deformações, e deslocamentos plásticos e elásticos na superfície. Deslocamentos ao longo da geogrelha foram monitorados utilizando o sistema tell-tales. Como resultado, mecanismos de reforço foram identificados neste estudo. O uso de uma geogrelha polimérica reduziu consideravelmente as deformações na fibra inferior da capa asfáltica, assim como as tensões verticais nas camadas subjacentes do pavimento. Resistência à formação de trilhas de roda e solevamentos laterais foram também evidenciadas. As medidas de deslocamentos ao longo da geogrelha forneceram entendimento da distribuição de deformações durante o carregamento. Foi identificado o comprimento de geogrelha mobilizado durante os ensaios, mostrando que a aderência entre a geogrelha e as camadas asfálticas e a rigidez da geogrelha asseguraram o desempenho satisfatório das seções de pavimento. Os resultados também mostraram que o efeito do mecanismo de restrição lateral é um mecanismo que governa a melhora no desempenho da capa asfáltica com o uso da geogrelha através do desenvolvimento de resitência ao cisalhamento. Estas observações permitem concluir que a geogrelha na camada asfáltica atua como reforço e não apenas reduzindo a o potencial de trincamento, levando à um aumento no desempenho de estruturas de pavimentos flexíveis.

Recently, the railway pavement structure system, as an integral part of the transport infrastructure, has been under fast development in some countries such as China, Turkey, and some European Union countries, particularly for the use of high-speed trains. In designing and constructing the railway pavement structure, it is necessary to take into account the infrastructure demand of the High-Speed Railway Lines (HSRL). Compared to traditional railway trains, HSRL can cause more significant problems to the ballast or base layer of commonly used ballasted railway pavements. The deteriorated ballast or base layer may further result in substructure degradation that may cause safety issues and catastrophic accidents. As a consequence, heavy goods or high-speed trains will affect railway efficiency. As a countermeasure, a railway pavement structure may be reinforced by geosynthetic materials in the ballast or base layer. In the literature, however, there is still a need to quantify the effect of geosynthetic materials, geogrid in particular, on the mechanical responses of railway pavement structures to HSRL loads, which is necessary knowledge in supporting the selection of appropriate material and placement location of geogrid. Therefore, the goal of this study is to investigate how a geogrid reinforcement layer can change the essential characteristics of a ballasted railway pavement structure, with focus on the material type and placement location of geogrid that can help minimize the rate of deterioration of the railway pavement structure system. This research attempts to validate the advantage of geogrid reinforcement through numerical simulation in a realistic railway setting. All technical literature on the use of geogrids in the railway system has been studied. A three-dimensional (3D) finite element model was constructed for the numerical simulation, in which three different types of geogrid placed at two different locations (i.e., within the ballast layer, between the ballast and the sub-ballast layer) within a railway pavement structure were analyzed under a range of vertical wheel loads. Therefore, four possible applications of geogrid reinforcement systems (G0: no-reinforcement; G1: reinforced with geogrid having the lowest density and Young’s modulus; G2: reinforced with geogrid having the intermediate Young’s modulus and density; G3: reinforced with geogrid having the highest density and Young’s modulus) were modeled to represent different situations in ballasted railway systems. Railway mechanical responses, such as vertical surface deflection, maximum principal stress and strain, and maximum shear stress were analyzed and compared among the four geogrid reinforcement scenarios and under four vertical wheel load levels (i.e., 75, 100, 150 and 200 kN). The advantages of such geosynthetics in ballast are indicated by result difference in the mechanical responses of railway pavement structures due to the use of different geogrid materials. The results also show that the reinforced structures have lower vertical surface deflection, lower maximum shear stress at the interface of sleeper and ballast, and maximum principal stress at the bottom of the ballast layer than a non-reinforced railway pavement structure. Consequently, the addition of geogrid into the ballast layer, and between the ballast and sub-ballast layer has been shown to reduce critical shear and principal stresses and vertical surface deflection in a ballasted railway pavement structure. Besides that, the results of the analysis confirm that geogrid reinforced layers exhibit higher resistance to deformation than the non-reinforced layers.

COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
O principal objetivo deste trabalho foi avaliar o comportamento mecânico de misturas asfálticas reforçadas com geogrelhas. Inicialmente foram previstos ensaios a serem executados em um modelo físico de verdadeira grandeza. Entretanto, devido a um comprometimento estrutural localizado num dos componentes deste modelo físico durante a realização dos ensaios, optou-se por interromper a execução destes e então, elaborar um programa experimental de laboratório, que consistia da extração de amostras deste modelo físico de verdadeira grandeza e moldagem de corpos de prova por amassamento através de compactador giratório. Cada conjunto de amostras (extraídas e moldadas) possuía corpos de prova sem ou com reforço, onde foram estudados dois tipos de geogrelha (de fibra de vidro e poliéster). Foram realizados os ensaios de Resistência à Tração por Compressão Diametral, Módulo de Resiliência, Fadiga por compressão diametral sob carga controlada e Tração em Disco Circular com Fenda. Os resultados dos ensaios mostraram que a presença do reforço de geogrelha melhorou o comportamento mecânico das misturas asfálticas, com a tendência de maior resistência à fratura, fato este evidenciado principalmente pelo ensaio de Tração em Disco Circular com Fenda, onde tais corpos de prova não atingiram o critério de finalização do ensaio (redução da carga aplicada a 0,10 kN). Nos ensaios de fadiga constatou-se que a melhor influência das geogrelhas ocorre para os menores níveis de tensão aplicada, sendo que nesta condição é permitido um maior período para as geogrelhas se deformarem, condição essencial para sua atuação como elemento com a função de atrasar a propagação de trincas. Constatouse uma melhoria significativa nos resultados obtidos com as amostras reforçadas com as grelhas, tendo as amostras com camada de geogrelha de poliéster apresentado os melhores resultados.
The objective of this study was to evaluate the mechanical behavior of geogrid reinforced asphalt mixtures. Initially tests were planned to be executed on a physical model, however, this tests had to be stopped due to structural problems. Samples were extracted from the physical model and samples were shaped through gyratory compaction, both for analyze the mechanical laboratory tests. Tensile Resistance (Brazilian Test), Resilient Modulus, Fatigue (controlled load) and Disk-Shaped Compact Tension Geometry Tests were carried out in extracted and shaped samples, without reinforcement and with the reinforcement of two geogrid types (fiberglass and polyester). The reinforcement improved the mechanical behavior of asphalt mixtures, with the trend of greater resistance to fracture, and this was evidenced by Disk-Shaped Compact Tension Geometry Tests, where the final criterion of the test was not reached (reduction of the applied load of 0.10 kN). The influence of geogrid is better for lower applied stress levels according with the Fatigue Tests. This condition allows the geogrid to deform for a long period, witch is essential for the performance as an element for delay crack propagation. There was a significant improvement in the results obtained with the reinforced samples, for both geogrids studied, but the polyester geogrid reached better results when compared to fiberglass geogrid.

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.

Track deterioration has a serious influence on the safety and efficiency (speed restriction) of train operations. Many expensive, disruptive and frequent repair operations are often required to maintain the ballast characteristics due to the problem of settlement. Because of this, a geogrid solution that has proved to be a simple and economical method of reinforcing track ballast is widely used. This project presents an evaluation of the behaviour of geogrid-reinforced railway ballast. Experimental large box pull-out tests were conducted to examine the key parameters influencing the interaction between ballast and the geogrid. The experimental results demonstrated that the triaxial geogrid with triangular apertures outperforms the biaxial geogrid with square apertures and the geogrid aperture size is more influential than rib profile and junction profile. The discrete element method (DEM) has then been used to model the interaction between ballast and geogrid by simulating large box pull-out tests and comparing with experimental results. The DEM simulation results have been shown to provide good predictions of the pull-out resistance and reveal the distribution of contact forces in the geogrid-reinforced ballast system. The discrete element method has also been used to simulate cyclic loading of geogrid-reinforced ballast under confined and unconfined conditions. For the confined condition, box tests have been simulated on unreinforced samples and reinforced samples with different geogrid positions and geogrid apertures. The response of the ballast layer reinforced with geogrid under repeated loading agrees with experimental results. It was found that the optimum location of geogrid is 100 mm depth from base, and the triaxial geogrid outperforms biaxial geogrid. For the unconfined condition, cyclic loading of a trough of ballast has also been simulated, and the sample with the geogrid at 50mm from the sub-ballast layer performs best. It was also found that the used of two geogrids at both 50mm and 150mm from the sub-ballast gave a smaller settlement than using a single layer geogrid, or the unreinforced ballast. The geogrid reinforcement limits the lateral displacement in reinforced zone, which is approximately 50mm above and below the geogrid. Previous investigations have shown that the abrupt stiffness change in track support is often associated with accelerated rates of deterioration of track geometry, high maintenance demand, and poor ride quality. However, at present, there is no detailed understanding of the mechanisms of track geometry deterioration at transition zones. This work provides insight into the factors that can cause or accelerate track degradation at the transition zones, in order to identify and evaluate appropriate mitigation design. A simple track transition model with dimensions 2.1m x 0.3m x 0.45m was simulated by using PFC3D. In order to identify and evaluate appropriate mitigation methods, two kinds of transition patterns, including a single step change and a multi step-by-step change for subgrade stiffness distribution were tested. The influence of the train direction of travel and speed on the transition were also investigated. In addition, geogrid was used in the ballast layer to examine the effects of geogrid reinforcement.

