Helical piers (also called screw piles, helical piles, or helical anchors) are steel foundation elements with one or more helical plates welded to a central shaft. They are installed by rotating (screwing) them into the ground using hydraulic torque motors attached to excavators or skid steers. The helical plates cut through the soil like a screw, pulling the shaft downward until the plates reach competent bearing soil.
How Helical Piers Develop Capacity
Unlike micropiles (which develop capacity through grout-to-ground friction) or driven piles (which develop capacity through soil displacement and shaft friction), helical piers develop their capacity primarily through **end bearing on the helical plates**. Each plate acts as an individual bearing element, and the total capacity is the sum of the bearing capacity on all plates minus the weight of the soil column above.
The capacity of a helical pier can be estimated in the field using the **torque-to-capacity correlation**: the installation torque (measured in real-time) is multiplied by an empirical factor (Kt, typically 9–12 for most soils) to estimate the ultimate capacity. This provides immediate verification during installation — a significant advantage over systems that require post-installation load testing.
Components of a Helical Pier
- **Lead section:** The first section installed, containing the helical plates (typically 8–14 inch diameter plates)
- **Extension sections:** Plain shaft sections added to reach bearing depth (typically 3, 5, or 7 foot lengths)
- **Helical plates:** True helix-shaped steel plates welded to the shaft (not flat plates bent into shape)
- **Central shaft:** Square shaft (1.5–2.0 inch) for residential or round pipe shaft (2.875–4.5 inch OD) for commercial
- **Bracket:** Connection hardware that transfers load from the structure to the pier
Applications
Foundation Repair (Most Common) Helical piers are the dominant technology for residential foundation repair in many markets. They stabilize settled foundations and can lift them back toward original position. Typical residential projects use 8–20 piers at $1,200–$3,500 each.
New Construction Helical piers are increasingly used for new construction foundations — especially for additions, decks, boardwalks, solar arrays, and light commercial buildings. Their speed of installation and immediate load capacity make them attractive for fast-track projects.
Tiedowns and Anchors Helical anchors (same technology, loaded in tension) resist uplift forces from wind, buoyancy, or overturning. Common for manufactured homes, transmission towers, retaining walls, and pipeline buoyancy control.
Temporary Structures Because helical piers can be unscrewed and removed, they're ideal for temporary structures — construction trailers, event structures, temporary bridges, and environmental remediation facilities.
Limitations
Helical piers are not suitable for every application:
- **Cannot penetrate rock** — Helical plates cannot advance through bedrock or very dense cemented soils
- **Limited capacity** — Maximum practical capacity is about 200 tons (vs. 500+ for micropiles)
- **Depth limitations** — Torque requirements increase with depth; practical limit ~100 feet
- **Cobbles and boulders** — Large obstructions deflect or damage helical plates
- **Very soft soils** — If no competent bearing stratum exists within reach, capacity cannot be developed
Conclusion
Helical piers have revolutionized the foundation repair industry and are making significant inroads into new construction. Their speed, clean installation, immediate loading capability, and real-time capacity verification make them an excellent choice for moderate-load applications in favorable soil conditions. Understanding their capabilities and limitations helps engineers and project owners choose the right foundation solution.