Thesis (Ph.D.)--University of Wollongong, 2006. / Typescript. Includes bibliographical references: leaf 191-207.

Neste trabalho apresentou-se a simulação numérica de aterros reforçado sobre argila mole com uso de drenos verticais pré-fabricados. O objetivo foi analisar o comportamento de um aterro reforçado com geossintético aliado ao uso de drenos verticais pré-fabricados. As análises numéricas de tensão-deformação foram realizadas pelo software PLAXIS 8.2. 2D. Pretendeu-se analisar as influências da rigidez do reforço, espaçamento entre drenos, velocidade de construção, construção do aterro em etapas, no comportamento dos aterros, como recalques verticais, deformações laterais e deformação do reforço. Foi utilizada a metodologia apresentada por Li & Rowe (2001), para a validação da modelagem dos aterros. A calibração do programa foi feita com a literatura de aterros reforçados. Nos resultados apresentados foram verificadas vantagens, como por exemplo: aceleração dos recalques e possibilidade da construção de aterros mais altos. O MEF mostrou que pode ser útil na escolha do reforço mais adequado para a condição de obra desejada, juntamente com espaçamento entre drenos. Foi possível verificar que a combinação de ambos os elementos pode ser bastante vantajosa em relação à utilização de apenas um deles. As deformações do reforço determinadas pelo MEF podem ser usadas para escolher o reforço adequado para um aterro sobre solo mole. Através dos resultados do método de elementos finitos pretendeu-se definir uma metodologia para calcular as deformações do reforço para uma altura de aterro determinada. / This paper presents the numerical simulation of reinforced embankment on soft clay with the use of prefabricated vertical drains. The objective is to analyze the behavior of a geosynthetic reinforced embankment along with the use of prefabricated vertical drains. The numerical analyzes of the stress-strain were performed by software PLAXIS 8.2. 2D. It was intended to analyze the influence of the stiffness of the reinforcement spacing between drains, construction speed, construction of the embankment in stages, the behavior of the landfill as settlements vertical, lateral deformations and deformation strengthening. We used the method presented by Li & Rowe (2001), to validate the modeling of landfills. The calibration was performed with the program literature reinforced embankments. In the following results were observed advantages such as: speeding up the possibility of repression and construction of embankments higher. MEF showed that may be helpful in selecting the most suitable for enhancing the desired work condition, with the spacing between drains. It can be seen that the combination of both elements can be quite advantageous over the use of just one. The deformation of the reinforcement determined by MEF can be used to choose the proper reinforcement for an embankment on soft soil. Through the results of the finite element method was intended to define a methodology to calculate the deformations of the reinforcement to a height of embankment determined.

Drainage methods for liquefaction remediation have been in use since the 1970's and have traditionally included stone columns, gravel drains, and more recently prefabricated vertical drains. The traditional drainage techniques such as stone columns and gravel drains rely upon a combination of drainage and densification to mitigate liquefaction and thus, the improvement observed as a result of these techniques cannot be ascribed solely to drainage. Therefore, uncertainty exists as to the effectiveness of pure drainage, and there is some hesitancy among engineers to use newer drainage methods such as prefabricated vertical drains, which rely primarily on drainage rather than the combination of drainage and densification. Additionally, the design methods for prefabricated vertical drains are based on the design methods developed for stone columns and gravel drains even though the primary mechanisms for remediation are not the same. The objectives of this research are to use physical and numerical models to assess the effectiveness of drainage as a liquefaction remediation technique and to identify the controlling behavioral mechanisms that most influence the performance of sites treated with prefabricated vertical drains. In the first part of this research, a suite of three large-scale dynamic centrifuge tests of untreated and drain-treated sloping soil profiles was performed. Acceleration, pore pressure, and deformation data was used to evaluate the effectiveness of drainage in reducing liquefaction-induced lateral deformations. The results showed that the drains reduced the generated peak excess pore pressures and expedited the dissipated of pore water pressures both during and after shaking. The influence of the drains on the excess pore pressure response was found to be sensitive to the characteristics of the input motion. The drainage resulted in a 30 to 60% reduction in the horizontal deformations and a 20 to 60% reduction in the vertical settlements. In the second part of this research, the data and insights gained from the centrifuge tests was used to develop numerical models that can be used to investigate the factors that most influence the performance of untreated and drain-treated lateral spread sites. Finite element modeling was performed using the OpenSees platform. Three types of numerical models were developed - 2D infinite slope unit cell models of the area of influence around a single drain, 3D infinite slope unit cell models of the area of influence around a single drain, and a full 2D plane strain model of the centrifuge tests that included both the untreated and drain-treated slopes as well as the centrifuge container. There was a fairly good match between the experimental and simulated excess pore pressures. The unit cell models predicted larger horizontal deformations than were observed in the centrifuge tests because of the infinite slope geometry. Issues were identified with the constitutive model used to represent the liquefiable sand. These issues included a coefficient of volumetric compressibility that was too low and a sensitivity to low level accelerations when the stress path is near the failure surface. In the final part of this research, the simulated and experimental data was used to examine the relationship between the generated excess pore water pressures and the resulting horizontal deformations. It was found that the deformations are directly influenced by both the excess pore pressures and the intensity of shaking. There is an excess pore pressure threshold above which deformations begin to become significant. The horizontal deformations correlate well to the integral of the average excess pore pressure ratio-time history above this threshold. They also correlate well to the Arias intensity and cumulative absolute velocity intensity measures. / text

