Once that Vulcan hammer is ready to work, the next question is: will it drive the pile? This page deals with the issue of how to estimate that drivability.

Driven piles are unique in that their driving resistance--and thus their axial capacity--can be estimated/verified by the performance of the hammer during driving. That's why the Pile Driving Contractors Association's motto is "A Driven Pile is a Tested Pile." The methods for correlating the hammer performance with the pile resistance have changed over the years, and Vulcan hammers have been and are involved in almost all of the changes that take place.

Dynamic Formulae

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 early 1970's.

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 weaknesses of the dynamic formulae were recognised by Vulcan (if not by many engineers,) until the 1970's 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.

Wave Equation

It's interesting to note that the individual who made the wave equation for piles a practical reality--E.A.L. Smith--was Raymond Concrete Pile's chief mechanical engineer and an equipment designer. Wave propagation in piles is a dynamic phenomenon, and until recently dynamic phenomena were not an important part of geotechnical engineering.

Today both GRLWAVE and TNOWAVE--the most popular wave equation programs--have Vulcan hammer data included in their hammer database. We feature three different wave equation programs that can be used to evaluate the drivability of Vulcan hammers:

• WEAP (including SPILE for estimation of ultimate pile capacity, which is related to drivability)
• TTI/Microwave
• TAMWAVE -- our own online wave equation program, for academic use

We also have information on ZWAVE, Vulcan's own wave equation program in the 1980's, and the closed form solution of the wave equation for piles.

Dynamic Pile Analysis

Vulcan first encountered dynamic pile analysis offshore, where this technique, like many others, was first applied. A description of the technique from the late 1970's is found here. As with other impact hammers, Vulcan hammers are subject to dynamic analysis in the field.

Other Information

• Efficiency and Energy Transfer in Pile Driving Systems