It's always good to hear pile driving superintendents say that Vulcan hammers are "hard driving hammers." As edifying as that is for the salesman and equipment manufacturer, it isn't very informative from an engineering standpoint. Estimating the drivability of a given pile with a certain hammer is an important part of the design and installation process of a driven pile. Some questions that need to be answered are as follows:

• What maximum blow count (blows per inch, foot, centimetre or metre) of penetration will be experienced during driving?
• How does this compare with the refusal criterion associated with the specific hammer?
• How high do the driving stresses--tension and compressive--rise in the piles during driving?
• How long does it take to drive the pile?

This section deals with the issue of how to answer all of these and more questions, which are related to the issue of "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. Although Vulcan hammers are featured in this section, most of these principles apply to any impact hammer. Some of the topics are featured below.

This subject is treated in greater detail in the Vulcanhammer.info Guide to Pile Driving Equipment, which includes a worked example.

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

The wave equation for piles has a long history; much of that history is described here, on our companion site. It was a long process to sell the basic concept of wave propagation in piles, and then making their modelling a practical tool for estimating hammer-pile-soil performance during driving.

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 GRLWEAP and TNOWAVE--the most popular wave equation programs--have Vulcan hammer data included in their hammer database. On this site we feature a number of aids to estimating drivability of Vulcan and many other types of hammers using the wave equation:

• Wave equation programs for free download or use:
  • 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
• Information on wave equation programs and routines developed by Vulcan or its personnel
  • ZWAVE, Vulcan's own wave equation program in the 1980's
  • Closed form solution of the wave equation for piles, the definitive work on the subject, from the 1990's
  • The Wave Equation Page for Piling, the final legacy of Vulcan's involvement with the wave equation and the beginning of a new era
• Information relating to drivability and hammer performance
  • Efficiency and Energy Transfer in Pile Driving Systems
  • Design and Construction of Driven Pile Foundations, a comprehensive reference on the subject

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.