Neste trabalho apresentou-se a simulação numérica de aterros reforçado sobre argila mole com uso de drenos verticais pré-fabricados. O objetivo foi analisar o comportamento de um aterro reforçado com geossintético aliado ao uso de drenos verticais pré-fabricados. As análises numéricas de tensão-deformação foram realizadas pelo software PLAXIS 8.2. 2D. Pretendeu-se analisar as influências da rigidez do reforço, espaçamento entre drenos, velocidade de construção, construção do aterro em etapas, no comportamento dos aterros, como recalques verticais, deformações laterais e deformação do reforço. Foi utilizada a metodologia apresentada por Li & Rowe (2001), para a validação da modelagem dos aterros. A calibração do programa foi feita com a literatura de aterros reforçados. Nos resultados apresentados foram verificadas vantagens, como por exemplo: aceleração dos recalques e possibilidade da construção de aterros mais altos. O MEF mostrou que pode ser útil na escolha do reforço mais adequado para a condição de obra desejada, juntamente com espaçamento entre drenos. Foi possível verificar que a combinação de ambos os elementos pode ser bastante vantajosa em relação à utilização de apenas um deles. As deformações do reforço determinadas pelo MEF podem ser usadas para escolher o reforço adequado para um aterro sobre solo mole. Através dos resultados do método de elementos finitos pretendeu-se definir uma metodologia para calcular as deformações do reforço para uma altura de aterro determinada. / This paper presents the numerical simulation of reinforced embankment on soft clay with the use of prefabricated vertical drains. The objective is to analyze the behavior of a geosynthetic reinforced embankment along with the use of prefabricated vertical drains. The numerical analyzes of the stress-strain were performed by software PLAXIS 8.2. 2D. It was intended to analyze the influence of the stiffness of the reinforcement spacing between drains, construction speed, construction of the embankment in stages, the behavior of the landfill as settlements vertical, lateral deformations and deformation strengthening. We used the method presented by Li & Rowe (2001), to validate the modeling of landfills. The calibration was performed with the program literature reinforced embankments. In the following results were observed advantages such as: speeding up the possibility of repression and construction of embankments higher. MEF showed that may be helpful in selecting the most suitable for enhancing the desired work condition, with the spacing between drains. It can be seen that the combination of both elements can be quite advantageous over the use of just one. The deformation of the reinforcement determined by MEF can be used to choose the proper reinforcement for an embankment on soft soil. Through the results of the finite element method was intended to define a methodology to calculate the deformations of the reinforcement to a height of embankment determined.

