Foundation Specifications 0101

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CALTRANS FOUNDATION MANUAL

In the early 1950's a new type of pile driving hammer was introduced - the Diesel Hammer.

Basically, it is a rudimentary one cylinder diesel engine. It is fed from a fuel tank and pump

mounted directly on the hammer, in contrast to air and steam hammers which require an

external energy source. Simple to operate, diesel hammers are commonly used on most

bridge contracts today.

Single Acting Diesel Hammers. The fundamental makeup and operation of all

diesel hammers are similar. They consist of a cylinder-encased ram, an anvil block, a

lubrication system, and a fuel injection system which regulates the same amount of fuel to

each cycle. New models added a variable fuel metering system which can change the energy

delivered by the ram, thereby making them more versatile for varying soil conditions. The

energy imparted to the driven pile is developed from gravitational forces acting on the mass

of the piston. Refer to Figure 7-13.

The operational cycle of the single acting diesel hammer is shown on Figure

7-14 and is described in the following paragraphs.

To start operations, a cable from the crane lifts the ram. At the top of the stroke, the lifting

attachment is "tripped" and the ram allowed to drop.

The ram falls by virtue of its own weight and activates the cam on the fuel injector which

injects a set amount of fuel into the cup-shaped head of the impact block. As soon as the

falling ram passes the exhaust ports, air is trapped in the cylinder ahead of the ram, and

compression begins. The rapidly increasing compression pushes the impact block (anvil)

and the helmet immediately below it against the pile head prior to the blow.

Upon striking the impact block with its spherically shaped leading end, the ram drives the

pile into the ground and, at the same time atomizes the fuel which then escapes into the

annular combustion chamber. The highly compressed hot air ignites the atomized fuel

particles and the ensuing two-way expansion of gases continue to push on the moving pile

while simultaneously recoiling the ram.

As the upward flying ram clears the exhaust ports, the gases are exhausted and pressure

equalization in the cylinder takes place. As the ram continues its upward travel, fresh air is

sucked in through the ports, thoroughly scavenging and cooling the cylinder. The cam on

the fuel injector returns to its original position allowing new fuel to enter the injector for

the next working cycle. The operator may stop the hammer manually by pulling a trigger

which deactivates the fuel supply.