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Heard this one?…
“Helical piers might be fine for axial loads, but they’re a bad choice for lateral loads.”
Yep, it’s a common myth. I’ve even touched on it before in a previous post, which you can check out here. I didn’t have the space in that post to go in-depth on what battered helical piers are and how they can make your foundation better.
So, I wanted to give battered helical piers the attention they deserve.
On paper, battered helical piers are a technique we can use to increase the lateral capacity of your foundation.
In practice, they do a whole lot more than that.
1) What's a Lateral Foundation Load?2) Truth of Helical Piers & Lateral Loads3) What Milkshakes & Helical Piers Have in Common4) The Milkshake Helical Pier Experiment5) What Are Battered Helical Piers (And How Do They Work)?6) Where Are Battered Helical Piers Used?7) Benefits of Battered Helical Piers8) Conclusion
When it comes to the types of load your structure can face, the two that make the most impact on the design of your foundation are axial loads and lateral loads.
Axial loads are exerted in a vertical direction, or downwards, on your foundation. Imagine pushing a stick down into the ground - you're putting an axial load on the stick.
Lateral loads, conversely, are exerted in a horizontal direction on your foundation. Picture lateral loads like a pushing or pulling on your structure, they occur parallel to the ground instead of perpendicular.
Lateral loads are commonly seen in construction projects in industries like renewable energy, oil & gas, and transmission & distribution. Imagine a tall wind turbine, a slug catcher subject to sudden lateral forces, or a towering hydro transmission line. You need horizontal resistance as well as vertical resistance to safely support these types of loads.
Tall and narrow structures, like these, can be subject to high lateral forces that threaten to topple it if not appropriately dealt with
Now, the claim is that helical piers can’t support lateral loads. Their reasoning is that the comparably narrow helical pier shaft can hold axial loads, but will be ‘pushed over’ and fail under lateral loads. They say that because of the design of a helical pier, it will never be able to defend against lateral loads like other foundation solutions can.
At S&B Helical, we’re big believers in backing up what we claim. So, I’m going to show you exactly why that claim is 100% bogus.
A helical pier functions on a simple and effective concept.
The main body is comprised of a pier shaft that, in comparison to the width of the helix plates, is relatively narrow. Helix plates are attached along the shaft, and it’s these plates that provide much of the load resistance of the helical pier.
Instead of relying on a large shaft diameter to provide support, a helical pier transfers the structural load down the shaft and into the helix plates. In turn, these helix plates are anchored into a firm layer of stratum.
It’s the resistance of the soil on the helix plates that give a helical pier much of its load capacity.
To fully appreciate why helical piers are so versatile and how they can help your project, it helps to understand the basics of how they work
Helical piers, because of this design, have excellent resistance to compression and tension axial loads. But, what about a helical pier's resistance to lateral loads? The common claim is that helical piers can be easily "pushed over" in the soil and essentially cause your structure to topple over.
Is this really the case? Are helical piers unsuitable for structures with demanding lateral loads?
Here’s the truth: It’s complicated.
There’s a ton of engineering that we could go into here and talk about all the things that affect a helical pier’s lateral resistance. Trust me, there’s a lot of them. Foundation science is complicated like that sometimes, but I don’t want us to get stuck in the weeds.
The simple answer is this: In supportive soil there’s many forces that act together on a helical pier to give it excellent lateral load capacity. They don’t have dramatically less lateral resistance than other foundation solutions. From the helix plate to skin friction along the pier shaft, all the components work together to defend against horizontal forces.
That said, you know I’m always honest with you. And in this case there’s a grain of truth to the claim about helical piers and lateral loads.
Let’s picture it with an experiment you can do yourself (and get a milkshake out of the deal).
Imagine you have a delicious, frozen, thick milkshake. In that milkshake is a drinking straw standing vertical.
If you try to push the straw over by 15 or 30 degrees, the frozen ice cream will offer a good amount of lateral resistance. This is because the ice cream, when frozen, is dense and has resistance on the straw. In order to overcome the resistance, you have to exert enough horizontal force to overcome the resistance of the frozen ice cream. You might even bend the straw before you can overcome the lateral resistance.
This is similar to a helical pier in dense and consolidated soil. The tight bond of the soil particles has resistance on the helical pier. Along with other design aspects like the resistance of the helix plates, this helps defend against lateral movement of the pier.
What happens if you have loose and poorly consolidated soil?
Take your tasty frozen milkshake and leave it the counter for 5 minutes. Now try pushing the straw over.