Construction in soft soils has been a challenging task for engineers due to the excessive time taken for dissipation of construction induced pore water pressure and the ensuing postconstruction settlement. Use of vertical drains has proven to be an effective and economical method for soft ground improvement and hence extensive research has been carried out to further improve its efficiency. Effect of temperature on radial consolidation is one aspect of such research among many others that have been pursued. Elevated temperature certainly has a pronounced effect on the hydraulic conductivity due to the reduction it causes in the viscosity of water. Furthermore, temperature also generates excess pore water pressure due to the tendency for differential volumetric expansion between the soil grains and pore water. Thermally induced volumetric strains can have an effect on the magnitude of settlement as well. A numerical methodology based on the NavierStokes equations of flow and thermoelasto-plastic soil compressibility relationships was developed to model transient fluid flow in a clay under thermal treatment. Experimentally verified soil compressibility relationships coupling the loading and thermal effects obtained from literature were employed in this model. The transient temperature distribution within the consolidation soil was modeled using the Fourier’s equation of heat transfer. The effect of temperature on consolidation of clay was investigated by a parametric study involving different maximum temperatures, surcharge loads and initial porosities of clay. It was concluded that the improvement in the magnitude and rate of settlement at elevated temperature is more significant at relatively smaller surcharges and low initial porosities. Since there is a possibility for thermally induced volumetric expansion even in normally consolidated clays, an optimum combination of surcharge and thermal treatment should be employed for given initial conditions of the soil, in order to achieve the maximum improvement in settlement. The developed numerical model will provide the framework to carry out further investigations and determine the viability of the practical implementation of coupled thermomechanical consolidation using prefabricated vertical drains.

In this thesis, some aspects concerning building embankments founded on sulphide clay are studied, with special reference to ground improvement by preloading in combination with prefabricated vertical drains (PVD’s). The main purpose of the research was to increase empirical knowledge of the mechanical behaviour of sulphide clays subjected to embankment loadings and of the interaction between vertical drains and sulphide clays. Important aspects related to ground improvement with PVD’s in more general terms are also treated, in particular how various uncertainties regarding the properties of the clay and the clay-drain interaction imposed in the design phase can be addressed. The benefits of using theobservational method for handling these uncertainties are discussed, and a description of how the method was used in an embankment project is presented. The results from the research are presented in one conference paper and two papers submitted to peer-reviewed international journals, which are appended. The design of PVD’s involves describing the consolidation characteristics of the clay and the interaction between the drains and the clay. Primarily, the rate of consolidation is determined by the hydraulic conductivity (permeability) of the clay in the horizontal direction. Hence, accurate determination of this material property is of paramount importance in making reliable design predictions. As conventional laboratory tests for assessing the consolidation characteristics of a clay only provide information about its properties in the vertical direction, one is often left to make assumptions about the horizontal properties based on empirical correlations. Reliable empirical knowledge of these correlations for a certain clay is there forevital. A large number of CRS tests were performed on horizontal and vertical samples ofsulphide clay in order to investigate the correlation between the horizontal and verticalhydraulic conductivity and coefficient of consolidation. The results show that there is very small anisotropy in these parameters and that the scatters in the results are large. For designpurposes, sulphide clays should therefore be assumed to be isotropic in this respect. In orde rto handle the variation in properties, several parallel tests should be made and partial factors of safety should be introduced in the design. Introducing partial factors of safety in the design of PVD’s is one of the main topics suggested for further research. Regarding the clay-drain interaction, a study of the disturbance effects (smear effects) during the installation of drains in sulphide clays was performed. Back-calculations of measurements of pore pressure dissipation were made via a parameter study. It was shown that smear affects the consolidation rate to some extent but that the natural (undisturbed) hydraulic conductivity is more significant. The undrained shear strength su of a clay is dependent on the preconsolidation pressure σ 'p . As the clay consolidates under a loading, the effective stress increases, possibly to magnitudes surpassing the initial preconsolidation pressure and thereby leading to increased undrainedshear strength of the clay. The relation between su and σ 'p, i.e. the ratio su /σ 'p for asulphide clay, was investigated based on results from a large number of in situ tests andlaboratory tests. There were large scatters in the measurements, but su /σ 'p =0.25 is suggested as being relevant in the direct shear zone for design purposes in sulphide clays. / <p>QC 20101101</p>

