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Leaders is the generic term for the guide which allows the pile hammer to be positioned on top of the pile and then started to drive the pile to its desired head elevation. Although not a prominent part of Vulcan product line, the company did produce leaders of many kinds. This page is also intended to give an overview of pile hammer leaders in general.
Leaders can be broadly categorised in two ways: the method by which they interface with the hammer and the way by which they are connected to (and guided by) the crane.
Pile hammer leaders basically guide the hammer in one of two ways: from the side or from the back.
Vulcan hammers--in commmon with most American pile hammers--were guided from both sides of the hammer, with both hammer and pile between the guides. Leaders such as this are referred to as "U-type" leaders. Most of the Vulcan hammers shown on this site are riding in U-type leaders, both onshore and offshore.
Below: onshore, "U-type" leaders, at the West Palm Beach yard in July, 1973. The hammer (and driving accessory) rode between the two large pieces of square tubing at the bottom of the leaders. Structurally sound, the leader system suffered the disasvantages of a)bolted connections (most contractors preferred pinned ones for easy assembly and disassembly, and b) the protruding triangular gussets on the back caught the air hose.
European practice prefers to guide the hammer from the back. This is generally referred to as a "spud" type leader. The spuds have both a structure for stiffness and rails to interface with the hammer. These rails can be of several types, including round rails (Delmag, Nilens) or two channels back to back (Russian.)
There are several methods of interfacing the leaders with the crane, depending upon the nature of the job and the preference of the contractor:
The most common type of leaders, these are simply suspended from the crane (at some distance.) For most plumb pile applications, they are suitable.
Right: an example of swinging leaders in use. The concrete piles are being driven for a marina in Norfolk, VA, September 2009. The leaders are suspended from the crane and are hanging from the hook block. There is an additional line for the Vulcan hammer as well.
Note: the "headache ball" immediately to the left of the leaders is a useful part of the rigging. Although the hammer is heavy, when the hammer is disconnected from the cable, if there is no weight, the weight of the cable behind the boom point will pull the cable back through the boom point. To remedy this problem requires one of two solutions:
The headache ball, in reality, saves many other headaches on the job.
Below: swinging leaders used to drive a batter pile in Arkansas. Swinging leaders can be used to drive batter piles, but this requires a) leads with good structural integrity (a must in any case,) b) a good place on the ground to stab or secure the leaders, to prevent slippage and c) a skilled, experienced crane operator.
Below: the Vulcan IC-30 diesel hammer in "U-type" leaders. The leader is a swinging type adapted to work as a spud-type leader, similar to the offshore hammers.
An example of a complete fixed leader system is shown below. The leaders themselves were fixed at two points: the boom point and the spotter. Included in fixed leaders is the ability to perform in and out batter using the spotter, to lift and lower the pile and hammer using the headblock and rooster sheaves, and in this case to perform side batter using the moonbeam spotter.
Definition of "in" and "out" batter in English and French, from the Nilens literature, showing a spud type leader.
Below: the "universal saddle adapter," to mate the fixed leaders to the crane boom. Note the ladder on the sides of the leaders are made of rebar, to create a skid-resistant rung.
The hydraulic moonbeam spotter, built for the U.S. government. Unfortunately,even in the 1970's, the moonbeam spotters were being displaced by hydraulic "parallelogram" type spotters, which afforded more flexibility in manoevering the leaders and hammer.
These leaders are a shortened version of swinging leaders. They are intended for use with a template, which both holds the pile in place and sets the batter angle of the pile as well. Virtually all of Vulcan hammers used offshore were run in these leaders.
Right: 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.