Geogrid reinforced structures have been successfully used for over 25 years. However their design procedures have remained largely focused on ultimate failure mechanisms, originally developed for steel reinforcements. These are widely considered over conservative in determining realistic reinforcement and lateral earth stresses. The poor understanding of deformation performance led many design codes to restrict acceptable soils to selected sand and gravel fills, where deformation is not as concerning. Within UK construction there is a drive to reduce wastage, improve efficiency and reduce associated greenhouse gas emissions. For geogrid reinforced structures this could mean increasing reinforcement spacing and reusing weaker locally sourced soils. Both of these strategies increase deformation, raising concern about the lack of understanding and reliable guidance. As a result they fail to fulfil their efficiency potential. This Engineering Doctorate improved the understanding of horizontal deformation by analysing performance using laboratory testing, laser scanning industry structures and numerical modelling. Full-scale models were used to demonstrate a reduction in deformation by decreasing reinforcement spacing. Their results were combined with primary and secondary case studies to create a diverse database. This was used to validate a finite element model, differentiating between two often used construction methods. Its systematic analysis was extended to consider the deformation consequences of using low shear strength granular fills. The observations offered intend to reduce uncertainty and mitigate excessive deformations, which facilitates the further optimisation of designs.

The potential human and economic loss due to structural collapse of geo-synthetic reinforced soil walls during earthquakes us huge. This substantiates the need for reliable design of such structures. The focus of this study was numerical and analytical design geo-synthetic reinforced soil walls under dynamic loading. Two topics were addressed; the effect of reinforcement parameters and verification of pseudo-static methods. The study is based on a 1 m high reduced-scale shaking table model loaded using stepped-amplitude harmonic base acceleration amplitude. A numerical PLAXIS model was developed and verified using physical model data. Material properties of the components (e.g. backfill and reinforcements) were based on information from a similar model developed using FLAC. The numerical model was used in a parameter study of the effects of reinforcement length and strength on the failure surface, facing displacements and reinforcement loads. The accuracy of pseudo-static methods was studied by comparing physical model results with predictions using the Mononobe-Okabe, the horizontal slices and two-part wedge method. Furthermore, guidelines for the Mononobe-Okabe method in different seismic design codes (i.e. Eurocode, FHWA/AASTHO and PIANC) were compared. Based on this comparison a new pseudo-static coefficient was developed. The reinforcement length and strength were found to have a significant effect on model response. For example, an increase in reinforcement axial stiffness will give a shallower failure surface and reduced the lateral facing displacements. Neither the Mononobe-Okabe, nor the horizontal slice, or the two-part wedge method was able to predict both the failure surface and the earth forces for a wide range of acceleration amplitudes. It was found that different pseudo-static methods are suitable for different predictions (e.g. of the failure surface) at different acceleration amplitudes. For example, single wedge pseudo-static methods gave good predictions for the active earth force and failure surface shape for acceleration amplitudes up to 0.30g, but not for higher amplitudes. FHWA/AASHTO were found to give better predictions for the failure surface and earth forced (when using Mononobe-Okabe) than the Eurocode and PIANC guidelines. Even so, the failure surface predicted using FHWA/AASHTO was too shallow compared to the physical measurements for acceleration amplitudes up to 0.30g.

Geogrid reinforcement can improve the performance of pavements by stiffening the aggregate base material and decreasing pavement deformations. Understanding the effects of cyclic loading on the modulus of geogrid-reinforced base materials would help engineers better anticipate actual increases in the modulus of aggregate base materials under given traffic loads. The objective of this laboratory research was to investigate the effects of cyclic loading on the resilient modulus, the modulus to peak axial stress, the elastic modulus, and the modulus at 2 percent strain of geogrid-reinforced aggregate base materials. The scope of the research included two aggregate base materials (Wells Draw and Springville) having different particle-size distributions and particle angularity. Geogrid-reinforced and unreinforced specimens were subjected to conditioning periods consisting of cyclic loading ranging from 10 to 10,000 cycles. Immediately following cyclic loading, all specimens were tested using the quick shear portion of the American Association of State Highway and Transportation Officials T 307 (Determining the Resilient Modulus of Soils and Aggregate Materials). Specimen preparation involved material weigh-outs, compaction, and membrane applications. Specimen testing in the loading machine consisted of two testing portions, including cyclic loading and quick shear testing. The cyclic loading data were used to calculate the resilient modulus on 200-cycle intervals throughout the duration of the conditioning period. The quick shear data were used to calculate the peak axial stress, the modulus to peak axial stress, the elastic modulus and the modulus at 2 percent strain. For the Wells Draw material, the resilient modulus increases by 11 percent for the specimens with geogrid and increases by 8 percent for the specimens without geogrid as the number of load cycles increases from 1,000 to 10,000. For the Springville material, the resilient modulus increases by 2 percent for the specimens with geogrid and increases by 3 percent for the specimens without geogrid as the number of load cycles increases from 1,000 to 10,000. As with other studies, the results do not show a consistent or significant effect of geogrid reinforcement on the resilient modulus of the tested materials. The modulus at 2 percent strain has the most potential for consistently showing improvements to aggregate base materials due to both cyclic loading and geogrid reinforcement. For the Wells Draw and Springville materials, the modulus at 2 percent strain increases by 31 and 9 percent, respectively, as the number of load cycles increases from 10 to 10,000. Additionally, for the Wells Draw and Springville materials, the modulus at 2 percent strain of the specimens with geogrid is 23 and 46 percent, respectively, greater than that of the specimens without geogrid. The results show a consistent and significant positive effect of geogrid reinforcement on modulus at 2 percent strain of the tested materials. According to the modulus at 2 percent strain results, a sufficient conditioning period appears to occur at 5,000 cycles for the Wells Draw material and 10,000 cycles for the Springville material.

Reliability and safety represent key features of any successful railway system and compromising either has undeniable ramifications. Railway industry practitioners are continually challenged to deliver reliability and performance improvements whilst facing ever increasing service demands. These improvements are typically achieved through track maintenance and renewal activities, which have to be balanced against a requirement to reduce whole life-cycle costs. Research focusing on the optimisation of railway track components, which can then be translated to field practice, presents a real opportunity to reduce the frequency of disruptive and often costly track maintenance activities and ultimately prolong the life span of a railway track. A laboratory study of track performance with particular emphasis on railway sleeper type and geogrid type as the main variables has been undertaken. The types of sleepers investigated were the concrete monoblock, twin-block, timber, plastic, and steel sleepers. The geogrids variants tested were the SSLA30 biaxial and TX130 triaxial geogrids with square and triangular apertures respectively. Testing undertaken involved the application of low frequency cyclic loads to railway sleeper sections and full-size sleepers installed on a 300 mm thick ballast with and without geogrid reinforcement. Bending tests, friction tests and hardness tests were initially performed to characterise the material and mechanical properties of the sleepers investigated. Preliminary cyclic tests were conducted with a Box Test apparatus and Composite Element Test (CET) apparatus to approximate field conditions. Full scale tests were subsequently performed with the Nottingham Railway Test Facility (RTF) which is designed to provide a closer representation of field conditions and simulate the passage of an axle load over three sleepers. The outer sleepers in the test facility provided the necessary boundary conditions for the middle sleeper, which was the primary focus of the tests performed. Measures of track performance included vertical track settlement, trackbed stiffness and formation pressure. Additional measurements were made of the differential deflection along the length of the middle sleeper to ascertain if sleeper bending occurred during the tests. Linear elastic and finite element analysis to determine the pressure on top of the subgrade and at the sleeper-ballast interface respectively were performed for idealised sleeper support conditions. The results of the numerical analysis were compared with the RTF pressure plate measurements and estimates of subgrade pressure calculated using empirically derived equations. The results showed that sleeper type influences the permanent settlement that develops in a railway track as well as the magnitude of transient live loads that is transmitted to an underlying subgrade. In line with the permanent settlement results, it is also apparent that trackbed stiffness is a function of sleeper bending stiffness. Measurements of formation pressure and resilient sleeper deflection revealed differences between sleeper types with regards to their ability to retain the as-built geometry of a trackbed, underlining the importance of the sleeper-ballast interface characteristics and sleeper bending stiffness. Traditionally used empirical equations for determining subgrade pressure were found to be conservative compared to subgrade pressures determined using linear elastic analysis and measurements of made of the same using pressure plates in the RTF. Finite element analysis to determine the pressure distributions at the base of different sleepers for a range of support conditions found the shape and magnitude of pressures determined to be consistent with the sleepers’ bending stiffnesses suggesting that sleeper properties should be an important consideration when predicting track performance. The use of the biaxial geogrid installed 100 mm above the base of the ballast reduced permanent settlement for all sleeper types without any significant bias towards any one sleeper type. Additionally, the use of the biaxial geogrid resulted in the delayed deterioration of sleeper support for all sleeper types. The application of the TX130 geogrid resulted in increased settlement and increased deterioration of the as-built trackbed geometry for all sleeper types owing to the grid aperture which proved unsuited to the standard Network Rail ballast gradation. It was proposed that a triaxial geogrid with a larger aperture may offer better results. It was also suggested that sleeper choice that includes consideration for the relative performance of sleeper types is possible for railway practice although it must be commensurate with the intended use of the track with due regard to cost and safety. The research concluded that the concrete monoblock sleeper, which is currently the prevalent sleeper type in the UK (with and without the biaxial geogrid), for the conditions simulated, presents the best opportunity to minimise the maintenance requirements of a railway track.

