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Thousands of piles installed on busway

Contractor BAM Nuttall is designing and building a 25.1km guided busway for Cambridgeshire County Council. When complete the £116.2M project will provide alternative public transport for people travelling along the busy section of the A14 between St Ives and Cambridge.

The two busway tracks are made up of two longitudinal precast concrete longitudinal beams with kerbs each side BAM’s piling subcontractor Aarsleff Piling is installing 2,150 piles to support the busway over a 4km section.

The initial piling scheme involved installing predetermined lengths of piles, but the ground conditions proved to be unpredictable. The combination of 250mm2 and 350mm2 section piles have to be driven through made ground, plus soft clay overlying variable bands of sands and gravels over stiff clay.

It was the intention for all piles to be end bearing and found in the gravels. "We [BAM and Aarsleff] agreed on supplying all of the smaller section piles – about 1,400 of the total – with a half pin joint. If a pile didn’t achieve the set in the gravel it was then just a simple task of pinning on an overpile section and driving to completion into the clay. Less than 10% of the piles have been extended in this way," says Aarsleff contracts manager Steve Gilbank.

Aarsleff started on site in October 2008 and planned to complete its £630,000 contract in one visit. However, flooding along one part of the site meant that piling had to be done in two visits. Aarsleff is expected to complete piling in February.

BAM Nuttall started on the £87M design and build contract in January 2007 and is on scheduled for the guided busway service to start operating in Spring 2009.

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