Variability in jacking resistance of adjacent steel pipe piles under controlled pile installation

The pile bearing capacity varies even within the same site. This study aims to gain a better understanding of the effect of pile penetration techniques on the variability of bearing capacity. The study uses data from 83 jack-in test piles to explore the variations in penetration resistance at the pile head, base, and shaft. The semivariance increases with an increase of the horizontal distance, so we focus on the semivariance between 5 m range, whose error was defined as the error due to piling workmanship. The analysis shows that the errors follow a lognormal probability distribution, and the coefficient of variation (COV) in penetration resistance at the heads and bases is about 10%, while the COV in extracted resistance varies widely, with a range of 5–25%. Little difference in the variations due to piling workmanship was observed among different penetration motions, speeds, and soil types.