About the Influence of Time on the Bearing Characteristics of Precast Driven Piles-Paper

Paper

Pdf Summary

The paper examines how the axial resistance of precast driven piles changes after installation (“set-up”) and evaluates practical prediction methods using field tests and project data. Set-up occurs mainly through increased shaft friction; toe resistance generally remains constant or may decrease slightly. In cohesive soils, it is associated chiefly with dissipation of excess pore pressure and creep. In sands, ageing-related changes in soil structure and radial stress are thought to contribute, though mechanisms remain incompletely understood.<br /><br />Two field investigations produced contrasting results. At Constance, shaft resistance increased substantially—more than threefold relative to the one-day value by 76 days—while toe resistance remained stable. At Emden, resistance showed no significant time-dependent increase. Broader project data likewise showed considerable variability, influenced by soil conditions and testing history.<br /><br />The commonly used Skov–Denver semi-logarithmic model broadly matched data for sands and normally consolidated cohesive soils, but did not adequately reflect the variability of cohesive soils. An approach accounting for overconsolidation ratio and plasticity performed reasonably for normally consolidated clays; a method based on undrained shear strength was not supported by the evaluated data. Predictions tended to overestimate resistance in overconsolidated soils.<br /><br />The authors recommend assessing set-up over a period relevant to construction, typically around 60 days. For sands, a 30% resistance increase may be assumed after 60 days, or estimated with the Skov–Denver method. For cohesive soils, suggested increases after 60 days are about twofold in normally consolidated soils and 1.3-fold in overconsolidated soils. Repeated load tests are recommended to verify set-up and predictions, particularly in cohesive ground.

Keywords

precast driven piles

axial resistance

pile set-up

shaft friction

toe resistance

cohesive soils

sands

Skov-Denver model

overconsolidation ratio

field load tests