A programme of 20 centrifuge tests was carried out on piled embankments without reinforcement to assess the influence of geometric parameters on surface settlement and on the load transfer mechanism. The three main geometric parameters studied were pile spacing, embankment height and area ratio, which were varied in ranges commonly adopted in practice. The measurements of the forces on the piles allowed assessment of the load transfer mechanisms, and thus the efficiency, which were shown to increase with embankment height and area ratio. Subsoil stress between piles was also assessed and compared with literature data. The centrifuge model test results for stress on the subsoil at the point of ‘maximum arching’ presented good agreement with the method proposed by Hewlett and Randolph in 1988. Measurements of the surface settlements allowed evaluation of the critical height at which surface differential settlements did not occur. The values of critical height obtained herein are in good agreement with recent literature recommendations.
This paper presents numerical and analytical models to complement experimental data obtained from 40 centrifuge tests of geosynthetic-reinforced piled embankments, 12 of which had a surcharge applied at the embankment surface. The main parameters of study were pile diameter, pile spacing, embankment height and geosynthetic stiffness. The tests measured the force transferred to the piles, the embankment surface settlements and the maximum geosynthetic reinforcement deflections below the embankment under conditions without any support from the underlying soil. Maximum geosynthetic deflections measured longitudinally between piles were then compared with values predicted by European design guidelines. A 3D numerical model, initially validated by centrifuge tests, was then used to compute those geosynthetic tensile forces not measured in the reduced-scale physical models. Numerical values of geosynthetic tensile forces were also compared with corresponding values predicted by European guidelines.
The main purpose of this paper is to describe the geotechnical behaviour of a deep water marine clay obtained from Campos basin oil field located offshore the state of Rio de Janeiro in Brazil. The soil samples were obtained at a depth of about 1500 m using a Kullenberg piston corer. Characterization tests were undertaken on the clay samples, including water content, Atterberg limits, particle size distribution and specific density. Isotropic and anisotropic undrained triaxial tests were also carried out on both normal and over-consolidated samples to assess both the conventional strength and Cam-clay parameters. Additionally, oedometer tests were performed to evaluate the compressibility of both undisturbed and reconstituted soil samples. Finally, a series of T-bar penetrometer tests were performed on the mini-drum geotechnical centrifuge at COPPE, the University of Rio de Janeiro to establish the undrained shear strength profile. The results obtained from the T-bar tests were compared with the theoretical strength curves that were established based on the Cam-clay parameters derived from the laboratory tests. The results obtained in this study indicated a useful methodology to assess and capture the behaviour of marine clay. The assessment of strength behaviour of marine clay is quite essential in modelling of wide range of soil-offshore structure interaction problems such as pipelines, mudmats and anchors.
Fundações profundas exigem cuidados especiais por estarem inseridas em um meio de difícil análise que é o solo. Buscando verificar o comportamento das estacas ao sofrerem carregamento, ensaios de prova de carga estática podem ser realizados. O objetivo deste trabalho é realizar uma análise dos resultados dos recalques ocorridos em uma estaca sujeita a carregamentos através de um modelo numérico. A modelagem da prova de carga foi efetuada utilizando-se o método dos elementos finitos através do software PLAXIS 2D AE. Os parâmetros geotécnicos do local foram estimados utilizando os valores de um ensaio SPT efetuado próximo ao local da estaca, através de correlações sugeridas na literatura. Constatou-se que os resultados obtidos através de modelagem numérica utilizando o PLAXIS 2D foram satisfatórios e coerentes com o relatório de prova de carga estática executado no local. Realizar uma análise numérica de testes de carregamento em estacas pode ser uma alternativa rápida e eficaz para estimar recalques de forma preliminar.
Nenhum modelo prevê perfeitamente a realidade de um determinado sistema; consequentemente, os cálculos em engenharia têm incertezas, que, por conseguinte vão repercutir diretamente em erros de diversos tipos. Em especial, as obras sobre depósitos de argilas moles apresentam uma alta dificuldade devido ao comportamento caracterizado por elevada compressibilidade e baixa resistência desse solo. Os projetos geotécnicos de aterros sobre solos moles são tradicionalmente analisados por intermédio de um fator de segurança global obtido por meio de métodos determinísticos, não incorporando as incertezas inerentes no cálculo. Já a abordagem probabilística possibilita a quantificação das incertezas oriundas da variabilidade dos parâmetros, bem como a avaliação mais abrangente do nível de segurança esperado para a obra através da probabilidade de falha. Desse modo, é possível desvincular a ideia que altos valores de fator de segurança sempre garantem projetos mais seguros. Neste contexto, o presente estudo tem como objetivo comparar as soluções obtidas pelos Métodos Probabilísticos de Rosenblueth, Monte Carlo, Hipercubo Latino e First Order Second Moment (FOSM), além de avaliar os resultados pela abordagem determinística pelos métodos de Bishop Simplificado, Janbu Simplificado, Spencer e Morgenstern & Price. As análises referentes a estabilidade foram realizadas com o auxílio da ferramenta computacional Slide v.6. Os resultados oriundos das análises evidenciam a importância da inserção do coeficiente de variação nos parâmetros, já que a incerteza repercute diretamente no nível de desempenho esperado para a obra.
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