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.

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.

The 1999 Kocaeli Earthquake (M=7.4) struck northwestern Turkey on August 17, 1999 and caused significant damage in urban areas located along Izmit Bay. The sites that suffered the greatest damages were located primarily in areas of poorest soil conditions, typically containing soft clays and silts and/or loose, liquefiable sands. Because the affected region is heavily developed with infrastructure and there is a preponderance of poor soils, a wide range of soil improvement measures had been used to mitigate anticipated earthquake damages throughout the region. Following the earthquake and significant aftershocks, Virginia Tech researchers traveled to Turkey to investigate the affected area to document geotechnical field performance. Primary focus of the Virginia tech team was given to investigating the performance of improved soil sites and reinforced soil structures. The sites were subjected to ground motions ranging from about 0.10g to 0.35g. The site locations ranged from 0 to 35 km from the zone of energy release. This dissertation presents in detail, the findings from the two most instructive sites. The investigation of these sties involved field reconnaissance, field and laboratory testing of soils, seismic analysis, numerical modeling, and other analytical work. / Ph. D.

This dissertation evaluates the behavior of Geosynthetic-Reinforced Soil (GRS) retaining structures under various soil stress states, with specific interest in the development and distribution of soil and reinforcement stresses within these structures. The stress distribution within the GRS structures is the basis of much of the industry’s current design. Unfortunately, the stress information is often not directly accessible through most of current physical testing and full-scale monitoring methods. Numerical simulations like the finite element method have provided good predictions of conservatively designed GRS structures under working stress conditions. They have provided little insight, however, into the stress information under large soil strain conditions. This is because in most soil constitutive models the post-peak behavior of soils is not well represented. Also, appropriate numerical procedures are not generally available in finite element codes, the codes used in geotechnical applications. Such procedures are crucial to properly evaluating comparatively flexible structures like GRS structures. Consequently, this study tries to integrate newly developed numerical procedures to improve the prediction of performance of GRS structures under large soil strain conditions. There are three specific objectives: 1) to develop a new softening soil model for modeling the soil’s post-peak behavior; 2) to implement a stress integration algorithm, modified forward Euler method with error control, for obtaining better stress integration results; and 3) to implement a nonlinear reinforcement model for representing the nonlinear behavior of reinforcements under large strains. The numerical implementations were made into a finite element research code, named Nonlinear Analysis of Geotechnical Problems (ANLOG). The updated finite element model was validated against actual measurement data from centrifuge testing on GRS slopes (under both working stress and failure conditions). Examined here is the soil and reinforcement stress information. This information was obtained from validated finite element simulations under various stress conditions. An understanding of the actual developed soil and reinforcement stresses offers important insights into the basis of design (e.g., examining in current design guidelines the design methods of internal stability). Such understanding also clarifies some controversial issues in current design. This dissertation specifically addresses the following issues: 1) the evolution of stresses and strains along failure surface; 2) soil strength properties (e.g., peak or residual shear strength) that govern the stability of GRS structures; 3) the mobilization of reinforcement tensions. The numerical result describes the stress response by evaluating the development of soil stress level S. This level is defined as the ratio of the current mobilized soil shear strength to the peak soil shear strength. As loading increases, areas of high stress levels are developed and propagated along the potential failure surface. After the stress levels reach unity (i.e., soil reaches its peak strength), the beginning of softening of soil strength is observed at both the top and toe of the slope. Afterward, the zones undergoing soil softening are linked, forming a band through the entire structure (i.e., a fully developed failure surface). Once the band has formed and there are a few loading increments, the system soon reaches, depending on the tensile strength of the reinforcements, instability. The numerical results also show that the failure surface corresponds to the locus of intense soil strains and the peak reinforcement strain at each reinforcement layer. What dominates the stability of GRS structures is the soil peak strength before the completed linkage of soil-softening regions. Afterward, the stability of GRS structures is mainly sustained by the soil shear strength in the post-peak region and the tensile strength of reinforcements. It was also observed that the mobilization of reinforcement tensions is disproportional to the mobilization of soil strength. Tension in the reinforcements is barely mobilized before soil along the failure surface first reaches its peak shear strength. When the average mobilization of soil shear strength along the potential failure surface exceeds approximately 95% of its peak strength, the reinforcement tensions start to be rapidly mobilized. Even so, when the average mobilization of soil strength reaches 100% of its peak shear strength, still over 30% of average reinforcement strength has not yet been mobilized. The results were used to explain important aspects of the current design methods (i.e., earth pressure method and limit equilibrium analysis) that result in conservatively designed GRS structures. / text

