Pile Driving Hammer Types

1. The drop hammer Rarely used, except for installing compacted-concrete piles.

2. Single-acting hammers Powered by steam or air pressure, which is used to raise the hammer ram for each down stroke. Gravity and the weight of the hammer deliver the kinetic energy required to drive the pile.

3. Double-acting hammers Generally powered by compressed air or hydraulics, which provides the power to raise the hammer ram and accelerate its fall.

4. Vibratory hammers Paired, oscillating rotating weights connected to the pile delivers anywhere from 0 to 2000 vibrations per minute at low frequency or from 0 to 8000 vibrations per minute for high-frequency hammers to drive the pile to design depth. This type hammer is effective only in granular or cohesiveless soils.

Diesel Pile Hammer Operation -A Five-Stage Cycle

Diesel pile hammers are operating as follows:

1. Raising of piston

For starting the Diesel pile hammer, the ram weight (piston) is raised by means of a tripping device and automatically released at a given height.

2. Injection of Diesel fuel and compression

While dropping, the piston will actuate the pump lever so that a given quantity of Diesel fuel is sprayed on top of impact block. After passing the exhaust ports, the piston will start compressing the air in the cylinder chamber.

3. Impact and explosion

The impact of the piston on the impact block will atomize the Diesel fuel in the combustion chamber. The atomized fuel will ignite in the highly compressed air. The resulting explosive energy will force up the piston.

4. Exhaust

While moving upwards, the piston will expose the exhaust ports.

Exhaust gases will escape and the pressure in the cylinder will equalize.

5. Scavenging

The piston keeps jumping upwards and will draw fresh air through the exhaust ports for scavenging the cylinder, while also releasing the pump lever. The pump lever returns to it’s starting position, so that the pump will again be charged with fuel.

Double-Acting Hydraulic Hammer-Type Pile Driver

The ram in a hydraulic hammer is lifted by hydraulic pressure, and on the downward stroke, additional energy is added to the ram. Pressurized nitrogen pushes the ram down.

Vibratory Pile Drivers

These types of pile drivers use vibration to penetrate the soil strata, using the theory of vibration to reduce the friction between the pile and the soil. These vibrations create soil liquefaction to some degree, causing soil particles to “float” and provide a significant decrease in resistance between the soil and the pile. The pile can be driven into the ground with very little added weight or pressure.

This vibratory head generates oscillations inside a vibration case where eccentric weights are geardriven by one or more motors. The crane from which the vibratory driver is attached must be isolated from the vibration case by rubber or spring cushions. The vibratory pile driver is frequently used to extract previously driven piles since the upward pull is substantially reduced. Vibratory pile drivers work best in noncohesive soils such as gravel and sand. These types of pile drivers also work quite well in water-saturated soils.

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