The installation of geogrid as a means of extending the service life of a roadway or reducing the required base course thickness of a pavement structure has become increasingly popular. The realization of these benefits depends largely on the degree to which the geogrid reinforcement leads to an increase in the stiffness of the aggregate base course layer. The objective of this research was to investigate the structural capacity of geogrid-reinforced aggregate base materials in flexible pavements through full-scale testing. The scope involved field testing at two sites in northern Utah that each included five different geogrid-reinforced sections and five accompanying unreinforced control sections. Five different geogrid types were utilized to ensure that the experimentation was representative of the geogrid products available in the industry at the time of the study. At each of the two field sites, 10 test sections were established, and several field tests were conducted during and following construction of the two pavements to characterize the in-situ structural properties of the subgrade, base, and hot mix asphalt layers of each geogrid-reinforced and unreinforced test section. The procedures involved nuclear density gauge, soil stiffness gauge, Clegg impact soil tester, dynamic cone penetrometer (DCP), portable falling-weight deflectometer, and falling-weight deflectometer testing of each test section. Samples of the subgrade and base materials were also obtained from both field sites for laboratory testing, which included dry and washed sieve analyses, Atterberg limits testing, and material classification. An analysis of covariance (ANOCOVA) was conducted on the results of each field test to determine if the structural capacity of the geogrid-reinforced sections was different than that of the accompanying unreinforced control sections.Among the 24 ANOCOVA models developed for the two field sites, only four indicated that geogrid presence was statistically significant. Of these four models, three indicated that the presence of geogrid reinforcement led to higher values of the given measurement of structural capacity compared to the unreinforced condition; however, in none of the cases was the difference practically important as defined in this research and would therefore not result in a different input in the pavement design process. Notably, in all three of these models, the same testing procedure, namely the DCP, was used for the testing. A measurable increase in the structural capacity of the reinforced layer may not be immediately observable using standard pavement testing procedures. Further field research is recommended to investigate the duration of the required conditioning period and also the extent of the zone of influence of geogrid reinforcement in aggregate base courses.

The modulus of aggregate base layers in pavement structures can potentially be increased through the use of geogrid. However, methods for determining how much structural benefit can be expected from a given geogrid product have not been standardized. A laboratory testing protocol is therefore needed to enable evaluation, in terms of modulus or California bearing ratio (CBR), for example, of the degree of improvement that may be achieved by a given geogrid. Consequently, the objective of this research was to identify a laboratory test method that can be used to quantify improvements in structural capacity of aggregate base materials reinforced with geogrid. For this research, National Cooperative Highway Research Program Report 598 repeated load triaxial, American Association of State Highway and Transportation Officials (AASHTO) T 307 quick shear, and CBR testing protocols were used to test unreinforced and geogrid-reinforced aggregate base materials from northern Utah. Biaxial and triaxial geogrid were investigated in multiple reinforcement configurations. Several statistical analyses were performed on the results of each test method to identify the test that is most likely to consistently show an improvement in the structural capacity of aggregate base materials reinforced with geogrid. The results of this research indicate that, for the methods and materials evaluated in this study, calculation of the modulus at 2 percent strain from the AASHTO T 307 quick shear data is the test method most likely to consistently show an improvement in structural capacity associated with geogrid reinforcement. Of the three configurations investigated as part of this research, placing the geogrid at an upper position within a specimen is preferred. Given that the end goal of the use of geogrid reinforcement is to improve pavement performance, additional research is needed to compare the results of the AASHTO T 307 quick shear test obtained in the laboratory with the structural capacity of geogrid-reinforced aggregate base materials measured in the field. In addition, correlations between the results of the AASHTO T 307 quick shear test and resilient modulus need to be investigated in order to incorporate the findings of the AASHTO T 307 quick shear test on reinforced base materials into mechanistic-empirical pavement design.

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CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico
This work aims at the realization of geogrid pullout tests in a typical soil of the city of Manaus, using a small laboratory equipment. The soil in natura used in the tests was collected within an Area of Permanent Protection (APP) at the Federal University of Amazonas campus, representing a wide area of topsoil from the city of Manaus, the clayeysilty- sandy composition. From the original sample mixture with the addition of 20%, 40% and 60% sand deposit by mass were prepared. The soil samples and mixtures were characterized by the writings of Grit, Real Density, Liquid Limit, Limit Plasticity, Compression (Standard Proctor), California Support Index (CSI) and Triaxial Compression. Subsequently, tensile testing of Tensar geogrids in pullout of small laboratory equipment, experimental in nature, in which they varied the type of soil were performed, aiming a comparison with the manufacturer's specifications, and the test speed and type geogrid. During the research, a computer program was developed to facilitate statistical analysis of the results of pullout tests and enable the design of reinforced embankments with geogrids. Those tests proved that the insertion of the geogrid coupled to sanding, the original soil increments the geotechnical performance of the assembly, opposite the pullout requests, in which the mixture of 60% sand that best represents the quality of the strength parameters for reinforced embankments.
Este trabalho visa à realização de ensaios de arrancamento de geogrelha em um solo típico da cidade de Manaus, utilizando um equipamento reduzido de laboratório. O solo in natura utilizado nos ensaios foi coletado dentro de uma Área de Proteção Permanente (APP), no campus da Universidade Federal do Amazonas, representando um solo superficial de vasta área da cidade de Manaus, de composição argilo-silto-arenosa. A partir da amostra original, foram confeccionadas misturas com a adição de 20%, 40% e 60% de areia de jazida, em massa. As amostras de solo e misturas foram caracterizadas através dos ensaios de Granulometria, Densidade Real, Limite de Liquidez, Limite de Plasticidade, Compactação (Proctor Normal), Índice de Suporte Califórnia (ISC) e Compressão Triaxial. Posteriormente, foram realizados ensaios de tração das geogrelhas, visando um comparativo com as especificações do fabricante, e ensaios de arrancamento das geogrelhas em um equipamento reduzido de laboratório, de cunho experimental, em que se variou o tipo de solo, a velocidade do ensaio e o tipo de geogrelha. Durante a pesquisa, um programa computacional foi desenvolvido, para facilitar a análise estatística dos resultados dos ensaios de arrancamento e possibilitar o dimensionamento de taludes reforçados com geogrelhas. Esses ensaios comprovaram que a inserção da geogrelha, aliada à aplicação de areia, ao solo original, incrementa o desempenho geotécnico do conjunto, frente às solicitações de arrancamento, sendo a mistura com 60% de areia a que melhor representa a qualidade dos parâmetros de resistência, para os taludes reforçados.

The thesis deals with numerical modeling of reinforced earth wall. The first part of the thesis characterizes and describes these constructions in general and also describes variations of their faces. In the next part the modeling of basic reinforced earth wall construction elements in Plaxis 2D is described. Subsequently the real reinforced earth wall is modeled and some variations of face-modeling are compared.

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

O intenso crescimento populacional traz consigo uma preocupação ambiental, já que, diante da necessidade de exploração dos recursos naturais, a adoção de políticas de reciclagem faz-se fundamental para alcançar o desenvolvimento sustentável. Neste cenário, apesar dos resíduos de construção e demolição (RCD) possuírem alto potencial de reciclagem, a estes sempre foi dispensado o tratamento de lixo. Além disso, os estudos realizados visando à reciclagem dos RCD mostram-se bastante concentrados na produção de agregados para a fabricação de concreto e para a aplicação em pavimentação. Diante disso, neste trabalho procurou-se definir uma nova aplicação para os resíduos de construção e demolição reciclados (RCD-R), buscando caracterizar suas propriedades geotécnicas como material de construção e verificando o seu desempenho como material de preenchimento de estruturas de solo reforçado. Ensaios de caracterização, de resistência ao cisalhamento e ensaios de arrancamento de geogrelha revelaram que o RCD-R apresentou baixos coeficientes de variação nas suas propriedades e excelente comportamento mecânico, o que justifica a sua utilização na aplicação proposta.
The intense population growth brings some environmental concerns due to the need of exploitation of natural resources, and the adoption of recycling policies is basic principle to reach sustainable development. In this scenario, however, the high potential of recycling the construction and demolition wastes (CDW) has been ignored. Moreover, studies focus mainly on the recycling of CDW for the production of aggregates for use in pavements and concrete. The present study deals with a new application of the recycled construction and demolition waste (RCDW) as backfill of reinforced soil structures. Characterization, direct shear and pullout tests on geogrids has depicted that RCDW shows low coefficients of variation of its properties and excellent mechanical behavior that justify its use for proposed application.

Les géosynthétiques sont utilisés depuis les années 70 dans le renforcement des plateformes granulaires reposant sur des sols de faible portance pour des applications de routes non revêtues. La complexité des mécanismes développés et la diversité des produits de renforcement nécessitent encore d’étudier ces plateformes renforcées. Un essai au laboratoire permettant de tester des plateformes à échelle réelle a été développé. Une plateforme granulaire non revêtue reposant sur un sol de faible portance a été reproduite. Un protocole de mise en place de ce sol a été élaboré pour assurer son homogénéité et la répétabilité des essais. Une instrumentation spécifique a été développée pour collecter le maximum de mesures utiles pour l’interprétation du transfert de charge et du comportement des géogrilles utilisées. Trois types de géogrille ont été testées : une géogrille extrudée et deux géogrilles tricotées de rigidité différente. Après de nombreux essais de faisabilité, dix essais ont été effectués sous un chargement cyclique sur plaque circulaire, la plateforme testée a été placée dans un banc d’essai de 1,8 m de large, 1,9 m de long et 1,1 m de haut. Sur la base du même protocole de mise en œuvre, des essais de circulation avec un Simulateur Accélérateur de Traffic (SAT) ont été effectués. Ce simulateur a été spécifiquement conçu et construit pour cette application. Pour ces essais, la plateforme testée a été placée dans le banc d’essai allongé à 5 m. La plateforme a été soumise à deux types de sollicitations : un chargement cyclique sur plaque et un chargement de circulation. Des essais de répétabilité ont permis de vérifier le protocole mis en place. A partir des essais, plusieurs observations ont pu être faites sur le comportement des plateformes granulaires, le sol peu porteur, et sur l’efficacité du renforcement. De plus, ces essais ont permis de montrer que le chargement de circulation est beaucoup plus endommageant que le chargement sur plaque. Parallèlement à ces essais, un modèle numérique a été développé en se basant sur la méthode des différences finies avec le logiciel FLAC 3D. Cette modélisation a permis de prédire le comportement de la plateforme sous le premier chargement de plaque
Geosynthetics were used since 1970 in the base course reinforcement supported by soft subgrade in unpaved road application. The various factors and parameters influencing the dominant mechanism and its relative contribution on the platform improvement explain the need of more investigations in this topic. In this research work, large-scale laboratory test was developed to study the reinforcement contribution in the unpaved road improvement. Therefore, an unpaved platform was built of 600 mm of artificial subgrade supporting a base course layer. A detailed experimental Protocol was established regarding the soil preparation, the installation and the soils compaction procedure to reproduce the site conditions and insure the platform repeatability for each test. Three geosynthetics were tested first under a cyclic plate load test. Cyclic load was performed on the prepared platform, with a maximum load of 40 kN resulting in a maximum applied pressure of 560 kPa. The platform was subjected to 10,000 cycles with a frequency of 0.77 Hz. An advanced and complete soil instrumentation was provided in order to collect the maximum data needed for thorough analysis. Quality control tests were performed before each test to verify the soil layers homogeneity and properties. Two base course thicknesses were tested under this test condition, 350 and 220 mm. Once the developed protocol was confirmed under the circular plate load tests, further tests using the Simulator Accelerator of Traffic (SAT) were performed. Indeed, the laboratory prepared platform was placed in a larger box of 1.8 m in large, 5 m in length and 1.1 m in height. The prepared platform was subjected to two solicitations: a particular plate and traffic load. The Simulator Accelerator of Traffic was developed specially for this application. A machine that simulates the traffic load under an effective length of 2 m and a velocity of 4 km/h. The two areas were instrumented: the area under the circulation load, and the area under the plat load, located aside. In addition, a numerical model based on the differential element method using FLAC 3D was developed. The model simulated the circular plate load test with the same platform configuration under monotonic load. The results were compared to the first monotonic load applied on the rigid plate experimentally

