A Field Study to Analyze Pile Setup Behavior and Comparison of Pile Capacity Methods from CPT-Paper

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The study examined pile capacity and time-dependent setup at a Louisiana bridge project using five instrumented test piles: two 54-inch open-ended concrete cylinder piles, one 30-inch open-ended steel pile, and two prestressed concrete piles. Vibrating-wire strain gauges measured load distribution and helped distinguish shaft friction from end bearing. High-strain dynamic tests were performed at multiple intervals after driving, alongside static or statnamic load tests.<br /><br />Four CPT-based approaches—Schmertmann, De Ruiter and Beringen, LCPC, and Lehane et al.—were compared with measured capacities. Overall, the methods estimated shaft friction reasonably well but were less reliable for end bearing. Schmertmann performed well for the prestressed concrete piles, while Lehane et al.’s method was the most suitable for predicting shaft friction in open-ended piles.<br /><br />All piles showed substantial capacity gain after installation. This setup was primarily caused by increasing shaft friction; end-bearing capacity generally remained nearly constant. The exception was the open-ended steel pile, whose end-bearing capacity increased markedly during the static test, likely because a soil plug formed inside the pile. Similar setup rates for solid and open-ended piles indicated that friction between the pile’s inner surface and the soil plug made little contribution to setup.<br /><br />Capacity development followed an approximately linear relationship with logarithmic elapsed time. The back-calculated setup parameter, A, ranged from 0.31 to 0.41 across the piles. The findings highlight the importance of accounting for setup when interpreting pile tests and comparing measured capacities with CPT-based predictions.

Keywords

pile capacity

time-dependent setup

bridge project

Louisiana

instrumented test piles

shaft friction

end bearing

CPT-based methods

dynamic load testing

soil plug formation