Ideas to Improve Driven Pile Foundation Design and Installation Procedures-PPT Presentation

PPT Presentation

Pdf Summary

The presentation examines how installation methods and timing affect the capacity of driven piles, particularly in cohesive soils.<br /><br />Static load tests conducted too soon after installation may underestimate long-term capacity because piles gain strength through setup. At a Louisiana site, a seven-day wait yielded about 60% of full setup capacity, compared with roughly 87% after 28 days. The presentation recommends considering load tests after more than 28 days where appropriate.<br /><br />Re-driving piles after setup can substantially reduce their capacity. At the Drayton, North Dakota, and Pentre, England, sites, re-driven piles had markedly lower shaft resistance than initially driven piles. The authors caution that re-driven piles should not be used to develop empirical correlations for pile shaft resistance.<br /><br />Vibratory hammer installation can disturb supporting cohesive soils and significantly reduce pile capacity. Long installation times can also damage side resistance, especially for large-diameter, open-ended piles. Examples from the Annacis and Port Mann bridges illustrate reduced capacity associated with re-driving, prolonged installation, and vibratory driving.<br /><br />The presentation proposes a construction influence factor (CI) to account for installation effects in capacity calculations. Preliminary values include 1.0 for normally installed or closed-end piles, 0.55 for the original pile length after re-driving, 0.5 for vibratory installation, and 0.6 for slow jacking. These values are guidance only: CI can vary with conditions, and project-specific load testing is needed to confirm it.

Keywords

driven piles

installation methods

pile capacity

cohesive soils

static load tests

setup effect

re-driving

vibratory hammer

shaft resistance

construction influence factor