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For many years the main method of drivability/resistance correlation were the dynamic formulae. It's interesting that the Engineering News formula and the Vulcan #1 hammer came into the world at about the same time. Vulcan featured the Engineering News formula in its literature as early as 1906, and this continued until the 1970's.

We explore various topics regarding these, including the following:

The dynamic formulae first made driven piles tested piles, as the resistance of the pile could be estimated by the blow count of the hammer, which is readily monitored during driving. The Engineering News formula had the additional advantage that only the hammer's rated striking energy and the blow count are necessary to make an estimate of the pile's resistance.

Although the limitations of the dynamic formulae were recognised by Vulcan (if not by some engineers,) for many years they were the accepted method of correlating resistance to hammer performance. Some specifications--especially for timber piles--still call for the Engineering News or other dynamic formulae.

Vulcan included charts in its literature based on the Engineering News formula. A more convenient way to use this formula is the interactive chart at Vulcan Foundation Equipment's website. That interactive chart actually contains two formulae: the Engineering News formula traditional in Vulcan literature, and the Gates Formula, featured extensively in FHWA literature and a useful tool for preliminary estimation of hammer size.

Other Monographs on Dynamic Formulae

Design of Timber Foundation Piling for Highway Bridges and Other Structures

James S. Graham
Ritter, Micheal A.; Duwadi, Sheila Rimal; Lee, Paula D.Hilbrich, eds. 1996. National Conference on Wood Transportation Structures. Gen. Tech. Rep. FPL-GTR-94. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 494 p.

Presented information on structures supported by treated timber piling, including details of the East Side (FDR) Drive in New York City. Determined the average and mean Factor of Safety of the Engineering News Formula for 43 site-specific cases. Showed examples of present-day design for timber piling supported by friction, end bearing, or a combination of both. Considered practical and theoretical geotechnical design criteria. Furnished timber piling and preservative specifications. Reviewed durability for foundation, fresh water, and marine piling. Addressed environmental considerations. Concluded that local Geotechnical engineers apply empirical experience to design treated round timber foundation piling.

Pile Driving Formulas for Friction Piles in Sand

Roy E. Olson and Kaare Flaate

In this investigation, seven different pile-driving formulas were used to predict the capacityie of timber, concrete and steel friction piles. A linear relationship was assumed between the measured and computed pile capacities, and the reduced major-axis type of linear regression analysis was used to determine the slope and intercept of the regression line. Correcation coefficients were used as measures of the scatter about the regression lines. The statistical data were then used to adjust the formulas to improve their accuracy. Conclusions were then drawin regarding the accuracy of the various formulas.

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