The Science Behind Helical Piers: Soil, Torque, & Load Calculations

In residential construction, helical pier design plays a crucial role in stabilizing structures where traditional footings may fail due to soil movement or poor load-bearing conditions. These deep foundation elements aren’t just driven into the ground, they’re engineered with precise calculations that take into account soil characteristics, installation torque, and load-bearing requirements. Understanding the science behind helical piers helps homeowners, builders, and engineers make informed decisions when tackling foundation problems.

How Helical Piers Work

Helical piers, also known as screw piles, are steel shafts with helical plates welded to them. During installation, they are mechanically screwed into the soil, much like a large screw. As each pier is advanced, the torque resistance is carefully measured, which helps determine the pier’s bearing capacity.

The goal is to transfer the load of a home to deeper, more stable soil layers, bypassing weaker topsoil. Once the target depth and torque are reached, the pier can be capped and connected to the foundation to provide structural support.

Soil Load-Bearing Capacity: The Foundation of Design

A helical pier’s ability to support structural loads begins with understanding the soil it will bear against. Different soils—clays, silts, sands, and gravels—provide very different levels of resistance, and this variation directly governs how the helical plates must be sized. In foundation engineering, the goal is to advance the pier into soil with sufficient shear strength to support the structure, and once that soil is reached, the diameter and spacing of the helical plates determine how much load the pier can carry.

Under ICC-ES AC358, the design method used to size helical plates is known as the Individual Bearing Method. In this approach, each helical plate acts like a small circular footing, and its capacity is determined by the area of the plate and the strength of the soil surrounding it. Larger plates provide greater load-bearing area, which is essential in softer soils such as clays with low undrained shear strength. In contrast, dense sands and gravels can provide significantly higher bearing capacity, often allowing smaller plates to achieve the required performance. Typical design soils may range from 500 to 1,500 psf in soft clays, 1,500 to 3,000 psf in medium clays, and 3,000 to over 6,000 psf in dense sands or gravels, though actual values should come from a geotechnical report or on-site testing such as SPT, CPT, or vane shear measurements.

Helical plates must also be spaced correctly along the shaft—typically at least three times the diameter of the lower plate—to ensure they act independently rather than interfering with one another. When spaced properly, the total capacity of the pier is effectively the sum of the individual capacities of each plate. This is why adding a second or third plate, or increasing plate diameter, can substantially increase the allowable load of the helical system.

Torque Monitoring & Load Correlation

Installation torque is one of the most critical indicators of pier performance. Engineers use an empirical relationship—commonly known as the torque correlation method—to estimate axial capacity. This relationship is typically expressed as:

Qᵤ = K × T

Where:

Qᵤ = Ultimate capacity (lbs)

T = Installation torque (ft-lbs)

K = Torque correlation constant (commonly 9 for 2.875” OD Helicals)  

For example, if the final installation torque is 2,500 ft-lbs, and K = 9, the estimated capacity is:

Qᵤ = 9 × 2,500 = 22,500 lbs

This real-time data allows installers to verify performance on-site.

Corrosion Protection for Longevity

Helical piers are often installed below grade and exposed to moisture. Without adequate protection, steel components can corrode, reducing their effectiveness. That’s why quality piers are hot-dip galvanized or coated with corrosion-resistant finishes per ASTM A123 or ASTM A153 standards. Additional considerations include:

• Soil resistivity testing to evaluate corrosion risk
• Zinc-rich primers or epoxy coatings in aggressive environments
• Cathodic protection systems for long-term preservation in high-risk areas

These safeguards ensure that the helical system maintains integrity for decades.

Why Standards & Certification Matter

Homeowners should only trust foundation products that meet or exceed ICC-ES AC358 and ASTM standards. These certifications confirm that the helical piers have been independently tested for performance, safety, and durability. Reputable manufacturers will also provide:

• Load testing data
• Engineering documentation
• Transferable warranties

Adhering to these foundation repair standards ensures consistent quality and peace of mind for homeowners investing in long-term stability.

Engineered for Stability

Helical pier design is a science rooted in soil mechanics, structural engineering, and real-world performance metrics. From assessing subsurface conditions to monitoring torque during installation, every aspect of a helical system is engineered to deliver reliable, long-lasting support.

But the confidence behind helical piers doesn’t come only from modern engineering—it comes from a proven history. Helical foundations have been used for more than 180 years, dating back to the 1830s when engineer Alexander Mitchell first introduced screw piles to stabilize lighthouses in soft coastal soils. Many of those early structures still stand today, supported by the original helical foundations. Since then, helical piers have been used worldwide to support bridges, utility towers, boardwalks, commercial buildings, and homes in challenging soil conditions.

That long track record gives homeowners and contractors something rare in the foundation world: a technology that blends modern innovation with nearly two centuries of successful performance. Today’s helical systems benefit from advanced materials, precise engineering, and third-party evaluation through standards like ICC-ES AC358, but the core principle remains the same—transfer structural loads deep into competent soil using a stable, screw-like foundation element that has stood the test of time.

When you combine this rich history with modern engineering and rigorous quality control, you get a foundation solution that isn’t just effective—it’s proven.

Need Help Choosing the Right Helical System?

Titan Products manufactures high-performance, certified helical pier systems backed by engineering support and industry-standard compliance. Contact our team to learn more or request a quote for your next residential foundation project.