Abstract
Laboratory tests were carried out on non-piled rafts, single piles, surface contacting and non surface-contacting piled rafts which were made of aluminum and instrumented with strain gauges and deflection gauges. The foundations were installed in dry sand contained in a large metal tank to minimize boundary effects. Maintained loads were applied to each foundation until failure was closely approached. In parallel, analyses were performed using PLAXIS™ 3-D finite element program to compare the calculated and measured load-settlement trends hence assess the influence of soil stiffness on the foundation behaviour. The results confirmed that group efficiency of non-surface contacting piled increased with increasing pile–pile spacing and approached unity at a spacing equivalent to 8D (D = pile diameter). The data obtained from the strain gauges provided valuable insight into the load-transfer characteristics of different foundations and subsequently proved that the capacity of a surface contacting piled raft is significantly enhanced compared to that of either a non-piled raft or a non-surface contacting piled raft.
Highlights
Introduction and Literature ReviewPiled rafts are commonly installed to support heavy structures and are usually designed with the aid of computer software such as PLAXIS 3D, which overcomes limitations of simple older methods such as Poulos (2001)
Lee and Chung (2005) suggested that a piled raft is subject to two conflicting effects; the unfavorable settlement inducing effect and the favorable settlement reducing effect, which is due to increase in lateral stress in the surrounding soil as a consequence of driving a cluster of piles
It is seen that the highest capacities were produced by the single piles whilst the capacities of the non-surface contacting piled rafts increased with increasing pile–pile spacing
Summary
Piled rafts are commonly installed to support heavy structures and are usually designed with the aid of computer software such as PLAXIS 3D, which overcomes limitations of simple older methods such as Poulos (2001). The piles were well instrumented and had different configurations, i.e. ground-contacting versus floating pile caps, various pile–pile spacing and overlap of cap from edge piles They investigated the simultaneous effects of pile driving and group interaction on the densification of the sand, load capacity of the piled rafts. There are three research hypotheses to be tested or verified: (a) piled raft capacity increases with increasing pile–pile spacing and (b) a piled raft has an enhanced capacity compared to both a non piled raft and a single pile, (c) a piled raft with surface contacting cap has greater capacity and settlement resistance compared to all other cases. Along with the laboratory tests and finite element work, the above analytical methods (Eqs. 1–3) have been applied to ground-contacting piled rafts in order to assess the relative contribution of pile cap to total load resistance of piled rafts
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