Evaluation of several design methods for calculating axial compression capacity of large diameter open-ended piles

The efficacy of eight pile design methods to calculate capacities of large diameter open-ended pipe piles (LDOEPs) is explored using data made possible by the 2016 release of the U.S. Federal Highway Administration (FHWA) deep foundation load test database. The analyses were performed using APILE Offshore 2019 software by Ensoft Inc. Capacities were predicted using four SPT based methods proposed by (1) FHWA; (2) the U.S. Army Corps of Engineers; (3) American Petroleum Institute (API); and (4) the Lambda method; and four recently adopted CPT based methods proposed by (5) Norwegian Geotechnical Institute (NGI); (6) Imperial College Pile (ICP); (7) University of Western Australia (UWA); and (8) Fugro. Three plugging conditions were considered for each method, and predictions were compared to the interpreted capacities from static load test data using the Original and/or Modified Davisson Criteria per American Association of State Highway and Transportation Officials (AASHTO) recommendations. The study demonstrates that CPT based methods are somewhat superior to SPT methods, but all methods exhibit scatter between measured and predicted capacities with the computed capacity off by a factor of two in many cases. In particular, API and the Revised Lambda methods best predict pile capacity when using SPT data, while the NGI method seemed to be the best among the CPT methods and arguably the best method overall. Seven of the eight methods (all except NGI) better predicted pile capacity considering that the piles are unplugged and ignoring contributions of soil internal friction on the pile inside diameter. FHWA was the least conservative and the worst predictor of LDOEP capacity.