Blood, sweat and concrete: building the Brittenpassage

How do you build a station passageway straight through an existing embankment – and not just any embankment, but one carrying trains, metros and 300,000 vehicles every day? This was Zuidasdok’s first major challenge, back in the previous decade. Simply starting to excavate and build the passageway was not an option: that would have required lengthy closures of the railway tracks and motorway. At one of the busiest locations in the Randstad, that was simply not feasible. So the decision was made to start by building the roof. With the right support beneath the railway and motorway, subsidence during excavation could be prevented, while keeping both the number and duration of closures to a minimum.

The roof of the Brittenpassage is no ordinary roof: it consists of seven enormous concrete slabs, known as roof sections, weighing between 2 and 4 million kilos each. Because of their size, it was impossible to build the sections elsewhere and transport them to the site. They had to be built on site, in a very confined space. These enormous slabs are needed to withstand the forces generated by accelerating and braking metros and trains. To cope with those forces, the seven roof sections are supported at either end by substantial foundations known as abutments. We built and installed the first of the seven roof sections in 2019. It would take at least another five years before the remaining six were finally in place.

How do you build a concrete slab 70 metres long, 12 metres wide and 2 metres thick, and then get it underneath an existing railway track? By building the roof section alongside the motorway, as close as possible to its final position. You then remove the motorway and the relevant railway tracks and slide the enormous structure into place. It sounds simple. It was anything but. We did this for the first time on 1 November 2019. We closed the A10 Zuid for a weekend and removed the road and tracks. It was a remarkable sight: an actual gap in the A10 Zuid. We then slid the prefabricated roof section into position, millimetre by millimetre. The operation took hours and there were plenty of challenges along the way. Once it was complete, we rebuilt the railway tracks and motorway, and on Monday morning, unsuspecting motorists were once again driving over a freshly laid layer of asphalt.

That very first sliding operation was spectacular, to say the least. Hundreds of interested spectators watched nervously, both in person and via our webcams, as a piece of history was made. Building and sliding in the subsequent roof sections proved no less exciting. In the summer of 2021, we slid another two roof sections into place, followed by numbers four and five in 2023. We organised several live events during these operations, giving construction enthusiasts and local residents the opportunity to watch not only via webcam but also from the site itself as we slowly moved millions of kilos of concrete into position.

What made the work even more complex was that the foundations had to be ready before each roof section could be slid into place. During every closure, we therefore also worked on the abutments. This involved installing dozens of piles, all of which had to be driven into the ground with millimetre precision. A prefabricated reinforcement cage, made of concrete rebar, was then lowered into position on top. Formwork was installed around it, after which we poured the concrete and allowed it to cure. Each sliding operation was therefore a kind of domino effect, with one activity depending on the previous one. Every time, it became a race against the clock. Some operations went more smoothly than others, but fortunately they all ended successfully.

For the final two roof sections, construction consortium Nieuw Zuid (Mobilis, Boskalis and Van Gelder) had a little more room to manoeuvre. We built them almost exactly where they were needed, on what was then our construction site between the metro tracks. This is now where the tracks for Metro Line 52, the North/South metro line, are located. To slide the penultimate concrete slab into place, we ‘only’ had to remove the metro tracks. For once, the A10 Zuid could remain untouched. We completed the operation on 29 July 2024. The seventh and final roof section followed in November that year. This one ‘only’ had to be moved around 15 metres northwards to reach its final position. It was by no means the most complicated operation, but it marked a huge milestone in the construction of the new passenger tunnel: after five years of sliding roof sections into place, the Brittenpassage finally had a roof.