Column-supported, geosynthetic-reinforced embankments provide effective geotechnical foundations for applications in areas of weak subgrade soils. The system consists of a soil bridging layer with one or more embedded layers of geosynthetic reinforcement supported by driven or deep mixed columnar piles. The geosynthetic promotes load transfer within the bridging layer to the columns, allowing for larger column spacings and varied alignments. This technique is generally used when differential settlements of the embankment or adjacent structures are a concern and to minimize construction time. Recent increase in the popularity of this composite system has generated the need to further investigate its behavior and soil-structure interaction. Current models of geosynthetics are oversimplified and do not represent the true three-dimensional nature of the material. Such simplifications include treating the geosynthetic as a one-dimensional cable as well as neglecting stress concentrations and pile orientations. In this thesis, a complete three-dimensional analysis of the geosynthetic is performed. The geosynthetic was modeled as a thin flexible plate in a single square unit cell of the embankment. The principle of minimum potential energy was then applied, utilizing central finite difference equations. Energy components from vertical loading, soil and column support, as well as bending and membrane stiffness of the geosynthetic are considered. Three pile orentation types were implemented: square piles, circular piles, and square piles rotated 45° to the edges of the unit cell. Each of the pile orientations was analyzed using two distinct parameter sets that are investigated in previously published and ongoing research. Vertical and in-plane deflections, stress resultants, and strains were determined and compared to other geosynthetic models and design guides. Results of each parameter set and pile orientation were also compared to provide design recommendations for geosynthetic-reinforced column-supported embankments. / Master of Science

A geotechnical composite foundation system that has become increasingly popular over the years is a column-supported, geosynthetic-reinforced embankment. This system consists of strong columns or piles placed in soft clay, a bridging layer of sand or sand and gravel, and one or more layers of geosynthetic reinforcement. It is often used in soft ground situations where there is a need for faster construction and/or where there are adjacent structures that would be affected by settlement caused by the new embankment. The geosynthetic reinforcement is placed in the bridging layer to help transfer the load to the columns and decrease the total and differential settlements. Current methods of analysis for this material are extremely simplified, and do not thoroughly model the behavior of the system. Therefore, a more comprehensive analysis needs to be conducted that will better predict the true effect of the geosynthetic layer or layers. In this thesis, one geosynthetic layer was considered. Models were developed using two different computer programs: Mathematica and ABAQUS. In Mathematica, the Rayleigh-Ritz method was used to approximate the deflections and tensile forces in the membrane. This method considered the geosynthetic reinforcement as a plate and minimized the total energy of the system. In ABAQUS, a finite element modeling program, the membrane was analyzed as a shell, and results were compared with some results from Mathematica. A parametric study was completed in Mathematica to determine the effects of different parameters. The parameters varied involved the geogrid properties (Poisson's ratio, modulus of elasticity, and thickness), the vertical load, the soil stiffness above the piles, the soil stiffness between the piles, the size of the piles, and the distance between the piles. / Master of Science

Pile-supported geogrid-reinforced embankments are an exciting new foundation system that is utilized when sites are limited by a soft soil or clay. In this system, an embankment is supported by a bridging layer, consisting of granular fill and one or multiple layers of geogrid reinforcement. The bridging layer transfers the load to piles that have been driven into the soft soil or clay. The load from the embankment induces large deformations in the geogrid reinforcement, causing tensile forces in the ribs of the geogrid. Many of the current methods used to design geogrid reinforcement for this system simplify the approach by assuming that the reinforcement has a parabolic deformed shape. The purpose of this thesis is to thoroughly examine the behavior of the geogrid in a pile-supported embankment system, in an effort to determine the accuracy of the parabolic deformed shape, and identify the most important parameters that affect reinforcement design. The geogrid was analyzed using a three-dimensional model that included a cable net to represent the geogrid and linear springs to represent the soil underneath the geogrid. A larger pressure was applied to the geogrid regions that are directly above the pile caps so that arching effects could be considered, and the stiffness of the springs on top of the pile were stiffer to account for the thin layer of soil between the geogrid and the pile cap. A Mathematica algorithm was used to solve this model using the minimization of energy method. The results were compared to another model of this system that used a membrane to represent the geosynthetic reinforcement. Additionally, the maximum strain was compared to the strain obtained from a geosynthetic reinforcement design formula. A parametric study was performed using the Mathematica algorithm by varying the pile width, embankment pressure applied to the soil, embankment pressure applied to the pile, stiffness of the soil, stiffness of the soil on top of the pile, stiffness of the geogrid, geogrid orientation, rotational stiffness of the geogrid, and the layers of geogrid reinforcement. / Master of Science

