The deck of the 450m-long Wendover Dean Viaduct – which stretches for 450m – was assembled in three stages and in sections ranging in length from 90m to 180m. Each section was pushed out from the north abutment before the next section was attached behind it.
The whole process took eight months, with the weight of the deck increasing with each push – from 590 tonnes initially to 3,700 tonnes by the time in reached the south abutment last Saturday (10th August).
To reduce friction and assist the launch process, engineers placed special Teflon pads between the underside of the deck and the temporary steel bearings on top of each of the concrete piers. The steel deck beams were manufactured and installed by French specialist Eiffage Metal.
With the steelwork now in place, main contractor EKFB joint venture (comprising Eiffage, Kier, Ferrovial Construction and Bam Nuttall) will now lower the deck 600mm onto the permanent bearings. This two-month operation involves lowering the steelwork in 200mm increments, sequentially pier-by-pier.
When this is completed, EKFB will use special travelling formwork to cast the concrete rail bed on top of the deck
The Wendover Dean viaduct is one of 50 major viaducts on the HS2 project and the first major railway bridge in the UK to employ a double composite structure which, according to HS2, 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 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 the EKFB joint venture using beams made by Eiffage Metal.
Nicola Henderson-Reid, HS2’s head of delivery, 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.”
EKFB’s senior project engineer, James Collings, added: “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.”
HS2 said that there has also been 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 station.
In total, HS2 is building more than 500 bridging structures, ranging from small road bridges to the Colne Valley viaduct which will be the longest railway bridge in the UK when the deck is finished later this year.
Watch timelapse video of the operation
