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Sun November 28 2021

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Support structure saves £70m on railway flyover

17 Nov Network Rail and its contractors have saved £70m on a railway flyover project by changing the design.

The Bletchley flyover is supported by a prefabricated concrete box on top of the West Coast main line
The Bletchley flyover is supported by a prefabricated concrete box on top of the West Coast main line

Instead of putting the flyover on columns, it lies across a prefabricated deck.

Network Rail and the East West Rail Alliance are restoring the Oxford-to-Cambridge line by removing and replacing a flyover which crosses the West Coast main line at Bletchley.

The East West Rail project is being carried out with minimum disruption to live train operations. East West Rail Alliance is comprised of VolkerRail, Atkins and Laing O’Rourke.

The new structure, on the line between Bicester and Bletchley, is being built to last 120 years with minimal future maintenance required.

Instead of replacing the old flyover like-for-like, which would involve closing the West Coast main line below to build five supporting columns in between the tracks, it a protective box structure has been built over the West Coast main line.

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It acts like a rectangular railway tunnel, removing the need for separate supporting columns and providing a platform for the flyover to sit on. In the coming months track will start to be laid over the new flyover structure.

This means the West Coast main line does not have to be closed during the flyover replacement taking place above as the box structure provides a protective, physical barrier.

East West Rail Alliance project director Mark Cuzner said: “By working smarter we’ve been able to speed-up the project by around six months. At the start of the project, we built a protective wall next to the West Coast main line so we could safely build the box structure during the day when the railway is open, instead of working piecemeal at night-time when the railway is closed.

“Most of the components for both the box structure, and the flyover, arrived pre-built and were simply assembled on site, like a model kit or set of Duplo bricks. The simplicity of construction meant we could safely reduce the workforce onsite by 60%, cut the previously-forecast cost by £70m and get the job done six months quicker than planned.”

The flyover support structure is made from 138 concrete shell abutments and 103 precast concrete beams (each weighing 40 tonnes). A line possession over early May bank holiday this year enabled the lifting work to take placed and t replaced the power cables beneath the new flyover.

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