With the switching on of Dominique, the 700t bridge building machine known as a launch girder, HS2 engineers began putting in place the 1,000 unique pre-cast elements that will make up the 3.4km Colne Valley Viaduct, which will soon be the longest railway bridge in the UK.

The viaduct construction is being led by Align JV – made up of Bouygues Travaux Publics, Sir Robert McAlpine and VolkerFitzpatrick. However, work for the creation of the bridge did not start with Dominique.

Its construction truly began with the erection of the enormous pre-cast factory, which has an internal volume of 105,000m3 – making it larger than the Royal Albert Hall. Since it came into operation, the factory has been gradually casting the enormous concrete puzzle pieces, each weighing up to 140t, at a rate of around 12 per week. The pieces made so far had been waiting in a holding area, preparing to be put in place.

Before that could start, there needed to be bridge piers for them to be fitted on to. There will be a total of 56 piers (and the two abutments) across the stretch of the viaduct, some bolted right into the riverbed in areas where it has to cross water. So far the piers have been put in place for the first 900m, meaning that Dominique can now get to work.

The launch girder was shipped in pieces from Hong Kong, where it has already been put to work on several bridge building projects, starting with the East Tsing Yi Viaduct in 2004. HS2 senior project manager Billy Ahluwalia has seen a similar bridge building machine at work before on the Docklands Light Railway extension, but it was nowhere near the size of Dominique. “It arrived here earlier this year and it’s taken three or four months to get it all assembled, moved onto the location, tested and commissioned,” he explains. “It’s been modified specifically for HS2. These were carried out by the original fabricator, a company called Deal from Italy.”

The gargantuan machine sits atop the bridge piers, propped up by two ‘legs’ that sit on consecutive piers. It waits there for the correct concrete segment to be brought into place between these two legs, then it can begin to lift.

It is essential that the right concrete element is brought at the right time, as there is only one unique piece that will fit in each position. HS2 Colne Valley Viaduct superstructure manager and precast factory manager Ludovic Vergne explains: “Each segment is unique because we’re using match-casting technology, which means that the face of a segment is used as the formwork for the next one.” Each segment has a unique pattern of ridges that interlocks perfectly with the next one along, to a precision of millimetres. To ensure that the right segment is brought at the right time, each has an identifying catalogue number and QR code printed right on to the trench.

Once the correct piece has been picked up from the precast factory and brought across the HS2 site to the bridge on the back of a trailer, it is positioned in place under Dominique. A series of heavy duty chains and winches are dropped down holding an enormous steel rack (the yellow part in the pictures). Four fork-like bars pointing down from this rack slot right into specially-made holes in the top of the segment and these are then bolted from beneath to provide a secure lift.

The machine can then pick up the enormous segment and rotate it. While Dominique makes it look easy, there is still a lot of care that must take place. A team of two operators and a supervisor are in place atop the machine, fastened on by harness for safety and using a console to move the segment incrementally, at a rate of about 8m per minute. “It’s better to go slowly and to arrive at a final position without any safety issues,” Vergne says. “And everything takes time to be sure that it’s precise.”

A group of 10 to 15 remain on the ground to fasten it in place and help with the final movements. Once the team operating Dominique has managed to lift the segment practically in line with where it needs to go, the team on the ground use 800kg jacks – one on either side – to nudge into place with a precision of 3mm, ensuring the complementary ridges perfectly interlock.

A strong epoxy covers the faces of the segments, providing the initial bond. The holes along the top of the segments all line up with those of the ones previously put in place, and thick strands of steel cable are fed through them to tighten and strengthen the connection.

Building the bridge starts from the piers, directly onto which are placed two symmetrical segments to form an anchor. The following segments are then put in place in pairs, first one side and then the other, balancing each other out in a cantilever fashion as they go along. The spans between piers will be either 45m, 60m or 80m, with between 20 and 24 elements per span. This means that Dominique will put into place 10 or 12 segments on each side of the pier before it moves onto the next one.

As each new element is fastened into place, a new thread of steel cable is fed through it. This means that the segments closer to the centre of each pier will have more steel cabling running through them, while the ones that are furthest from the piers, at the top of the arches, will have less. The steel cables are tightened to pull all the segments together, creating a post-tensioned segmental box girder.

Dominique’s legs are then lifted one at a time and moved along to the next pier, essentially ‘walking’ to where it next needs to start putting segments in place. Things will get a little trickier when it comes to putting in Colne Valley Viaduct’s curves, but Ahluwalia is not worried. “It’s a very large radius curve because it’s a high speed railway,” he says. “We have taken the complexity out of it as much as we are able.”

The HS2 bridge building team is currently working at a rate of fitting one segment per day, or six per week. With 1,000 pieces to be placed, this would take until 2025, but HS2 has said it aims to finish the structure by the end of 2024, when it will be handed over to the rail operations team. “We’ll go faster as we get used to it,” Ahulwalia assures. “And then it will be there for hundreds of years.”

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And not a word about the concrete diverting underground water in a way which causes contaminated drinking water. What is more important. Sorry we forgot – the corporate profit from destruction of our natural world. Shameful reporting. Not one mention of the destruction of 1000’s of years of a beautiful natural landscape and wildlife habitat. HS2 riddles with corruption and organised crime Shameful and a disgusting BLIGHT ON OUR LANDSCAPE.

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