Field measurements were performed about the negative skin friction on piles whose diameters were 50 cm and the lengths were about 40 m. One of the four piles was free on the bead, and the others were foundation piles of a jib crane, which were asphalt coated piles to decrease the negative skin friction. While the ground subsided 2 cm in 1 year after the pile driving, the free-headed pile subsided 2 mm, the axial force of which became 90 t, though these values of the foundation piles showed only the magnitudes produced by the axial load on the pile head. The ways of estimation by the current design criteria of port and harbour construction, by Bjerrum, by Zeevaert, and by the authors are examined by the comparison with the measured values.
　The results of the measurements when the crane was moving are discussed, and the observations of the old foundation which was removed because of damages by the negative skin friction and a design criterion of asphalt coating are reported as appendices.