How do helical piers support a foundation?

Reviewed by Preston, Oklahoma foundation repair consultant · Updated 2026-10-14

In short: A helical pier is a steel shaft with screw-shaped plates that is turned into the ground by a hydraulic motor and then bracketed to the foundation. Because it is screwed in rather than pushed, it does not need the building's weight to install, which suits light structures and situations that need resistance to upward pull. In Oklahoma clay, its plates have to end up below the soil layer that swells and shrinks.

How does a helical pier work?

Trade words used on this page:

• Shaft: a square steel bar or round steel pipe, added in sections as it goes deeper.
• Helix (helical plate): a round steel plate formed into one turn of a screw, welded near the lead end; a pier may have one or several.
• Torque: the turning force the motor applies, read from a calibrated gauge during installation.
• Bracket: the steel seat that connects the pier to the footing, slab edge or beam.
• Tension capacity: the ability to resist being pulled upward.

The pier is screwed down until it reaches the planned depth and torque, then the bracket transfers the structure's load to it, and the structure can be lifted from it.

Why is torque recorded?

Turning resistance is used as a measure of soil strength in federal rules: HUD's manufactured home installation standard uses a torque probe, a small screw-tipped rod turned into the soil, to classify soil strength: readings over 550 inch-pounds indicate class 2 soils such as gravel and dense sand, while readings under 175 indicate class 5 soils: uncompacted fill, peat and organic clays ¹. High-plasticity clays without torque probe or blow count data must use anchors rated for class 4B soil ¹. HUD also requires ground anchors to be certified by a registered engineer or architect, with the working load set at the ultimate load divided by a factor of safety of 1.5 ¹.

For helical piers, the final torque at each pier is logged as the installation record, and converting it to a design capacity is part of the engineered design.

How deep must helical piers go in clay?

• Expansive soils swell with added moisture and can lift a structure, and shrink with moisture loss and let it settle ⁴.
• Seasonal moisture change in clay can reach from 3 to 40 ft deep, and the upper part of a pier can lose contact with shrinking soil ³.
• Engineering guidance for swelling soils calls for piers to extend well below the zone of seasonal moisture change and to be anchored in non-swelling soil against uplift ².

A helical plate set below that zone acts as an anchor, because the swelling clay above it has to pull the plate up through stable soil. A plate set within the zone moves with the clay. For context on bearing depths in Oklahoma, steel push piers in Tulsa installation records typically reached 8 to 16 ft, with a median of 12 ft ⁵.

Where are helical piers used?

What are the limits of helical piers?

• Plates that end inside the active zone do not provide reliable anchorage, which depends on soil below the zone of seasonal moisture change ²³.
• Corner piers on swelling soil can be lifted in wet seasons, then lose skin friction as the soil shrinks in dry seasons and drop ³.
• The design depth depends on site soil data; soil survey reports are the minimum resource for locating expansive soils ⁴.

How do helical piers compare to other piers?

Helical piers, steel push piers, pressed concrete piles and drilled piers are compared side by side in the method selection matrix. Spacing and load questions are covered in loads, pier spacing and capacity, and the mechanism behind pier movement after repair in pier uplift or movement after repair. Light additions that move differently from the main house are covered in differential movement at additions.

Related

• Steel Push Piers
• Method Selection Matrix
• Loads Pier Spacing and Capacity
• Manufactured Homes on Piers
• Shrink-Swell and Active Zone