On many projects in the southeast, pile-supported footings are a staple. Numerous pile systems have been developed and utilized across the region, and one that is gaining increased attention in the northern Georgia area is the helical pile system manufactured by Cantsink Manufacturing and installed by Cantsink of Atlanta, the contracting arm of the company.
Cantsink was launched in 1988 as a company focusing primarily on residential structural repairs.
"We developed the piling system about five years ago," note Cantsink assistant manager Andrew Carter, adding that the piles are manufactured by Cantsink Manufacturing at its plant in Lilburn, Ga. "The piles are an alternative to driven or augercast piles, which are more expensive and which cannot be placed in some locations." This sort of pile system, he adds, require no additional support operations such as ready mix trucks or hole casings. Additionally, since the piles are augered into the soil, vibration (as with driven pile systems) is not a factor, and no soil removal is required.
Cantsink's helical piles are constructed using steel pipe, with galvanized pipe being used where soil conditions require it. At the heart — or rather the tip — of each pile is 3/8-inch steel plate pitched like a screw. This "structural helix," as it's called, serves to thread the pile into the soil as it is rotated and pushed downward during the installation operation. Depending on the design of the individual pile, this helical plate has a diameter of 8 inches or 14 inches.
The piles sections are produced in lengths of 5 feet, 7 feet and 10.5 feet. Individual sections are designed to be quickly joined in the field using three 3/4-inch bolts to achieve any length required. All pile components, as well as specialized underpinning brackets which are utilized during structure stabilization projects, are manufactured at the company's Lilburn facility.
"We fabricate everything except the machinery we use," Carter says.
Installation of the piles is handled by Cantsink of Atlanta, the contracting arm of the company. The company handles projects in the northern half of Georgia in an area extending approximately from Macon to the North Carolina and South Carolina state lines.
Generally, when Cantsink's crews arrive at a site, the footing excavations have already been prepared. That means that pile installation can begin immediately.
To actually place the piles, the crew typically utilizes one of several Bobcat S250 Turbo Highflows for pile installation. Each of the Bobcats is outfitted with a drill head, driven by the Bobcat's high-flow auxiliary hydraulics. The drill head is located at the end of an arm extending from the front of the machine; in use, the operator precisely positions it for installation of each pile.
"The arm typically extends about 8 feet in front of the machine," Carter says, though he adds that some projects require extension to 12 feet or even 16 feet. In extremely tight settings, where access is very limited, the piles can also be installed using hand-positioned hydraulic drivers.
For most applications, however, the Bobcats are used. These machines have proven to be well suited to this application, Carter says, though on some projects crews may utilize tracked excavators instead.
A typical Cantsink crew consists of three people — one to operate the pile placement rig, one to handle the steel pile sections and transport them when and where needed, and one to bolt pile sections together as the installation moves ahead.
During installation, the machine operator monitors drill head hydraulic pressure throughout the operation. This gives the operator a real-time indication of the soil's strength, and thus the pile's capacity, at the tip elevation of the pile.
On large projects, multiple crews may be installing these helical piles at multiple locations at the same time. That was the case on a recent Cantsink project located in an Atlanta suburb. The project, a large warehouse of about 260,000 square feet, utilizes traditional footings in some areas. However, on the northeast end of the site, subsurface conditions were not suitable for typical footing construction methods.
To deal with the foundation challenges in those areas of the site, the general contractor turned to Cantsink's helical piles.
"The project required a total of 191 piles installed at 58 individual footing locations," notes Carter.
At most of the footing locations, the design called for three piles to be placed in a triangular configuration with a spacing of 3 feet. However, the project also includes four footing locations which utilize four piles; these will support heavy column loads on the structure's exterior. In addition, a number of larger footings utilize either six columns per footing or 12 columns per footing. The average depth of penetration was about 32 feet, though some went as deep as 48 feet.
"In this case we went all the way to refusal to yield as much load capacity as each pile is capable of," Carter says.
Once the piles were in place, a pile cap was affixed to the top of each one. This cap consists of an 8-inch-square plate of 3/8-inch-thick steel which is welded to the top of each pile; eventually, the pile cap will be embedded in the footing concrete.
"The pile cap transfers compressive forces, which are always there," notes Pat Hutchinson, Cantsink manager. He adds that the caps also take care of any wind load by fixing the pile cap to the piles. Installation of #5 rebar and placement of concrete completed the construction of each footing.
On most Cantsink projects, crews place the piles vertically. However, some specialized projects require angled or even horizontal placement, perhaps for various tension applications. For example, helical pile tieback systems can be used in tension applications to anchor retaining walls.
"Helical tiebacks have shorter bond lengths than grouted ones," Carter notes, "so they can be used where it is necessary to not encroach beyond the property line." Additionally, he notes, helical tiebacks can be combined with horizontal pipes to allow anchoring of MSE geogrid walls without excessive excavation.
Whether the installation is vertical or horizontal, Carter notes that one thing that developers and contractor have said they like about this system is its speed of installation.
"On a good site, one of our crews can place 1,000 linear feet of pile a day," he says.