Trudging through a man-made trench at Manson’s North Extension Stabilization Step 1
(NES-1) project at the Port of Alaska in Anchorage, Piledriver John Cowin grabs the end of a suspended vibratory hammer and connects it to a pair of sheet piles sticking out from the ground. After securely fastening the chain to the sheet pile, he signals to the Manitowoc 4100 crane operator to begin the pile extraction.
When it comes to the replacement and construction of marine infrastructure such as wharves, piers, bridges, etc., pile extraction (or “pulling pile”) is the standard process used to remove existing foundational structures.
What Are Piles?
The most common type of pile is a long, cylindrical column that is driven into the ground to support various structures including marine infrastructure. Depending on the project, the quantity of piles for installation and extraction can range from dozens to several hundred. Piledrivers often work with several pile types including sheets, pipes, and H- and I-beams.
These piles often serve as temporary or permanent foundations for in-water and over-water infrastructure, according to Senior Estimator Bill Shorey.
“Historically made of timber due to availability and cost, pile types now typically range from concrete to steel due to the required load capacity of new structures,” Bill explains. “Timber piles were often treated with creosote—a wood preservative made of tar—to withstand harsh water conditions, but it’s harmful to the marine ecosystem.”
What Is Pile Extraction?
Pile extraction can be completed in two ways: The first is with a vibrational (vibro) hammer—a metal, box-shaped piece of construction equipment that helps drive or extract piles through vibrational movement. The second way is the “press-in” method, where a hydraulic-powered box uses upward force while pushing into the ground to remove columns. This method is vibration and noise-free.
“There are several factors to consider when it comes to pile extraction, as it is a complex process that takes know-how and confidence from both the engineering and operations sides,” says Construction Superintendent Drew
Edwards.
“The two groups work together to select and review proper equipment, pile type, and site conditions, and to implement efforts to protect natural habitats and coastal communities.”
Selecting the Right Hammer
Knowing which hammer to use is by far the most important part of the pile extraction process. Varying in model and size, selecting the right hammer for a pile extraction job depends on the pile type, size, and site conditions.
Vibro-Hammers
Power-driven hydraulic vibro-hammers can be installed via crane or excavator for pile-pulling jobs.
Crane-suspended vibro-hammers are connected to a crane and can be attached to piles with hydraulic clamps. This method disrupts the physical state of the soil through oscillation—back and forth motion—which reduces friction between the pile and natural material, which allows the pile to be removed quickly.
Notable advantages for crane-suspended vibro-hammers include performance, adaptability, cost, and underwater use—which is beneficial for marine contractors.
Excavator-Mounted Hammers
These vibro-hammers are attached to an excavator for landside pile extractions. Excavator-mounted hammers are preferred due to their easy set-up, extraction power, and mobility.
Press-In Extraction
The press-in extraction method consists of a hydraulic powered box that clamps to installed piles, generating an upward force by pushing into the ground to remove the columns—which can be likened to lifting a car with a jackstand. This method is great for construction crews working in sensitive environments because of the reduced noise and elimination of working at a tall height, which reduces falling hazards.
Site Conditions
Common site conditions encountered on pile extraction projects include sand, gravel, glacial till, or clay-like material—the latter of which has a stronger bond between the pile and natural material. With the use of engineering software and client record-keeping, most vibro hammer suppliers provide exact specifications and offer expert advice for contractors working in a variety of site conditions.
Environmental Safety
Vibro-hammers are not only the go-to pieces of construction equipment for pile extraction work, but they offer a positive environmental impact by producing less noise in heavily populated areas and natural environments. Equipped with water-tight seals and covers, vibro-hammers produce little to no (environmentally friendly) leaks and are great for in-water and over-water work.
As the final sheet pile of the day is extracted at the NES-1 project, the pile-driving crew steps aside, allowing the crane operator to skillfully swing the pile toward the waiting forklift operator. The forklift then carries the remaining pieces to the dump site, marking the completion of another productive day of pile extraction.
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