On the Study of Pile Driving Formula Based on Blow Counts

Abstract

Accuracy of predicting pile capacities by pile driving formulas have been investigated. Five test piles were driven up to a depth of about 9 m of clay deposit and the penetrations due to final blows were recorded. The pile bearing capacity of each pile was predicted using 6 different pile driving formulas and the predicted pile capacity was compared with measured pile capacity from the pull up tests. Hiley formula, Modified Engineering News Record (ENR) formula, Janbu formula, Dutch formula, Danish formula, and Gates formula were used. The performance and accuracy of each formula was evaluated and the correlation coefficient of each pile driving formula was determined for a more accurate pile capacity prediction. Methods used to evaluate the performance of each formula were; (1) the best fit line for Q p versus Q m (2) cumulative probability for Q p /Q m and (3) the arithmetic mean and standard deviation for Q p /Q m . From the study, it was found that using Dutch formula provided the most accurate pile capacity estimate compared to the other formulas with an average of 7% deviation from value obtained from the field pull up test. It was followed by the Danish formula, Janbu formula, Hiley formula, Modified ENR formula, and Gates formula. The ability to predict the accuracy of estimating pile capacity using an appropriate method is very important and valuable to contractors, developers, geotechnical engineers, and manufacturers.

Contrasting soil penetration resistance values acquired from dynamic and motor-operated penetrometers

“…This formula assumes that all the energy loss is absorbed by the shaft and there is negligible friction between the penetrometer and soil. The formula is commonly used in geotechnical engineering, also for calculation of pile bearing capacity (Ali et al, 2011). For a complete derivation of the formula, see Minasny and McBratney (2005).…”

“…Obviously energy loss is higher for stronger soil and cannot be accounted for in the calculation. While there are other formulae that attempt to take into account the friction (see Ali et al, 2011) it proves to be difficult to determine the fudge factor empirically. We believe that comparison of penetration strength should be made on the penetration resistance value (in MPa) which is widely used.…”