"How much does a helical pile/anchor cost?"
That’s a lot like calling the local car dealership and asking, “How much does a car cost”? For both the car and the helical pile, it really depends on what you need. There’s no such thing as a one-size-fits-all helical pile. The cost of a pile varies with shaft type, shaft size, length of the pile, installation cost and to a lesser extent, the helix configuration. Helical pile shafts are available in various shapes and sizes.
The size and shape of the shaft you need for any given application depends on the magnitude of the load capacity needed and the strength/properties of the soil you are screwing them into. Accordingly, to determine what the cost of your pile would be, we would need to know the magnitude of the load to be resisted, the application (i.e. new construction pile, earth retention anchor, etc.) and the site-specific soils data (preferably an SPT boring). We offer free estimates and can give you a better feel for the costs once we understand the conditions specific to your situation.
"I've always understood that helical piles and anchors are only good for relatively lighter loading applications. Is that true?"
This is a common misconception. Helical piles are offered in a range of shaft sizes; the larger the shaft size, the more mechanical capacity it can offer. The largest square shaft pile, SS225 (2.25”x2.25” square) is rated for up to 200 kips ultimate and can achieve even more capacity when used as a Pulldown (grouted) micropile. The larger pipe shaft piles (like 6.5” OD and 8.5” OD) offer 200 kips and 300 kips ultimate, respectively.
"Is this helical pile and anchor technology new?"
The technology is not new and has been around since the mid 1800s; it was the major deep foundation technology of the mid to late 19th Century. The first recorded use of Screw-Piles was by Alexander Mitchell (1780-1868) in 1836 for ship moorings and was then applied by Mitchell as Foundations for Maplin Sands Lighthouse in England in 1838. It has only been over the last 25 years that we have seen a very dramatic resurgence in its use throughout the world, primarily due to the fact that we now have high capacity torque motors to perform the installation.
"Why does CHANCE® offer four different shaft types—don't they all do the same thing?"
CHANCE® offers four (4) different shaft types because not all soil conditions are conducive to every type. For instance, some soil conditions are simply too hard for an all-pipe shaft pile to install effectively, so a square shaft pile or even a combination pile would be a better and more efficient choice in harder soil conditions. By contrast, in weak/loose soils conditions that will have appreciable compressive loads, one of the round shaft options most likely will be the best choice.
"Are there any helical pile spacing requirements?"
Yes - helical piles observe the same minimum horizontal spacing requirements that other end-bearing deep foundation elements observe. The industry standard is typically 3 x diameter as measured from center to center. We typically use the largest helical plate, so for a lead section with an 8”/10”/12” helix configuration, the minimum spacing should be 3 x 12” = 36” center to center. The helical pile minimum spacing is only important down at bearing depth where the helical plates are so if you have multiple piles under a pile cap and you want to minimize the area of the pile cap, you can typically install the helical piles at a batter (angle) to get the separation you need at bearing depth and the piles can be terminated in a smaller footing. If the helical piles do have to be installed closer than the minimum, you can use normal group effect formulas to de-rate the capacities accordingly.