[pt] O método empírico de Terzaghi (1943) para cálculo do recalque de adensamento primário com carregamento dependente do tempo é comparado com dois métodos propostos nesta pesquisa: o primeiro, baseado na alteração da fração de tempo em que cada incremento de carregamento é aplicado de forma instantânea, e o segundo mantendo a proposta inicial de Terzaghi (1943), porém realizando reduções percentuais do grau médio de adensamento para o período de construção e obtendo novas frações de tempo para o período pós-construção. Os resultados mostram que com a adoção das frações de tempo, apresentadas em tabelas, a diferença entre os valores do grau médio de adensamento determinados pelas curvas teórica e empírica varia entre 1,50 por cento a 3,50 por cento, dependendo das condições iniciais de excesso de poropressão. O segundo método, mais exato, apresenta diferenças menores, com ambas as curvas praticamente sobrepostas. Adicionalmente, outras duas soluções alternativas são investigadas considerando o carregamento em degraus e discretizado. Uma solução matemática rigorosa também é apresentada para representar o problema de adensamento com drenos verticais, considerando a hipótese de deformações livres. Uma comparação com a solução proposta por Olson (1977), fundamentada no conceito de deformações iguais, mostra que a hipótese de deformações iguais subestima o grau médio de dissipação dos excesoss de poropressão entre 1,15 por cento a 4,84 por cento, e que essa diferença tende a diminuir para tempos de construção elevados. Finalmente, soluções para fluxo vertical e radial combinados também são obtidas, considerando a hipótese de deformações livres e a formulação proposta por Carrillo (1942). / [en] Terzaghi s (1943) empirical method for calculating primary consolidation settlement due to ramp loading is compared with two methods proposed in this research: the first one, based on changing the fraction of time in which each loading increment is applied instantly, and the second keeping Terzaghi s initial proposal (1943), but making reductions in the average degree of consolidation for the construction period and determining new fractions of time for the post-construction period. The results show that with the hypothesis of time fractions, the difference between the values of the average degree of consolidation determined by the theoretical and empirical curves varies between 1.50 percent to 3.50 percent, depending on the initial conditions of excess poropressure. The second method is even more accurate with both curves practically overlapping. Additionally, two other alternative solutions are investigated considering step and discretized loadings. A rigorous mathematical solution is also presented to represent the consolidation problem with vertical drains, considering the hypothesis of free deformations. A comparison with the solution proposed by Olson (1977), based on the concept of equal deformations, shows that the hypothesis of equal deformations underestimates the average degree of consolidation between 1.15 percent to 4.84 percent, and this difference tends to decrease for long construction periods. Finally, solutions for the vertical and radial flow combined is also obtained, considering the hypothesis of free deformations and the formulation proposed by Carrillo (1942).

Soil improvement methods are used to minimize the consequences of liquefaction by changing the characteristics and/or response of a liquefiable soil deposit. When considering sites with previous development, the options for soil improvement are limited. Traditional methods, such as compaction and vibratory techniques, are difficult to employ because of adverse effects on adjacent structures. One potential method for soil improvement against soil liquefaction in developed sites is accelerated drainage through in situ vertical drains. Vertical drains expedite the dissipation of excess pore water pressures by reducing the length of the pore water drainage path. For more than thirty years, vertical gravel drains or stone columns have been employed to ensure the excess pore water pressure ratio remains below a prescribed maximum value. In recent years, the use of prefabricated vertical drains (PVDs) has increased because the drains can be installed with less site disruption than with traditional soil improvement methods. To date, little-to-no field or experimental verification is available regarding the seismic performance of sites treated with PVDs. The effectiveness of PVDs for liquefaction remediation was evaluated via small-scale centrifuge testing and full-scale field testing. A small-scale centrifuge test was performed on an untreated soil deposit and on a soil deposit treated with small-scale vertical drains. Compared to the untreated condition, the presence of the small-scale vertical drains provided numerous benefits including smaller magnitudes of excess pore water pressure generation and buildup, smaller induced cyclic shear strains, reduced times for pore pressure dissipation, and smaller permanent horizontal and vertical displacements. In addition, full-scale in situ field experiments were performed in an untreated soil deposit and in a soil deposit treated with full-scale PVDs using a vibrating mandrel as the dynamic source. In the untreated test area, the maximum induced excess pore pressure ratio reached about 0.95. In the treated test area, the vibratory installation of the first few drains generated significant excess pore pressures; however, significant excess pore pressures were not generated during the vibratory installation of additional drains because of the presence of the adjacent drains. Additionally, the vibratory installation of the drains caused significant settlement and significantly altered the shear wave velocity of the sand. Dynamic shaking after installation of all of the drains induced small accelerations, small cyclic shear strains, and negligible excess pore water pressures in the soil. The results of the field experiment indicate that the prefabricated vertical drains were effective at dissipating excess pore water pressures during shaking and densifying the site. / text

