Introduction

One of the most common questions we get asked at Postech Moncton (by a mile) is...

"What size helical pile do I need for my project?"

It's a great question! 
After all, you wouldn't want to end up with an under-sized helical pile that can't support the structural loads of your project. In fact we once heard of a multi-family housing project in Manitoba that was built on under-sized helical piles, and the only solution was to laboriously install new ones.

That said it's equally important to avoid a helical pile that's larger than you need. While your project would certainly sit on an incredibly sturdy foundation, you'd be wasting money on piles that simply aren't required.

So how do we determine the right size of helical pile on your project? What are the key factors to consider? And why could two identical structures require different sizes of helical pile?

Read this article to find answers to those questions (and a whole lot more)!

Understanding Helical Piles

In order to understand the factors that influence the choice of helical pile for your project, it's important start by covering how they work. That's because the relationship between the design of a helical pile and soil conditions plays a huge role in determining which size is right for your project.

Let's take a look at the components of a helical pile and how they contribute to its' performance. Then, we'll explore the key factors that influence the size of helical pile for your project.

Pile Shaft

Forming the main body of a helical pile, the shaft is (typically) made from a length of steel pipe with a slant-cut at the end. Besides being the "core" of a helical pile, the pile shaft is responsible for transferring structural loads down into the helix plates.

The strength of this pile shaft plays an important role, unsurprisingly, in determining overall load capacity for the helical pile - particularly where lateral loads are concerned. Larger diameter piles will tend to have higher resistance to horizontal forces, owing to their increased strength and skin friction.

Speaking of skin friction, that's another aspect of a pile shaft that can affect load capacity. While much of a helical pile's strength comes from the helix plate (more on that in a moment), soil pressure along the shaft contributes as well.

However, skin friction tends to play more of a role as the pile shaft diameter increases. This is because a larger pile shaft will have more surface area for soil to exert pressure on, thus boosting skin friction. 

Helix Plate

The helix plate (pl. helices) can be found towards the bottom of a helical pile and it performs two important functions:
● Allows the helical pile to smoothly advance into the ground without "auguring" the soil● Anchors the helical pile in firm soil layers to deliver the required load capacities

Like the pile shaft, a helix plate can be found in a range of diameters. Our 2-3/8" helical piles at Postech Moncton, for example, are available with helices ranging anywhere from 8" to 16" in diameter.

As a helical pile is rotated into the ground, soil puts pressure on the helix plate. This soil pressure anchors the pile in place and resists movement up, down, or side-to-side.

Generally speaking, larger helix plate diameters will provide more surface area and therefore deliver more "holding force". That said, you can't simply crank-up the helix plate diameter if you need more foundation strength.

But, we'll dive into that in the next section.

Pile Adapter

In order to turn your helical piles into a cohesive foundation, you'll need a pile adapter. There are many off-the-shelf designs we offer at Postech Moncton, or you can even have a custom solution fabricated. Our adapters are designed to be height-adjustable, making it easy to achieve a perfectly-level foundation.

Now, while pile adapters are an interesting topic and important component of a helical foundation, they don't usually play a role in determining the size of helical pile. So for the purposes of our topic today, we'll move on to examining the factors which do influence helical pile size selection.

Three Key Factors That Influence Your Helical Pile Size

1: Soil Conditions

Seeing as helical piles are a deep foundation that need to be installed underground, it's no great shock that soil conditions are one of (if not the) most important factor that influences helical pile size.
Here in New Brunswick, our soils range from loose sand to sticky clay and everything in-between. Some areas have high water tables and soft materials, where others tend to stay dry and tough. Structures near shorelines must consider erosion or flooding, while coastal buildings need to resist violent storms and winds.
That's why, like we said in the introduction, two identical structures can require two different sizes of helical pile.
Let's explain with an example...
Pretend you're looking to build a cozy cabin, but you haven't decided on where to put it yet. There's two potential sites you're considering, one located along a beautiful river and the other tucked away in the woods.
The river site has soils that are highly saturated with water and comprised of a mucky clay/sand mixture. Conversely, the wooded site has relatively dense soil that doesn't see excessive moisture and is well-drained.

Even though the design of your cabin doesn't change between the two sites, your foundation certainly has to!
For your site near the river, we may recommend a helical pile with a larger helix plate that's better-suited for the loose and muddy conditions. By increasing the helix plate diameter, there's more surface area for the soil to put pressure on. 
But if you were building in an area with soils that are more dense and consolidated, you might actually need a smaller helix plate to deliver the same load capacity. That's because dense soil can exert more pressure on the helix plate, meaning it doesn't need as much surface area to provide the right amount of strength.
That's a simplified demonstration, but it illustrates the outsize effect your soil conditions have on the choice of helical pile. What's great about the technology is our ability to modify specific aspects of the pile in order to achieve exactly the support you need, no matter the conditions.
It also means you won't be paying for more foundation than is required for your project.

