The Second Coming of Christ in Foundations
This is what we need to build in tight spaces (in the forest, additions to houses, etc.) No concrete, no excavation. Just a giant screw driver and some giant screws :)
"Helical piers are basically large metal screws that are driven into the ground."
"Helical piers minimize time spent installing a foundation, causes little disturbance to the soil and transfers the weight of the structure, to soils deep into the earth that would bear the load."
"Helical piers are also fast becoming the go-to footing solution for decks, porches and additions. No matter how hard you try, the use of the heavy equipment needed to build concrete footings is going to destroy a finished yard and likely frustrate the homeowner. Helical piers don’t require any excavation, and there’s no need for concrete trucks. There are some walk-behind machines that are so small and maneuverable that they can even drive down piers inside a home."
From Deck Magazine
- A helical pile is a manufactured steel foundation that screws into the soil (Figure 1). It has a lead or shaft - usually 7 feet long - welded to a helical bearing plate or helix, and a cap that attaches the shaft to the framing.
- Typically, piles for residential use are hot-dipped galvanized steel (Figure 2). If the soil is particularly corrosive, sacrificial anodes (similar to those used to protect underground LPG tanks) can be used. In most commercial and industrial applications, however, the piles aren't even galvanized.
- The size of the helix will vary based on soil conditions. Generally, a helical pile installer will select a smaller helix for rocky soils and a larger one for marshy and clay soils. Once the pile is set, a variety of caps are available to tie the pier to the framing; some of them have a screw assembly that allows fine tuning of the elevation (Figure 3).
- My first inclination was to dismiss helical piles as just another gimmick. But it turns out that they have been used for more than 100 years in the United States, mainly on heavy commercial projects. Structures far more engineered than a backyard deck, sunroom, or addition rely on helical piles for their foundations.
- Helical piles are screwed into the ground to below the frostline using hydraulic machinery. The load-bearing capacity of a helical pile usually relates to the amount of torque required to install it, a function of both the size of the helical plate and the soil's bearing capacity. A pressure gauge on the installation machine reads the torque as the pile is rotated into the ground. As the driver turns the pile, it simply screws into the ground until the installer is confident it's below the frostline and in soil with sufficient bearing capacity. If the soil is weak, the pressure gauge will read low numbers, which means the pile must be screwed in deeper to stronger soil. When the helix is below the frostline and the pressure gauge hits a high enough number relative to the loading requirements of the structure, the installation is complete. This pressure reading is plugged into a formula called a torque correlation that calculates the actual bearing capacity of the pile.
- When poor soil conditions mandate going deeper than the standard 7-foot-long shaft, an extension is welded on (Figure 6). Sometimes all it takes is a foot more depth to go from utterly terrible soil to rock-hard soil. This is particularly relevant if you're building a free-standing deck where the piers close to the house might start out in backfill. With a concrete footing, you have to dig down to virgin ground at the house foundation level, as much as 7 feet or 8 feet if the house has a basement. It's no problem to drive a helical pile to this depth.
From Deck Magazine
- Helical piles offer a number of advantages over traditional footings. Two big ones are that they eliminate the tasks of digging footing holes and dealing with concrete. But I've found several other reasons to use them.
- For instance, footing inspections aren't required. The installer records the pressure readings, pile depth, and load-test results for each pile in a field report (Figure 9). The company I work with can then have the field report stamped by an engineer and sent directly to the building department, if required. (Some departments don't require a stamp. Your local installer will know the acceptable way to proceed.) The cost of this engineering is built into the cost of every helical pile we install; a different manufacturer may charge separately for an engineering report. A field report filled out by the installer notes the piles' location and depth and either their torque readings or the amount they sank in a sledge-hammer test. The report is sent to an engineer for review and stamping.
- In frozen or wet ground, traditional footings can be difficult or impossible to install. For helical piles, frozen ground isn't an obstacle, so in colder climates they make building decks all year round easier to manage. They can also be installed where a traditional footing hole would fill with water as it was dug, making helical piles a good solution for boardwalks, docks, and lakeside decks. Driving a helical pile in frozen ground begins with inserting a proprietary heating rod in a hole drilled with a rotary hammer (above). Once the ground is warmed, the pile is driven normally (right).
- The process of installing helical piles leaves most of the ground undisturbed (Figure 12). There's no spoil dirt to lose on the site or haul away. A helical pile in poor soil might extend down 20 feet; think about a traditional excavation that deep - if it were even possible to do - and how much dirt would be brought up. With piles, there's barely a trace other than the pipe protruding from the ground. Plus, the equipment is lightweight and can traverse a manicured lawn without damaging it.
- Helical piles also save a lot of time and offer a lot of load capacity in the bargain. Driving a helical pile in average soil takes only about 10 minutes - and it's 100 percent ready to build on, with great bearing capacities. The smallest pile I install can support a 6,800-pound load, whereas a concrete pier would need to be bigger than 16 inches in diameter in verified 4,000-psi soil to achieve the same capacity. Another benefit of the larger capacity is that you can usually use fewer piers, although you may have to use larger beams to achieve the greater spans.
- With helical piles, the torque correlation combined with per-pile load testing also means there is no need to test the soil capacity or rely on guessing. You will absolutely know the bearing capacity of each pile. Because helical piles' load capacity can be verified, it's often possible to use fewer footings and a larger support beam. In this case, the span between piles is over 15 feet.
- Helical Pile application and design
- Techno Metal Post
- Foundation Technologies
- GIC and also
- Design Guide
Helical Piers are not available off-the-shelf in the US. Instead, manufacturers train dealers/installers. However, some appear open to selling the piers and providing training to contractors. I imagine the best approach for us would be to get trained by one of the manufacturers - so we can better understand how to replicate both the piers and the installation equipment.
It's important to note that the equipment needs to provide data on the install - this is how we know that we're on "solid ground" and how we meet building department requirements.
Houston area - Someone bought an old house in sinking Houston and the company we hired to “jack-up” the house and level installed said piers—very fast, very clean and Very stable foundation repair. I’d sure use them everywhere as they allow you to avoid costly study in poor soils and thus projects can remain on time and on budget. Do I take it you are going to manufacture them along with the machines? They need to be made like short drill stem so they can be put down in tight spaces in series, so you can insert them as deep as they need to go to hit some kind of solid base somewhere down there. The ones in Houston varied from 9ft to 15ft. before they felt like they could not move even in an earthquake! The only problem with code is how you fix the framing or foundation to them, but there are many ways to make that stronger and cheap too.