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State your position

Global positioning systems are finding increasing use in the construction industry, and take-up in the piling industry could be about to accelerate.Max Soudain reports.

When the US military developed the Global Positioning System (GPS) in the late 1970s and early 1980s, it heralded the start of a new era in navigation.

Offering unprecedented accuracy, GPS has been whole-heartedly embraced by sailors, explorers and of course the military. Now the construction industry, often viewed as slow to react to new technology, has begun to appreciate its benefits.

Neil Ackroyd, technical manager of GPS manufacturer and supplier Trimble Navigation, says that the role of the military is part of GPS's image problem.

'People worry about military involvement but the US Congress has passed legislation for civil use of GPS, which means it will never be switched off or restricted.'

Another reason for the construction industry's slow take-up of the technology is, says Ackroyd, because 'the technology is not recognised as being as accurate or as mature as it is'.

Trimble experienced similar patterns when it first started promoting its systems in the offshore and mining industries, where GPS has become an integral part of operations.

'There was a long period of slow take up as the technology matured, 'Ackroyd says, 'but as it matured, the speed of take-up accelerated.'

Although the signal is degraded for commercial systems, they can now offer accuracy of between 10mm and 30mm, well within the needs of the construction industry, he says.

In construction, Trimble has had most success in the field of earthmoving, especially on large-scale infrastructure projects, offshore piling and, to some extent, in onshore foundation work.

It was not plain sailing, however.

'One of the first problems we found was in the robustness of the equipment, ' admits Ackroyd. 'Most of the problems were mechanical - our systems were not designed for the vibrations and hard working environment.'

Development over the last two or three years has been focused on beefing up the on-board hardware.

The other area of concern was the operators, so development has also looked at operational use. Ackroyd claims drivers can get to grips with the systems within a couple of hours and that they have been very receptive to the new technology.

'We haven't had as many problems as we expected with driver acceptance, ' he says. He atrributes this to the realisation that the systems are useful tools, rather than a hindrance.

'It is enabling technology, allowing drivers to work faster and more efficiently.'

For large infrastructure projects such as rail or road construction, one or more GPS reference stations are set up at accurately surveyed points to provide a fixed grid for the lifetime of the project. These provide reference points for the on-board GPS receivers, so that the driver can tell exactly where the machine is in 3D space, reducing the need for traditional 'pegs in the ground' surveying. (As Ackroyd points out, surveyors have been using GPS for some time. ) GPS is being used on the first phase construction of the Channel Tunnel Rail Link in Kent, with six permanent reference stations managed by client Rail Link Engineering allowing a common site reference system for all the subcontractors.

Trimble launched its SiteVision system for earthworks last year. The 'earthmoving grade control system' consists of two GPS antennas mounted at each end of the bulldozer blade, a GPS receiver, a driver display and three lightbars mounted on the cab.

Site design in the form of plans or a digital terrain model is downloaded to the on-board computer which then works out where the machine is and how much cutting or filling is needed at that point by referring to the site grid.

This information is transmitted to the operator via the colour display and the light bars, which guide the driver up and down (for blade control) and left and right for alignment.

Ackroyd says the plan over the next year or so is to bring all the different machines working on a construction site under an umbrella system of a 'virtual grid', integrating the different systems used by different subcontractors.

At the moment, GPS is still only used regularly on big projects and is not filtering down to smaller jobs. He expects the situation to change in the next two to five years.

'It is not difficult to imagine. Two to three years ago, GPS was very rarely used on construction sites and is now common on earthmoving contracts.'

There is already great interest from the trenchless technology industry, where it is essential to define where pipes are being laid.

Ackroyd believes this is partly because contractors are more receptive to new technology, 'as they are innovating themselves'.

GPS is also finding its niche in other areas of geotechnics such as piling. Trimble carried out developmental work on rig positioning systems with Stent in the mid-1990s. The biggest practical use to date was at the Bluewater shopping development near Dartford in Kent where a joint venture of Kvaerner Cementation Foundations and Stent used GPS to place more than 16,000 piles, with piling positions downloaded directly from electronic drawings stored on the site computer network.

Despite such high profile applications, the piling industry is one of the slowest areas of the construction market in terms of take up, but Ackroyd is being pat ient .

GPS shows its benefits on difficult sites, where survey pegs can be lost for example, he says, although he admits that the system also depends on the accuracy of the rig. For example, the development of continuous flight auger piling computer systems means that these are the most suitable at the moment.

'Control of the piling process itself is very important - if you don't have accuracy then it is difficult to use GPS.'

Availability of GPS is set to increase over the next few years, with the launch of the Galileo network. This European system is now at the funding stage and satellites should be in place by the end of the decade.

A purely civilian system, it has been dubbed GNSS, or Global Navigation Satellite System, to differentiate it from GPS. Whether this will increase the use of such systems in the construction industry remains to be seen.

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