La presente investigación alcanza una alternativa de utilizar los muros de suelo reforzado como estribos de puente en la mina Cuajone situado en el departamento de Moquegua, con el objetivo de comprobar si es posible que estas estructuras soporten las altas cargas de los camiones mineros que transitan por los “Haul Road” de la mina. Luego, se desarrolla los procedimientos de diseño estructural del muro MSE con la metodología LRFD según la norma AASHTO. Finalmente, se verifica los resultados que se obtuvieron mediante el modelo y el análisis de los elementos finitos del diseño consolidado en el software PLAXIS y se presentan las conclusiones del caso. En primer lugar, está el capítulo introductorio, que presentar de manera resumida y cualitativa el tema de la tesis y las motivaciones del caso. Se desarrolla el problema planteado y finaliza esta sección con la descripción de los antecedentes históricos de los muros MSE, hipótesis, objetivos y alcances de la presente investigación. Asimismo, se describe de manera extendida los conceptos de los muros MSE, ventajas, desventajas, tipos de sistemas, tipos de refuerzo, tipos de paramentos y sus aplicaciones. Además, se presentan los pasos diseño de los muros como estribo de puente y el procedimiento del análisis sísmico de estos. Finalmente, se describen los conceptos del método de elementos finitos y el análisis del software PLAXIS. En el segundo lugar; se presentan el material y método, considerando el nivel y diseño de investigación, variables y técnicas que se emplearon para poder desarrollar de manera satisfactoria el argumento de la presente tesis. En el tercer lugar, se presentan los resultados de acuerdo a cada objetivo planteado. Al finalizar esta sección, se presentan los desplazamientos de muro MSE como estribo de puente modelado en el software PLAXIS, concluyendo con la afirmación o la negación de la hipótesis. Por último, se presenta las conclusiones, comentarios y recomendaciones de acuerdo al desarrollo y resultados de la presente investigación.
The present investigation achieves an alternative use of the reinforced soil walls as bridge abutments in the Cuajone mine in the department of Moquegua, with the objective that these structures bear the high loads of the mining trucks that transit through the "Haul Road" of the mine. Then, the structural design procedures of the MSE wall are followed with the LRFD methodology according to the AASHTO standard. Finally, the results obtained by means of the model and the analysis of the finite elements of the consolidated design in the PLAXIS software are verified and the conclusions of the case are presented. In the first place, there is the introductory chapter, the summary and qualitative presentation of the topic of the thesis and the motivations of the case. The problem raised and finalized in this section was developed with the description of the historical background of the MSE walls, hypotheses, objectives and scope of the present investigation. In the next chapter, we describe how to extend the concepts of MSE walls, advantages, disadvantages, types of systems, types of reinforcement, types of walls and their applications. In addition, the steps of the walls are presented as bridge abutment and the procedure of the seismic analysis of these. Finally, the concepts of the finite element method and the analysis of the PLAXIS software are described. In the second place; It presents the material and the method, the level and design of the research, the variables and the techniques used to successfully develop the argument of the present thesis. In the third place the results are presented according to each objective. At the end of this section, the displacements of the wall are presented as a work program in the PLAXIS software, concluding with the affirmation or denial of the hypothesis. Finally, the conclusions, comments and recommendations are presented according to the development and results of the present investigation.
Tesis

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.

A series of large-scale pavement model tests were conducted in a laboratory environment to investigate the effect of geosynthetics in improving the modulus of weak subgrades. Then, a series of supplement design charts that could be useful for industry practitioners to design geosynthetic reinforced flexible pavements were developed. The outcomes of this study promote the use of geosynthetics in road construction to make economical, environmentally friendly, climate resilient, and sustainable road infrastructure.

O conhecimento dos mecanismos de interação entre o solo e os geossintéticos é fundamental para o dimensionamento de obras em solo reforçado. Entretanto, em função das diferentes formas geométricas das superfícies das inclusões, a interação pode ocorrer de maneiras distintas. Para as geogrelhas, o arrancamento representa o mecanismo de interação que, em alguns casos, melhor retrata as situações que ocorrem no campo. Esta tese apresenta uma análise dos principais fatores que influenciam na interação entre o solo e as geogrelhas quando solicitadas ao arrancamento, utilizando equipamentos de teste de portes grande e pequeno, bem como um equipamento que testa isoladamente os elementos longitudinais e transversais das geogrelhas. Apresenta-se ainda dois modelos numéricos que permitem avaliar o comportamento de geogrelhas de comprimento qualquer a partir de resultados de ensaios de arrancamento de pequeno porte ou dos ensaios nos elementos isolados da geogrelha. Os resultados dos ensaios realizados são comparados entre si, sugerindo a viabilidade de se utilizar equipamentos de pequenas dimensões para executar ensaios de arrancamento em geogrelhas em meio a solos finos, em detrimento dos testes de grande porte que demandam uma grande quantidade de solo e de mão-de-obra para serem executados. Por fim, apresenta-se um método que, utilizando os resultados obtidos dos testes de pequeno porte, pode ser usado para determinar os esforços de tração nas inclusões de estruturas em solo reforçado, considerando aspectos como a interação solo–reforço e a rigidez à tração das inclusões
The knowledge of interaction mechanisms between soil and geosynthetics is fundamental for designing reinforced-soil structures. However, due the variety of surface geometry found in commercially available geosynthetics, the interaction between soil and inclusions can occur on different ways. For the geodrids, the pullout interaction mechanisms is the one that, in some cases, best represents the field situations. This thesis presents an analysis of the main factors influencing the soil-geogrid interaction during pullout phenomena, using large and small-scale test boxes, as well as an device that tests longitudinal and transversal geodrid elements isolated. Two numerical models for evaluating the pullout behavior of large geogrid samples using small-scale and on element tests are also presented. The results of different tests are compared, showing the viability of using small-scale tests for testing geogrids embedded in fine soils instead of large-scale tests, that demand large quantities of soil and labor to be done. On the penultimate chapter, a method for evaluating the maximum tensile effort of reinforced slopes and walls is presented. This method uses the results obtained from small-scale pullout tests and considers some important aspects as soil-geogrid interaction and reinforcement rigidity

Este trabalho apresenta resultados de ensaios de arrancamento de geogrelha, obtidos com a utilização de equipamento de dimensões reduzidas. A força de arrancamento foi aplicada por uma máquina universal com capacidade máxima de 30kN, dotada de instrumentação que permitiu registrar a força de arrancamento e o deslocamento da geogrelha em relação ao solo envolvente. Além disto, o ensaio foi instrumentado com uma célula de tensão total instalada no nível da inclusão. A grande vantagem deste equipamento é o pequeno volume de solo utilizado, resultando em um ensaio mais rápido e econômico, proporcionando um controle maior do teor de umidade e do grau de compactação do solo. Considerando que uma grande parte do estado de São Paulo é coberto por solos de granulometria fina, esse equipamento passa a ser uma excelente alternativa para obtenção dos parâmetros de ensaios de arrancamento necessários ao desenvolvimento de projetos em solo reforçado. Para averiguar a possibilidade de uso do ensaio de pequeno porte, nestas condições, para substituir uso das caixas de grandes dimensões foram inicialmente realizadas comparações, através do coeficiente de interação, entre os resultados obtidos através desses dois tipos de ensaios. Os resultados obtidos mostraram que, para as condições de ensaio empregadas utilizando solos com 100% passando na peneira de abertura 2mm e geogrelhas de abertura de malha aproximadamente de 20mm, a resposta do equipamento, se comparada à de ensaios de grandes dimensões, foi excelente. Isto permitiu que se procedesse a uma ampla análise paramétrica, de cunho experimental, em que se variou a velocidade de ensaio, a tensão confinante, as dimensões das amostras de geogrelha, o tipo de solo e a geogrelha, com o intuído de cobrir diferentes situações possíveis de se encontrar nos projetos de engenharia. O trabalho apresenta os principais resultados desta análise
This work presents results of geogrid pullout tests conducted using small scale equipment. The pullout load was applied using a universal load frame, with a maximum capacity of 30kN, capable of recording the pullout load and front displacement. In addition, the test was instrumented with an earth pressure cell installed at the level of the geogrid inclusion. The primary advantage of this equipment is the small volume of soil used in test preparation, resulting in reduced testing time, greater control of the water content and degree of compaction, and significant reduction in overall testing costs. Furthermore, a significant area of the state of Sao Paulo in Brazil is covered by fine grained soils which could be tested according to its pullout behavior using the proposed equipment. To investigate the feasibility of the small scale test facility, comparisons were made between the coefficient of interaction obtained from tests of small and large dimensions. The results show that for the tested materials there were no differences between pull out parameters from both equipment. Additionally it was investigated the effects of testing speed, confining pressure, sample dimensions, and soil and geogrid materials. Results of these tests are presented and discussed

This study investigated the use of geogrids for ground improvement based on numerical analysis using Plaxis and Geostudio software. Owing to the low shear strength and excessive settlement of the sandy soil, geogrids materials were used to reinforce the soil taking advantage of their good tensile strength. Geogrids were applied in three layers after the design output. The reinforced mechanism of geogrids was analyzed based on modelling outputs and results. Output results from the Plaxis and Geostudio software showed a significant decrease in displacement and increase in factor of safety after reinforcing the soil with geogrids materials. The total displacement in the unreinforced slope is 670.67 mm which reduced to 19.30 mm when reinforced with geogrids. This reduction is over 900 % of the original total settlement. The slope was also analyzed for different amounts of surcharge in both reinforced and unreinforced case. The effect of groundwater fluctuation and rapid drawdown of water were analyzed. The influence of rainfall intensity and duration is also analyzed. The factor of safety results after the analysis are compared with different parameters. Based on the results of this study, it was concluded that geogrids could be used as soil reinforcement materials to improve the shear strength of the soil and reduce its settlement potential significantly.

