Helical Piers: Torque-Verified Deep Foundations for Repair and New Construction
Helical piers are screw-in steel deep foundations whose load capacity is verified by installation torque. They're the right tool for lighter residential loads, additions, decks, tight-access work, and new construction over expansive Colorado soils.
Quick Answer
A helical pier is a steel shaft with one or more welded helix plates that is rotated into the ground like a screw. Installation torque correlates to ultimate capacity, so each pier is load-proofed as it is installed. They install with low vibration, can be loaded immediately, and work in both retrofit underpinning and new construction.
A helical pier is a deep-foundation element installed by rotation rather than driving. A drive head equipped with a high-torque hydraulic motor turns a square or round steel shaft fitted with one or more helical bearing plates. As the helices advance, they pull the shaft into the soil and bear on increasingly competent strata. Installation continues until the measured torque, integrated over the final 3 ft of advancement, indicates the pier has reached its design capacity through an established torque-to-capacity correlation.
Helical piers are uniquely suited to Colorado projects where helicals out-compete pushed piers: lighter residential loads (one-story slab-on-grade, additions, decks, sunrooms), tight-access work inside crawlspaces or against zero-lot-line neighbors, and new construction where there is no structure yet to push against. The installation generates minimal vibration, so it can be performed adjacent to fragile masonry, near historic structures, or in occupied buildings without disturbance.
Because the capacity-confirmation method is real-time torque rather than reaction against the structure's weight, helical piers can be loaded the moment installation finishes. For new construction this means continuous wall pours can follow the foundation crew within the same week. For retrofit work, transfer brackets can be torqued down and load shifted immediately after the last pier is locked off.
The Torque-to-Capacity Correlation
The core engineering principle behind helical piers is that installation torque is proportional to ultimate axial capacity in the soil being penetrated. The relationship, originally formalized in research collected by ICC-ES AC358, is expressed as Qult = Kt × T, where T is the average installation torque over the final 3 ft and Kt is a shaft-diameter-dependent constant (commonly 10/ft for 1.5 in. square shafts, 9/ft for 1.75 in., and 7/ft for 2-7/8 in. round shafts, with manufacturer-specific values). That means we don't guess at capacity — the installation torque, recorded with a calibrated digital indicator, is the load test.
Helix Geometry & Shaft Selection
- Helix plates: 8, 10, 12, and 14 in. diameters; spacing between helices on a multi-helix lead is 3 times the smaller helix diameter to ensure each plate bears on undisturbed soil.
- Lead and extension sections: shafts in 5 ft and 7 ft sections coupled with bolted sleeves, allowing piers to extend to any practical depth.
- Shaft sizes: 1.5 in. and 1.75 in. solid square shaft (better for advancing through dense soils), and 2-7/8 in. and 3-1/2 in. round shaft (better for higher capacities and buckling resistance in soft soils).
- Coatings: hot-dip galvanized per ASTM A153 is standard; bare-steel sacrificial thickness designs are used where soils have been tested non-aggressive.
- Brackets: bolt-on retrofit brackets for underpinning existing footings; new-construction brackets cast into the footing for piers installed before the pour.
Installation Sequence (Retrofit Underpinning)
- 1. PE-sealed design. Tributary loads, target capacities, helix configuration, and pier spacing are set by the engineer before mobilization.
- 2. Excavation at each pier. A compact pit is dug to expose the footing face. The footprint is small enough that landscaping disturbance is minimal.
- 3. Lead installation. A lead section with the helix configuration specified by the engineer is engaged in the drive head and rotated into the soil at a controlled crowd pressure.
- 4. Extensions until target torque. Extension sections are bolted on as the pier advances. Torque is logged continuously; advancement stops when the running 3 ft average meets the design value.
- 5. Cut-off and bracket installation. The shaft is cut to bracket elevation; the underpinning bracket is fitted around the footing and secured to the pier.
- 6. Load transfer. A jack on the bracket lifts the structure off the failed soil and onto the pier. For stabilization-only jobs the load is simply transferred; for lift jobs, restoration of elevation proceeds in monitored increments.
- 7. Documentation. Torque logs, depths, and pier-by-pier capacities are included in the engineer's closeout report.
When Helicals Are the Right Call
| Situation | Helical pier | Push pier |
|---|---|---|
| New construction (no structure yet) | Preferred — torque is the load test | Not viable — no reaction available |
| One-story home, slab-on-grade addition, deck | Preferred — loads within typical helical range | May not generate enough reaction |
| Heavy two-story masonry on deep fill | Possible with round-shaft, higher torque | Preferred — load capacity verified against structure |
| Vibration-sensitive neighbor or historic adjacent | Preferred — low vibration | Acceptable, monitor closely |
| Interior pier in crawlspace | Preferred — small drive head fits | Possible with handheld rams |
Colorado Soil Considerations
Across the Front Range, helicals are commonly terminated in weathered claystone, dense sandstone, or glacial outwash gravels at depths between 15 and 35 ft. In areas with significant expansive-clay heave (much of El Paso and Douglas counties, parts of Jefferson and Adams), helical lead sections are selected with multi-helix configurations so the bearing plates engage below the active moisture zone. When the project is in a swelling-soil area, we add a sleeve through the upper soils so seasonal heave doesn't apply uplift to the shaft itself.
Lifespan, Warranty, & Maintenance
Galvanized helical piers in typical Colorado soils have a service life on the order of a century by sacrificial-thickness analysis. The system is maintenance-free. The two things that shorten effective service life are aggressive soils (low resistivity, low pH, or chloride contamination — rare residentially but worth a soil test on suspect sites) and tensile loading from heaving soil acting on an unsleeved shaft, which is why we sleeve through expansive zones when conditions require it.
What Drives the Cost
- • Number of piers (a function of wall load and the perimeter of the distressed area)
- • Required design capacity — higher capacity demands larger shafts and more helices
- • Depth to target torque — deeper sites use more extensions and labor
- • Access — crawlspace and interior installs take longer than open exterior work
- • New-construction vs. retrofit (retrofit adds excavation and bracket cost)
- • Engineering, permitting, and inspection requirements in the local jurisdiction
Key Benefits
- Real-time torque-verified capacity per ICC-ES AC358
- Suitable for retrofit underpinning and new construction
- Low vibration — safe next to fragile or historic structures
- Loads can be transferred immediately after installation
- Range of helix configurations engineered to site soils
- Sealed engineering documentation provided on completion