Em geral, as recomendações normativas sugerem a utilização de materiais granulares para a construção de estruturas em solo reforçado, principalmente devido à sua elevada resistência ao cisalhamento e boa capacidade de drenagem. No entanto, nem sempre há disponibilidade deste tipo de material no entorno das obras, tornando o uso dos solos finos imperativo para a viabilização desta solução. No Brasil, solos residuais finos são encontrados em abundância e, muitas vezes, apresentam excelentes parâmetros de resistência ao cisalhamento e baixa compressibilidade. Contudo, o seu uso pode induzir poro-pressões indesejáveis durante a construção ou cisalhamento do aterro reforçado. Por outro lado, as elevadas sucções matriciais que podem persistir em seu interior geram um aumento na estabilidade dos maciços reforçados. Neste contexto, este trabalho apresenta os resultados experimentais e discute o efeito da variação climática (umedecimento e secagem) na resistência de interface solo coesivo-fita polimérica de uma estrutura de contenção em solo reforçado. Os ensaios foram realizados com amostras compactadas de um solo residual de gnaisse típico da cidade de São Paulo e uma fita polimérica de alta aderência. Os corpos de prova foram submetidos a ensaios de cisalhamento direto e de arrancamento sob três diferentes níveis de tensão normal e de sucção, além da condição inundada. Ensaios triaxiais saturados (CU) e não saturados (CW) foram realizados para a determinação da envoltória de resistência tridimensional do solo, avaliação da eficiência da interação solo-reforço e para a verificação do comportamento da água intersticial durante o cisalhamento. Os resultados indicam que o solo coesivo em questão apresenta excelentes parâmetros de resistência ao cisalhamento, elevada capacidade de se manter sob pressões negativas da água intersticial e uma eficiente interação com as fitas poliméricas, o que possibilitaria a execução de estruturas estáveis quanto ao arrancamento dos reforços. Além disso, sugerem um crescimento não linear da máxima resistência de interface com o aumento da sucção matricial do solo e uma tendência de redução dos coeficientes de atrito aparente solo-reforço (f*) com o umedecimento das amostras. Porém, mostraram que a sucção matricial exerce pouca influência na resistência residual da interface solo reforço. / Current specifications for reinforced soil structures generally require the use of granular backfill due to their high strength, well drainage capacity and low volume change potential. However, in cases where granular fills are not easily and readily available, poorly draining soils should be used to enable the implementation of a mechanically stabilized earth wall (MSEW). In Brazil, the fine-grained residual soils that cover large areas of its territory frequently present high shear strengths and low compressibility. However, the use of cohesive soils can cause unwanted effects in structure stability due to the water content variations of the backfill soil, and the potential development of pore-water pressures or loss of strength. On the other hand, matric suctions may increase the soil-geosynthetic interface shear strength. In this context, this study presents the experimental results and discusses the effects of seasonal climatic variations (wetting and drying) on shear strength of soil-geosynthetic straps interfaces under unsaturated conditions. For the laboratory investigation, a compacted residual soil of gneiss composed of 80% silty sand passed through a 0.075mm sieve, sourced from São Paulo city, and a high-tenacity polyester strap were used. Direct shear and pullout tests were conducted with three different net normal stresses and levels of matric suction, besides the inundated condition. Triaxial tests under saturated (CU) and unsaturated (CW) conditions with suction measurement using a high capacity tensiometer were performed in order to evaluate the shear strength parameters of the unsaturated soil, the interface efficiency of the soil-geosynthetic strap and the pore water pressure variations during shear. The results indicate that the cohesive soil used in this study has excellent shear strength parameters, a high capacity to maintain negative pore water pressures and presents an efficient interaction with the geosynthetics straps, which would allow the implementation of a stable MSEW for failure by pullout. Furthermore they reveal that the peak shear strength of the soil-geosynthetic strap interface increases nonlinearly with the soil suction, while the apparent friction factor (f*) decreases with the increase in molding moisture contents. On the other hand, the effect of suction on the post-peak shear strength of the interface was negligible.

