Pile driver

For other uses, see the mechanical device used in construction.

A crane with a pile driver.

A pile driver or piledriver is a mechanical device used to drive piles into soil to provide foundation support for buildings or other structures. The term is also used in reference to members of the construction crew that work with pile-driving rigs.

Pile drivers include a heavy weight placed between guides so that it is able to freely slide up and down in a single line. The weight is raised, which may involve the use of hydraulics, steam, diesel, or manual labour. As the weight reaches its highest point, the system contains mechanical energy stored as potential energy. The weight is then released, and the mechanical energy is converted to kinetic energy which drives the pile into the ground.

History

There are a number of claims to the inventor of the pile driver. A mechanically sound drawing of a pile driver appeared as early as 1475 in Francesco di Giorgio Martini's treatise Trattato di Architectura. Also, several other prominent inventors — James Nasmyth (son of Alexander Nasmyth), watchmaker Sebastiaan Valouè, Count Giovan Battista Gazzola, and Leonardo da Vinci — have all been credited with inventing the device. However, there is evidence that a comparable device was used in the construction of Crannogs at Oakbank and Loch Tay in Scotland as early as 5000 years ago.

Types

Ancient pile driving equipment used manual or animal labor to lift heavy weights, usually by means of pulleys, to drop the weight onto the end of the pile. Modern piledriving equipment uses various methods to raise the weight and guide the pile.

Diesel hammer

A modern diesel pile hammer is a very large two-stroke diesel engine. The weight is the piston, and the apparatus which connects to the top of the pile is the cylinder. Piledriving is started by having the weight raised by auxiliary means - usually a cable from the crane holding the pile driver - which draws air into the cylinder. The weight is dropped, using a quick-release. The weight of the piston compresses the air, heating it to the ignition point of diesel fuel. Diesel fuel is added/injected into the cylinder. The mixture detonates, transferring the energy of the falling weight to the pile head, and driving the weight back up. The rising weight draws in more fuel-air mixture, and the cycle starts over until the fuel runs out or is stopped by the pile crew.

From an army manual on pile driving hammers: The initial start up of the hammer requires the piston (ram) to be raised to a point where the trip automatically releases the piston, allowing it to fall by gravity. As the piston falls, it activates the fuel pump, which discharges a metered amount of fuel into the ball pan of the impact block. The falling piston also blocks the exhaust ports, and com- pression of fuel trapped in the cylinder begins. The compressed air exerts a pre-load force (approx. 44,000 lbs. or 20,000 kg.) to hold the impact block firmly against the drive cap and pile. At the bottom of the compression stroke, the piston strikes the impact block, atomizing the fuel and starting the pile on its downward movement. In the instant after the piston strikes, the atomized fuel ignites, and the resulting explosion exerts an even greater force on the already moving pile, driving it further into the ground. The reaction of the explosion rebounding from the resistance of the pile drives the piston upward. As the piston rises, the exhaust ports open, releasing the gases and force of the explosion into the atmosphere. After the piston stops its upward movement, it again falls by gravity to start another cycle.

Hydraulic hammer

A hydraulic hammer is a modern type of piling hammer used in place of diesel and air hammers for driving steel pipe, precast concrete, and timber piles. Hydraulic hammers are more environmentally acceptable than the older, less efficient, hammers as they generate less noise and pollutants.

Hydraulic Press

Specialty equipment which installs piles by clamping onto the pile itself and hydraulically pressing it into the ground utilizing reaction force, preferably of previously drivin piles. Some types of Press equipment operate free from excessive noise and vibrations allowing for the installation of piles in close proximity to occupied structures where traditional methods may threaten the stability.

Such equipment and methods are specified into portions of the internal levee system in New Orleans after hurricane Katrina as well as many projects around the world where noise, vibrations and limited access are a potential problem in the engineering phase.

Unlike other systems the Press-In Method from Giken America is a top down construction system which actually rides on top of the installed piles and utilizes the reaction force from them in order to install the next pile with static force. The Press-In Method can be accomplished with the full GRB system that converts steel sheet piles into a moving work platform. The GRB system is a combination of the "Silent Piler" (with or without the simultaneous augur), a pile mounted Crane named the "Clamp Crane" in order to pitch the piles and the "Pile Runner" which carries the piles down the pile line without anything even touching the ground.

Vibratory Pile Driver/Extractor

A vibratory pile driver on a steel H-pile powered by a diesel engine.

Vibratory pile hammers contain a system of counter-rotating eccentric weights, powered by hydraulic motors, and designed in such a way that horizontal vibrations cancel out, while vertical vibrations are transmitted into the pile. The pile driving machine is lifted and positioned over the pile by means of a crane, and is fastened to the pile by a clamp and/or bolts. Vibratory hammers can either drive in or extract a pile - extraction is commonly used to recover steel "H" piles used in temporary foundation shoring. Hydraulic fluid is typically supplied to the driver by a diesel engine powered pump mounted in a trailer or van and connected to the driver head through a set of long hoses. Vibratory pile hammers are often chosen to mitigate noise, as when the construction is very close to residence or office buildings, or when there is not enough vertical clearance above the foundation to permit use of a conventional pile hammer (for example when retrofitting additional piles to a bridge column or abutment footing). Hammers are available with several different vibration rates, ranging from about 1200 vibrations per minute to about 2400 VPM; the vibration rate chosen is influenced by soil conditions at the site and other factors such as power requirements and purchase price of the equipment.

See also

• Deep foundation
• Auger