If you have been hearing more about screw piles on SA construction sites and want to understand what they actually are and whether they are worth looking at for your next project, this guide is for you.

No engineering jargon. No sales pitch. Just a straight explanation of what screw piles are, how they work, and when they make sense.

The Simple Version

A screw pile is a steel tube with a helical plate, like a large corkscrew, that is mechanically driven into the ground. Once it reaches the required depth and bearing capacity, it locks into stable soil and supports the structure above it.

That is the whole concept. Steel in the ground, structure on top, no concrete required.

They go by a few different names depending on who you talk to. Screw piles. Screw piers. Helical piles. Helical piers. Ground screws. They are all referring to the same product. In South Australia, the most common terms you will hear on site are screw piles and screw piers.

What Do They Actually Look Like?

A standard screw pile has three parts.

The first is the shaft, which is a hollow steel tube, typically circular or square in cross-section. The shaft is what transfers the load from the structure above down into the ground.

The second is the helix, which is a circular steel plate welded to the shaft at an angle, forming the screw thread. This is what drives the pile into the ground during installation and what gives it its bearing capacity once in place.

The third is the pile cap or bracket, which is the connection point at the top of the pile where it interfaces with the slab, beam or structural frame above.

Anchorpile systems use a 300mm cast iron helix as standard, with a safe working load range from 80kN to 500kN depending on the pile specification and soil conditions.

How Are They Installed?

Installation is straightforward and fast.

An excavator or purpose-built installation rig is fitted with a hydraulic torque head. The screw pile is placed at the required location, set to the correct angle, and driven into the ground by rotating it under hydraulic pressure. The helical plate screws the pile into the soil in the same way a corkscrew moves through a cork.

The pile is driven to a specified minimum depth and a minimum installation torque. Both are monitored and recorded during installation. When the pile reaches the required torque, it has achieved the bearing capacity the engineer has designed for.

The cap or bracket is then fitted, and the pile is ready to receive load. No concrete. No curing time. No waiting.

On a standard residential project, a full set of screw piles can typically be installed in a single day.

What Holds Them in the Ground?

This is the question most builders ask when they first see screw piles. There is no concrete surrounding them. So what stops them moving?

The answer is skin friction and end bearing.

The helical plate at the base of the pile bears against the surrounding soil, locking the pile in place vertically. The shaft of the pile also develops friction along its length as it passes through the soil. Together, these two mechanisms give the pile its capacity to resist both downward loads from the structure above and upward forces from reactive or expansive soils below.

This is why pile depth matters. The deeper the pile is driven, generally the greater its capacity. The engineer specifies the required depth and installation torque based on the geotechnical report for the specific site.

How Are They Different from Concrete Bored Piers?

Concrete bored piers are installed by drilling a hole into the ground, placing a steel reinforcing cage inside and filling the void with concrete. The concrete then needs to cure for several days before the pile can be loaded.

Screw piles skip all of that. There is no drilling required, no reinforcing cage, no concrete and no curing period. The pile goes in and it is ready to load the same day.

Screw piles also produce far less soil disturbance. Concrete bored piers generate significant spoil that needs to be removed from site. Screw piles displace the soil as they are driven in, leaving virtually no material to dispose of.

On tight access sites, in weather that would prevent a concrete pour, or in locations where spoil removal is difficult, screw piles have a clear practical advantage.

Are They Engineered or Off the Shelf?

Engineered. Every time.

Screw piles are not a product you buy from a hardware store and install yourself. A legitimate screw pile installation starts with the site geotechnical report. The engineer uses that report, along with the structural loads from the building design, to specify the pile diameter, helix size, minimum depth and installation torque for each pile on the project.

That specification is what the installation crew works to. And when the job is complete, the engineer issues a Certificate of Compliance under AS2159, the Australian Standard for piling design and installation.

That certificate is what confirms to your certifier, your client and your insurer that the foundation has been designed and installed to the required standard.

At Anchorpile, every project includes a site-specific engineering design and a Certificate of Compliance on completion. There are no exceptions to that process.

What Projects Are They Suited To?

Screw piles are used across a wide range of project types in South Australia.

Residential single and dual occupancy builds are the most common application, particularly on sites with reactive clay soils, deep fill, restricted access or trees. Multi-dwelling residential projects and townhouse developments are another significant area, where speed of installation and program certainty are important. Aged care and community facilities, where ground conditions are often challenging and certification requirements are high, are also a strong fit. Commercial and light industrial projects rounding out the application range.

If the site has difficult ground conditions, limited access or a tight program, screw piles are worth a serious look.

What Does It Cost?

Screw pile pricing is fixed before work begins. The cost depends on the number of piles, the specified depth, the pile diameter and the site conditions.

Unlike concrete footings, where the final cost can vary depending on what the excavation reveals, screw pile pricing does not change once the proposal is accepted. What is quoted is what is invoiced.

For a more detailed breakdown of screw pile costs in South Australia, read our guide: How Much Do Screw Piles Cost in SA?

Want to Know If Screw Piles Are Right for Your Project?

The fastest way to find out is to send through your geotechnical report and site details. Anchorpile will review them and come back with a fixed-price proposal and a straight answer on whether screw piles are the right solution for the site.

Anchorpile is a division of IdealCorp. Engineered screw pile supply and installation across South Australia. AS2159 certified. Certificate of Compliance on every project.