Em geral, as recomendações normativas sugerem a utilização de materiais granulares para a construção de estruturas em solo reforçado, principalmente devido à sua elevada resistência ao cisalhamento e boa capacidade de drenagem. No entanto, nem sempre há disponibilidade deste tipo de material no entorno das obras, tornando o uso dos solos finos imperativo para a viabilização desta solução. No Brasil, solos residuais finos são encontrados em abundância e, muitas vezes, apresentam excelentes parâmetros de resistência ao cisalhamento e baixa compressibilidade. Contudo, o seu uso pode induzir poro-pressões indesejáveis durante a construção ou cisalhamento do aterro reforçado. Por outro lado, as elevadas sucções matriciais que podem persistir em seu interior geram um aumento na estabilidade dos maciços reforçados. Neste contexto, este trabalho apresenta os resultados experimentais e discute o efeito da variação climática (umedecimento e secagem) na resistência de interface solo coesivo-fita polimérica de uma estrutura de contenção em solo reforçado. Os ensaios foram realizados com amostras compactadas de um solo residual de gnaisse típico da cidade de São Paulo e uma fita polimérica de alta aderência. Os corpos de prova foram submetidos a ensaios de cisalhamento direto e de arrancamento sob três diferentes níveis de tensão normal e de sucção, além da condição inundada. Ensaios triaxiais saturados (CU) e não saturados (CW) foram realizados para a determinação da envoltória de resistência tridimensional do solo, avaliação da eficiência da interação solo-reforço e para a verificação do comportamento da água intersticial durante o cisalhamento. Os resultados indicam que o solo coesivo em questão apresenta excelentes parâmetros de resistência ao cisalhamento, elevada capacidade de se manter sob pressões negativas da água intersticial e uma eficiente interação com as fitas poliméricas, o que possibilitaria a execução de estruturas estáveis quanto ao arrancamento dos reforços. Além disso, sugerem um crescimento não linear da máxima resistência de interface com o aumento da sucção matricial do solo e uma tendência de redução dos coeficientes de atrito aparente solo-reforço (f*) com o umedecimento das amostras. Porém, mostraram que a sucção matricial exerce pouca influência na resistência residual da interface solo reforço. / Current specifications for reinforced soil structures generally require the use of granular backfill due to their high strength, well drainage capacity and low volume change potential. However, in cases where granular fills are not easily and readily available, poorly draining soils should be used to enable the implementation of a mechanically stabilized earth wall (MSEW). In Brazil, the fine-grained residual soils that cover large areas of its territory frequently present high shear strengths and low compressibility. However, the use of cohesive soils can cause unwanted effects in structure stability due to the water content variations of the backfill soil, and the potential development of pore-water pressures or loss of strength. On the other hand, matric suctions may increase the soil-geosynthetic interface shear strength. In this context, this study presents the experimental results and discusses the effects of seasonal climatic variations (wetting and drying) on shear strength of soil-geosynthetic straps interfaces under unsaturated conditions. For the laboratory investigation, a compacted residual soil of gneiss composed of 80% silty sand passed through a 0.075mm sieve, sourced from São Paulo city, and a high-tenacity polyester strap were used. Direct shear and pullout tests were conducted with three different net normal stresses and levels of matric suction, besides the inundated condition. Triaxial tests under saturated (CU) and unsaturated (CW) conditions with suction measurement using a high capacity tensiometer were performed in order to evaluate the shear strength parameters of the unsaturated soil, the interface efficiency of the soil-geosynthetic strap and the pore water pressure variations during shear. The results indicate that the cohesive soil used in this study has excellent shear strength parameters, a high capacity to maintain negative pore water pressures and presents an efficient interaction with the geosynthetics straps, which would allow the implementation of a stable MSEW for failure by pullout. Furthermore they reveal that the peak shear strength of the soil-geosynthetic strap interface increases nonlinearly with the soil suction, while the apparent friction factor (f*) decreases with the increase in molding moisture contents. On the other hand, the effect of suction on the post-peak shear strength of the interface was negligible.

