The best known setup for pile driving equipment is a crane and a set of full-length (of the pile and hammer) leaders, attached to the crane in a variety of ways. But another alternative is to use a “stub” leader, i.e., one that is very short, and a template to align, position and guide the pile. This is traditionally associated with steel piling, so we’ll look at this first.
A Vulcan 040 driving pile off of Ingram’s barge, 1966.
Another 060 driving pile for McDermott, February 1976. Photos in the same sequence as this one graced Vulcan’s literature during the late 1970’s and early 1980’s, including Vulcan’s one and only Spanish brochure.
Vulcan 060 driving pile. The leaders are typical Vulcan construction, using beam yokes and pipe legs, with the forward legs as support for the H-beams that actually guided the hammer. The platform acts as a driving template; the ability to use a stub leader made pile driving much simpler. It was not until the early 1980’s that Vulcan took the lead of platform designers and used a light weight, pipe construction leader. Note also that the pipe is marked; this made taking the blow count easier. As the pile was driven in to the sea bed, the number of blows per foot were recorded to help insure that the pile had the resistance to load (uplift was most important with offshore platforms) it needed to keep the platform in place.
Another view of Santa Fe’s Vulcan 560 at work. This wasn’t the ideal way to lean the hammer, but one of the things that make Vulcan hammers popular was their ability to perform when misused or mishandled.
A Vulcan 560 in Vulcan manufactured offshore leaders driving pile for the Korean contractor Daelim in 1991. Although Vulcan would have considered this an “onshore” job, it is a classic example of an offshore style hammer used to install a steel jacket. Note that the jacket is acting as the template, which in turn aligns and positions the piles. The leader and hammer assembly is lowered through the conical, adjustable stabbing bell and than the pile is threaded onto the pile cap, the assembly assuming the batter of the piles. The assembly is suspended from the hinged lifting bale at the top of the leaders. As the hammer drives the pile, the leaders are lowered to keep up with the hammer’s progress.
For these hammers the platform itself is the template, the piles are driven from the top through the legs. Most conventional platforms had angled legs so the hammers almost invariably drove on a batter, which gave rise to the “stick-up” problem, more about that below.
But using stub leaders and a template isn’t restricted to steel piles; it has also been done on concrete piles, as can be seen below.
Misener Marine using a Vulcan 010 hammer in a stub leader with a template aligning the concrete piles (as can be seen at the water line) at Port Canaveral, November 1974.
Cleary Brothers Construction, West Palm Beach, FL, driving 20″ sq. prestressed concrete piles on a batter with a Vulcan 0R operated with an Ingersoll-Rand 600 CFM compressor and a barge mounted Lima Crane on 1220′ bridge across St. Johns River between Seminole and Volusia Counties, State Road 46. Courtesy of Dixie Contractor.
A Vulcan 020 getting ready to drive concrete cylinder piles for the Fort Randall Bridge Project, 10 October 1963. The contractor was Peter Kiewit & Sons. The stub type leaders were fabricated by Conmaco. This setup also included suspension type cables at the top of the hammer. It presaged most of Vulcan’s offshore setups during the next several decades.
Vulcan 535 hammer driving piles near Trenton, NJ, during the mid-1990’s. The contractor was Bellezza. A template was used (below the bottom of the photo) to align the concrete cylinder pile.
Vulcan 530 Offshore style hammer in Vulcan offshore style leaders being lifted to drive concrete cylinder piles in Dover, DE, June 1998. You can see the template at the bottom of the photo surrounding the concrete pile. The template is maintaining the pile at a plumb (vertical) angle during driving. The job included some predrilling and that helps to align the pile as well.
Warrington-Vulcan hammer driving square concrete piles on a batter. Note that the hammer is suspended directly from the crane, and that the leaders are attached to the hammer. Pile is on a batter. Photo Courtesy of Miami Herald, permission granted by Kathyn Kelly.
From a contractor’s standpoint, handing hammers in stub leaders requires a considerable level of skill from the crane operator, but the weight savings and ability to handle the hammer in difficult situations makes the use of stub leaders, when possible, a very attractive option.
Engineering Aspects of Stub Leaders
From the photos above, you can see that piles can be driven with stub leaders either plumb or on a batter. Plumb piles are not much different with stub leaders than with conventional leaders: the key is to have the hammer straight and square on the pile, which means that the leader setup should be balanced to hang straight and side forces on the hammer be avoided.
With batter piles, since the offshore industry used them (and still does) intensively, the most complete specification for such piles is the American Petroleum Institute’s RP2A specification. With stub leaders the pile basically supports the hammer during driving, and the hammer in turn loads the pile with both the impact loads and the static load of the hammer assembly, which in turn acts both parallel and perpendicular to the axis of the pile. Basically there are two important engineering aspects to configuring driving batter piles with stub leaders on a template:
- Column buckling due to the weight of the hammer acting on the axis of the pile.
- Beam loading of the hammer due to the component of the weight which acts perpendicular to the axis of the pile. This creates a cantilever beam with a maximum bending moment at the template. Obviously the weight of the hammer assembly (along with the weight of the pile) will induce bending stresses. These stresses are both tensile and compressive, and both are important to the structural integrity of the pile during driving. The template must also be designed to handle the loads and moments on its structure.
With steel piling, the combined weights of hammer assembly and pile limit the permissible length of the “stick-up” of the pile. Steel piles are easily spliced and added on to, so piles which are much longer than the stick-up can be drive. (Piles which are much longer than practical lengths of conventional leaders can be driven as well.) With concrete piles, these can be splices but there is less flexibility and less resistance to bending moment with splices, which limit the possibilities of driving these with stub leads on a batter. (The ability or lack thereof of concrete to withstand bending stresses also complicates the situation.)
One more important point: the weight of the hammer assembly cannot generally be assumed to be at the pile head, but above it. That’s why the center of gravity information is so important for offshore driving, which led to Vulcan tips such as this.
Stub leaders combined with templates is an attractive option for driving piles, but proper engineering and construction procedures must be followed for successful results.