For the past three decades, geosynthetics have been recognized as materials that can significantly improve the performance of pavements on weak subgrade. Pavements exhibit non-linear elasto-plastic behavior. The addition of geosynthetics is undoubtedly beneficial. This being said, researchers have concentrated more on lower life cycle cost and high benefit-cost ratio whereas much less attention has been given to the complex behavior of the reinforced pavement system. Comprehension of the short-term and long-term field performance of reinforced pavements under continued traffic and cyclic environmental loading has remained unexplored. There is empirical evidence indicating quantitative benefits of reinforced versus unreinforced pavement structure. However, quantification of the relative benefits of different types of reinforcement like geogrids and geotextiles lacks information. Further, evaluation of the benefits and comparison of chemical stabilization in the form of lime treatment with mechanical stabilization in the form of reinforcement for pavements on soft soils has received lack of attention. In view of this, full-scale instrumented reinforced and lime treated pavement sections with different schemes were studied. Regular Falling Weight Deflectometer (FWD) testing was conducted in a Farm-to-Market Road, in Grimes County, Texas. Three different geosynthetic products were used for base reinforcement and lime treatment was used for subbase stabilization. Deflection measurements for 9 field trips in 3.5 years were evaluated. Modified deflection basin parameters (DBPs) were defined to typically identify layer properties and were used to measure the relative damage to the base, subbase and subgrade for different sections. A modified Base Damage Index (BDI) and a modified Base Curvature Index (BCI) were defined as a part of this study to capture the benefit of reinforced base and lime stabilized subbase respectively. The variation in the DBPs over three periods of wetting and drying along with explanation of the observed trends forms a part of this research. In addition, a number of condition surveys were performed, during 3 years, to visually identify distresses in various sections. A unique distress quantification technique was developed for measuring deterioration of the pavement sections in terms of the observed distresses and FWD measurements. With this, an index of pavement performance was developed. Thus, the FWD deflection data analyses complemented by visual observation, reveals important information on performance of different geosynthetics with the same base course. Analysis of the field performance of the multiple experimental sections throws light on the relative merits of base reinforcement against lime stabilization.
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With Emphasis on greater connectivity, there is a need of unpaved road to achieve economy. In this study a large scale laboratory plate load test was conducted on a circular footing resting on with and without geogrid reinforced bed. Sand and granular materials are used as subgrade and subbase layer. The experiments were conducted for both static and dynamic loading .Test result reveals that with the addition of geogrid the settlement has reduced up to 40-60% as compared to unreinforced section. The experimental static results have validated with numerical modelling using both Finite element method and Finite difference method (Plaxis2D and FLAC2D) and dynamic results have validated by using empirically by Giroud and Han‟s equation. Based on the experimental and numerical studies, predictive models are proposed using two recently developed artificial intelligent techniques, Genetic Programming (GP) and Multiple adoptive Regression Spline (MARS).

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007.
Source: Dissertation Abstracts International, Volume: 68-06, Section: B, page: 3986. Adviser: Erol Tutumluer. Includes bibliographical references (leaves 216-228) Available on microfilm from Pro Quest Information and Learning.

碩士
國立成功大學
土木工程學系碩博士班
96
The study discussed the stress-strain behavior and volumetric-strain behavior of reinforced soil, and the tension-strain of reinforcement at plane strain test by numerical method. The numerical model was also verified from the laboratory data of the plane strain test. The numerical method adopted the analytic model of two-dimensional (2D) and three-dimensional (3D) modes. First phase is to construct the 2D analytic model, and correct the parameters by the laboratory result of the plane strain test. Then 3D model was developed from converting the 2D analytic model to 3D version by equivalent cross-section method. The results indicated that the effect of analytic result upon the size effect of reinforcement at plane strain direction by comparing the analytic result between 2D and 3D modes, and to estimate the restriction and appropriateness of 2D and 3D analytic models. At last, changing the size of container to proceed with parameter study, and predict the strength of composite soil by the methods of cover ratio and strength ratio. The numerical analysis shows that the plane strain tests have good simulate in this research. Moreover, the different sizes of container and the different cover ratio of the strength of composite soil are predictable by results obtained from parameter study. Consequently, this method has good prediction result through the proof of many numerical tests.

碩士
國立雲林科技大學
營建工程系
104
In this study, a series of plane strain model tests on wrap-faced geogrid-reinforced soil (GRS) retaining wall bacfilled with gravels were conducted. Three types of geogrids having different nominal strengths were used. The dimensions of the model wall were 183 cm (width) × 80 cm (depth) × 112 cm (height). A strip footing of 30 cm wide, having its setback distance equal to 50cm was located on the surface of backfill to resist the applied vertical load during model test. The vertical pressure and displacement of footing base were measured in the tests. Besides, by using photogrammetric analysis method, the deformation patterns of soil particle, the lateral movement of facing and the progressive failure process of soil based on the calculated shear strain contours were also obtained. The test results indicated that compared to unreinforced soil, the bearing capacity of reinforced gravel was increased. It was found that the higher stiffness of reinforcement the higher value of bearing capacity and lower value of later deformation of facing. The figures of deformed grid point, the contour of maximum shear strain and vector of the zero-extension line of soil all revealed the process of progressive shear failure of retaining wall. The deformation pattern and shear zone area were found to be significantly influenced by the inclusion of reinforcement.

Soil Reinforcement is an effective and reliable technique for improving the strength and stability of soil. The reinforced soil or mechanically stabilized earth is a compacted soil fill, strengthened by the inclusion of tensile elements like geogrids, geotextiles, metal bars and strips. It is now well established in heavy construction industry for the construction of structures like retaining walls, embankments over soft soil, steep slopes etc. Several papers relating to the evaluation of the ultimate and allowable bearing capacities of shallow foundation supported by geogrid reinforced sand and saturated clay have been published. This thesis pertains to the study of the behavior of centrally loaded strip foundation on multi layered geogrid reinforced sand bed. Laboratory model test results for the ultimate bearing capacity of a strip foundation supported on multi-layered geogrid reinforced sand and subjected to central loading are presented. Only one type of geogrid Tensar BX1100 and one variety of sand at one relative density were used. The ultimate bearing capacities obtained from model tests have been compared with the theory given by Huang and Menq (1997)

The disposal of enormous quantity of pond ash from thermal power plants has been a major environmental concern over a period of last few decades that encourages civil engineers worldwide to use pond ash extensively to protect the environment and save natural resources. An infrastructure project such as reclamation, highways, water reservoirs, railways etc, require earth material in very large quantity as there is a shortage of good soil in most urban areas. In such situations construction of pond ash embankments with steep slope is worth considering, as the pond ash is freely available material in vicinity of a thermal power plant. In the present work an attempt has been made to use pond ash for construction of road embankment. This will not only solve the problems associated with the disposal of pond ash but will also help to conserve the precious top soil and land required for growing food as well as protecting environmental pollution. A parametric study has been carried out to investigate the effect of inclination of slope, vertical spacing of geogrid reinforcement on reinforced pond ash embankment, and effect of providing pond ash – lime mixed layer on top and side slopes of unreinforced pond ash embankment. The Pond Ash sample was collected from the ash pond site of Rajghat thermal power station, Delhi, soil was collected from DTU campus, Delhi and the lime was procured from the open market in the form of quick lime. This lime was then mixed with pond ash, by weight (= 9%) (Gupta et al, 2013).Further, in the present work an experimental program was carried out to characterize the materials and strength tests were performed to study the behavior of pond ash mixed with lime; the results shows that in the presence of moisture, pond ash chemically reacts with lime at ordinary temperature and forms cementations material which is attributed to the increase in strength of pond ash. Numerical analysis was performed using the FEM based software PHASE2 (Rocscience). Results divulge that use of full length of geogrid covering whole width of embankment increases the critical strength reduction factor (SRF) of embankment at steeper slope inclination. Also, the application of either geogrids layers or pond ash-lime mix layer, results in safer designs in comparison to unreinforced pond ash embankment. In this research a substantial number of parameters were considered to study their effects on the stability of embankment which may prove useful from execution of actual prototypes.

