HS2 have just revealed stunning new timelapse footage showing engineers carefully sliding a 3,700-tonne viaduct deck almost half a kilometre uphill into position near the town of Wendover in Buckinghamshire.

The deck of the Wendover Dean Viaduct – which stretches for 450m – was assembled in three stages, ranging from 90m to 180m, with each one pushed out from the north abutment before the next section was attached behind it.

This painstaking, eight-month long process meant that the weight of the deck increased with each push, up from an initial 590 tonnes at the start of work in January – to 3,700 tonnes by the time it reached the south abutment on Saturday.

It is one of 50 major viaducts on the HS2 project – which is designed to improve connections between London, Birmingham and the North while freeing up space on the most congested southern end of the existing West Coast Main Line.

During the slide, special pads covered in Teflon – a material usually found on the surface of a non-stick frying pan – were used to minimise friction between the deck and the temporary steel bearings on top of each of the concrete piers.

To help maintain control, the deck – which weighs the same as 264 double-decker buses – was pushed slightly uphill, with the finish point approximately 1.8m higher than the start point.

With the steelwork now in position, engineers can begin the challenging job of lowering the deck 60cm onto the permanent bearings which will support the full weight of the structure.

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

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.”

Once the deck is in its final position, work can begin on the concrete that will support the railway using a specially designed travelling formwork. Moving slowly from north to south, this stage is expected to take around a year and will be followed by the installation of the parapets along the edge of the viaduct.

The Wendover Dean Viaduct is the first major railway bridge in the UK to be built with a ‘double composite’ structure, which uses significantly less carbon-intensive concrete and steel than a more traditional design.

Instead of using solid pre-stressed concrete beams to form the spans between the viaduct piers, the hollow ‘double composite’ structure uses two steel beams sandwiched between two layers of reinforced concrete to create a more efficient super strong span.  A similar approach is also being used at Small Dean, Westbury, Lower Thorpe and Turweston, which are all at an earlier stage of construction.

All five viaducts are being built by HS2 Ltd’s main works contractor, EKFB – a team made up of Eiffage, Kier, Ferrovial Construction and BAM Nuttall – with the manufacture and installation of the beams being led by specialists at Eiffage Metal.

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.”

The last few months has also seen significant progress at HS2’s other major viaducts, including the key structures that will form the Delta Junction in North Warwickshire and the viaducts taking the railway into Birmingham Curzon Street.

In total, HS2 is building more than 500 bridging structures – ranging from small road bridges to the record-breaking Colne Valley Viaduct which will become the longest railway bridge in the UK when the deck is finished later this year.

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