p-y Curves for Analyzing Micropiles in Sandy Soils Using Lateral Load Test Data-Paper

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The paper evaluates lateral-load behavior of vertical micropiles in sandy and silty soils using field tests and p-y analyses. The study addresses urban projects where nearby structures or utilities may prevent installing battered micropiles.<br /><br />Three production micropiles at a 43-story building site in Queens, New York, were tested under static lateral loading. Each had a 13.375-inch-diameter steel casing, varied in length, and was socketed into gneissic schist bedrock. The soil profile above bedrock comprised loose to very dense sand, silty sand, sandy silt, and glacial till. Each pile had a design load of 14,000 lb and was loaded to 28,000 lb. At maximum load, measured pile-head displacements were 0.66, 1.28, and 0.67 inches; the larger displacement of the second pile may have resulted from disturbed, poorly compacted soil near its head.<br /><br />The measured responses were compared with LPile analyses using Reese et al.’s widely used sand p-y curves and lower- and upper-bound soil properties. The standard curves generally predicted greater displacements—and thus lower lateral resistance—than observed in the tests. Analyses using upper-bound soil properties were generally closer to the field results. Modification factors were applied to the standard curves to produce site-specific curves that matched the measured behavior.<br /><br />The authors caution that lower-bound properties are not always the most appropriate choice: softer curves may underestimate lateral soil support, while stiffer curves can result in higher predicted bending moments when piles experience ground movement or settlement. They recommend considering realistic or stiffer soil parameters in such cases. The proposed curves are specific to the site’s sandy and silty soils; further testing of instrumented micropiles is needed to develop more reliable New York City-specific p-y curves.

Keywords

micropiles

lateral-load behavior

sandy soils

silty soils

field tests

p-y analysis

LPile

Reese p-y curves

urban construction

New York City