Examination of Open-Ended Pile Capacity Methods in Estimating Axial Response-Paper

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The paper evaluates methods for predicting the axial capacity and load response of open-ended steel piles used in offshore structures. It compares API, ICP and UWA design methods against 21 pile tests in clay and 21 in sand, focusing on how each method estimates total capacity and its division between shaft friction and end bearing.<br /><br />A one-dimensional finite-element model, VIRTUPLUG, is used to represent pile–soil–plug interaction and progressive mobilisation of resistance. The study finds that a method’s accuracy in predicting total capacity does not necessarily mean it correctly predicts the shaft and base contributions.<br /><br />In clay, API generally estimates the distribution of shaft and base resistance better than ICP, although it tends to overestimate shaft friction and underestimate end bearing. A modified API finite-element approach accounts for shaft softening and produces lower total-capacity estimates than the original method.<br /><br />In sand, ICP gives the strongest estimate of the shaft–base distribution. UWA predicts total capacity reasonably well, but its component estimates are biased: shaft resistance is generally underestimated and end bearing overestimated. Adjusting these components can improve their distribution, but the required corrections are not straightforward.<br /><br />Overall, the results show that shaft and end-bearing capacities are interdependent and that fixed correction factors cannot reliably capture their relationship across different pile and soil conditions. The authors recommend numerical modelling to represent nonlinear soil behaviour and progressive failure. They suggest using modified API-based finite-element analysis for clay and pursuing an ICP-based numerical approach for sand; for the modified UWA approach, intermediate correction factors may improve the component estimates.

Keywords

axial capacity

open-ended steel piles

offshore structures

pile-soil interaction

end bearing

shaft friction

API method

ICP method

UWA method

finite-element model