Design of retaining structures depends upon the load which is transferred from backfill soil as well as external loads and also the resisting capacity of the structure. The traditional safety factor approach of the design of retaining structures does not address the variability of soils and loads. The properties of backfill soil are inherently variable and influence the design decisions considerably. A rational procedure for the design of retaining structures needs to explicitly consider variability, as they may cause significant changes in the performance and stability assessment. Reliability based design enables identification and separation of different variabilities in loading and resistance and recommends reliability indices to ensure the margin of safety based on probability theory. Detailed studies in this area are limited and the work presented in the dissertation on the Optimum design of retaining structures under static and seismic conditions: A reliability based approach is an attempt in this direction. This thesis contains ten chapters including Chapter 1 which provides a general introduction regarding the contents of the thesis and Chapter 2 presents a detailed review of literature regarding static and seismic design of retaining structures and highlights the importance of consideration of variability in the optimum design and leads to scope of the investigation. Targeted stability is formulated as optimization problem in the framework of target reliability based design optimization (TRBDO) and presented in Chapter 3. In Chapter 4, TRBDO approach for cantilever sheet pile walls and anchored cantilever sheet pile walls penetrating sandy and clayey soils is developed. Design penetration depth and section modulus for the various anchor pulls are obtained considering the failure criteria (rotational, sliding, and flexural failure modes) as well as variability in the back fill soil properties, soil-steel pile interface friction angle, depth of the water table, total depth of embedment, yield strength of steel, section modulus of sheet pile and anchor pull. The stability of reinforced concrete gravity, cantilever and L-shaped retaining walls in static conditions is examined in the context of reliability based design optimization and results are presented in Chapter 5 considering failure modes viz. overturning, sliding, eccentricity, bearing, shear and moment failures in the base slab and stem of wall. Optimum wall proportions are proposed for different coefficients of variation of friction angle of the backfill soil and cohesion of the foundation soil corresponding to different values of component as well as lower bounds of system reliability indices. Chapter 6 presents an approach to obtain seismic passive resistance behind gravity walls using composite curved rupture surface considering limit equilibrium method of analysis with the pseudo-dynamic approach. The study is extended to obtain the rotational and sliding displacements of gravity retaining walls under passive condition when subjected to sinusoidal nature of earthquake loading. Chapter 7 focuses on the reliability based design of gravity retaining wall when subjected to passive condition during earthquakes. Reliability analysis is performed for two modes of failure namely rotation of the wall about its heel and sliding of the wall on its base are considering variabilities associated with characteristics of earthquake ground motions, geometric proportions of wall, backfill soil and foundation soil properties. The studies reported in Chapter 8 and Chapter 9 present a method to evaluate reliability for external as well as internal stability of reinforced soil structures (RSS) using reliability based design optimization in the framework of pseudo static and pseudo dynamic methods respectively. The optimum length of reinforcement needed to maintain the stability against four modes of failure (sliding, overturning, eccentricity and bearing) by taking into account the variabilities associated with the properties of reinforced backfill, retained backfill, foundation soil, tensile strength and length of the geosynthetic reinforcement by targeting various component and system reliability indices is computed. Finally, Chapter 10 contains the important conclusions, along with scope for further work in the area. It is hoped that the methodology and conclusions presented in this study will be beneficial to the geotechnical engineering community in particular and society as a whole.