After sitting on the warm counter, the ice cream will have melted a little and become less consolidated. The bond has weakened and can’t exert the same force on the straw. So, it’s easier for you to push the straw over in the milkshake.
The particles in loose soil have weak bonds, so like the melted milkshake can’t offer the same resistance to lateral movement of the helical pier. Just like pushing over a straw in a poorly-“consolidated” milkshake takes less force, it could also take less force to cause lateral movement in a helical pier that’s anchored in poorly-consolidated soil.
That soil interaction could be where the claims of helical piers not being able to resist lateral loads came from.
Except, that claim still isn’t true. Not only are helical piers more than capable of resisting lateral loads, in many cases they can even provide more lateral support.
Whether you have loose soil or your structure simply needs extra lateral support, designers have a few strategies to increase the lateral capacity of a helical pier foundation.
One method is to increase the diameter of the pier shaft, thereby increasing the pier’s skin friction. Imagine if you doubled the diameter of your milkshake straw in our experiment – the increased surface area would make it even harder to push over.
Increasing pier shaft diameter isn’t the only tactic designers and engineers can use to increase the lateral support of a helical pier foundation.
A popular solution are battered helical piers, and it’s time to take a look at how this foundation concept can give your project epic lateral support.
(By the way don’t forget to drink your milkshake, you earned it. Sorry if it’s a little melted by now, all in the name of foundation science)
The concept behind a battered helical pier is simple:
By installing a helical pier on an angle, we can use the unique properties of the helical pier to provide outstanding lateral load resistance.
An example of one way battered helical piers can be used to increase the lateral support of a structure
This diagram, while not to scale, gives you an example of a common configuration for a battered helical pier foundation.
The two helical piers installed at an angle increase the lateral resistance of the foundation. A vertical pier, placed in the middle, provides axial strength. To tie the group of piers together a support structure like a pier cap or grillage is used.
Like most things when it comes to helical piers, the design can be customized to suit the specific application. For example, you might see a battered pier on just one side of the foundation instead of both. Or, there may be multiple battered helical piers surrounding a central one. It all depends on the unique demands of the project, type of structure, soil conditions, loads, and more.
These battered pier shafts coming from the ground will be coupled the support rack on the right, giving lateral resistance to this slug catcher support
Installing helical piers on an angle wouldn’t be possible at all if they didn’t have their unique design. Because they install by turning into the ground with hydraulic power, we can install them in locations and configurations other solutions couldn’t. Not only that, but with a well-trained and efficient crew they don’t even take much longer to install than a vertical helical pier.
One of the S&B Helical crews ensuring a battered pier is being installed with precision and accuracy
Generally speaking, a battered helical pier can be used wherever more lateral support is required. This might be because soil conditions require it or because the structure is subject to particularly high lateral loads.
Another configuration for a battered pier to increase lateral support to a structure
To give you an idea of where you might see a battered pier configuration, here’s some places we’ve used them (and seen them used):
● Pipelines● Oil & gas facilities (slug catchers, equipment supports)● Renewable energy (solar farms, wind turbines)● Tall and narrow structures (transmission towers, communication antennas● Battery energy storage systems● Tiebacks and anchors● Supports for cement pads● Commercial buildings and high-rises
● Increases lateral support while keeping minimal footprint● Faster to install than other foundation solutions● Versatile and adaptable to almost any project● Easy to transport and handle● Efficient and economical● No extensive excavation required● Smaller crews and less equipment to install
The versatility of helical piers means engineers can carefully design a precise foundation that meets the needs and demands of your project.
Of course, the only way for you to know if helical piers are better for your project is to talk to an experienced helical pier contractor. A good contractor will be honest about the pro’s and con’s and give you the data you need to make an informed decision.
I talk a lot on this blog about the versatility of helical piers. Battered piers are a great example of that versatility. Where some people saw the design of a helical pier as a weakness when it came to lateral load scenarios, foundation engineers saw a simple solution.
Too many projects end up being limited by the technologies they use. For thousands of years we’ve been limited in where we can build and what we can build. Now, technologies like helical piers are opening up the world in a way we’ve never seen before.
Instead of making your structure fit the foundation, helical piers can give you a foundation that fits your vision for the structure. In my opinion, that’s the way it should be.
If you’re planning a project and want to make sure you’re getting the right support, scroll down to get in touch with our team of helical pier experts. We’re happy to discuss your project, offer our advice, and see what solutions might be right for you.
Questions or comments about what you just read?
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