2: Load Requirements

This one might seem obvious, but the load requirements for your project are a big deciding factor when it comes to foundation design. From backyard decks to boardwalks, every project has its' own set of structural "needs" that must be met.
And hey, why don't we illustrate that point with another example?
Take a boardwalk, for instance. Since they're (usually) built in wet, marshy, or sandy areas, we already know we'll probably want a larger helix plate to overcome soft conditions. However, what should we do about the pile shaft diameter?
Remember that we covered how skin friction can increase the lateral load resistance of a helical pile, by providing more surface area for soil pressure to act upon. To ensure the boardwalk doesn't wobble or feel unsteady, we may also opt for a larger-diameter pile shaft to increase lateral (horizontal) strength.
Of course we could also implement tactics like battered piles, which involves installing a helical pile at an angle to increase lateral capacity, but you get the idea. By adjusting the pile shaft size, we can increase the horizontal strength of your foundation.

3: Physical Pile Limitations

Grab a drinking straw and hold it in your hands. Then, rotate both ends of the straw in opposite directions. As you increase rotational pressure you'll notice the "body" of the straw will begin to deform, eventually giving way and twisting around itself.

What you've just done is demonstrate the power of "torsional torque", so congratulations! If you've ever experienced a broken driveshaft on a vehicle, it's quite possible this force was to blame.

Now, imagine that drinking straw is a helical pile shaft. As we rotate each helical pile into the ground it experiences resistance from the soil. We can read this resistance as torque, using monitors attached to our installation equipment.

As resistance from the soil increases, we must apply more torque in order to continue installing the pile. This increases torsion on the pile shaft, and much like our drinking straw example it's possible to apply too much and break it.

So, if your soil conditions were quite dense, we may use a smaller diameter helix plate to allow the pile to reach correct depth without "torquing out". Remember that a larger helix plate will experience more resistance from the soil, thereby increasing torsion along the shaft.

By the way, this showcases another reason why the soil conditions are so important when it comes to selecting a helical pile size. We don't simply choose a pile that's "technically" strong enough, we're balancing your project needs with the real-world conditions that must be accommodated. 

There Is No "One Size Fits All" Helical Pile Foundation

As you've seen here, there's plenty our team considers when designing a foundation for your project. And we could have written even more about what goes into determining the size of helical pile you need, but we wanted to avoid a 3000 word article.

Our point with all this is that a "one size fits all" helical pile foundation does not exist.

This is a common misconception about helical foundations which is, unfortunately, often perpetuated by the industry itself. Many people think that because a given helical pile is rated for a certain load capacity, it's guaranteed to reach it.

Not the case.

When you see a load capacity rating on a helical pile, it indicates the ultimate performance of that pile as tested in specific soil conditions. It would be impossible for a manufacturer to test their helical piles in every possible soil type, so they go for a "middle ground" scenario to provide a baseline.

In the real world soil conditions can be tricky, varied, and downright difficult to deal with. Like we covered in the earlier example, two identical structures could required completely different helical foundation designs depending on where they're built.

That's why when people ask us for a "5000lb helical pile" or a "15,000lb foundation", we have to take a step back and consider those key factors first. Because while a given size of helical pile may deliver 5000lbs of capacity in one location, it may not offer the same performance in different conditions.

We understand this can sometimes be frustrating for those who are just trying to wrap their heads around helical foundations and identify if they're a good fit for their project. When you're in "research mode" you want answers, not more questions!

However, if we were to try and offer a generic "one size fits all" answer to that question it would only cause more problems and confusion. What if we quoted you for 2-3/8" piles with a 12" helix plate, only to find out later that your soil conditions are too loose and require a larger size? The result would be wasted time, effort, and money.

Over the past 13+ years in business, our team has learned it's far better to spend a little extra time gathering the correct information in order to deliver as precise a quote as possible. It avoids a whole lot of headaches down the line!

Summary & Conclusion

Helical piles are a streamlined and straightforward foundation solution, but that doesn't mean serious thought isn't put into every project we work on. Whether it's a small deck, expansive boardwalk, or cozy cabin, our team understands the importance of installing a proper foundation.

In this article we explored only some of the things our team has to keep in mind when selecting the helical pile size for your structure. To summarize...
● Choosing the right size of helical pile is vital to ensure proper performance without spending more than needed● Pile shaft and helix plate diameter can be adjusted in order to "tweak" a helical pile to suit your specific soil conditions● Soil conditions are one of the most important factors that determines the size of your helical piles● The idea of a given helical pile being a "5000lb" or "10,000lb" pile is a myth, ultimate pile load capacity is influenced by your specific soil conditions and pile design● Pile size can also be determined by the types of loads you need to support (up/down/side-to-side)● Physical limitations of the pile itself, such as how much torque we can apply during installation, also dictate size● There is no "one size fits all" helical pile solution - it must be designed according to your structure, load requirements, and site conditions

We would love to be able to give a stock answer to the question, "What size helical piles do I need?" It sure would make our lives a lot simpler when it comes to quoting projects!

The reason we don't do that is because we know it wouldn't be a fair answer to you. Without knowing the unique requirements of your project, we'd essentially be making a wild guess and hoping it's right.

Not a good way to design a sturdy, safe, and long-lasting foundation.

If you want a foundation quote that represents reality and prevents unwanted surprises, the best thing you can do is connect with an experienced helical pile contractor. They'll know what it takes to deal with various structures and soil conditions, delivering an effective and economical foundation.

Get in touch with our team at Postech Moncton, with over 13 years experience with helical piles in the region we'll make sure your project sits on a robust foundation solution.