Barrett Byrd Associates

Excited youngsters will descend on LEGOLAND near Windsor this spring to take a ride on the attraction’s latest rollercoaster. Mike Walter reports on the structure’s firm foundations.

Further proof that LEGO bricks can be used for constructing far more than simple static models will be provided next Easter when the new ‘Jungle Coaster’ rollercoaster opens for business at LEGOLAND. Riders will sit in cars that resemble fully functioning LEGO models, no doubt excited but nonetheless secure in a first class structure.

The rollercoaster will take riders around a 400m long track that rises to a height of 16m and snakes 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.

Structural stability for the rollercoaster is founded on 123 Continuous Flight Auger (CFA) piles, bored through fill and London Clay by the House Foundations division of specialist contractor Roger Bullivant Limited (RBL). This method of providing a foundation was chosen by engineer Mott MacDonald, the project being overseen by main contractor Brymor Contractors.

RBL’s divisional manager Andy Preece says that CFA piles were a good choice for the rollercoaster because they are able to cope with dynamic changes in both tension and downward load. “Forces exerted on the foundations of a rollercoaster are unusual and are unlike those associated with a conventional structure that has a static load,” he says.

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 180 degrees while suspended from the main structure on a cantilever. “Forces will be exerted in a horizontal direction rather than a vertical one at the moment a vehicles passes this point and the CFA piles effectively accommodate this change in load,” he adds.

Each CFA pile measures 450mm in diameter, was installed to depths of between 10m and 11.5m and reinforced with a cage of six T32 steel bars to a depth of 10m. Conventional driven piles would have been unsuitable for the site because any lateral displacement of earth associated with the driven method could have disturbed adjacent pile positions, adds Preece.

Piles were created using a 12m high, 5004 series CFA rig. The rig’s auger was bored through 5m of fill before hitting London Clay at a depth of 7m. With RBL’s system used on site, two cubic metres of pre-mixed concrete were fed down the centre of the auger for each pile, the pressure of an 11m head of material then causing a plastic bung at the tip of the auger to blow free. As the excavated ground began to fill with concrete, the auger was withdrawn and the concrete was pumped through the void created by the auger to form the pile.

CFA 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 in situ cap. A series of single piles was also created that was topped with a mass concrete base.

Each of the in situ pile caps had cast into them a special holding bolt arrangement, designed to receive vertical columns that support the rollercoaster. The bolt arrangement is about one metre tall and features 10 threaded bolts held together with two circular disks, one at each end. The steel columns were screwed down onto the holding bolts once their positions were accurately verified.

Brymor Contractors site manager Robert Burr says: “It is critical that the holding bolts are 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, after which time the steel rollercoaster structure was assembled. Two weeks of testing at the ride will be followed by safety training for staff at LEGOLAND ahead of the ride’s official opening on 20 March.

The groundworks contractor also installed a series of piles for a new plant room where the ride’s vehicles will be maintained and for an open platform where visitors will stand to join the ride.

Robert Burr says: “LEGOLAND was previously home to Windsor Safari Park and the rollercoaster site was occupied by a lake where hippopotamuses bathed. This was one of the last areas of the site left to develop and there are plans to construct a bridge across an adjacent lake for people to use.”

Bullivant’s Andy Preece adds: “This is the second time we have provided foundations for a new rollercoaster ride, following a contract to install piles at Thorpe Park. CFA is a well tried method of piling and its use at LEGOLAND goes to show that ways of providing a relatively traditional foundation for buildings can equally be applied for more unusual structures such as a rollercoaster.”

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