Wednesday, January 26th, 2011 by Cassi Sherman
Brief Details on Square Shaft Piers for Comparison
This is another section of our examination of helical pier couplers. How a helical pier fits together is an integral part of its overall ability to get the job done. That's why we've tapped Jeff Kortan, P.E. and Director of Engineering at Foundation Supportworks, to give us the skinny on couplers.
In previous parts of this series, we have examined strictly round shaft helical piers, not only because they are the most common helical pier, but also because they are currently approved by virtually every building department in Colorado. Square shaft helical piers are not as common. However, it's important to understand a little bit about square shaft piers when you're comparing couplers.
The most common coupler detail for solid square shaft helical piers utilizes a forged and upset end. Cast detached couplers have also been used in lieu of the upsetting process. As a review, upset couplers are formed by heating one end of the shaft, placing this end in a form and then enlarging the end with a hammer-like tool, or heavy press.
The upset end of the square shaft is created in a similar manner as for the round shaft, except for forming a square shaft.
Things to Consider when Purchasing Piers with this Coupling Method:
--With this method of manufacturing, it is difficult to create tight connections to strict tolerances.
--It is not uncommon to have 1/8 inch or more difference between the outside diameter and the inside diameter of the upset coupler of the round shaft
--Greater freedom allowed in this connection leads to a greater potential variance from straightness
--The connection variance leads to the higher the potential for bending or buckling of the pile under high compressive loads.
--The risk of pile buckling further increases with unsupported lengths above the ground surface, or if the pile extends through soil strata consisting of soft clays or loose sand.
--The square shaft coupler is usually comprised of a single bolt connection, which can also allow for greater variance from straightness and higher potential for bending or buckling.
There are obvious, significant differences in coupling details and it's important to know what you're paying for before signing any contracts. After all, the differences are in the details, and the details are what determine engineering soundness.
What Peak Installs when we use helical piers
Now that you've gone through the different types of couplers, the benefits and drawbacks, and the important questions to ask, it's probably a good time to learn about what our company installs. Peak wants you to know exactly what we install and why, as well as the benefits and drawbacks to our solutions.
We utilize round shaft helical piles that are manufactured with external welded or detached couplers. These systems are manufactured to strict tolerances to allow the pile shafts to be in direct contact inside the coupling.
Why is this important?
The load path for piles under compression is then directly through the shafts of the extensions and lead section without having to pass through welds and bolts at each connection. The annular space between the pile shaft and coupler is also kept as tight as is practical to maintain pile rigidity while also providing connections that are easily joined in the field.
Still concerned? Don't just take our word for it!
We invite you to contact our engineer, or the staff engineers with our manufacturer. You can obtain technical documents on our piers free of charge that you can have reviewed by your engineer of choice. Your engineer can give you a solid, non-biased opinion of the stability of our piers versus other systems.