Behavior of a Piled Raft in Dry Cohesionless Soil Subjected to Lateral Loading-Paper

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The study investigates the lateral-load behavior of piled raft foundations in dry, cohesionless sand using laboratory model tests and three-dimensional finite-element analysis.<br /><br />Small-scale tests used a concrete raft supported by a single central pile in Kasai River sand. The raft was subjected to lateral loads of 6.25–25 N, with a vertical surcharge of 1.5 kPa. Pile strains were measured and used to calculate bending moments. Numerical predictions agreed reasonably well with the experimental results; comparison with the Matlock–Reese theoretical approach showed greater differences near the top of the pile.<br /><br />A further numerical parametric study examined a 5 m square raft supported by 1, 2, 5, or 9 piles under equivalent static loads derived from the Loma Prieta and Darfield earthquakes. Adding a second pile substantially reduced the maximum pile bending moment—by about a factor of four—and lateral deformation—by about 2.4 times. Increasing the number of piles to five or nine produced comparatively little additional improvement, indicating a saturation in system response. The study also found that individual pile bending moments generally decreased as pile numbers increased.<br /><br />Overall, the results suggest that a small number of strategically placed piles can improve the lateral performance of a raft, while adding more piles beyond a certain point may offer limited benefit. The findings may help guide economical piled raft design, although the authors note some unexpected differences in the deformation curves for the five- and nine-pile configurations.

Keywords

piled raft foundations

lateral load behavior

cohesionless sand

finite element analysis

laboratory model tests

pile bending moment

lateral deformation

parametric study

earthquake loading

pile number effect