Analyzing Drivability of Open Ended Piles in Very Dense Sands-Article

Article

Pdf Summary

The paper examines how friction fatigue affects the drivability of open-ended piles in very dense sands. Friction fatigue is the decline in shaft friction at a soil horizon as the pile tip advances deeper. Its magnitude and dependence on pile diameter remain uncertain, complicating predictions of installation resistance.<br /><br />The authors back-analyzed driving records for piles 0.356–2 m in diameter at three sites: Pigeon Creek, Indiana; Euripides, the Netherlands; and Trans Tokyo Bay, Japan. Cone penetration test data characterized the soils, and GRLWEAP wave-equation analyses estimated driving resistance. Two CPT-based methods were compared: Alm and Hamre (AH-01), developed for drivability, and a modified UWA-05 method, originally developed for static pile capacity.<br /><br />Both methods generally reproduced observed driving behavior, but their performance varied with pile geometry and site. AH-01 worked well for the larger piles when the diameter-to-wall-thickness ratio was about 40. It required an effective-area-ratio correction to better model the smaller Pigeon Creek pile, where partial plugging and the larger relative wall thickness mattered. Modified UWA-05 better matched that pile but tended to overpredict resistance for the larger piles when internal shaft friction was assumed to be half the external friction. The authors note that UWA-05 is based on load tests conducted, on average, nine days after installation, so time-related capacity gains may partly explain the overprediction.<br /><br />The study concludes that reliable drivability analyses should account for friction fatigue, pile area ratio, and plugging. It recommends depth-specific drivability analyses using average incremental shaft friction rather than relying solely on bearing graphs, particularly where resistance distributions change with depth. The assumed ratio of internal to external shaft friction also has a substantial effect on predictions and remains poorly understood. Because the study covers only three case histories, broader datasets and further experimental work are needed, especially to clarify diameter effects and internal shaft resistance.

Keywords

friction fatigue

open-ended piles

dense sands

drivability analysis

shaft friction

pile diameter effect

cone penetration test

GRLWEAP

Alm and Hamre AH-01

modified UWA-05