Mechanically stabilized earth (MSE) retaining wall is a distinctive structure which is used extensively in the recent days. Generally, there are various types of soil reinforcement can be used in mechanically stabilized earth retaining wall. Steel strip, welded steel grid, wire mesh, geogrids, and geotextile sheets are examples of modern soil-reinforcing elements. The adoption of a facing system minimizes soil erosion between reinforcing parts and enables for the safe construction of steep slopes and steep walls. Since the early 1970s, geosynthetic materials are produced and then used as reinforcement material in soil retaining structures. Geosynthetics have been increasingly popular in reinforced soil constructions, and they currently account for a considerable percentage of reinforced soil industry. Technological advances in the polymer sector have been regularly comprised into new geosynthetic products, improving the qualities of geosynthetic materials used in geotechnical applications. Geogrid is one of the main products of geosynthetic materials. Tieback anchors are developed to reach the optimum rigidity achievable within financial constraints in order to limit wall displacement and ground settlement. Horizontal deflection, vertical deflection and factor of safety under the effect of various stiffness of geogrids are studied. Geogrids are applied into varying height of wall too. Tie back anchor is coupled with geogrid and the effect on reducing horizontal deflection has been studied. The length of geogrid and the surcharge load are taken constant and comparison has been drawn between with and without geogrid structure. Significant improvement of stability of structure is shown after application of geogrid. While collaborating with tie anchors it gives better result in controlling horizontal deflection of structures. The combination of geogrid and soil effectively enhances the deformation of the retaining wall structure and the overall stability.

碩士
國立雲林科技大學
營建工程系
102
In this study, the re-analyzed test results of facing deformation of a series of model tests on wrap-faced geogrid-reinforced soil (GRS) retaining wall were presented. The adopted backfill of GRS retaining wall was sand or gravel. Four types of geogrids having different nominal strengths were used. For the case of setback distance equal to 50cm, the dimensions of the model wall were 183 cm (width) × 80 cm (depth) × 112 cm (height). A strip footing of 30 cm wide, having its setback distance equal to 35cm, 50cm, or 65cm, was located on the surface of backfill to resist the applied vertical load during model test. The analyzed results indicate that the maximum lateral deformation occurs at the top of facing of unreinforced wall and at central height for reinforced case. Under the same applied footing pressure, the lateral deformation of reinforced wall is smaller than that of unreinforced one. For unreinforced wall, the lateral deformation decreases with an increase in the setback distance of footing; however, the above trend is not significant for reinforced wall. It is found that under otherwise identical conditions the lateral deformation of gravel wall is smaller than that of sand wall both for reinforced and unreinforced cases. To sum up, the lateral deformation of wrap-faced retailing wall is found to be influenced by the stiffness of geogrid, the setback distance and the particle size of backfill.

Although lot many research works have been conducted on shallow foundations, still eccentric loadings under geogrid reinforced sand bed for different overburden depths are manifested very less. In this thesis, a sharp look has been given to the behavior of square footings under different loading conditions. Here, a number of tests have been carried out on square footing ,of dimension, 10cm x 10cm, on reinforced sand bed. The eccentricities of the footing are varied from 0.05B to 0.15B,with an increment of 0.05B. The biaxial geogrid used here is TGB-40, placed in varying number of layers as 0, 2, 3, 4. The embedment depth is also varied as 0.5B to 1.0B (where B is the width of the footing). The distance between the consecutive geogrids is maintained in a constant manner for all the experiments. A relative density of 69% is achieved during all the tests. The Settlement occurred at increasing loading rate is plotted on graphs, from where the load carrying capacity is found out using tangent intersection method. From the limited experiments conducted in the laboratory, an empirical equation has been developed to determine the load carrying capacity of square embedded footing under eccentric load resting over geogrid-reinforced sand by knowing the bearing capacity of the same footing under similar conditions but under centric load. This is achieved by use of reduction factor. Keywords – load carrying capacity, eccentricity, embedment depth, settlement, number of geogrid layers

Yes
Three-dimensional finite element models were executed and validated to investigate the performance of buried flexible high-density Polyethylene (HDPE) pipes, in unreinforced and multi-geogrid-reinforced sand beds, while varying pipe burial depth, number of geogrid-layers, and magnitude of applied cyclic loading. Geogrid-layers were simulated considering their geometrical thickness and apertures, where an elasto-plastic constitutive model represented its behaviour. Soil-geogrid load transfer mechanisms due to interlocked soil in-between the apertures of the geogrid-layer were modelled. In unreinforced and reinforced cases, pipe burial depth increase contributed to decreasing deformations of the footing and pipe, and the crown pressure until reaching an optimum value of pipe burial depth. On the contrary, the geogrid-layers strain increased with increasing pipe burial depth. A flexible slab was formed due to the inclusion of two-geogrid-layers, leading to an increase in the strain in the lower geogrid-layer, despite its lower deformation. Inclusion of more than two geogrid-layers formed a heavily reinforced system of higher stiffness, and consequently, strain distribution in the geogrid-layers varied, where the upper layer experienced the maximum strain. In heavily reinforced systems, increasing the amplitude of cyclic loading resulted in a strain redistribution process in the reinforced zone, where the second layer experienced the maximum strain.

碩士
國立雲林科技大學
營建工程系
104
In this study, a series of plane strain model tests on wrap-faced geogrid-reinforced soil (GRS) retaining wall were conducted. Two types of coarse-grained soils, namely, sand and gravel, were adopted as the backfills of GRS retaining wall. Two types of geogrids having different nominal strengths were used. The dimensions of the model wall were 183 cm (width) × 80 cm (depth) × 112 cm (height). A strip footing of 30 cm wide, having its setback distance equal to 50cm was located on the surface of backfill to resist the applied vertical load during model test. The vertical pressure and displacement of footing base were measured in the tests.Besides, by using photogrammetricanalysis method, the deformation patterns of soil particle, the lateral movement of facing and the progressive failure process of soil based on the calculated shear straincontours were also obtained. The test results indicated that compared to unreinforced soil, the bearing capacity of reinforced soil was increased and the higher stiffness of reinforcement the higher value of bearing capacity. Under the same footing pressure, the lateral movement of facing of unreinforced soil was larger than that of reinforced one. The figure of deformed grid point, the contour of maximum shear strain and vector of the zero-extension line of soil all revealed the process of progressive shear failure of retaining wall. The larger mean particle size the wider area of shear zone and lower value of its corresponding shear strain. To sum up, the ultimate bearing capacity, the lateral deformation of facing and the deformation pattern of wrap-faced retaining wall were found to be significantly influenced by the mean particle size of backfill.

A number of works have been carried out for the evaluation of a ultimate bearing capacity of shallow foundation, supported by geogridreinforced sand and subjected to centric load. Few experimental studies have been made on the calculation of bearing capacity of shallow foundation on geogrid-reinforced sand under eccentric loading. The purpose of this research work is to conduct model tests in the laboratory by utilizing rectangular surface foundation resting over the reinforced sand. The model tests have been conducted using rectangular footing with B/L=0.5 & 0.33. The average relative density kept up throughout all the tests is 69%. The sand is reinforced by multiple layers (2, 3 & 4) of geogrid. The eccentricity varies from 0 to 0.15B with an increment of 0.05B. Distance of first layer of geogrid layer from bottom of footing and the distance between two consecutive geogrid layers have been kept constant. The load settlement curve for each tests have been plotted to calculate ultimate bearing capacity.Parametric studies have been made to find the impact of eccentricity on bearing capacity of the foundation. The ultimate bearing capacity of eccentrically loaded square footings can be computed by knowing the ultimate bearing capacity of square footing under central load and a reduction factor (RkR)for reinforced condition. The reduction factor is developed based on the results of laboratory model tests on geogrid reinforced soil. The ultimate bearing capacity of eccentrically loaded rectangular footing resting over geogrid reinforced sand can be calculated by knowing the ultimate bearing capacity of rectangular footing resting over reinforced sand bed and subjected to central vertical load by using reduction factor (RkR). An equation for reduction factor for rectangular footing resting over geogrid reinforced sand is developed based on laboratory model test results.

Since Terzaghi gives his hypothesis “Theoretical soil Mechanics (1943)”, various researches have been published their works on the ultimate bearing capacity of the foundation. Most of these works are related to vertical centric loading. A few works have also done on eccentric loading. After going through a lot of existing literature, evidence suggested that reinforcement could be an effective method to increase the bearing capacity of foundation in eccentric and centric loading. But a detailed study for eccentric loading for square footing is not done. The purpose of this work is to find the optimum value of depth ratio (u/B), (h/B), width ratio (b/B), the number of geogrid layers (N), and also the effect of eccentricity on bearing capacity of the foundation. To achieve this numerical simulation of square footing (B=3m, D=0.5m) embedded in a reinforced sand bed is carried out using OPTUM G2 software. Mohr-Coulomb material model is used in the simulation. The impact of placement depth of geogrid layer, number of the geogrids, and width of geogrid layer on bearing capacity of footing for the various eccentric load (e/B = 0, 0.05, 0.1, 0.15) are examined. The Test result shows that the optimum value of u/B varies between 0.3–0.4, the optimum value of h/B varies between 0.3-0.4, the optimum value of b/B = 7, and the optimum value of N=3 for square footing.

India will launch a high-speed rail project to improve the travel time between cities in the upcoming years. Upgrading its current speed of 180 km/h to a high speed of 360 km/h will be a turning point in railway transportation. The Vande Bharat Express is the current high-speed train that travels at a speed of 180 km/hr. India intends to start its first bullet train by 2026. But as the travel speed increases, the stresses will increase on the existing soil formation. The strains on India's railway subgrade component would significantly rise with the addition of high-speed railways and bullet trains. The strains may cause failure in more brittle soil. For thousands of years, soils are mixed with different fibers, fabrics, and vegetation to improve quality and stability. Geosynthetics which are polymer products are used in Civil engineering for decades. Utilizing geo-synthetics in the lengths of currently weak formations is an alternate strategy to reduce the number of stress. This paper gives a numerical analysis of the behavior of railway embankments built on sand. Finite element software was used to simulate the model. Using the finite element software PLAXIS 3D, a railway embankment's vertical deformations and stresses are calculated under a moving train load of 90 kN. The speeds of the moving train are taken as 180 km/h and 360 km/h for the modeling. Geogrid is installed as per the recommendations by RDSO (2018). The blanket layer and ballast layer are reinforced with geogrids at different depths. It was observed that on using geogrid in the different layers, the deformations and the stresses could be reduced up to certain levels. After analyzing the model, it can be concluded that Geogrids are beneficial in restricting the deformations and the stresses at particular sections but further studies are required to check the suitability of geogrids for the long run.

