A Driveability Study of Precast Concrete Piles in Dense Sand-Article

Article

Pdf Summary

The study evaluates the driveability of precast concrete piles installed in very dense sand at the Blessington test site in Ireland. Five 275 mm square piles were driven toward a target depth of 7 m using a 4-tonne hammer. The main concerns were whether the hammer could overcome soil resistance and whether driving stresses would damage the concrete.<br /><br />A one-dimensional wave-equation analysis used the Alm and Hamre (A&H) method to estimate static resistance to driving (SRD), including friction fatigue. The analysis predicted that the available hammer could install the piles, but that stresses could become high. Limiting hammer drop heights to 400–600 mm helped manage stresses while maintaining practical driving rates.<br /><br />Four piles reached the target depth; one, PC3, failed about 1.3 m short after cracking and spalling near the pile head. Testing showed that PC3’s concrete cores had lower strength than those from the other piles. Measured driving stresses on a neighboring instrumented pile exceeded the stress level considered allowable for PC3’s concrete, indicating that its weaker material was the likely cause of failure.<br /><br />Dynamic monitoring showed that driving resistance increased with depth and that shaft friction decreased as the pile advanced, confirming the importance of accounting for friction fatigue. The measured resistance was broadly consistent with the A&H predictions, while the UWA-05 and IC-05 methods gave higher, more conservative estimates. The API method substantially underestimated driving resistance and was therefore non-conservative for this application.<br /><br />The case study highlights the value of driveability analysis and pile monitoring, particularly in dense soils. Where high driving stresses are predicted, stronger concrete or longer curing times may reduce the risk of pile damage.

Keywords

precast concrete piles

driveability

dense sand

wave-equation analysis

static resistance to driving

friction fatigue

driving stresses

pile damage

Alm and Hamre method

dynamic monitoring