HS2 has published new timelapse footage of engineering workers completing the deck slide at the Small Dean viaduct in Buckinghamshire.
HS2 has been working on this viaduct for four years. It has prepared the site, diverted utilities, realigned the road, built the abutments and the six piers that support the viaduct, and assembled the deck.
Last year, it installed the support piers.
The single-stage viaduct deck slide is the heaviest and longest on the project to date.
It took four days, and was completed Sunday 2 February. It involved sliding the 4,500-tonne deck across a road and railway line.

Before beginning the slide, workers assembled the viaduct’s concrete and steel deck to its full, 345-metre length.
More of the precast concrete deck slabs had been installed in advance of the launch. This made the slide heavier, but will save time later stages in the project.
Workers used pads covered in Polytetrafluoroethylene (PTFE) to reduce friction between the deck and the steel bearings placed temporarily on top of each support pier.
They then used a cable system to slide the deck forward. They moved the deck at speeds of up to ten metres per hour.
The next stage of the viaduct’s construction is for engineers to lower it by 60cm onto the permanent bearings. These will support the full weight of the viaduct.
This work will take two months, and will involved lowering each pier by twenty centimetres at a time.
Like the nearby Wendover Dean viaduct, the Small Dean viaduct’s deck is made from weathering steel. This naturally ages to a dark russet colour, which HS2 believes will echo the natural tones of the local environment.
HS2 will realign Small Dean Lane and the A413 under the viaduct. It will create landscaping in the form of a series of subtle terraces. These will manage the change in height between road, paths, railway and viaduct. There will be a shared foot and cycle path alongside the main road.

“Small Dean is the longest continuous deck slide on the project and an amazing engineering achievement. But it would not have been possible without the huge amount of preparatory work put in over the last few years and I’d like to thank everyone involved. Two years ago, we set a target to install the deck in summer 2025 and it’s great that we came in ahead of schedule.”
Jason Bicknel, HS2 Ltd Project Manager
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