Pile-Driving Formulas for Friction Piles in Sand

Seven different pile-driving formulas are used to calculate the capacities of 93 timber, precast concrete, and steel piles, for which field load test data are available. The relationship between the computed and the measured capacities is analyzed using the reduced major-axis form of linear regression analysis. The accuracy of the formulas varies with the type of pile. The Gates, Janbu, and Danish formulas yield the highest correlation coefficients, followed closely by the Pacific Coast Uniform Building Code and Hiley formulas. The capacities calculated using the Gow and Engineering News formulas correlate poorly with measured capacities. A statistical adjustment is applied to the formulas to bring them into conformance with the field measurements. The adjusted forms of the Gates, Janbu, and Danish formulas are equally accurate and appear satisfactory for general use. The Gates formula is the simplest to use.