Balfour Beatty Civil Engineering Ltd

A404(M) Western Region Railway Bridge

Birse Civils, a division of Balfour Beatty Regional Civil Engineering, was the main contractors appointed by The Highways Agency. It replaced the Western Region Railway Bridge, which carries the A404(M) over the mainline railway between London and the West of England.

The re-opening marks the completion of the two-year project, which has used innovative techniques to keep the A404(M) open to traffic at all peak times throughout construction, as well as minimising disruption for passengers on the Great Western Main Line railway beneath.

The £10m scheme has involved dismantling and the rebuilding the bridge in sections, and then sliding the newly built sections, weighing up to 1,300 tonnes each, into place. In total, three of these bridge slides have been carried out. This innovative process used a Demolish, Build, Slide, Switch methodology to simplify the reconstruction process whilst maintaining live traffic lanes.

The final bridge slide was carried out 25 June 2011

To facilitate the 12.344m bridge slide within a 3 ¼ hour full railway closure of the Great Western Railway a 53 hour road closure of the motorway was required.

The overall weight of the bridge was 1,400 tonnes and involved the use of eighteen 150 tonne Jacks for the vertical jacking of the bridge onto the skid shoes. Once jacked the bridge was pushed/pulled using six hydraulic push/pull cylinders for the slide operation. Upon completion of the bridge slide, the carriageway was resurfaced and the traffic management reconfigured for the new road layout to allow the final stage of construction to commence.

The final stage of the works involved the removal of the temporary trestles which enabled the new bridge deck to be constructed offline and slid into position. It also involved the finishing operations to the structure with the installation of the Gallery steelwork access platforms, completion of the earthwork embankments, verges, environmental acoustic barriers, h4a and VRS barriers adjacent to the highway.

Once these operations were completed, then the traffic was switched again to allow the central reservation works to be completed which involves reinstalling the filter drains and VRS safety barriers. This allowed the final wearing course to be installed and the motorway to be reopened to the national speed limit.

Highways Agency structures manager Steve Cobb said:

"Replacing this bridge has been a complicated and technically challenging task, and everyone on the project team has worked extremely hard to keep disruption to an absolute minimum - for local people, railway users and of course the 53,000 drivers who depend on the A404(M) every day.

"The new bridge will help keep journeys on the motorway safe and reliable for decades to come. People living near the road will also benefit from the project, as noise reducing barriers along the road near the bridge have been upgraded, and are also being provided on the bridge itself for the first time.

"Our contractor Birse Civils and supervising agents EnterpriseMouchel have produced a quality, good value design and have carried out the work in a surefooted yet flexible way. I'd particularly like to thank drivers on the A404(M), as well as people living and working in Maidenhead for their patience and goodwill while we've carried out this important work."

The scheme was winner of the Highways Magazine Major Projects Excellence Award.

Due to the complexity and success of the A404(M) Western Railway Bridge scheme, it was entered into the Highways Magazine Major Project Excellence Awards. The scheme was shortlisted along with other high profile prestigious schemes within the UK. Birse Civils and The Highways Agency were delighted when, against tough competition, the A404(M) scheme rose to the top and was awarded Winner of the Major Project Excellence Award 2011.

Judges comment; "some good innovative design to deliver a technically challenging scheme with minimal disruption to either road or rail users"

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