Thesis (M. Phil.)--University of Hong Kong, 1999. / Includes bibliographical references (leaves 80-84).

Thesis (M.S.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains xii, 210 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 100-101).

Prefabricated vertical drains represent a soil improvement technique that achieves liquefaction mitigation by decreasing the drainage path length and hence expediting the dissipation of excess pore pressures. When evaluating the required spacing between vertical drains to achieve the desired reduction in pore pressure response, simplified design charts or more sophisticated finite element analyses are used to predict the pore pressure response. These charts and programs have not been evaluated in terms of their accuracy because there exists little data with which to compare the numerical predictions. More recently, the effectiveness of prefabricated vertical drains for liquefaction mitigation has been evaluated via small – scale centrifuge testing performed on untreated soil deposits and on soil deposits treated with vertical drains. In particular, the performance of the soil deposits subjected to sinusoidal motions and actual earthquake recordings was tested. The main goal of this research is to compare the experimental observations of pore pressure response from the centrifuge experiments with the numerical predictions. The comparison focuses on the average excess pore pressure ratio (r_(u,avg)) that was developed in the location of a vertical pore pressure array in both the untreated and drain – treated sides of the models. In parallel, a parametric study is performed for the numerical predictions in order to study the effect of each input parameter that influences the pore pressure prediction, namely the effect of soil properties, ground motion characteristics and drain parameters. The numerical predictions are found to provide reliable predictions of the pore pressure response despite the simplicity of the constitutive model employed. The numerical predictions of r_(u,avg) time – histories are generally in good agreement with the recorded values in the centrifuge experiments. In most of the cases, the numerical model managed to predict the same maximum average excess pore pressure ratio, which is the parameter that is used in drain design. To incorporate any uncertainty on the soil properties or on the characteristics of shaking, the use of a smaller pore pressure threshold for drain design is recommended. / text

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 280-284). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 198-204). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 198-204). Also available on the Internet.

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.

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>