Geotechnical projects typically achieve load transfer to the ground using shallow or deep foundations. The conventional design approach does not provide for the combination of these two types of foundation. The piled raft philosophy allows the association of the soil elements, raft, and piles to obtain technical and economic advantages over conventional design. The city of João Pessoa, in northeastern Brazil, has developed foundation practices with hollow auger piles in piled raft design. The coastal area of the city has topsoil layers with favorable conditions for using such a technique. This paper addresses the results of a research project with instrumented load tests on foundation systems of hollow auger piles and a piled raft. The analysis is based on the load-settlement curve through extrapolation criteria. The Poulos-Davis-Randolph (PDR) method is applied according to a trilinear and hyperbolic approach to simulate the load-settlement curve of piled rafts. The results indicate that the raft absorbs most of the load, and the raft-soil contact significantly increases the load capacity of the foundation. The PDR hyperbolic method could apply to practical use in the foundations of the region, as it allows a more detailed assessment of the behavior of the foundation and can forecast the behavior of the (locally nontraditional) piled raft foundation system. Résumé :Dans les projets géotechniques, le transfert de charge vers le sol est habituellement réalisé à l'aide de fondations superficielles ou profondes. La méthode traditionnelle de conception ne prévoit pas l'association de ces deux types de fondations. L'approche des radiers sur pieux permet de combiner les éléments de sol, le radier et les piles de manière, ce qui comporte des avantages techniques et économiques par rapport à la méthode de conception traditionnelle. La ville de João Pessoa, dans le Nord-Est du Brésil, a mis en place des pratiques de construction des fondations prévoyant l'utilisation de pieux à tarière creuse lors de la conception de radiers sur pieux. La couche superficielle du sol dans la zone côtière de la ville est favorable à l'utilisation d'une telle technique. Le présent article présente les résultats d'un projet de recherche comportant des essais instrumentés effectués sur des systèmes de fondations constitués de pieux à tarière creuse et d'un radier sur pieux. L'analyse est basée sur la courbe charge-tassement et fait appel à des critères d'extrapolation. La méthode de Poulos-Davis-Randolph (PDR) est appliquée en suivant une approche trilinéaire et hyperbolique afin de simuler la courbe charge-tassement de radiers sur pieux. Les résultats montrent que le radier absorbe l'essentiel de la charge et que le contact entre le radier et le sol a pour effet d'augmenter de manière significative la capacité de charge de la fondation. La méthode hyperbolique PDR pourrait s'appliquer dans la pratique aux fondations construites dans la région de João Pessoa étant donné qu'elle permet d'évaluer plus en détail le comportement de la fondation et...

This work presents some geotechnical parameters in sandy soil improved by compaction piles installed by vibro-displacement on the cost of the city of João Pessoa in Northeastern Brazil. Significant increases on bearing capacity can be achieved with this ground improvement technique allowing the use of shallow foundation, even in the case of high buildings. Forty eight sand piles with diameter of 0,30 m and 3,5 m long were installed on three different groups varying distance between the piles. Standard Penetration Tests, Cone Penetration Tests and plate load tests were carried out before and after the installation of piles. The comparison between the tests allows quantify the benefit of soil improvement by compaction piles. Empirical relationships between N SPT before and after improvement, and relationships between q c and N SPT were established. These relations and results of plate load tests allowed an assessment of the influence of distance between the piles in the compacted soil. A prediction of bearing capacity of shallow foundations in sandy soil improved by sand piles, based on N SPT values is presented.

RESUMO: O solo grampeado é uma técnica de estabilização do maçiço de solo, utilizada em solos que apresentem coesão efetiva mínima de 10 kPa. Ele visa aumentar o fator de segurança através da inserção de grampos envoltos por uma injeção de bainha com pasta de cimento, podendo ser utilizadas reinjeções, acrescido a uma rede de drenagem e concreto na superfície do talude. O artigo avalia os resultados de resistência ao cisalhamento na interface solo-grampo (qs) obtidos através de dois ensaios de arrancamento, um em grampo com injeção simples ou única e outro, com reinjeção ou injeção de reforço. O dois grampos analisados foram inseridos em uma camada de silte argiloarenosa, espaçados entre si em 1,35 m, horizontalmente, em um talude vertical que varia de 6,40 a 7,49 m. Os resultados mostram que há um aumento considerável de qs nos grampos que passaram pela reinjeção, sendo de 52 kPa e 73,3 kPa, para o caso de injeção simples e reinjeção, respectivamente, representando aproximadamente um aumento de 40%. Isso é devido ao fato que ao reinjetar a calda de cimento, o atrito na interface solo-cimento aumenta. Os dados obtidos foram confrontados com a literatura e são coerentes, visto que os valores se assemelham.

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