Haus zum Falken – a complex project at a transport hub

Allreal is realising the Haus zum Falken right next to Zurich Stadelhofen train station on behalf of Axa-Anlagestiftung. The five-floor office and commercial building designed by the architect Santiago Calatrava will also be home to a public bike station with 800 parking spots and direct access to the train station. The limited space available and the proximity to the train and tram lines are making the building work more complex and there’s a need to plan every last detail with precision and take extensive security measures. The project is proving to be a challenge for everyone involved.

It’s one night in October. Looking down on the building site at Zurich Stadelhofen train station from above, it looks like a long, pointy wedge with the curved glass platform roof on one side and Kreuzbühlstrasse on the other side with its two tram lines and trams, cars and bikes everywhere. The station square is at the wedge’s short flat end. Around 80,000 passengers travel to and from here every day. People can cross over the signature pedestrian bridge or head down to the shops, which are open all year round. There’s still a four-floor building here at the moment, taking up the space almost all the way to the edge of the plot.

And today’s the day that a team of eight or so workers are starting to take that building back down to its foundations. They have four nights to get the job done. And the time they have at night is not flexible in the slightest. They can start at 1.00 a.m. when the overhead tram and train lines will be switched off... And they must be finished by 4.55 a.m. Overrunning is simply not an option. The power will be switched back on after a final security check has been performed and the first tram will leave at 5.06, followed by the first train of the day two minutes later.

The excavator being used for the dismantling work weighs 65 tonnes and has a 22-metre-long boom that can reach the building’s roof ridge with no problem. A huge safety screen has been lifted up on the construction crane between the building and the roof over the platform. The operator waits for the signal to proceed and starts by grabbing onto part of the roof structure. Carefully and controlled, he drops it to the ground. Over the next few hours, he will work with speed and skill to dismantle the building from top to bottom. The materials will be roughly sorted at this point and care will be taken at all times to avoid any building rubble landing on the platform or pavement below. It’s a bit like one of those wire loop games that tests your physical skill as you attempt to move a loop along a length of bent wire without touching it.

Planned to perfection

Dismantling the existing building is just one important milestone. Allreal Project Manager Bruno Schumacher and his team have been coordinating all the aspects of this highly complex construction project since the very start of the planning stage. And there are plenty of aspects to think about. “Noise protection, health and safety, traffic diversions, lightning protection... the list of authorities involved is five pages long.” On top of the usual measures taken to keep the workers and the public safe, extensive requirements set out by the Swiss railway company (SBB) and other transport companies have to be followed too. Requests to switch off the SBB overhead lines during the dismantling work have to be submitted at least six months in advance for safety reasons. And then there are rules and regulations for cordoning off the platform area for the building work, diverting pedestrians and measuring any vibrations that could cause disruption to the trains. Basically, the main priority is avoiding any kind of disruption to the public transport here.

With all of that in mind, the first step for the project was the construction of a safety tunnel stretching some 70 metres across the entire construction site and covering the tram and train platforms and a bit of the road. This is being used as a storage and logistics centre for building materials since there is no direct access to the construction site itself for lorries or construction vehicles. It’s also a home for the construction and office trailers as well as a base for the crane. Just concreting the base for this impressive steel structure took a month and a half because all the work had to be done overnight when the trams weren’t running.

The operator can switch off his excavator just before 5.00 a.m. No doubt he’ll be tired, but he can also be pleased with the progress made by him and his team. Without any interruptions or incidents – and that’s the most important thing. It doesn’t matter how carefully each stage has been planned out – a problem with just one piece of machinery would be enough to jeopardise the entire schedule.

During daylight hours, the wood, metal, plastic and insulation materials are sorted and separated ready to be collected and taken away. A telescopic excavator weighing over 40 tonnes will appear on the tram tunnel later to lift all the leftover concrete and rubble over the road and into a lorry – one load at a time. It’ll be several weeks before everything is cleared away at street level.

18 months of preparation work

The next step – scheduled to start in December 2022 – will be to drill the holes for the geothermal probes for the heat pump heating system. After that, the pit excavation will be the next big challenge. It’ll be 12 metres deep in the end, which would be deep enough to make the entire building that was originally here completely disappear from sight. And the vertical walls will be less than five metres away from the platforms. Heavy-duty steel beams will be needed to support the concrete walls. All of the excavated materials will also need to be moved to the other side of the road via the protective tunnel. It’s no wonder that the pit excavation work alone is going to take almost an entire year.

The cornerstone for the building itself will be laid at the end of 2023, when the base plate is concreted. When the finished building is handed over to its owner almost two years later, nobody will really be able to tell how many night shifts it took to build it.

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