There is a stubborn belief on job sites that a helical pile has one number, a load rating you can read off a spec sheet and apply anywhere. It is not true, and acting on it gets general contractors into trouble. The capacity of a pile on your site is a product of the pile, the soil it bears in, and the safety factors the engineer applies. Our commercial and industrial steel pile work turns on exactly that distinction, and the GCs who understand it schedule and budget far more accurately.
This article unpacks what a load rating actually means, what the research and field practice say, and how a GC should read capacity numbers on a real project. Claims first, then the evidence behind them.
Quick take
A helical pile does not have a single universal load rating. Its capacity is set by the weakest of two things, the steel itself (mechanical capacity) and the soil it bears in (geotechnical capacity), then reduced by a safety factor. The number that matters is the engineered allowable capacity for your specific site, confirmed by installation torque, not a catalogue figure.
In this article
The Myth of the Single Load Rating
The myth is understandable. Manufacturers publish mechanical ratings, the maximum load the steel shaft and helices can handle before they fail structurally. A GC sees a big number, assumes that is the capacity, and plans around it. The problem is that the steel is almost never the limiting factor. The soil usually is. A pile rated mechanically for a high load will still settle or fail if it is bearing in soft, loose, or inadequate soil.
What the Engineering Says
Every helical pile has two distinct capacities, and the governing one is whichever is lower. The first is mechanical capacity, set by the steel. The second is geotechnical capacity, set by how much the soil can support through the helices bearing on it. The engineer calculates both and designs to the lower of the two, then divides by a safety factor to get the allowable working load. That allowable load is the only number a GC should plan against.
| Capacity type | Set by | What limits it |
|---|---|---|
| Mechanical capacity | The steel pile | Shaft and helix strength under load |
| Geotechnical capacity | The soil | How much load the bearing soil can carry |
| Allowable working load | The engineer | Lower of the two, divided by a safety factor |
Did you know: safety factors are not optional padding
The ultimate capacity a pile can reach is divided by a safety factor, commonly in the range of two, to set the allowable working load the structure is actually designed to. That factor accounts for soil variability, long-term behaviour, and uncertainty. A GC who plans against the ultimate or mechanical number rather than the allowable working load is removing the very margin the engineer built in to keep the foundation safe over decades.
How Installers Confirm Capacity in the Field
Here is where helical piles do something a poured footing cannot. Capacity is verified during installation through torque. As the pile is driven, the torque required to advance it correlates to the soil’s resistance, and through an engineered factor, that torque maps to capacity. The installer drives each pile until it reaches the target torque the engineer set, then records it. The result is a documented, pile-by-pile capacity, not an assumption.
What Does This Mean for a GC on a Project
For a GC, the practical takeaways change how you scope and schedule. You do not specify a pile by its catalogue rating. You give the engineer the structural loads, get an allowable working load per pile, and the pile count flows from there. You also accept that piles may reach target torque at varying depths depending on soil, which can affect time on site. And you treat the torque logs as deliverables that protect everyone on the project.
People often ask: Can two identical piles have different capacities? Yes, and this surprises people. Two piles of the exact same specification, installed on the same site, can carry different loads if the soil beneath them differs, which is common across a single lot. That is precisely why capacity is confirmed by torque at each pile rather than assumed from the spec. The pile is identical; the ground is not. An engineer designs for that variability, and the torque record proves each pile met its target.
Permits, Stamps, and Who Carries the Liability
Structural and permit note: This article is general information, not engineering advice. Foundation, underpinning, and load-bearing work in Ontario is regulated under the Ontario Building Code and usually requires a permit plus a design stamped by a licensed professional engineer. The right pile type, helix size, and capacity for your site must be set by a qualified engineer based on a soil report. DiamondTech Piles is not responsible for outcomes from work done without proper engineering, permits, or inspection. When in doubt, confirm scope with your municipality and a licensed engineer before anything is installed.
On a regulated project the engineered design is not optional. The pile capacities, layout, and the foundation as a whole are typically reviewed under the Ontario Building Code and require a design stamped by a licensed professional engineer, with a permit from the authority having jurisdiction. The GC who insists on seeing the allowable working load, the engineer’s stamp, and the torque logs is protecting the project and themselves. A capacity claim with no engineering behind it carries liability no GC should absorb.
Frequently asked questions
Does a helical pile have a single load rating I can use anywhere?
No. A manufacturer publishes a mechanical rating for the steel, but that is rarely the limiting factor. The capacity of a pile on your site is the lower of its mechanical capacity and its geotechnical capacity, which depends entirely on the soil it bears in, then divided by a safety factor. The same pile carries different loads in different soils. The number a general contractor should plan against is the engineered allowable working load for that specific site, confirmed by installation torque, not a figure copied from a catalogue or another project.
What is the difference between ultimate and allowable capacity?
Ultimate capacity is the maximum load a pile and soil system can reach before failure. Allowable working load is that ultimate value divided by a safety factor, commonly around two, and it is the load the structure is actually designed to carry day to day. The safety factor accounts for soil variability, long-term behaviour, and uncertainty. A general contractor should always plan, schedule, and budget against the allowable working load, because designing to the ultimate number removes the margin the engineer built in to keep the foundation safe over the life of the structure.
How is helical pile capacity verified on site?
Through installation torque. As a helical pile is driven into the ground, the torque needed to advance it rises with soil resistance, and that torque correlates to capacity through an engineered factor the designer sets. The installer drives each pile until it reaches the target torque, then records the final value. This gives a documented, pile-by-pile confirmation of capacity that a poured footing cannot provide. For a general contractor, those torque logs are a key deliverable: they prove every support point met its engineered target and they are what an inspector and the engineer rely on.
Why do I need an engineer if the manufacturer gives ratings?
Because the manufacturer rates the steel, not your soil. The mechanical rating tells you what the pile can withstand structurally, but it says nothing about whether the ground at your site can support that load. Only an engineer, working from the loads and soil data, can determine the geotechnical capacity, set the safety factor, and produce the allowable working load and stamped design that the Ontario Building Code and your permit require. Skipping the engineer means planning a structure against a number that does not apply to your ground, which is both unsafe and a liability the general contractor would carry.
Quick recap for GCs
- A helical pile has no single universal load rating; capacity is site-specific.
- Plan against the engineered allowable working load, not the mechanical or ultimate number.
- Geotechnical capacity, set by the soil, usually governs, not the steel.
- Installation torque confirms and documents capacity pile by pile.
- On regulated work, insist on the engineer’s stamp, the allowable loads, and the torque logs.
Download the free quick guide
A one-page reference that explains mechanical, geotechnical, and allowable capacity, plus what to demand from your pile contractor.
