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Screwing down the contracts

Spotlight - A piling technique that was invented more than 170 years ago to support lighthouses is being reintroduced into the UK.

Screw piling was invented in the UK in 1833, and used for the foundations of piers at Brighton and Blackpool, as well as numerous lighthouses in tidal basins around the coastline. Their use declined, however, until they were re-introduced in the USA after the First World War.

For the last four years ScrewFast has been working to develop the market for screw piles in the UK, and has found great success in the telecommunications and rail industries.

'Screw piles are particularly suitable for structures that are subject to overturning moments and have reciprocal load - such as signal gantries and telecommunications towers, ' explains ScrewFast's Rod Ward Able. 'Both tension and compression loads can be taken on the same pile providing the design is done correctly.' While ScrewFast's initial success came in telecomms, its fastest growth area is rail.

It has worked with many of Network Rail's contractors to install foundations for signals and overhead line electrification gantries. Ward Able admits: 'At one stage we almost threw in the towel, because every time we went to a new contractor we had to prove the system again.' However, persistence paid off, and the company has helped Network Rail write its specification for screw piling.

'The standard we have now is quite onerous, so many new entrants into screw piling will steer clear, ' he says.

His next target is the highways sector, and ScrewFast has applied for product approval for the system from the Highways Agency, believing it would be highly suited to the construction of sign gantries.

'The highways sector could benefit greatly, because this system saves a lot of time and money in producing foundations, ' he explains. 'We can install foundations in hours - rather than days - and the method is more environmentally friendly than conventional piling methods as, usually, no excavation is required. And if the structure is taken down the pile can be screwed out and re-used, so you're not creating dig and dump problems.' Ward ble escribes screw pile as a 'giant selftapping screw', buts says the real trick is in the design.

ScrewFast carries out all the designs itself and has them independently checked by a consulting engineer, but installation is carried out by the main contractor using equipment supplied by ScrewFast, which also provides training for the contractor's operatives.

The theory behind the technique is exactly the same as spread foundations: the steel piles work on bearing plate theory rather than friction or end bearing. Other than solid rock, Ward Able says, screw piling can be used in almost any ground conditions where conventional piling would be used. The company has adapted mining applications to deal with particularly dense materials.

If you carry out a direct cost comparison on the basis of a steel screw pile versus a conventional concrete bored or augered pile, screw piling comes out more expensive, but ScrewFast says clients are looking for methods that are faster and less disruptive.

'With screw piling there's no excavation and you are not on site for days, ' says Ward Able. 'The whole thing is completed very quickly, and speed these days really equates to money.' This aspect is, he says, particularly appealing to the highways sector, where engineers are keen to reduce the length or number of road closures, diversions or traffic management systems.

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