This paper presents a method of analysis of the behaviour of piled rafts in clayey soils, in which a deep excavation was necessary for buildings with two or more basements. In these cases, the piled raft foundations are called a “compensated piled raft.” The soil stresses reduce due to excavation, and the reloading of the soil should be taken into account for this kind of foundation. Many important factors that are required to achieve a satisfactory comparison of “measurement versus prediction” are pointed out, and they are grouped in a proposed simplified method of analysing compensated piled rafts using numerical tools that can consider the raft–soil–pile interaction. Finally, two well-known cases of compensated piled rafts (Hyde Park Barracks in London and the Messeturm building in Frankfurt) and a newer building (the Skyper Tower, Frankfurt) are analyzed using the presented approach and the computed and measured time–settlement behaviours are compared.
Model pile load testing is effective to study the load-settlement behaviour of pile foundations given the controlled environment in which the testing is done. This paper reports a testing program in a large calibration chamber involving individual piles and pile groups installed in sand samples of three different densities. Tests on both nondisplacement and driven piles are evaluated to assess the influence of the pile installation process on pile load-settlement response. A method is proposed to predict the load-settlement response of a pile group based on the response of a single pile. The method is shown to produce estimates that are in good agreement with measurements. The influence of pile group configuration, pile spacing, soil density and method of pile installation is discussed.
The need for understanding the interaction between the elements of a piled-raft foundation system becomes relevant when one of the piles collapses, presents a defect related to the installation procedure, or when it is sought to optimise the number of piles to meet the criteria of load capacity and admissible settlement. In the paper, 20 small-scale 1g load tests were performed in model piled-raft foundations placed within a cylindrical container. Pluviated sand under vertical loading was adopted to evaluate the cross-correlated qualitative behaviour of piled rafts with and without the presence of a single defective pile in systems of four, nine and 16 piles. The defects were simulated by the variation of the length of the pile, considering it shorter or absent, at distinct positions on the system – that is, corner, edge and centre of the raft locations. The results indicate that the position of the defective pile may be more detrimental to the foundation stiffness and load capacity than the level of damage of the pile, such as the cases evolving the presence of defective piles in the corner position.
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