Liquefaction is a costly phenomenon where soil shear modulus degrades as the generation of excess pore pressures begins. One of the methods to mitigate liquefaction, is the use of prefabricated vertical drains. Prefabricated vertical drains provide a drainage path to effectively mitigate the generation of pore pressures and aid in shear modulus recovery. The aims of this study were to define shear modulus degradation vs. shear strain as a function of excess pore pressure ratio; define the effects of prefabricated vertical drains on the behavior of pore pressure generation vs. shear strain; and to define volumetric strain as a function of shear strain and excess pore pressure ratios. A large-scale laminar shear box test was conducted and measured on clean sands with prefabricated vertical drains spaced at 3-feet and 4-feet. The resulting test data was analyzed and compared to data without vertical drains. The results show the effect of increasing excess pore pressure ratios on shear modulus and curves where developed to encompass these effects in design with computer programing like SHAKE or DEEPSOIL. The data also suggests that prefabricated vertical drains effectively mitigate excess pore pressure build-up, thus increased the shear strain resistance before pore pressures were generated. Regarding volumetric strain, the results suggests that the primary factor governing the measured settlement is the excess pore pressure ratio. This indicates that if the drains can reduce the excess pore pressure ratio, then the resulting settlement can successfully be reduced during a shaking event. The curves for shear modulus vs. cyclic shear strain as function of pore pressure ratio were developed using data with high strain and small strain which leaves a gap of data in the cyclic shear strain range of 0.0001 to 0.01. Further large-scale testing with appropriate sensitivity is needed to observe the effect excess pore pressure generation on intermediate levels of cyclic shear strain.

[pt] A história registra ao longo dos séculos muitos casos de colapso de depósitos de solos arenosos, com consideráveis prejuízos econômicos, perdas de vidas humanas e danos ao meio ambiente, causados pela liquefação dinâmica ou por mobilidade cíclica. Quando um desempenho satisfatório de estruturas não puder ser garantido sob carregamento sísmico, métodos de mitigação devem ser empregados para reduzir o potencial de liquefação. Dentre estes, a execução de drenos verticais é solução interessante, mas desafiadora, pois drenos verticais podem ser utilizados caso dissipem suficientemente rápido os excessos de poropressão e transportem eficientemente o volume de água durante os poucos segundos de duração de terremotos. Uma dificuldade é a avaliação do coeficiente de permeabilidade do depósito de solo, o que afeta e torna incerta a distância desejável entre drenos. Nesta dissertação, análises do desempenho de drenos verticais para mitigação de liquefação dinâmica são realizadas com base em formulações matemáticas e modelos numéricos pelo método dos elementos finitos. / [en] Throughout centuries there are many recorded cases of collapse of sandy deposits with considerable economic losses, loss of human life and damage to the environment caused by the dynamic liquefaction or cyclic mobility. When a satisfactory performance of structures can’t be guaranteed under seismic loading, methods of mitigation must be employed in order to reduce the potential of liquefaction. Among these methods, the execution of prefabricated vertical drains is an interesting, but challenging, solution, because drains can be used if they dissipate very quickly the excess of porepressure generated during the small duration of earthquakes. One of the main challenges is to evaluate the coefficient of permeability of the deposit which affects and brings uncertainties to the desirable distance between the drains installed. On this work, analysis of the performance of vertical drains to mitigate dynamic liquefaction are performed based in mathematical formulations and numerical models through the Finite Element Method.