The risk of falling glass was identified when the effect of the vibrations from installing the sheet piles was evaluated in detail. This is a classic example of how a radical and highly complex project like upgrading Amsterdam Zuid station, while also keeping it open to passengers, will always have some surprises in store. ‘The trick is to take the right measures at the right time’, says Rogier Licht, project leader for the Minervapassage at the Nieuw-Zuid construction consortium.
Putting the right measures in place is exactly what has happened since mid-October 2022: under the glass roof – sometimes called ‘the cathedral’ because of its shape – a ceiling of wooden boards has been added, with strong canvas along the sides. This step was not planned in advance. ‘We still aren’t even sure whether it’s absolutely necessary, but we don’t want to take any chances – now it’s impossible for any glass to fall onto passengers’, says Licht. Sheet piles need to be installed close to the glass roof, between the metro platforms and tracks. This is done using a vibratory hammer, leading to considerable vibration nearby. The first time we did that job was in the weekend of 5 and 6 November 2022, close to the glass roof over the entrance to the metro platform, where lines 50 and 51 depart for Gein and Amsterdam Central. ‘After talking to the Environment Agency, we began to wonder whether that the glass could fall due to all the vibration nearby.’
Licht and his team did not know the answer for sure. ‘We had an evaluation done, but there was still no conclusive answer. On the one hand, the glass roof is quite old, so there’s a chance that a pane of glass could come dislodged due to the vibration. But on the other hand, there have been metro trains running through the station for thirty years and they cause vibrations every day – even though a moving metro train is different to the vibrations caused when you are installing a deep sheet pile. In the end, nobody wanted to stick their neck out and state that our work definitely wouldn’t pose any risk to passengers and contractors in the station.’ Zuidasdok and Nieuw-Zuid then decided on the best measure to mitigate this risk. ‘There was a simple answer, of course: just remove all the glass. But it would have been a huge job to remove all that glass, and the walkway and the entrance to the platform would have been completely exposed to the elements. So we didn’t choose that option. Instead, we decided to add some protection.’ Starting in mid-October, that protection was added in the evening and at night: a wooden ceiling underneath the glass roof structure. Strong canvas was also added along the sides. In the unlikely event of a pane of glass falling down, the ceiling will stop it from causing any damage. ‘We carried out an inspection with Zuidasdok, the GVB and the Environment Agency and all of us were confident that this set-up as safe as it possibly could be.’ The glass between the metro tracks, which allows light into the Minervapassage, is also protected. The roof structure above the other metro platform will be done later. That entrance will be closed completely during this work.
Enormous construction pit
The work that the contractor is now carrying out is installing sheet piles. A lot of those are needed, and they will enable us to dig an enormous construction pit, right next to the metro platforms. That is where the abutments and support points will be for the new, wider roof over the Minervapassage. The existing Minervapassage is 12 metres wide but the new pedestrian underpass will be 40 metres wide, with technical facilities and retail space on both sides. The ceiling of the Minervapassage will be made up of 100-metre-long concrete roof sections. ‘Gradually, the station is being turned into a construction site’, says Licht. ‘The installation of this sheet piling is just the start. In the near future, for example, we will need to build support points for the roof sections for the new pedestrian underpass. And that’s by no means the only work we will need to do. The station is going to be completely overhauled and passengers will be able to see that ever more clearly. We will do everything we can to minimize the inconvenience to passengers, but safety has to come first. Inevitably we will have to close some areas of the station at times.’
Vibrations but no damage
The sheet piles installed in the weekend of 5 and 6 November did not lead to any damage to the glass over the metro platforms.