Yes
The performance of buried rigid pipes underneath geogrid-reinforced soil while applying incrementally increased cyclic loading was assessed using a fully instrumented laboratory rig. The influence of varying two parameters of practical importance was investigated; the pipe burial depth and the number of geogrid-layers. Measurements were taken for pipe deformation, footing settlement, strain in pipe and reinforcing layers, and pressure/soil stress on the pipe crown during various stages of cyclic loading. The research outcomes demonstrated a rapid increase in the rate of deformation of the pipe and the footing, and the rate of generated strain in the pipe and the geogrid-layers during the first 300 cycles. While applying further cycles, those rates were significantly decreased. Increasing the pipe burial depth and number of geogrid-layers resulted in reductions in the footing and the pipe deformations, the pressure on pipe crown, and the pipe strains. Redistribution of stresses, due to the inclusion of reinforcing layers, formed a confined zone surrounding the pipe providing it with additional lateral support. The pipe invert experienced a rebound, which was found to be dependent on pressure around the pipe and the degree of densification of the bedding layer. Data for strains measured in the geogrid-layers showed that despite the applied loading value and the pipe burial depth, the tensile strain in the lower geogrid-layer was usually higher than that measured in the upper layer.
The full-text of this article will be released for public view at the end of the publisher embargo on 5 Jun 2021.

碩士
國立成功大學
土木工程學系碩博士班
100
In the past decade, numerous studies have shown that incorporating geogrid in the pavement could effectively improve the pavement performance. Pavement performance is usually measured in terms of individual pavement distress such as rutting, crack, etc. The major benefit of using geogrid in the flexible pavement is to improve its rutting performance as the result of the reinforcement function of geogrid. Mechanical-Empirical Pavement Design Guide (M-E PDG) developed under the National Corporative Highway Research Program (NCHRP) is a powerful tool to analysis and design of flexible pavement. In addition, one important feature of M-E PDG is its capability to provide the pavement performance prediction throughout its design life. However, at this point, M-E PDG is not able to consider the effect of incorporating geogrid in the flexible pavement. In this study, a design procedure was proposed to obtain an equivalent geogrid pavement structure, which satisfies M-E PDG design input requirements. In this procedure, a 2-D finite element method was used to simulate geogrid reinforced and non-reinforced pavement structures. The iteration process based on stress-strain analysis of finite element model was then used to obtain an equivalent structure inputs for M-E PDG. The geogrid reinforced rutting performance can then be predicted by analyzing the equivalent geogrid structure using M-E PDG software. A significant life improvement of pavement with geogrid was observed compared to pavement without geogrid

Key factors that influence the design of paved and unpaved roads are the strength and stiffness of the pavement layers. Among other factors, the strength of pavements depends on the thickness and quality of the aggregates used in the pavement base layer. In India and many other countries, there is a high demand for good quality aggregates and the availability of aggregate resources is limited. There is a need for the development of sustainable construction methods which can handle aggregate requirements with least available resources and provide good performance. Hence it is imperative to strive for alternatives to achieve improved quality of pavements using supplementary potential materials and methods. The strength of pavement increases with increase in the thickness of the base which has a direct implication on construction cost whereas decreasing the thickness of the base makes it weak which results in low load bearing capacity especially for unpaved roads. The use of different types of geosynthetics like geocell and geogrid are a potential and reliable solution for the lack of availability of aggregates and studies are conducted in this direction. To better understand the performance of any geosynthetically reinforced base layers, it is essential to characterize the pavement material by studying the behavior of these materials under static as well as repeated loading. For unpaved roads, the base layer, made of granular aggregates plays a crucial role in the reduction of permanent deformation of the pavements. The resilient modulus (Mr) of these materials is a key parameter for predicting the structural response of pavements and for characterizing materials in pavement design and evaluation. Usually, during the design of flexible pavements, pavement materials are treated as homogeneous and isotropic. The use of rollers in the field during pavement construction leads to a higher compaction of material in the vertical direction which introduces stress-induced anisotropy in the base material. The effect of stress-induced anisotropy on the properties of the granular material is studied and discussed in the first part of the research by conducting repeated load triaxial tests. Isotropic consolidated and anisotropically consolidated samples were prepared to investigate the behavior of base materials under stress induced anisotropic conditions. An additional axial load was applied on the isotropically consolidated sample to create anisotropically consolidated sample. The axial loading was provided such that the stress ratio (σ1/σ3), during anisotropic consolidation was kept constant for all the tests at different confining pressures. The effect of repeated loading on the permanent deformation and the resilient modulus for both isotropically and anisotropically consolidated samples, at different confining pressure and loading conditions, are discussed. The behavior of both anisotropically and isotropically consolidated samples has been explained using the record of the excess pore pressures generated during the experiments. The experimental studies show that the permanent strains measured in the vertical direction of the anisotropically consolidated samples are less compared to the results obtained for isotropically consolidated samples. The resilient moduli of the anisotropically consolidated samples were also observed to be higher than that of the isotropically consolidated sample. The study conducted on the pore pressure of both the samples explains better performance of the anisotropically consolidated samples. The studies showed that the isotropically consolidated samples showed higher pore pressures compared to the anisotropically consolidated specimens. Another factor which influences the resilient modulus of the pavement materials is the geosynthetic reinforcement. Geocell and geogrid reinforced triaxial samples were prepared to study the effect of reinforcement in the resilient modulus of the base materials. From the literature, it can be seen that most of the research in the triaxial testing equipment were carried out in the non-destructive range of confining pressure and deviatoric stress. Several studies have been conducted by the researchers to visualize the pavement response in the elastic range. However, the studies in the plastic creep range and incremental collapse range were highly limited. In the current study, testing is carried out on the triaxial samples for two different stress ranges. In the first sections, loading was applied in the elastic and elastic shakedown range as per AASTHO T-307. For various loading sequences, a comparative analysis has been done for the resilient modulus of the geogrid and geocell. In the next section, the loading was applied on the sample in the plastic shakedown range and incremental collapse range. The results of the permanent strains and resilient modulus of the sections are compared with the corresponding results of the unreinforced section. In the plastic shakedown and incremental collapse range also the permanent strains of reinforced samples were less than those observed in the unreinforced section. The performance of geosynthetically reinforced pavement layers can be better understood by studying the samples prepared under realistic field conditions. In the case of triaxial experiments the sample size is very less compared to the field conditions and the effect of other pavement layers on the performance of the base layers cannot be studied on triaxial samples. Samples were prepared in the laboratory by modeling the pavement sections in a cuboidal tank, in which different pavement layers are laid one over the other, and a static loading or repeated loading is applied to overcome the bottleneck of small sample size in the triaxial setup. The experiments were conducted on the unreinforced section; geocell reinforced section and geogrid reinforced section placed above strong and weak subgrade. The results of the study are examined regarding the resilient deformation, permanent deformation, pressure distribution and strain measurements for different thicknesses of base layers under repeated loading. The initial parts of the study present the results of experiments and analysis of the results to understand the behavior of geocell reinforced granular base during repeated loading. In this study, an attempt is made to understand the various factors which influence the behavior of geocell reinforced granular base under repeated loading by conducting plate load tests. The loads applied on the pavements are much higher than the standard axle loading used for the design of pavements. High pressure was applied on all the test sections to simulate these higher loading conditions in the field. The optimum width and height of the geocell to be provided, to get maximum reduction in permanent deformation is studied in detail. The effect of resilient deformation of reinforced and unreinforced base layers is quantified by calculating the resilient modulus of these layers. The studies showed that the geocell reinforcement was effective in reducing the permanent and resilient deformations of base layer when compared to the unreinforced samples. The resilient modulus calculated was higher for the reinforced sample with half of the thickness of the unreinforced sample. The effect of reinforcement in the stress distribution within the base layer is also studied by measuring the pressures at different depths of the base layer. The results showed that the pressure getting transferred to the subgrade level was much lower in the case of geocell reinforced base layer. The ultimate aim of any pavement design method is to reduce the distress in the subgrade level and thus leading to increased life of pavements. Pressures at the subgrade level for reinforced and unreinforced sections are studied in detail, the main parameter under study being the stress distribution angle, to investigate the distress in the subgrade level. It was observed that the geocell reinforced sample showed higher stress distribution angle when compared to its unreinforced counterpart. Another important factor that has to be studied is the strains at the subgrade level since it is the governing factor of causing rutting in the pavements. From the experiments conducted in the study, it was shown that the reinforcement is very effective in reducing the strains at the top of subgrades. The implications of the current study are brought out in terms of improved pavement performance as the carbon emission reductions. It is important to analyze the performance of reinforced section under realistic field conditions. To do that experiment were conducted on reinforced and unreinforced base layers placed on top of weak subgrade material. The study showed that the reinforcements are effective in reducing the deformations under weak subgrade conditions also but not as effective as it was under strong subgrade case. The experimental results were then validated with the two-dimensional mechanistic-empirical model for geocell reinforced unpaved roads for predicting the performance of pavements under a significant number of cycles. The modified permanent deformation model which incorporates the triaxial test results and strains measured directly from the base sections were used to model and validate. Plate load experiments were also conducted on base layers reinforced with geogrid to understand the behavior of these reinforced samples under repeated loading. Several factors like the width of the geogrid to be provided and the depth of placing the geogrid in the base layer were studied in detail to achieve maximum reduction in deformations. Permanent and resilient deformation studies were carried out for both reinforced and unreinforced sections of varying thicknesses, and a comparison was made to understand the effect of reinforcement. The geogrid reinforcement could effectively reduce the permanent and resilient deformations when compared to the unreinforced sections. A study was also carried out on the resilient modulus, which explained the better performance of the geogrid reinforced samples by showing higher resilient modulus for reinforced samples than the unreinforced specimens. The performance of the geogrid reinforced base layers was further verified by studying the pressure distribution at the subgrade level and by calculating the stress distribution angle corresponding to the reinforced and unreinforced samples. The strains at the subgrade level were also studied and compared with the unreinforced sample which showed a better performance of geogrid reinforced samples. The results from the strain gauges fixed in the geogrid were further used to model and validate the permanent deformation model. Experiments were conducted on geogrid-reinforced base layer placed above weak subgrade conditions. The results showed that the reinforcement was effective in reducing the deformations under weak subgrade conditions also. Apart from conducting the laboratory studies, experimental results were numerically modeled to accurately back-calculate the resilient moduli of the layers used in the study. 3D numerical modeling of the unreinforced and honeycomb shaped geocell reinforced layers were carried out using finite element package of ANSYS. The subgrade layer, geocell material, and infill material were modeled with different material models to match the real case scenario. The modeling was done for both static and repeated load conditions. The material properties were changed in a systematic fashion until the vertical deformations of the loading plate matched with the corresponding values measured during the experiment. The experimental study indicates that the geocell reinforcement distributes the load in the lateral direction to a relatively shallow depth when compared to the unreinforced section. Numerical modeling further strengthened the results of the experimental studies since the modeling results were in sync with the experimental data.

