Centrifuge modeling technique is widely used in geotechnical research. Due to the complexity of geosynthetic-reinforced soil retaining walls (GRS-RWs), the centrifuge models of such walls are typically constructed in one stage, where the model is prepared to full height under 1-g and then spun in a centrifuge to the desired g-level or till failure. However, for a retaining wall built in the field, the placement of new soil layer and compaction induces deformations on the previously constructed soil layers, and the wall facing is aligned according to the design at each construction stage. The different construction sequences will lead to differences in the wall performance, including the stress mobilized in the geosynthetic layers. In this study, a multi-stage constructed centrifuge modeling technique was proposed to simulate the construction sequence in the field. The wall facing deformation, tensile force in the geosynthetic layers, and lateral earth pressure behind the wall facing were measured and compared with the traditional one-staged centrifuge model. The results were verified with actual field measurements. The results obtained from multi-staged construction compared favorably to the field measurements. In addition to the construction sequence, the backfill close to the wall facing is usually not as well compacted in the field. The effects of such loose front backfill were also studied by a series of centrifuge models of reinforced soil retaining walls. In addition to the centrifuge modeling of the reinforced soil retaining walls, two series of finite element models were conducted to further study the wall performance. The first series of numerical models included a unified sand model, which was implemented into Abaqus to simulate the backfill. The sand model was firstly calibrated based on the triaxial test results; then, it was used to simulate the wall performance under gravity and dynamic loading. An additional series of FE models were constructed in OptumG2, a 2D finite element geotechnical software to numerically study the influence of loose front and construction sequence of the concrete block reinforced soil retaining walls. Based on the results of centrifuge modeling, simulation of the construction sequence is necessary to obtain a satisfactory assessment of GRS-RWs performance. In this study, the models prepared with multi-staged construction techniques showed better agreement with the field measurements than the models prepared with one-staged construction. In addition, the models with reinforcement simulating the stiffness of the prototype geogrid showed better agreement with field measurements than the models with reinforcement simulating the strength of the prototype geogrid. Besides, a loose front probably existed in the concrete block walls during the field construction based on the comparison of the test results and field measurements. Conclusions from the centrifuge modeling studies were verified by FEM analysis. The dynamic simulation results showed that the studied gabion walls are stable when subjected to a horizontal acceleration up to 0.4 at the bottom of the wall.

