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M4 overbridge

M4 Agricultural Overbridges, UK

We created a strengthening solution for nine reinforced concrete overbridges that were deemed at risk of failure due to thaumasite sulphate attack. Our solution avoided costly and disruptive bridge replacement.

Embodied carbon

80 year life extension

1970s bridges are supported on inclined reinforced concrete piers, the feet of which are connected by concrete tie beams buried beneath the motorway, and to the ends of the bridge deck by raking tie beams.

We installed a new reinforced concrete anchor beam at each end of the bridge deck, enabling it to be tied down by clusters of minipiles. A new cross tie was installed between each pair of piers to prevent existing foundations from being overstressed.

This made the original tie beams structurally redundant, restoring the bridges’ full 120 year design life. Replacing each bridge would have cost £3M, generated 210t of embodied carbon and taken six months to complete, with overnight motorway closures and narrowed lanes.

Our solution cost only £300,000 per bridge, with approximately 20t embodied carbon dioxide (CO2) and took six to eight weeks with motorway disturbance limited to hard shoulder closures.

Client: Highways Agency

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