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Testing the water

CONE PENETRATION TESTING

Land trials provided a chance to see a seabed CPT in action without diving under water. Gareth Beazant reports.

Abrisk day at a BRE test site in remote Cowden, East Yorkshire, seemed an unusual spot for staff from two firms, Gardline Geosciences and Lankelma, to meet and mingle following the Gardline Group's acquisition of the CPT site investigation company in November.

But the main reason for the event was to test the capabilities of the newest addition to Gardline Geosciences' geotechnical fleet - the GTeC-2 seabed cone penetrometer testing unit - before it makes its debut on offshore projects in the new year.

The test site has around 20m of stiff clay, replicating the type of geology encountered beneath the sea bed.

The rig builds on the success of its older sister, the GTeC-1, which has 2,000m water depth rating, battery power, modem communications, and 5cm 2cone options, explains Gardline Geosciences general manager Marcus Noakes.

What is new is a wider range of thrust options using one, two or three stacked AP van den Berg Roson drive units. The benefit, says Noakes, is that the system can stay lightweight for standard shallow push requirements but deliver a 120kN thrust where deep pushes are required.

The land-based tests were to see how far the rig could push with a 5cm 2cone compared to a 10cm 2cone.

Subject to vessel and configuration the aim is to have 10m to 15m penetration capability.

'Having a greater thrust can really open new markets for us, ' Noakes says. 'And because GTeC-2 can be operated with modems there is no requirement for a large umbilical cable and associated spooler, and of course no risk of lengthy standby time while repairing damaged cables.'

'We've tried the 5cm 2core to find the best combination to maximise thrust, ' explains Lankelma technical director Andy Barwise. 'A smaller cone needs less thrust and theoretically could reach deeper.'

A sensor on the control unit indicates when the seabed bottom is reached. And an X and Y inclinometer built into the frame ensures the frame is stable and flat, preventing wasted effort and expense drilling on slopes, Barwise adds.

Early results indicated that a 10cm 2cone was giving the best performance as it creates a void behind as it enters the ground, allowing the rods to flow through without friction.

For the tests, the CPT was mounted on a track/truck unit which Lankelma believes is unique in the UK. 'Tracks allow the vehicle to go across very soft ground, ' explains Lankelma managing director Eric Zon.

'Once the wheels have been raised, it can be operated from the front with the steering wheel or from the rear with levers.'

'In this sector you can almost be called out blind, where it is a gamble as whether to use tracked or truck based equipment, ' explains Barwise. 'Having the option of both on a truck that can use roads is a great asset.'

Inside the control centre a range of technology allows smooth running of the testing process. Each truck can email or fax results back to a client or office for immediate comments.

Re-testing can then be done, if required, while the team is still on site.

The yellow frame of the CPT is modular, allowing it to be packaged and despatched by air freight worldwide and installed ready to go within hours of delivery.

'We are confident the new system will prove particularly useful within the expanding offshore renewable energy industry and to assist with many of the ongoing deepwater oil and gas developments around the world.

It will also provide support to Gardline Geosurvey's regular pipeline route and site survey projects, ' Noakes adds.

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