Published at 10:43 on Friday 12th January 2024
Tags: HS2, Wendover Dean Viaduct, Construction, Bridgework

The temporary 'nose' of the beam resting on the first pier during the Wendover Dean deck slide on 10th January 2024. HS2

Engineers this week began a delicate job that will result in almost half a kilometre of bridge deck slid into position over the next year, above the Misbourne Valley in Buckinghamshire.

The 450m-long Wendover Dean Viaduct will be the first major railway bridge in the UK to be built with a ‘double composite’ approach, which uses significantly less carbon-intensive concrete and steel than a more traditional design. It is one of 50 viaducts on the HS2 project.

Instead of using solid pre-stressed concrete beams to form the spans between the viaduct piers, the ‘double composite’ structure uses two steel beams sandwiched between two layers of reinforced concrete to create a lightweight and super strong hollow span. Due to the length of the viaduct, the deck is being assembled in three stages, ranging from 90-metres to 180-metres, with each one pushed out from the north abutment before the next section is attached behind it. This painstaking process means that the weight of the deck will increase with each push, up from an initial 590 tonnes to 3700 tonnes by the end of the year.

A winch is used to push the deck forward at a speed of around 9 metres per hour, sliding across Teflon pads to reduce friction – a material usually found to the surface of a non-stick frying pan. It is the longest deck slide on the HS2 project to date. At this point in the Chilterns the railway will be on a slight gradient, so to help maintain control, the deck, which will eventually weigh the same as 264 double-decker buses, is being pushed slightly uphill, with the finish point approximately 1.8m higher than start point. The beams are made of ‘weathering steel’ which naturally fades to a dark brown colour over time and will help match the natural tone of the surrounding countryside.

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