HS2 has released time-lapse footage showing the 3,700-tonne deck of the Wendover Dean viaduct in Buckinghamshire being moved almost half a kilometre uphill into position.

It took eight months to complete the viaduct, with the weight of the deck increasing from an initial 590 tonnes at the start of work in January to 3,700 tonnes when it was completed by reaching the south abutment last Saturday, 10th August.

Wendover Dean is one of 50 major viaducts being built for the HS2 project.

Special pads covered in Teflon were used during the slide to minimise friction between the deck and temporary steel bearings on top of each of the concrete piers.

The deck weighs the same as 264 double-decker buses, and to help maintain control it was pushed slightly uphill with the finish approximately 1.8m higher than the start.

Engineers will now have a challenging two-month-long task of lowering the deck by 60cm onto permanent bearings that will support the deck’s full weight.

The steelwork above each pier will be lowered 20cm at a time, pier-by-pier, until the whole 450m long deck settles into its final position.

When the deck is in its final position, concrete to support the railway will be poured using a specially designed travelling formwork.

Starting at the north end, this will take about a year, followed by installation of parapets along the edge of the viaduct.

Wendover Dean Viaduct is the first major railway bridge in the UK to have a double composite structure that uses significantly less concrete and steel than a more traditional design.

Instead of using solid pre-stressed concrete beams, a hollow double-composite structure is used with two steel beams sandwiched between two layers of reinforced concrete to create a more efficient super-strong span.

A similar method is also being used for viaducts at Small Dean, Westbury, Lower Thorpe and Turweston, all of them being built by HS2 Ltd’s main works contractor, EKFB, comprising Eiffage, Kier, Ferrovial Construction and BAM Nuttall, and specialists at Eiffage Metal are leading the manufacture and installation of the beams.

HS2 Ltd s Head of Delivery, Nicola Henderson-Reid said:

“The last eight months have been incredible, and I d like to thank everyone involved in getting us to where we are today. It s been fascinating to watch the deck slowly inch into position, and we now look forward to the next stage of the project lowering the deck into final position and completing the complex concrete work that will support the new railway.

EKFB s Senior Project Engineer, James Collings, said:

“The final launch for Wendover Dean viaduct marks two years of teamwork from EKFB and our supply chain partners Eiffage Metal. I am very proud of our progress and would like to thank the team for their ongoing commitment to the safe delivery of the viaduct. Over the next three months, we will see the viaduct lowered onto its permanent bearings in preparation for its concrete deck.