Key factors that influence the design of paved and unpaved roads are the strength and stiffness of the pavement layers. Among other factors, the strength of pavements depends on the thickness and quality of the aggregates used in the pavement base layer. In India and many other countries, there is a high demand for good quality aggregates and the availability of aggregate resources is limited. There is a need for the development of sustainable construction methods which can handle aggregate requirements with least available resources and provide good performance. Hence it is imperative to strive for alternatives to achieve improved quality of pavements using supplementary potential materials and methods. The strength of pavement increases with increase in the thickness of the base which has a direct implication on construction cost whereas decreasing the thickness of the base makes it weak which results in low load bearing capacity especially for unpaved roads. The use of different types of geosynthetics like geocell and geogrid are a potential and reliable solution for the lack of availability of aggregates and studies are conducted in this direction. To better understand the performance of any geosynthetically reinforced base layers, it is essential to characterize the pavement material by studying the behavior of these materials under static as well as repeated loading. For unpaved roads, the base layer, made of granular aggregates plays a crucial role in the reduction of permanent deformation of the pavements. The resilient modulus (Mr) of these materials is a key parameter for predicting the structural response of pavements and for characterizing materials in pavement design and evaluation. Usually, during the design of flexible pavements, pavement materials are treated as homogeneous and isotropic. The use of rollers in the field during pavement construction leads to a higher compaction of material in the vertical direction which introduces stress-induced anisotropy in the base material. The effect of stress-induced anisotropy on the properties of the granular material is studied and discussed in the first part of the research by conducting repeated load triaxial tests. Isotropic consolidated and anisotropically consolidated samples were prepared to investigate the behavior of base materials under stress induced anisotropic conditions. An additional axial load was applied on the isotropically consolidated sample to create anisotropically consolidated sample. The axial loading was provided such that the stress ratio (σ1/σ3), during anisotropic consolidation was kept constant for all the tests at different confining pressures. The effect of repeated loading on the permanent deformation and the resilient modulus for both isotropically and anisotropically consolidated samples, at different confining pressure and loading conditions, are discussed. The behavior of both anisotropically and isotropically consolidated samples has been explained using the record of the excess pore pressures generated during the experiments. The experimental studies show that the permanent strains measured in the vertical direction of the anisotropically consolidated samples are less compared to the results obtained for isotropically consolidated samples. The resilient moduli of the anisotropically consolidated samples were also observed to be higher than that of the isotropically consolidated sample. The study conducted on the pore pressure of both the samples explains better performance of the anisotropically consolidated samples. The studies showed that the isotropically consolidated samples showed higher pore pressures compared to the anisotropically consolidated specimens. Another factor which influences the resilient modulus of the pavement materials is the geosynthetic reinforcement. Geocell and geogrid reinforced triaxial samples were prepared to study the effect of reinforcement in the resilient modulus of the base materials. From the literature, it can be seen that most of the research in the triaxial testing equipment were carried out in the non-destructive range of confining pressure and deviatoric stress. Several studies have been conducted by the researchers to visualize the pavement response in the elastic range. However, the studies in the plastic creep range and incremental collapse range were highly limited. In the current study, testing is carried out on the triaxial samples for two different stress ranges. In the first sections, loading was applied in the elastic and elastic shakedown range as per AASTHO T-307. For various loading sequences, a comparative analysis has been done for the resilient modulus of the geogrid and geocell. In the next section, the loading was applied on the sample in the plastic shakedown range and incremental collapse range. The results of the permanent strains and resilient modulus of the sections are compared with the corresponding results of the unreinforced section. In the plastic shakedown and incremental collapse range also the permanent strains of reinforced samples were less than those observed in the unreinforced section. The performance of geosynthetically reinforced pavement layers can be better understood by studying the samples prepared under realistic field conditions. In the case of triaxial experiments the sample size is very less compared to the field conditions and the effect of other pavement layers on the performance of the base layers cannot be studied on triaxial samples. Samples were prepared in the laboratory by modeling the pavement sections in a cuboidal tank, in which different pavement layers are laid one over the other, and a static loading or repeated loading is applied to overcome the bottleneck of small sample size in the triaxial setup. The experiments were conducted on the unreinforced section; geocell reinforced section and geogrid reinforced section placed above strong and weak subgrade. The results of the study are examined regarding the resilient deformation, permanent deformation, pressure distribution and strain measurements for different thicknesses of base layers under repeated loading. The initial parts of the study present the results of experiments and analysis of the results to understand the behavior of geocell reinforced granular base during repeated loading. In this study, an attempt is made to understand the various factors which influence the behavior of geocell reinforced granular base under repeated loading by conducting plate load tests. The loads applied on the pavements are much higher than the standard axle loading used for the design of pavements. High pressure was applied on all the test sections to simulate these higher loading conditions in the field. The optimum width and height of the geocell to be provided, to get maximum reduction in permanent deformation is studied in detail. The effect of resilient deformation of reinforced and unreinforced base layers is quantified by calculating the resilient modulus of these layers. The studies showed that the geocell reinforcement was effective in reducing the permanent and resilient deformations of base layer when compared to the unreinforced samples. The resilient modulus calculated was higher for the reinforced sample with half of the thickness of the unreinforced sample. The effect of reinforcement in the stress distribution within the base layer is also studied by measuring the pressures at different depths of the base layer. The results showed that the pressure getting transferred to the subgrade level was much lower in the case of geocell reinforced base layer. The ultimate aim of any pavement design method is to reduce the distress in the subgrade level and thus leading to increased life of pavements. Pressures at the subgrade level for reinforced and unreinforced sections are studied in detail, the main parameter under study being the stress distribution angle, to investigate the distress in the subgrade level. It was observed that the geocell reinforced sample showed higher stress distribution angle when compared to its unreinforced counterpart. Another important factor that has to be studied is the strains at the subgrade level since it is the governing factor of causing rutting in the pavements. From the experiments conducted in the study, it was shown that the reinforcement is very effective in reducing the strains at the top of subgrades. The implications of the current study are brought out in terms of improved pavement performance as the carbon emission reductions. It is important to analyze the performance of reinforced section under realistic field conditions. To do that experiment were conducted on reinforced and unreinforced base layers placed on top of weak subgrade material. The study showed that the reinforcements are effective in reducing the deformations under weak subgrade conditions also but not as effective as it was under strong subgrade case. The experimental results were then validated with the two-dimensional mechanistic-empirical model for geocell reinforced unpaved roads for predicting the performance of pavements under a significant number of cycles. The modified permanent deformation model which incorporates the triaxial test results and strains measured directly from the base sections were used to model and validate. Plate load experiments were also conducted on base layers reinforced with geogrid to understand the behavior of these reinforced samples under repeated loading. Several factors like the width of the geogrid to be provided and the depth of placing the geogrid in the base layer were studied in detail to achieve maximum reduction in deformations. Permanent and resilient deformation studies were carried out for both reinforced and unreinforced sections of varying thicknesses, and a comparison was made to understand the effect of reinforcement. The geogrid reinforcement could effectively reduce the permanent and resilient deformations when compared to the unreinforced sections. A study was also carried out on the resilient modulus, which explained the better performance of the geogrid reinforced samples by showing higher resilient modulus for reinforced samples than the unreinforced specimens. The performance of the geogrid reinforced base layers was further verified by studying the pressure distribution at the subgrade level and by calculating the stress distribution angle corresponding to the reinforced and unreinforced samples. The strains at the subgrade level were also studied and compared with the unreinforced sample which showed a better performance of geogrid reinforced samples. The results from the strain gauges fixed in the geogrid were further used to model and validate the permanent deformation model. Experiments were conducted on geogrid-reinforced base layer placed above weak subgrade conditions. The results showed that the reinforcement was effective in reducing the deformations under weak subgrade conditions also. Apart from conducting the laboratory studies, experimental results were numerically modeled to accurately back-calculate the resilient moduli of the layers used in the study. 3D numerical modeling of the unreinforced and honeycomb shaped geocell reinforced layers were carried out using finite element package of ANSYS. The subgrade layer, geocell material, and infill material were modeled with different material models to match the real case scenario. The modeling was done for both static and repeated load conditions. The material properties were changed in a systematic fashion until the vertical deformations of the loading plate matched with the corresponding values measured during the experiment. The experimental study indicates that the geocell reinforcement distributes the load in the lateral direction to a relatively shallow depth when compared to the unreinforced section. Numerical modeling further strengthened the results of the experimental studies since the modeling results were in sync with the experimental data.