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A definite Mabey

Belfast - One of the largest temporary bridge lifts in the UK is currently underway in Northern Ireland.

The upgrade of the A12 west of Belfast to motorway standard is a major project for the province. It is its first design, build, finance, operate (DBFO) scheme, it is a major arterial route with 65,000 daily road users, and it is calling for some pretty clever engineering.

The project has been let to the Highway Management Construction (HMC) joint venture comprising John Graham (Dromore), Northstone NI and Bilfinger Berger. Client is Northern Ireland Roads Service.

Work on the 'Westlink' began on 27 February this year, something that cannot have gone unnoticed by regular users.

But project director Leo Martin, who has been involved in the project since the tender prequalification in April 2004, is confident that HMC will deliver this highly complex project within the agreed programme. 'With 65,000 daily road users on the Westlink, we are well aware that the Northern Ireland public has more than a fleeting interest in this scheme, ' he says.

'The highly complex scheme involves all aspects of civil engineering from secant, CFA and precast piling to conventional road works, lightweight fill and extensive temporary works.' The main elements of the work are at the three main junctions: Stockman's Lane, Broadway and Grosvenor Road.

The latter is certainly the most dramatic, and is happening right now with Mabey Support Systems constructing a temporary diversion off Grosvenor Road bridging over the existing A12 to enable reconstruction of the road junction.

The Grosvenor underpass is a partial one with the Westlink carriageway being lowered by 4m and the Grosvenor Road being raised by 3m. Westlink traffic will be temporarily moved to the outside of the proposed underpass to facilitate top-down construction of the underpass, the permanent bridge and the approach embankments.

The 136m long bridge is being created from 600t of Mabey Universal bridging and Mat 75 trestling. It will form a seven span bridge with a 7.35m carriageway and two cantilever footwalks.

The real challenge came from the poor ground. The original concept was for a three span bridge but extra spans were added to reduce the volume of costly piled approach embankments. With the revised layout the temporary bridge can make use of secant piles already installed for the permanent structure. 'This makes it unusual because it puts the bridge's main supports on a skew, ' says Mabey product manager Bernard Ingham.

The bridge erection should take a total of three weeks. Erection began from each side with the main span sections lifted in at night. The bridge is on hire for a total of 56 weeks. After that it will be dismantled and reused.

'Around 95% of the equipment is standard stock and can be dismantled and reused, ' says Ingham. 'So it's pretty sustainable.'

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