El proyecto de investigación tuvo por finalidad evaluar las geomallas triaxiales, como elementos de refuerzo en la interfaz Subrasante – Subbase de la estructura del pavimento flexible, con el objetivo de optimizar espesores del pavimento, aumentar la capacidad de soporte de la subrasante y prolongar la vida útil de pavimento. En este trabajo se presenta la aplicación de una metodología de diseño para el uso de geomallas triaxiales, con las especificaciones técnicas para el diseño aplicado de las geomallas en pavimentos flexibles en Perú. La metodología de diseño está centrada en las investigaciones del doctor J.P. Giroud y el doctor Jie Han, que presentan un efecto de confinamiento generado, entre las geomallas y la capa de material sobre la subrasante. Los suelos al ser sometidos a cargas de llantas tienden a deformarse, generando ahuellamiento sobre la superficie de rodadura. Con la presencia de geomallas en el suelo este ahuellamiento se reduce de manera exponencial (Giroud & Han, 2005). Para la metodología planteada se desarrolla un ejemplo aplicativo para el diseño reforzado, de una base pavimentada, con geomalla triaxial y otro sin refuerzo. Para este ejemplo se recolecto datos con ayuda de los formatos de clasificación vehicular del MTC, inspección visual de la vía para la evaluación del índice de condición del pavimento (PCI) y los ensayos de laboratorio; la cual fue ejecutada a lo largo de los 2.3 km aproximadamente, en el cual se observó que el PCI del tramo es de 21%, esto significa que el nivel de servicio de la vía es malo, es decir requiere la intervención inmediata. Mediante esta metodología el uso de geomallas implicó disminución de espesores de 33.33%, cabe recalcar que se debe tener en cuenta que cada diseño variará de acuerdo con el proyecto a ejecutarse, por ende, dependerá de las características del suelo, el tráfico vehicular y el refuerzo (Tipo de geomalla) utilizado. / The purpose of this research project was to evaluate the triaxial geogrids, as reinforcement elements in the Subgrade - Subbase interface of the flexible pavement structure, with the aim of optimizing pavement thicknesses, increasing the support capacity of the subgrade and prolonging the useful life of pavement. This paper presents the application of a design methodology for the use of triaxial geogrids, with the technical specifications for the applied design of geogrids inflexible pavements in Peru. The design methodology is focused on the investigations of Dr. J.P. Giroud and Dr. Jie Han, who present a generated confinement effect, between the geogrids and the layer of material on the subgrade. The floors when subjected to tire loads tend to deform, generating rutting on the running surface. With the presence of geogrids in the ground, this rutting is reduced exponentially (Giroud & Han, 2005). For the proposed methodology an application example is developed for the reinforced design, of a paved base, with triaxial geogrid and another without reinforcement. For this example, data was collected with the aid of the vehicle classification formats of the MTC, visual inspection of the road for the evaluation of the pavement condition index (PCI) and laboratory tests; which was executed along the approximately 2.3 km, in which it was observed that the PCI of the section is 21%, this means that the service level of the road is bad, that is, it requires immediate intervention. Through this methodology the use of geogrids implied a decrease in thickness of 33.33%, it should be noted that it must be taken into account that each design will vary according to the project to be executed, therefore, it will depend on the characteristics of the soil, vehicular traffic and reinforcement (Type of geogrid) used. / Trabajo de investigación

