11th Feb 2022

HS2 opens new factory to produce segments for Colne Valley Viaduct

Our Align JV has opened a huge new factory as work ramps up on UK’s longest railway bridge.

Work on the UK’s longest railway bridge ramped up this week as HS2 began production of 1,000 enormous concrete segments that will form the deck of the Colne Valley Viaduct.

Stretching for 2.1 miles (3.4km) across a series of lakes and waterways just outside London, the viaduct will carry high-speed trains as part of the HS2 project, designed to improve rail links between London, Birmingham and North, boost the economy and provide a low carbon alternative to car and air travel.

The huge deck segments which weigh up to 140 tonnes are being made on site at a temporary factory built specifically for the project. The mammoth 100m long building, which is visible from the M25, has an internal volume of 105,000 cubic metres, making it larger than the Royal Albert Hall.

HS2 Project Client, David Emms said:

“We’re already making strong progress on the Colne Valley Viaduct, sinking the foundations, building the first piers, and now starting production at the new modular viaduct factory. Once complete, this iconic structure will carry trains at up to 200mph, improving connections across the UK, freeing up rail capacity and offering passengers low carbon travel options.

“It’s great to see how much progress has been made and I look forward to seeing work on assembling the deck structure later this year.”

Every segment will be a slightly different shape depending on where it fits into the viaduct and the modular approach was chosen to ensure quality, safety and efficiency in production and to avoid bringing them in by road.

At the peak of construction, around 12 segments each the size of a double-decker bus, will be cast every week using a ‘match-casting’ technique. This approach where each segment is poured against the previous one will ensure the whole arch fits perfectly when reassembled on site.

The huge project is being led by engineers from HS2’s main works contractor Align JV – a team made up of Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick.

Once construction is complete, the factory and surrounding buildings will be removed and the whole area between the viaduct and the Chiltern tunnel will be transformed into an area of chalk grassland and woodland as part of HS2’s ‘green corridor’ project.

The design of the Colne Valley Viaduct was inspired by the flight of a stone skipping across the water, with a series of elegant spans, some up to 80m long, carrying the railway around 10m above the surface of the lakes, River Colne and Grand Union Canal.

Set low into the landscape, wider spans will carry the viaduct across the lakes, with narrower spans for the approaches. This design was chosen to enable views across the landscape, minimise the viaduct’s footprint on the lakes and help complement views across the natural surroundings.

Work has also begun on the 56 giant piers that will support the viaduct, working from north to south. Weighing in at around 370 tonnes, the first 6m tall reinforced concrete pier was cast on site by a team of engineers who used a specially-designed formwork to create the shape of the structure. This was then removed after 4 days to reveal the final product.

Each pier is designed to support the full weight of the deck above and rests on a set of concrete piles going up to 55m into the ground. This foundation work began earlier this year and will require the construction of 292 piles and 56 pile caps across the whole length of the viaduct.

Once complete, the team will then use a specialised ‘launching girder’ resting on top of the piers to lift the deck segments into position.

In another visible sign of progress on the project, the team have also completed the construction of the first two of four jetties across the lakes to get equipment into position to support the construction thereby taking construction vehicles off local roads. Where the viaduct crosses the lakes, the piles are being bored directly into the lakebed, using a cofferdam to hold back the water while the pier is constructed.

Inside the HS2 mega-factory making the UK's longest railway bridge

So we're in precast factory for the viaduct segments
for the Colne Valley Viaduct.
It's a purpose built factory for the 1,000 segments
that we have to prefabricate for the viaduct.
This is a 3.4 kilometre long viaduct,
which we are building as a segmental bridge.
So meaning it's sliced into 1,000 segments,
and that's the first one of these 1,000 segments
that will effectively make up the deck.
So we're using the matchcast principle.
So basically, we are pouring each segment against the previous one.
So we have to pour them in the correct sequence in the same sequence
that we'll be erecting them.
That ensures that we have a perfect matching
between the two faces of the segments.
Behind me, you have the first segment that we poured.
We've now moved it into what we call the matchcast position
so that we can ready the rebar cage for the second pouring,
which will be done in a, in a few days.
Once the second segment will be
poured, we'll move the first segment out of the factory
through the big doors that are on the on this side,
and then it will go into a finishing area, if there's any finishing to be done,
and it will then go on to storage
where it will wait for the start of the erection of the viaduct.
When the factory will be running at full speed, basically,
the aim is to pour 12 segments a week. Each segment is unique.
They vary in size. They vary in the complexity of the reinforcement.
The only size that is always constant is the width,
which never changes throughout the viaduct. This is the first segment.
There's still 999 to go, so there's still a lot of hard work
ahead of us and a lot of challenges.
But we're really proud to show this first one
and hopefully it will be a proud moment
in a, in a few years to show the 1,000th.

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