A comparative study of ten pile driving formulas is described. The formulas are the Danish, ENR, Modified ENR, Eytelwein, Gates, Hiley, Janbu, Navy-Mckay, PCUBC, and Weisbach. The ultimate load for each of sixty-three pile load tests was determined using the Q-D over 30 method to determine ultimate capacity.
The predicted pile capacity was divided by the measured capacity to obtain normalized values. Statistical analyses for coefficient of variation were performed on the logarithm of the normalized capacities to determine which formula provided the most consistent prediction of pile capacity. The Gates formula proved to be the best and the widely used ENR one of the worst with a coefficient of variation approximately 2-3 times higher than that for the Gates formula.