Large Scale Lateral Testing of Pile Foundations-Article

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The study reports full-scale cyclic lateral-load tests on a reinforced-concrete single drilled shaft and a 3×3 pile group. Each shaft was 0.61 m in diameter and embedded about 7.6 m in stiff clay; group piles were spaced three diameters apart. The tests examined pile–soil–pile interaction, group efficiency, and whether published p-y multipliers could predict group behavior.<br /><br />The single pile was tested with a fixed head, while the group cap was allowed slight rotation. Modeling indicated that the group’s small measured rotation had negligible effect on its load–displacement response. The single pile reached 1.21 MN at 76 mm displacement; the group reached 10.23 MN at 102 mm. Excavation revealed the greatest damage in the leading-row piles, with cracking and plastic hinges concentrated near the ground surface.<br /><br />Because some group instrumentation failed, researchers calibrated an analytical model to the single-pile measurements and combined it with field group data. Estimated group efficiency was approximately 1.0 at very small displacements, dropped to about 0.8 as interaction developed, then rose toward 0.9 near 25 mm displacement.<br /><br />Published p-multipliers were also tested in the model. The commonly used Rollins values underestimated the measured group capacity, even after modification. Huang et al.’s multipliers produced the closest fit, likely because their tests also involved reinforced-concrete, fixed-head piles arranged at similar spacing. The results suggest these factors can help predict lateral response for comparable foundations, though differences in soil and test conditions should be considered.

Keywords

reinforced concrete

drilled shaft

pile group

cyclic lateral load

pile-soil interaction

group efficiency

p-y multipliers

fixed head pile

stiff clay

lateral response