[pt] Nesta dissertação é apresentada uma nova técnica para estabilização de encostas através da construção de um muro de gravidade usando pneus e solo. Esta técnica foi desenvolvida dentro de um trabalho de pesquisa realizado pela PUC-Rio, em colaboração com a Fundação Geo-Rio e a Universidade de Ottawa (Canadá). O trabalho consistiu na construção e análise de um muro experimental de solo- pneus localizado em Jacarepaguá, Rio de Janeiro. O muro possui 60m de comprimento e 4m de altura, sendo constituído por camadas horizontais de pneus preenchidos com solo residual compactado e amarrados entre si com corda ou arame. Atrás do muro de pneus foi executado um retro-aterro com 6m de altura, constituído do mesmo solo utilizado no muro de solo- pneus. O muro é composto por 4 seções com características diferentes quanto ao tipo de amarração, geometria e configuração dos pneus (cortados ou inteiros). Apresenta- se neste trabalho um estudo do comportamento tensão vs deformação do material solo-pneus das 4 seções do muro. Os valores previstos numericamente foram comparados aos resultados da instrumentação de campo, com o objetivo de obter os parâmetros de deformabilidade do material. Para a representação do comportamento tensão vs deformação do material solo-pneus, utilizou-se o modelo elástico linear. Foi considerada a existência de 7 camadas distintas do material solo-pneus, permitindo a variação do módulo E ao longo da altura do muro. O solo do retro-aterro foi representado pelo modelo elástico não linear (hiperbólico). Dentre as principais conclusões, pode-se ressaltar que o uso de pneus cortados facilita o processo construtivo e reduz a deformabilidade do muro. A amarração dos pneus com corda, apesar de menos eficiente que a amarração com arame, apresenta-se como a melhor alternativa quando se considera a relação custo vs benefício. A utilização de solo-pneus apresenta-se como uma alternativa que combina a eficiência mecânica do pneu e o baixo custo de execução quando comparada às técnicas convencionais de estabilização de encostas. / [en] Construction of a retaining wall using scrap tires and soil is presented in this thesis. The technique was developed as part of a research program at PUC-Rio in collaboration with University of Ottawa and Geo-Rio. The present work consisted of building and analyzing an experimental retaining wall which was constructed in Jacarepaguá, Rio de Janeiro and made of scrap tires and soil. The wall is 60m long and 4 meters high, made of horizontal layers tire, tied with ropes or wires, filled with compacted residual soil. The backfill was 6 meters high using the same residual soil. The wall has four different cross sections which have distinct geometry, tire configurations (cut tires and entire tires) and tire connections.It is also presented a study on the stress strain behavior of the soil tire composite, which shapes the four different cross sections. The numerical results were compared with field measurements in order to obtain the deformation characteristics of backfill. The retaining wall material was considered to exhibit a linear elastic behavior. The construction procedure was numerically simulated in seven increments and allowing variation of modulus of deformation of the wall with the height of the wall. The stress strain behavior of the backfill was simulated with the use of the hiberbolic model.Among the major conclusions it worth mentioning that the use of cut tires facilitates the construction procedure consequently reducing the deformation of the wall. The use of rope to tie the tires, although less efficient than the use of wire, is a better alternative from the cost effectiveness point of view. The use of tires and soil is an attractive alternative to build retaining walls, which associates efficient mechanical performance with low cost, when compared to the conventional methods to stabilize slopes. / [es] En esta disertación se presenta una nueva técnica para estabilización de encostas a través de la construcción de un muro de gravedad usando neumáticos y suelo. Esta técnica fue desarrollada dentro de un trabajo de investigación realizado por la PUC Rio, en colaboración con la Fundación Geo Rio y la Universidad de Ottawa (Canadá). El trabajo consistió en la construcción y análisis de un muro experimental de suelo y neumáticos localizado en Jacarepaguá, Rio de Janeiro. EL muro posee 60m de largo y 4m de altura, y esta compuesto por camadas horizontales de neumáticos llenos de suelo residual compactado y amarrados entre sí con cuerdas o alambre. Detrás del muro de neumáticos se ejecutó un retro aterro con 6m de altura, con el mismo suelo utilizado en el muro de suelo neumático. El muro está compuesto por 4 secciones con características diferentes respecto al tipo de amarre, geometría y configuración de los neumáticos (cortados o enteros). Se presenta en este trabajo un estudio del comportamiento tensión vs deformación del material suelo neumático de las 4 secciones del muro. Los valores previstos numéricamente fueron comparados con los resultados de la instrumentación de campo, con el objetivo de obtener los parámetros de deformabilidad del material. Para la representación del comportamiento tensión vs deformación del material suelo neumáticos, se utilizó el modelo elástico lineal. Fue considerada la existencia de 7 camadas distintas del material suelo neumáticos, permitindo la variación del módulo Y a lo largo de la altura del muro. El suelo del retro aterro fue representado por el modelo elástico no lineal (hiperbólico). Entre las principales conclusiones, cabe resaltar que el uso de neumáticos cortados facilita el proceso constructivo y reduce la deformabilidad del muro. El amarre de los neumáticos con cuerdas, a pesar de menos eficiente que el amarre con alambre, resulta ser la mejor alternativa cuando se considera la relación costo vs beneficio. La utilización de suelo neumático se presenta como una alternativa que combina la eficiencia mecánica del neumático y el bajo costo de ejecución cuando se compara a las técnicas convencionales de estabilización de encostas.

No description available.

