Pullout Capacity of Pile Groups in Sand-Paper

Paper

Pdf Summary

The study investigates the uplift capacity of single piles and pile groups embedded in sand, focusing on pile spacing and embedment depth. Laboratory tests used hollow aluminum piles 25.4 mm in diameter and 600, 750, or 900 mm long, giving embedment ratios (L/d) of 24, 30, and 36. Groups contained two piles (2×1) or four piles (2×2), with spacing-to-diameter ratios (S/d) of 3, 4, and 5. Tests were conducted in dense, dry sand, and results were compared with three-dimensional finite-element analyses using PLAXIS 3D and a Mohr–Coulomb soil model.<br /><br />Experimental and numerical results showed broadly similar trends, with numerical predictions generally overestimating measured single-pile capacities by about 15–20%. For single piles, increasing L/d from 24 to 30 and from 30 to 36 raised ultimate uplift capacity by approximately 20–25%. For a given group arrangement and embedment depth, capacity increased as pile spacing increased. Capacity also increased with embedment depth at a fixed spacing and arrangement.<br /><br />The normalized uplift capacity decreased as spacing increased for a given group size and also decreased as the number of piles increased, particularly for square groups. Observed failure surfaces began near the pile tips at an angle of approximately 45° minus half the soil friction angle relative to the vertical. They followed a logarithmic-spiral pattern, consistent between experiments and numerical analyses.<br /><br />Overall, the findings show that pile-group uplift resistance depends strongly on embedment depth, spacing, and group configuration, and that PLAXIS 3D can reproduce the general behavior observed in model tests.

Keywords

uplift capacity

single piles

pile groups

pile spacing

embedment depth

sand

PLAXIS 3D

finite element analysis

Mohr-Coulomb model

logarithmic spiral failure surface