Faq

To rust steel, you need a medium to allow rust like moist soil, iron (which you have in the steel pier), and oxygen.

The medium to allow rust will vary from soil to soil. A few tests of the soil reveal the soil’s ability to conduct electricity and promote rust. The pile can be designed to accommodate that conductivity – usually using a thicker wall section. Interestingly, many soils in western NSW exhibit such properties, so while there is not much water in that soil, it can still rot out fence posts at ground level very quickly.

There’s iron in steel, so you have to accept that. The thicker the steel, the longer it takes to rust away. A hot dipped galvanised coating can be applied.

You don’t have much oxygen under the ground, as it has been pretty well squeezed out. It is a different matter above the ground, so it is important that the steel pier is encased in concrete near the surface.

So yes, they will rust, but there are plenty of design approaches to take to ensure the pile is guaranteed to last as a structure for at least 75 years in house construction. Longer in other applications.

It depends on the ground conditions. Mostly they go 2 – 3 meters.

It depends on the ground conditions. In wet sand, silt, or clay, the hole will not stay supported and will fall in. The hole will also fill with water; you need to pump the water out before you place the concrete. Screw piers just engage the ground, wet or dry, very easily.

If concrete piers are founded too shallow and the pile settles with the house on it, the slightly dearer screw pier suddenly looks a good alternative to the cost of underpinning the house.

Screw piers are much faster to install, allowing the slab to be poured sooner, even the same day.

Per lineal meter, they are cheaper. They usually go deeper as they reach a stronger base than a concrete pier.

We think they are because the Structural Engineer can be advised the accurate SWL of each steel screw pile. Whereas a concrete pile is dependent on the operators reaching material that matches the expectations of the geotechnical engineer. Nobody actually goes down to the bottom of the bored pier hole and checks if it is as strong as they predicted. This is a worrying feature about concrete bored piers

They are always a lot quicker. Concrete piers need a hole bored, the spoil removed, a concrete truck to come, and men to place the concrete. Sometimes they need steel reinforcement to be placed if they are longer than say, 1.2 – 1.5m

And, concrete piers are weather dependant. It’s very hard to place concrete with an agitator truck when the site is wet. Steel piers are installed by an excavator, which can walk pretty well anywhere, anytime.

That’s the best question. The Structural Engineer will have specified a Safe Working Load (SWL).

Our East Coast Screw Pier excavators have a calibrated pressure gauge, which lets the installer know when the 50kn pressure/SWL is obtained. If not, we bolt on extensions and keep screwing in until the pressure is obtained. A fool proof method of confirming the pile will carry the specified required load.

East Coast Screw Piers can issue the design engineer with independent certification of the achieved pile loads if required, along with the install records (depth achieved and torque applied) of each individual pile.

Installation torque is the same as when you use a screw driver to screw a self-tapping screw into a piece of wood. The deeper you go, the harder it is to turn, so the more torque you need to apply to get the screw to continue to penetrate into the timber.

Once the operator gets that pressure – bingo, job done. That pile is then able to withstand that SWL with a safety factor of 2 ½ or more.

Most steel piers for residential work are designed for 5 tonnes – 50 KN SWL. The bulk of piles for houses have this safe capacity.

We have installed piers to 500KN (50 tonnes) using bigger machines to account for bigger loads. These are the exception rather than the rule for us.

Surprisingly, a 500Kn pier will penetrate about the same depth as a 50 KN pier. This is because the features of the pier (the helix) are designed specifically for the SWL.

(i.e.) the 50KN pier has smaller helix (much smaller!) than the 500 KN pier.

The screw pier can be installed in very poor ground. It is limited by the ability of the excavator to access the location. Water charged ground is no problem, whereas a concrete pier needs special equipment (sleeving) to perform. This sleeving equipment is not economic for residential work.

Yes, generally 50 – 60% of the compression SWL is the tension (uplift) SWL, as long is the pile is at least 2 m deep.

Yes, there is. AS 2159 – Piling Code. The Code covers all types of piles, including concrete and steel.

A professional engineer, registered with the State Government or an Association can design them. His/her design plans will be submitted to the Council for approval, and the designer’s details are explained on that drawing.

Just refer to our design aids on this web site.

A few come to mind:

1.1. Lateral stability in very, very soft material. Imagine a 10m long pile through very soft material, the pile could act like a stick of connected spaghetti. I have not had this in my experience, but it could happen.

1.2. Very expansive clay (Class “H”, “E”) need special attention. If you screw through that clay and engage well below, then the house moves up and down, the joint between slab and top of pile can fail. There are steps to take to remove the risk.

1.3. Very corrosive material. In our region (Mid North Coast – NSW), we might have met one poor site for corrosion (in hundreds or thousands). But it can happen. The chemistry these days is such that we can provide a thicker wall thickness to accommodate higher corrosion rates, to guarantee 75 years’ service.

1.4. Some structural engineers are not familiar with them (steel piers) and there can be a tendency to overdesign or pick a SWL that is not a common one. These issues can be resolved with a phone discussion with the structural engineer.

For houses the piles are usually in stock. A bit of paperwork, a check of geotechnical information, and within a week from first contact they can be in the ground, waiting for the builder to carry on with the house.

For bigger or specialised jobs, there is more paperwork, and the piles are usually different (higher SWL), so a couple of weeks will be needed. But this time frame always falls within the parameters of the larger jobs.