Geosynthetic reinforced soil (GRS) walls involve the use of geosynthetic reinforcement (polymer material) within the retained backfill, forming a reinforced soil block where transmission of overturning and sliding forces on the wall to the backfill occurs. Key advantages of GRS systems include the reduced need for large foundations, cost reduction (up to 50%), lower environmental costs, faster construction and significantly improved seismic performance as observed in previous earthquakes. Design methods in New Zealand have not been well established and as a result, GRS structures do not have a uniform level of seismic and static resistance; hence involve different risks of failure. Further research is required to better understand the seismic behaviour of GRS structures to advance design practices. The experimental study of this research involved a series of twelve 1-g shake table tests on reduced-scale (1:5) GRS wall models using the University of Canterbury shake-table. The seismic excitation of the models was unidirectional sinusoidal input motion with a predominant frequency of 5Hz and 10s duration. Seismic excitation of the model commenced at an acceleration amplitude level of 0.1g and was incrementally increased by 0.1g in subsequent excitation levels up to failure (excessive displacement of the wall panel). The wall models were 900mm high with a full-height rigid facing panel and five layers of Microgird reinforcement (reinforcement spacing of 150mm). The wall panel toe was founded on a rigid foundation and was free to slide. The backfill deposit was constructed from dry Albany sand to a backfill relative density, Dr = 85% or 50% through model vibration. The influence of GRS wall parameters such as reinforcement length and layout, backfill density and application of a 3kPa surcharge on the backfill surface was investigated in the testing sequence. Through extensive instrumentation of the wall models, the wall facing displacements, backfill accelerations, earth pressures and reinforcement loads were recorded at the varying levels of model excitation. Additionally, backfill deformation was also measured through high-speed imaging and Geotechnical Particle Image Velocimetry (GeoPIV) analysis. The GeoPIV analysis enabled the identification of the evolution of shear strains and volumetric strains within the backfill at low strain levels before failure of the wall thus allowing interpretations to be made regarding the strain development and shear band progression within the retained backfill. Rotation about the wall toe was the predominant failure mechanism in all excitation level with sliding only significant in the last two excitation levels, resulting in a bi-linear displacement acceleration curve. An increase in acceleration amplification with increasing excitation was observed with amplification factors of up to 1.5 recorded. Maximum seismic and static horizontal earth pressures were recorded at failure and were recorded at the wall toe. The highest reinforcement load was recorded at the lowest (deepest in the backfill) reinforcement layer with a decrease in peak load observed at failure, possibly due to pullout failure of the reinforcement layer. Conversely, peak reinforcement load was recorded at failure for the top reinforcement layer. The staggered reinforcement models exhibited greater wall stability than the uniform reinforcement models of L/H=0.75. However, similar critical accelerations were determined for the two wall models due to the coarseness of excitation level increments of 0.1g. The extended top reinforcements were found to restrict the rotational component of displacement and prevented the development of a preliminary shear band at the middle reinforcement layer, contributing positively to wall stability. Lower acceleration amplification factors were determined for the longer uniform reinforcement length models due to reduced model deformation. A greater distribution of reinforcement load towards the top two extended reinforcement layers was also observed in the staggered wall models. An increase in model backfill density was observed to result in greater wall stability than an increase in uniform reinforcement length. Greater acceleration amplification was observed in looser backfill models due to their lower model stiffness. Due to greater confinement of the reinforcement layers, greater reinforcement loads were developed in higher density wall models with less wall movement required to engage the reinforcement layers and mobilise their resistance. The application of surcharge on the backfill was observed to initially increase the wall stability due to greater normal stresses within the backfill but at greater excitation levels, the surcharge contribution to wall destabilising inertial forces outweighs its contribution to wall stability. As a result, no clear influence of surcharge on the critical acceleration of the wall models was observed. Lower acceleration amplification factors were observed for the surcharged models as the surcharge acts as a damper during excitation. The application of the surcharge also increases the magnitude of reinforcement load developed due to greater confinement and increased wall destabilising forces. The rotation of the wall panel resulted in the progressive development of shears surface with depth that extended from the backfill surface to the ends of the reinforcement (edge of the reinforced soil block). The resultant failure plane would have extended from the backfill surface to the lowest reinforcement layer before developing at the toe of the wall, forming a two-wedge failure mechanism. This is confirmed by development of failure planes at the lowest reinforcement layer (deepest with the backfill) and at the wall toe observed at the critical acceleration level. Key observations of the effect of different wall parameters from the GeoPIV results are found to be in good agreement with conclusions developed from the other forms of instrumentation. Further research is required to achieve the goal of developing seismic guidelines for GRS walls in geotechnical structures in New Zealand. This includes developing and testing wall models with a different facing type (segmental or wrap-around facing), load cell instrumentation of all reinforcement layers, dynamic loading on the wall panel and the use of local soils as the backfill material. Lastly, the limitations of the experimental procedure and wall models should be understood.

No description available.

Thesis (M.S.) in Civil and Environmental Engineering--University of Maine, 2003. / Includes vita. Includes bibliographical references (leaves 164-169).

Thesis (M.S.) University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on August 27, 2007) Includes bibliographical references.

The objectives of this dissertation are: (1) to examine the relationship between the accuracy and reliability of methods of estimating settlements of footings on sand and gravel, (2) to develop a procedure for estimating horizontal movements and rotations of footings without the need of determining soil modulus values, and (3) to develop a simple procedure for calculating movements of retaining walls due to the weight of backfill. The accuracy and reliability of twelve methods of estimating settlements of footings on sand and gravels were examined by comparing calculated settlements with the measured values. Eleven of the methods are based on Standard Penetration Test Results, while Schmertmann’s method is based on Cone Penetration Test Results. The study showed that methods which are more accurate tend to underestimate settlements about half of the time; while those which are more reliable (in the sense that they infrequently underestimate settlements) tend to be less accurate. The study also indicated that these methods of estimating settlements of footings on sands and gravels involve approximately the same relationship between accuracy and reliability, regardless of the approach that they use to calculate settlement. The results demonstrate that there is a tradeoff between accuracy and reliability. Any of the methods can be adjusted to achieve approximately the same combination of accuracy and reliability as other method. A simple procedure is presented to relate horizontal movements and rotations of footings to settlements. The procedure does not require the determination of soil modulus, and its accuracy and reliability can be assessed qualitatively by association with the method used to calculate the settlement. A simple procedure based on elastic theory was also developed to estimate movements of abutments and retaining walls due to the weight of backfill placed behind them. To avoid the inherent difficulty in determining the soil modulus, a procedure for relating these movements to the settlement of the wall was also developed. The new procedure was applied to a case history, and the calculated movements agree quite well with those calculated using the finite element method, and with field observations. / Ph. D.

published_or_final_version / Applied Geosciences / Master / Master of Science

published_or_final_version / Civil Engineering / Master / Master of Philosophy