abstract: A method for evaluating the integrity of geosynthetic elements of a waste containment system subject to seismic loading is developed using a large strain finite difference numerical computer program. The method accounts for the effect of interaction between the geosynthetic elements and the overlying waste on seismic response and allows for explicit calculation of forces and strains in the geosynthetic elements. Based upon comparison of numerical results to experimental data, an elastic-perfectly plastic interface model is demonstrated to adequately reproduce the cyclic behavior of typical geomembrane-geotextile and geomembrane-geomembrane interfaces provided the appropriate interface properties are used. New constitutive models are developed for the in-plane cyclic shear behavior of textured geomembrane/geosynthetic clay liner (GMX/GCL) interfaces and GCLs. The GMX/GCL model is an empirical model and the GCL model is a kinematic hardening, isotropic softening multi yield surface plasticity model. Both new models allows for degradation in the cyclic shear resistance from a peak to a large displacement shear strength. The ability of the finite difference model to predict forces and strains in a geosynthetic element modeled as a beam element with zero moment of inertia sandwiched between two interface elements is demonstrated using hypothetical models of a heap leach pad and two typical landfill configurations. The numerical model is then used to conduct back analyses of the performance of two lined municipal solid waste (MSW) landfills subjected to strong ground motions in the Northridge earthquake. The modulus reduction "backbone curve" employed with the Masing criterion and 2% Rayleigh damping to model the cyclic behavior of MSW was established by back-analysis of the response of the Operating Industries Inc. landfill to five different earthquakes, three small magnitude nearby events and two larger magnitude distant events. The numerical back analysis was able to predict the tears observed in the Chiquita Canyon Landfill liner system after the earthquake if strain concentrations due to seams and scratches in the geomembrane are taken into account. The apparent good performance of the Lopez Canyon landfill geomembrane and the observed tension in the overlying geotextile after the Northridge event was also successfully predicted using the numerical model. / Dissertation/Thesis / Ph.D. Civil and Environmental Engineering 2011

abstract: The objective of the research is to develop guidelines for identifying when settlement or seismic loading presents a threat to the integrity of geosynthetic elements for both side slope and cover systems in landfills, and advance further investigation for parameters which influence the strains in the barrier systems. A numerical model of landfill with different side slope inclinations are developed by the two-dimensional explicit finite difference program FLAC 7.0, beam elements with a hyperbolic stress-strain relationship, zero moment of inertia, and interface elements on both sides were used to model the geosynthetic barrier systems. The resulting numerical model demonstrates the load-displacement behavior of geosynthetic interfaces, including whole liner systems and dynamic shear response. It is also through the different results in strains from the influences of slope angle and interface friction of geosynthetic liners to develop implications for engineering practice and recommendations for static and seismic design of waste containment systems. / Dissertation/Thesis / M.S. Civil Engineering 2013

