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Kijlstra's factory at Henlade in Somerset has produced complex bespoke components for modernising and strengthening the existing middle slip jetty at Portsmouth Naval Base which will be capable of mooring the Royal Navy's new flagship, HMS Queen Elizabeth.

Precast was chosen for the jetty primarily for speed of construction - the jetty needs to be ready to receive HMS Queen Elizabeth which is currently being fitted-out at Rosyth Dockyard.

Main contractor Volker Stevin has demolished the old 1920s jetty - comprising 1m thick concrete supported on a complex lattice frame. Part of the existing structure, dating from the 1970s, has been strengthened.

The new precast jetty is being constructed on reinforced tubular piles driven into the bed of the dock basin. It comprises a number of custom-designed precast components, all of which have been manufactured at Henlade using moulds made for the purpose by specialist suppliers in The Netherlands.

“The main supports are 31 cruciform beams measuring 10m in length, 2m high and up to 3.6m wide,” says Kijlstra's production manager Rupert Treadaway.

These giant T-shaped beams are adjoined by some of the 44 transverse beams ranging in length from 9m to 13m. Each one of the transverse beams is unique and some have splayed ends while others have straight ends and include cast in fittings for temporary works.

Both types of beams have insitu reinforcement placed inside them at the precast yard to save vital time on site. These will then be filled with insitu concrete on site.

The cruciform and transverse beams support the 205 reinforced concrete planks which complete the upper surface of the jetty. There are also 24 precast concrete pile-caps, some of which, says Rupert, are among the most complex components he's ever had to produce.

“There are 16 fender pile-caps comprising two types. The smaller ones weigh 32 tonnes; the larger ones weigh 50.2 tonnes.

“They are being cast in a very large and complicated mould measuring 2.5m x 2.5m x 5m long. The pile caps are all hollow, so the mould incorporates a collapsible steel core which has a hydraulic mechanism for removing it from the mould after the concrete has cured,” explains Rupert.

There are also eight 'raker' pile caps which are slightly smaller than the fender pile-caps.

The fender pile-caps are designed to withstand the lateral forces imposed by the 65,000 tonne Queen Elizabeth-class vessels as they come in to dock. They are complemented by fender infill panels which have special stainless steel plates cast into them to add strength and absorb the high friction forces acting on the jetty.

“This is undoubtedly one of the biggest contracts Kijlstra has secured in the UK and it's one of the most prestigious,” says Rupert. “It has been a challenging project due to the geological constraints on site which has meant design and manufacture has had to be adapted to accommodate.”

And so far, it is also a satisfied client, with all the components delivered on schedule to keep the project on track. Manufacture began at Henlade in March 2016 and the first batch was delivered to site in May. Kijlstra delivered the last consignment in October 2016.


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