Study on the Applicability of Vertical Bearing Capacity Calculation Methods for Large-Diameter Pipe Piles Based on a Static Load Test Database

Large-diameter steel pipe piles (LDSPPs) are increasingly used for offshore wind turbines, marine terminals, long-span bridges, and other heavily loaded infrastructure. Their axial capacity is commonly estimated using design methods developed or calibrated mainly for smaller driven piles, and the extent to which those methods remain reliable at large diameters is not yet well established. This study compiles a database of 41 high-quality field static load tests from 21 sites, including 31 compression tests and 10 uplift tests, for piles with outer diameters of 0.8–3.0 m, embedded lengths of 9.86–100 m, and measured capacities of 1.21–71.56 MN. Associated cone penetration test (CPT/CPTU) profiles and geotechnical information were assembled to establish a consistent evaluation framework for eight axial capacity prediction methods, comprising six CPT-based methods (UWA, ICP, NGI, Fugro, Unified CPT, and Dutch CPT) and two conventional methods (API and MOT). Predictive performance was characterized using the mean and coefficient of variation (COV) of the calculated-to-measured capacity ratio and the root mean squared logarithmic error (RMSLE), with additional examination of pile geometry, effective stress, site conditions, pile age, and loading direction. Parameter sensitivity and site-cluster bootstrap frameworks were also introduced to assess uncertainties associated with geotechnical inputs and method rankings. The existing field-based comparison of the original six methods indicates that the four established CPT-based approaches (UWA, ICP, NGI, and Fugro) generally provide mean capacity ratios closer to unity (0.89–1.20) and lower COVs (0.42–0.51) than API (1.29 and 0.52, respectively). Shaft resistance was generally predicted more reliably than base resistance, whereas base-resistance predictions exhibited substantial scatter, potentially associated with uncertainties in soil plugging and internal shaft resistance. Prediction errors vary with pile geometry and stress conditions, although no consistent deterioration in accuracy with increasing pile diameter is evident within the investigated range. Apparent differences between offshore and onshore sites, pile ages, and loading directions remain subject to database imbalance and potential confounding factors. These findings highlight the importance of considering resistance components, plugging behavior, geotechnical input uncertainty, and statistical robustness when assessing the applicability of axial capacity prediction methods for LDSPPs.