Column-supported embankments with or without basal geosynthetic reinforcement can be used in soft ground conditions to reduce settlement by transferring the embankment load to the columns through stress redistribution above and below the foundation subgrade level. Column-supported embankments are typically used to accelerate construction and/or protect adjacent facilities from additional settlement. The column elements consist of driven piles or formed-in-place columns that are installed in an array to support a bridging layer or load transfer platform. The bridging layer is constructed to enhance load transfer using several feet of compacted sand or sand and gravel that may include one or more layers of high-strength geotextile or geogrid reinforcement. Mobilization of the mechanisms of load transfer in a column-supported embankment requires some amount of differential settlement between the columns and the embankment as well as between the columns and the foundation soil. When the embankment height is low relative to the clear spacing between columns, there is the risk of poor ride quality due to the reflection of the differential foundation settlement at the surface of the embankment. The minimum embankment height where differential surface settlement does not occur for a particular width and spacing of column is the critical height. The conventional approach is to express critical height as a fixed ratio of the clear span between adjacent columns; however, there is no consensus on what ratio to use and whether a single ratio is applicable to all realistic column arrangements. The primary objective of this research is to improve the understanding of how column-supported embankments deform in response to differential foundation settlement. A bench-scale experimental apparatus was constructed and the equipment, materials, instrumentation, and test procedures are described. The apparatus was able to precisely measure the deformation occurring at the sample surface in response to differential settlement at the base of the sample. Critical heights were determined for five combinations of column diameter and spacing representing a wide range of possible column arrangements. In addition, tests were performed using four different column diameters in a single column configuration with ability to measure the load acting on the column and apply a surcharge pressure to the sample. In total, 183 bench-scale tests were performed over a range of sample heights, sample densities, and reinforcement stiffnesses. Three-dimensional numerical analyses were conducted to model the experiments. The critical heights calculated using the numerical model agreed with the experimental results. The results of the laboratory tests and numerical analyses indicate that critical height depends on the width and spacing of the columns and is not significantly influenced by the density of the embankment fill or the presence of reinforcement. A new method to estimate critical height was developed and validated against extensive case histories as well as experimental studies and numerical analyses performed by others. / Ph. D.

Column-supported geosynthetic-reinforced embankments have great potential for application in soft ground conditions when there is a need to accelerate construction and/or protect adjacent facilities from the settlement that would otherwise be induced by the new embankment load. The columns in column-supported embankments can be driven piles, vibro-concrete columns, deep-mixing-method columns, stone columns, or any other suitable type of column. A bridging layer consisting of several feet of sand or sand and gravel is also used to help transfer the embankment load to the columns. Geosynthetic reinforcement is often employed in bridging layers to enhance load transfer to the columns and increase the spacing between columns. Several methods have been developed to calculate the load on the geosynthetic reinforcement, but the calculated loads differ by over an order of magnitude in some cases, and there is not agreement on which method is correct. In this research, a new method was developed for calculating the load on the geosynthetic reinforcement. The new method employs one of the existing mechanistically-based approaches, and combines it with consideration of the stiffnesses of the embankment, geosynthetic, column, and subgrade soil. The new method was verified against the results of a large numerical parameter study, for which the numerical procedures themselves were verified against closed-form solutions for membranes, pilot-scale experiments, and instrumented field case histories. The results of the numerical analyses and the new calculation procedure indicate that the net vertical load on the portion of the geosynthetic reinforcement between columns increases with increasing clear spacing between columns and increasing geosynthetic stiffness. The net vertical load on the geosynthetic decreases with increasing stiffness and strength of the foundation and embankment soils and with increasing elevation of the geosynthetic above the top of the columns or pile caps. A key finding of the research is that, if the subgrade support is good, geosynthetic reinforcement does not have a significant effect on system performance. The new calculation procedure is implemented in an easy-to-use spreadsheet, and recommendations for designing geosynthetic-reinforced bridging layers are provided. / Ph. D.

