Pile Driving Hammers
As its name implies, a pile driving hammer is used to drive a pile into the ground.
There are many types of pile driving hammers.
There are:
There is some tables about the efficiency, guidance and possible defects in displacement piles.
The simplest form of hammer, the drop hammer consists of a shaped a block of cast iron or steel, with a mass range of 1500 to 8000 kg. The hammer has a lug which fits into the leader of the piling frame, and a lifting eye for the winch rope.
The hammer is raised by a winch and then released to fall under gravity on to the pile head.
Drop hammers are best suited for driving piles in clay, marl or compact sand.
Single-acting Steam of Compressed Air Hammer
This type of hammer is similar to a drop hammer in that the hammer falls freely under gravity. The blows are provided by a heavy falling cylinder.
The cylinder slides up and down a fixed piston. The cylinder is raised when compressed air or steam is forced into the piston through the inlet value via the hollow piston rod. When the cylinder rises to the exhaust value, air and steam are exhausted, causing the cylinder to fall under gravity onto the head of the pile.
Normal working speed is about 40 blows per minute, with a maximum of 60 blows per minute. The height of drop of the cylinder is usually 1.4 m.
This hammer is more efficient than the drop hammer and can be used in the same soil conditions as for the drop hammer.
The double-acting hammer, is powered both upwards and downwards by compressed air or steam. It consists of a cylinder, the base of which is the anvil block. The cylinder, which is stationary and rests on top of the pile, carries a light piston or ram which delivers a large number of rapid blows which keep the pile moving.
The driving force is less than that of a drop hammer or single-acting hammer, but is works fast, delivering 90 to 225 blows per minute.
Double-acting hammers are suited to sites where the headroom is restricted and where the use of other types of hammer are prohibited. The double-acting hammer is also used in underwater piling where the hammer is activated by means of compressed air.
To start the diesel hammer, the ram in the cylinder of the diesel hammer is raised to the top of its stroke and then allowed to fall freely. On falling, a measured amount of fuel is injected into a cup located at the base of the cylinder. The falling ram compresses the air and the impact atomizes the fuel which then ignites. The resulting explosion of the fuel imparts an additional 'kick' to the pile which is already moving downwards under the impact of the ram. At the same time, this explosion raises the ram ready for the next down-stroke. Burnt gases are expelled from the cylinder on the up-stroke of the ram.
The cycle of operation is repeated continuously, giving 60 blows per minute.
This type of hammer is quite noisy. However, it is very efficient and is the most popular type of hammer used in the piling field.
The equipment consists of a vibrator mounted on the pile head. This unit vibrates the pile and temporarily negates the friction between the pile and the soil. The pile therefore sinks into the subsoil under its own weight and the weight of the vibrator.
There are several vibratory system in the market, such as Tomen and the Bodine Resonand Pile Driver.
This type of hammer is comparatively silent but can only be used in granular soil, such as gravel an loose sands.
