How screw piles work
A screw pile is a steel shaft with one or more helical plates welded near the tip — in effect a giant screw. A compact hydraulic drive head winds it into the ground beside the failed footing, and it keeps going down until it reaches a stratum firm enough to carry its design load. In reactive clay areas that can mean passing straight through the moisture-affected upper layers that caused the trouble in the first place, and founding in stable material well below them.
Once each pile is at depth, a small excavation exposes the underside of the footing and an engineered steel bracket is fixed between footing and pile head. The building's load is then jacked across onto the piles. The footing that was resting on failing soil is now resting on steel columns founded metres below it.
Torque: the built-in proof test
Here is the elegant part. The rotational force needed to keep winding a pile correlates directly with the strength of the soil around its helix. The engineer specifies a target installation torque; when the gauge on the drive head hits that number, the pile has demonstrated its capacity in the ground it actually sits in. Every pile is effectively load-tested as it goes in — something no concrete pin can claim.
The practical takeaway: ask for the torque records. A professional installer logs the final torque and depth of every pile and hands the log to the certifying engineer. If a contractor cannot explain their target torque or will not provide records, keep looking.
Where screw piles win
Screw piles are the default answer when good bearing soil is deep — say 3 m or more down, which is common in the reactive clays under many Australian suburbs. Digging a mass concrete pin that deep is slow, costly and hazardous; winding a pile down is routine. They also shine where access is poor, because the rigs are compact and some drive heads are hand-operated, and where you want minimal mess — each pile needs only a small pit, so there are no long trenches and very little spoil. The methods overview compares the trade-offs in one table.
The other genuine advantage is lift. The brackets incorporate jacking points, so once the piles are in, the wall can often be raised back towards level in a controlled way during installation, not merely stopped from sinking further. Cracks that close and doors that swing again are a realistic outcome, within limits the engineer will set.
An engineering-led method
Screw piles are not a product you buy off the back of a ute; they are a structural design. Pile diameter, helix size, target depth, spacing, bracket detail and torque all come from an engineer working off a soil test. Many pile companies offer design-and-construct packages, which is fine — but the design should still be done by a qualified engineer whose drawings and certification you receive. Our guide to engineer's reports covers what that documentation should include and what it costs.
Cost, downsides and quote checks
Budget around $3,000–$7,000 per pile installed. A typical settling corner needs 2–4 piles, so most corner jobs land between roughly $8,000 and $20,000 — similar territory to mass concrete, reached with far less digging. The cost guide compares the methods across whole-of-house scenarios.
The downsides are real but manageable. The cost per support point is high, so shallow problems on good soil are often cheaper in concrete. Underground obstructions — rock floaters, old footings, buried services — can stop or deflect a pile and add cost. And the result is only as good as the design behind it. When you compare quotes, check that each one states the pile specification, target torque and depth allowance, includes the engineer's design and certification, says whether re-levelling is included or the job is stabilise-only, and explains what happens if piles need to go deeper than allowed for.
Shallow good soil favours mass concrete; deep good soil, tight access or a wall you want lifted favours screw piles. If both quotes land close, the pile job's smaller footprint usually makes it the easier few weeks to live through.
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Common questions
Do screw piles rust out?
Steel in the ground corrodes very slowly, and engineers design for it — piles are galvanised and specified with sacrificial wall thickness so the design life runs to decades. Ask what standard the piles are manufactured and certified to; a reputable supplier will answer in writing.
Can screw piles lift my house back to level?
Often, yes. The jacking brackets allow controlled lifting during installation, and recovering height is one of the method's main advantages over mass concrete. The engineer sets safe limits — an old, brittle wall may only tolerate partial lift before new cracking risks outweigh the gain.
How deep do the piles go?
As deep as they need to: piles are wound down until the target torque confirms firm bearing, commonly several metres in reactive clay. Quotes include a depth allowance, so ask what the rate is if piles must run deeper than allowed.
Is a soil test really necessary first?
Yes. The soil test tells the engineer what stratum the piles must reach and what torque proves it. At $400–$1,000 it is a small fraction of the job and the difference between a designed solution and a guess.