Helical Anchors vs Helical Piles: Tension vs Compression

Helical anchors and helical piles are built from the same parts, a steel shaft with one or more helix plates, but they are designed for opposite loads. A helical pile carries compression, pushing weight down into the soil, like a foundation under a house or deck. A helical anchor resists tension, holding something from being pulled up or out, like a tower guy wire, a tieback behind a retaining wall, or a solar array in high wind. Many products can do both, and the difference lies in how each one is designed, installed, and tested.

Key takeaways

• Load direction: CHANCE defines piles as supporting axial compression and anchors as resisting tension from uplift or guyed structures (Hubbell).
• Common anchor uses: retaining wall and basement wall tiebacks, guyed towers and utility poles, uplift on solar and light structures.
• Common pile uses: new foundations, decks, additions, and foundation repair.
• Design differences: tension capacity usually runs lower than compression for the same helix, and tension anchors need more soil cover above the helix.
• Install angle: piles go in near vertical; tiebacks go in from horizontal to 45 degrees downward.

What is the difference between a helical anchor and a helical pile?

The difference is the direction of the load. A pile acts like a column, and its helix plates bear on the soil below them. An anchor works more like a ship's anchor, and its helix plates pull against the soil above them. CHANCE explains that a helix creates a stressed zone in the surrounding soil, above the plate for tension and below it for compression (Hubbell).

Terminology is loose in the field. "Helical pier" usually means a compression pile used in foundation repair, and "screw pile" is common in Canada. Many installers say "anchor" for anything helical. When you get a quote, ask whether the element is being designed for compression, tension, or both.

Tension vs. compression: why capacity differs

The same helix does not carry the same load both ways. In tension, the helix bears against soil it has already passed through during installation, so that soil is somewhat disturbed. In compression, the helix bears on undisturbed soil below it. Tension capacity also uses the effective helix area, which is the plate area minus the shaft area, while compression uses the full helix area. Field tests in sand cited by CHANCE found a load improvement factor of 4.7 for single-helix anchors in tension and 6.3 for piles in compression with the same geometry (Hubbell).

Both are verified the same basic way. Installation torque correlates with capacity through Qult = Kt × T, and ICC-ES evaluation reports such as ESR-2794 apply that correlation to both tensile and compressive capacity. For tension piles, ESR-2794 uses the average of the last three torque readings over the final 2 feet, and it requires at least 12 helix diameters of soil above the top helix for the torque correlation to apply. Our guide to how deep helical piles go explains those rules.

What are helical anchors used for?

Helical tiebacks for retaining walls

A tieback resists soil pressure pushing a wall outward. Supportworks describes helical tiebacks as installed in a horizontal-to-45-degree downward orientation to support the tops of earth-retaining structures. The anchor is screwed through or behind the wall until its helix plates reach stable soil beyond the zone that would slide, and then a threaded rod and a steel plate or waler tie it to the wall. Supportworks lists allowable tension capacities of up to 29.8 kips for its 1.5-inch shaft tieback and up to 50 kips for its 1.75-inch model.

Because each tieback is angled, it pulls on the wall with both a horizontal and a downward component, and the wall has to be designed for both. The same concept is used to stabilize bowing basement walls, where helical wall anchors are installed through the foundation wall into the soil outside.

Guyed towers and utility poles

This is where helical anchors started. The A.B. Chance Company traces its earth anchor to the sleet storm of 1912, which toppled telephone lines and poles in Missouri (Geoengineer.org). Today, CHANCE square-shaft guy anchors are rated for up to 200,000 pounds of tensile load (CHANCE) and are widely used on electric transmission structures.

Solar arrays and light structures

Ground-mounted solar panels are light but catch a lot of wind, so uplift often controls their foundation design. Helical piles work well for solar because they carry both compression and tension, resist uplift from high winds, and install with small equipment and no concrete cure time (Foundation Technologies). The same reasoning applies to canopies, signs, sheds, and light poles, and to decks in frost country, where a helix below the frost zone also resists frost jacking.

What are helical piles used for?

Helical piles support compression loads from structures. Typical uses include:

• New foundations for homes, additions, and light commercial buildings, often tied into grade beams or pile caps.
• Decks, porches, and walkways, covered in our guide to helical piles for decks.
• Foundation repair and underpinning, covered in helical piers for foundation repair.

Piles often see some tension and lateral load too. CHANCE notes that round-shaft piles offer greater lateral and bending capacity and resist buckling better than square shafts, while square shafts deliver the most axial capacity for the least torque (Hubbell). To size a pile, see how much weight a helical pile can hold and how far apart helical piers need to be.

Key design differences engineers consider

1. Embedment. Anchors need enough soil above the helix to mobilize tension capacity, which is why ESR-2794 sets a 12-diameter minimum for its tension torque correlation.
2. Helix configuration. Soft clays may need more or larger plates. Dense soils need fewer and smaller ones (Hubbell).
3. Creep and movement. Tension loads can include coupling slip. ESR-2794 notes that coupler slip in tension applications must be included in movement estimates unless the pile is preloaded.
4. Testing. Tension tests are simpler and cheaper to run than compression tests because they do not require reaction anchors, which is one reason tension testing is common (Hubbell).
5. Corrosion. Anchors and piles face the same soil, and galvanizing extends service life. See do helical piers rust.

Both anchors and piles go through the same code path, covered in our guide to helical pile permits and building codes.

Which one do you need?

If something needs to be held up, you need a pile. If something needs to be held down or held back, you need an anchor. Many projects need both: a solar racking system, a guyed tower, or a deck with a roof over it may see compression under gravity and uplift under wind. An engineer designs for every load case, and a competent installer documents torque on each element.

You can find installers who handle piles, tiebacks, and anchors in the Helical Pile USA state directory, including Texas, Florida, and Colorado. For budgeting, see our helical pier cost guide. Anchor and pile manufacturers and installers can get featured on Helical Pile USA.

Frequently asked questions

Is a helical anchor the same as a helical pile?

They use the same components, but a helical anchor is designed for tension and a helical pile is designed for compression. Many products can do either, depending on design and installation.

What is a helical tieback?

A helical anchor installed at an angle, typically from horizontal to 45 degrees downward, to hold a retaining wall or basement wall against soil pressure. It connects to the wall with a threaded rod and a plate or waler.

Can a helical pile resist uplift?

Yes. Helical piles can carry tension as well as compression when designed and connected for it, which is why they are common for solar arrays, light structures, and decks in frost-prone areas.

Are helical anchors weaker than helical piles?

For the same helix and soil, tension capacity is usually somewhat lower than compression capacity, because the helix pulls against disturbed soil and uses a smaller effective area. Anchors are sized to account for that.

How is helical anchor capacity verified?

By installation torque, using the torque correlation Qult = Kt × T, and on larger projects by load or proof testing. Tension tests are relatively easy to run, so they are common on anchor projects.