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CFA piles take on Legoland's rollercoaster forces


PROOF THAT Lego bricks can be used for building far more than simple models will be provided this Easter when the new Jungle Coaster rollercoaster opens for business at Legoland near Windsor, UK. Riders will sit in cars resembling functioning Lego models.

The rollercoaster will take riders around a 400m long track rising up to 16m high, sending them through a series of twists, turns and descents. The ride takes on the theme of a model test track where children can experience the concept of vehicles accelerating, braking and turning.

The rollercoaster is founded on 123 CFA piles installed by the House Foundations division of UK contractor Roger Bullivant.

Foundations were designed by consultant Mott MacDonald, with overall work carried out by main contractor Brymor Contractors.

Bullivant's divisional manager Andy Preece says CFA piles were a good choice as they are able to cope with dynamic changes in both tension and downward load. 'Forces exerted on rollercoaster foundations are unusual, compared to a conventional structure that has a static load.'

Conventional driven piles would have been unsuitable because any lateral displacement of ground during installation could have disturbed adjacent pile positions, he adds.

The distribution of load on the structure can vary as four seater vehicles race around the track. Vehicles at one point of the ride, for instance, will turn through 180infinity while suspended from the main structure on a cantilever. 'Forces will be exerted horizontally rather than vertically at the moment a vehicle passes this point and the piles accommodate this change in load, ' Preece says.

The 450mm diameter piles are between 10m and 11.5m long and reinforced with cages of six T32 steel bars down to 10m depth. They were installed through 5m of fill into the London Clay using a 12m high, 5004 series CFA rig.

Piles were installed in 22 groups of four where the structure's load was deemed to be greatest and were covered with a 2.1m square cast insitu cap. Thirty five single piles were installed, topped with a mass concrete base.

Each of the pile caps had a 1m high holding bolt arrangement cast into them, designed to receive columns supporting the rollercoaster.

The bolt arrangement has ten threaded bolts held together with two circular disks, one at each end. The steel columns were screwed down on to the holding bolts once positions were accurately verified.

Brymor Contractors site manager Robert Burr says: 'It is critical that the holding bolts were positioned in exactly the right place to receive the steel columns. Once in place, they can be adjusted only by 1mm in each direction.'

Around 30 CFA piles were installed in each of the seven days Bullivant was on site.

Foundations were constructed in a sequence that followed the route of the new track and each pile was integrity tested.

Installation of piles, caps and holding bolts was completed during January. Construction of the rollercoaster was then carried out, followed by two weeks of testing. The ride is due to open on 20 March.

As part of its contract, Bullivant also installed a series of piles for a new plant room and an open platform where visitors will queue for the ride.

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