Your browser is no longer supported

For the best possible experience using our website we recommend you upgrade to the newest version of your browser.

Your browser appears to have cookies disabled. For the best experience of Construction News, please enable cookies in your browser.

Welcome to the Construction News site. As we have relaunched, you will have to sign in once now and agree for us to use cookies, so you won't need to log in each time you visit our site.
Learn more

Time is ripe for another turn of the screw

PILING

Screw piles may have been around for more than a century and a half but they are still considered a niche product by many UK contractors.

Two South African pioneers have set out to change all that, writes Andrew Barker

DUNCAN McGREGOR had a business empire in South Africa that any aspiring entrepreneur would covet. In true, stuff-of-dreams style, he built it from nothing, bought a private plane, and flew around the country taking care of his myriad investments.

But one extraordinary and terrifying incident made him give it all up, move away and start again from scratch. He was hijacked at gunpoint in his hometown of Johannesburg.

Fortunately, he lived to tell the tale.

'During the ordeal, I asked that they spare my life because I would like to enjoy my grandchildren.

I kept watching the muzzle of the gun and no flash occurred, ' he recalls.

The hijacking was the final straw for Mr McGregor.

He and his previous business partner, Rod Ward Able, who had suffered a similar experience, decided to uproot and move to the UK to start again. They both had ancestral ties with Britain and within a couple of years they were fully fledged citizens.

The two men's friendship goes back about 15 years.

Mr Ward Able had previously looked after the sales side of Mr McGregor's business, selling fibreglass pool shells all over the world.

In the UK they initially purchased a small geotechnical business. But within a couple of years it grew into a multi-million pound company ScrewFast.

The two men were shocked that piling using screw piles was so rare in England.

'People would ask what a screw pile was. When we explained these things have been around since Adam, they couldn't believe us, ' says Mr McGregor.

Rack after rack of horizontally stored piles makes the yard outside their St Albans base look like a medieval jousting club. On close inspection, each pile has its own nuances, whether it's the radius of the helix, the number of helical plates or the arrangement and ferocity of Tungsten teeth on the tip.

There's a wide range of plate sizes, from 300 mm to a giant 900 mm radius. The larger ones are saved for peat soils and the smaller ones for stiffer, clay soils.

Mr Ward Able has found that screw piling in the UK has a reputation for being synonymous with poor ground conditions, which makes people think of it as a niche market.

In fact, he argues, screw piling works in any ground conditions, good or poor, which has allowed ScrewFast to take on areas where the foundation of choice has traditionally been a big chunk of concrete.

'I have no problems with concrete, ' says Mr McGregor. 'It's a very effective foundation. But concrete does have lim itat ions. Typically, a 30 m-high telecommunications mast would require a foundation base about 7 sq m and 1.5 m thick. That's quite a lot of concrete, and would probably take about three to four days to pour, and then a curing period before the mast could be erected. With screw piling we can hold the same tower up with four screw piles and it will just take one day, ' adds Mr McGregor, who completed a material science degree as well as studying mechanical engineering.

Each section of pile is 2 m in length for ease of handling. The sections simply bolt on to one another.

But the spacing, size and number of the helixes vary, and are installed in the ground using a hydraulic torque head. The appropriate size of each pile is determined by the load it will carry and the ground type into wh ich it is d r iven.

'We take a look at the soil profile and that will tell us the k ind of depth that we need to get to, ' says Mr Ward Able. Then torque heads are attached, which, crudely speaking, are a hydraulic gearbox and motor, fixed onto the end of an excavator.

ScrewFast owns about 60 to 70 torque heads in different shapes and sizes.

'We've got one monster that needs a 25-tonne machine to carry it, which can install a screw pile with an ultimate capacity in compression of 200 tonnes on a single pile. We're fabricating these ourselves to suit our own needs and every time they come back from being used we recalibrate. There's a direct relationship between installation torque and bearing capacity, ' says Mr Ward Able.

While ScrewFast remains a consultancy, hired by the contractors, huge outfits like the Highways Agency have specifically asked contractors to use ScrewFast.

The company can lay claim to providing the foundation for more than 30,000 civils st ructu res.

So, what is the thinking behind a screw pile?

'In essence it's a screw, and everybody knows how screws work. If you're putting a screw into a hardwood like mahogany, you don't have to put it in too deep to get a pretty good holding. But if you're putting it into a piece of balsa wood, you need a massive screw in order to achieve the same pull-out or push-in capacity.

'Our formula works; the design is our forte, ' says Mr Ward Able.

Designing bespoke piles has earned the company a good reputation with Network Rail. Railway embankments have notoriously poor ground. To combat this, it has designed a rig to carry three screws that spread the load laterally through being driven into the ground at an angle.

The design continues to evolve. Mr McGregor, the technical expert in the operation, discovered that 'you don't actually need three piles to carry the weight' on some of the lighter structures, a discovery which is, perhaps, his 'Eureka' moment.

One of his latest designs has a set of four 'angel wings' that can be driven over the top of a pile. This led to a second innovation, the star pile, which isn't screwed at all and is similar in design to the post you would use to put up a garden fence.

'The installation is so rapid it's unbelievable, just a m inute or two. It would hold a lamppost or light ing columns; on the highways it would hold noise barriers - it has a myriad of applications, ' enthuses Mr Ward Able. Needless to say, patent applicat ions are in.

What does he see as the advantages screw piling has over the alternatives?

'Piling rigs are cumbersome. A 6 m screw pile can be installed in 10 minutes, using an excavator. The energy consumption is low. There's no noise, no vibration, and no spoils are generated. The beauty is that they are easily removable and recycled regularly.'

The list of clients is impressive. Nuttall, Carillion and Balfour Beatty provide regular work. ScrewFast covers the materials and skills training.

'We've got some nice working alliances. They find the work. We design the piles. Their own men install the piles, which gives them f lexibility, and we provide the on-site technical supervision and the specialist machinery that fits on their excavators. We try to keep ourselves to what we know best, which is training people, and we're very good at getting things manufactured, ' says Mr McGregor.

Thoughts of retirement are far off for the two naturalised English pioneers. With a staff of 20, jobs cropping up in far-flung places such as Indonesia and Namibia , an annual turnover of about £5 million a year and a year-on-year growth of around 30 per cent, Mr McGregor is not done yet with his second global empire.

'I'd like to ret ire one day. At some stage or another we're hoping someone appropriate might make an offer for our company. I wouldn't mind being kept on for a while because I enjoy what I do and I still think I have a useful role to play, ' he says.

Evolution of screw pile technology

SCREW piles were invented in the UK in the 1840s. The method was instrumental in the building in the Thames estuary of navigation lights, which sat on screw piles.

Furthermore 14 piers along the south coast were built using the method, including the Brighton West Pier, which was damaged recently by a fire. They were screwed in by hand as simple, single-helix affairs, driven in until they refuse from the deck of a barge. It was hard, manual labour.

The advent of steam took piling from a manual operation to a mechanical operation. Steam hammers could bash out a piece of steel section into the ground or riverbed a lot more easily than a bunch of lads trying to screw it in on the deck of a barge.

It was technical evolution more than anything else that saw the demise of screw piling in the UK.

The United States has brought tremendous impetus to the use of steel piling, albeit by mechanical means.

Many skyscrapers have been standing on steel piles for half a century. What ScrewFast has developed is simply a more sophisticated approach with the same technology.

The placement of Helix plates is more st rategic. They have to be placed in the best possible alignment with soil layers so ScrewFast can get the highest possible loadings into those piles under the local soil conditions.