The previous E4 Råneå road embankment was prone to flooding. Risk of flooding in combination with settlements of the road due to the weak underlying sulphide soil was problematic. The Swedish Transportation Administration improved the length section E4 Råneå by rebuilding the road using the method light embankment piling. The centre-to-centre pile distance was chosen to 1.1 m and embankment height 1.8 m. The embankment is reinforced with geosynthetic reinforcements resting on timber piles, which were installed on till stratum. Two geosynthetics were installed, with their strength properties in opposite direction from each other. Their purpose was to stiffen the soil and reduce loading on the weak sulphide subsoil. Field monitoring equipment were placed in the road to measure the behavior before and after consolidation. To validify the results, used instruments in this thesis concerns: pressure cells, extensometers, piezometers and a hydrostatic profile gauge. The Swedish Transport administration wants to evaluate if an increase in piling distance is possible. From the conventional practice of maximum 1.2 m to 1.4 m. It is also interesting if the increased pile distance holds for a taller embankment of 2.5 m. Answering this would aid in increasing the cost-effectiveness of light embankment piling. The performed investigation has been done in the finite element analysis program Plaxis 3D 2021 by simulating half of an embankment with supplementary load model.  To capture field behavior, PLAXIS SoilTest has been used to calibrate the compressive material parameters obtained in oedometer testing. The geosynthetics have been modeled with regards to creep and their stiffness increase on surrounding soil due to interlocking of soil particles. Guaranteeing the reliability of the numerical analysis was made by a comparison of the base model to field monitoring equipment before conducting the parametric study. The base numerical model was reliable in capturing the result of field monitoring equipment. Deviations in pile loads was observed beneath the light trafficked road lane. Conducting the parametric study, the results indicated an increase in pile head loading, total settlements, differential settlements, and deformations in the geosynthetic reinforcement when pile distance and embankment height increased. With a taller embankment of 2.5 m and increased pile distance of 1.4 m numerical simulated pile head loads were in sizes of the design pile strength. Tensile stress in the geosynthetic reinforcement was below long-term design strength. The ratio pile efficacy, that is how effective the structure is at reducing sub soil load has been evaluated in the parametric study at three unit cells. A logarithmic growth is observed when reducing the pile distance at the middle of the road with consistent behavior between embankment height. When studying cells beneath the heavy trafficked lane a linear relationship could be seen instead. This study suggests it is possible to perform the increase in pile distance of 1.4 m for the current embankment height 1.8 m, but needs to be investigated further for the 2.5 m high embankment.

Este trabalho trata do desenvolvimento, montagem e teste de equipamentos para ensaios de materiais de baixa condutividade hidráulica, o qual inclui sistemas de controle hidráulico de volume constante, permeâmetros do tipo parede flexível e interfaces água-percolante. A vantagem desse arranjo está no maior controle dos ensaios e, notadamente, na redução do tempo de ensaio com emprego do sistema hidráulico de volume constante (sistema fechado), quando comparado aos ensaios que empregam o sistema aberto de controle hidráulico. Para testar o equipamento, foram ensaiados geocompostos bentoníticos (geosynthetic clay liners - GCLs) de fabricação nacional, em corpos de prova moldados com diâmetro de 100 mm e também, em uma mistura de solo com bentonita. Os resultados da condutividade hidráulica obtidos para os geocompostos bentoníticos se situaram na ordem de \'10 POT.-9\' e \'10 POT.-10\' cm/s, compatíveis com os publicados na literatura sobre o material, e os ensaios na mistura solo-bentonita produziu resultados na ordem de \'10 POT.-8\' cm/s, e foram conseguidos com cerca de 3 horas de ensaio. Aborda-se ainda a aplicabilidade da lei de Darcy aos materiais ensaiados. / This work describes the development, construction, calibration and test of equipment for testing low hydraulic conductivity materials, which includes constant volume hydraulic control system, flexible wall permeameters and permeating water interfaces. The advantage of this kind of apparatus is the greater test control, notably, the reduction of test duration due to the use of a constant volume hydraulic system (closed system), when compared to the opened system hydraulic control test. In order to test the equipment, geosynthetic clay liners (GCLs) manufactured in Brazil was used as test specimens of 100 mm diameter and also, a mixture of soil and bentonite. The results of hydraulic conductivity obtained for the GCL were in the range of \'10 POT.-9\' to \'10 POT.-10\' cm/s, comparable to what has been published by the specialized literature on this material, and the tests with the soil-bentonite mixture resulted in a conductivity about \'10 POT.-8\' cm/s, after 3 hours running the test. The applicability of Darcy´s law to the tested materials is also referred to.