Square vs. Round Shaft: What’s the Right Choice?

 

The square vs. round shaft debate is a common one in foundation design. While both options have their place, square shafts are often the preferred choice for most applications due to their efficiency and performance. Let’s explore why.

 

Four Shaft Types for Helical Pile Installations

 

  1. Square Shaft: Efficient and better at penetrating dense materials.
  2. Pipe (Round) Shaft: Larger section modulus for soft soils or scour conditions.
  3. Combo Pile: Combines square shaft leads with pipe shaft extensions for versatility in mixed soil profiles.
  4. Pulldown Micropile: A square shaft encased in grout for enhanced buckling resistance, friction capacity, and corrosion protection.

 

Why Square Shaft is Better in Most Cases

 

  • Efficiency in Capacity: Square shafts provide greater axial capacity for the same installation energy compared to round shafts.
  • Dense Soil Penetration: Their design excels in penetrating dense materials where pipe shafts struggle.
  • Corrosion Resistance: Solid steel construction has less surface area for corrosion compared to hollow pipe shafts.
  • Tension-Only Loads: Square shafts are the most logical choice for tension-only applications, offering superior durability and performance.
  • Cost-Effectiveness: Their high efficiency often reduces installation costs by requiring less equipment energy.

 

Square shafts can handle compressive loads well in soils with sufficient passive pressure (SPT values of 5 or higher). For extremely soft soils (SPT values of 4 or lower), round shafts or Pulldown™ micropiles may be better suited.

 

6 Design Elements to Consider

 

Choosing the right shaft type requires careful evaluation of these factors:

  1. Axial Capacity: Is the shaft capable of carrying the intended load? 
  2. Penetration Ability: Square shafts are better suited for dense soils. Round shafts often require more energy to penetrate due to their higher displacement.
  3. Lateral Loading: Helical piles are generally slender, so lateral support is limited. Square shafts offer almost no lateral support, so round shafts, combo piles, or Pulldown® micropiles can be used for minimal lateral support. For significant lateral loads, alternative designs, such as battered piles, may be required.
  4. Corrosion: Corrosion, or oxidation, is not generally a concern for helical piles, as the piles will rest deep in the soil where oxygen is very limited. In cases where corrosion is a concern, however, solid square shafts have less surface area for corrosion than hollow, round piles. Pulldown micropiles also offer additional protection with a grout column.
  5. Tension Loads: For tension-only applications, square shafts are the only logical option. 
  6. Reversing Loads: Pulldown™ micropiles provide stiffness and stability for piles subject to both compression and tension loads.

 

Why Do Some Only Offer Round Shaft?

 

Suppliers that exclusively promote round shafts are either inexperienced or prioritize their own cost-cutting over your project's success. Round shafts are cheaper to manufacture, but they don’t match the efficiency and versatility of square shafts in most scenarios.

At Foundation Technologies, we offer all four types of helical piles to ensure you get the right product for your project.

 

When to Use Round Shaft 

As we've touched on, there are specific scenarios where round shafts may be necessary:

  • Soft Soil Conditions: Larger section modulus prevents buckling in soils with SPT values of 4 or less.
  • Scour or Unsupported Lengths: Round shafts provide stability in areas with unsupported lengths.
  • Lateral Resistance: Offers limited lateral resistance for projects where this is a design factor.

 

Stronger Foundations, Shorter Timelines

The right shaft type is critical to getting the job done right. At Foundation Technologies, our mission is to supply contractors with the right materials, right on time. As a full-service partner, we provide design assistance and field training to ensure you have the confidence and expertise to tackle the next job where helical piles are specified. Reach out to us for a quote or assistance with your next project, and let’s build something great together.