Seven-week mammoth job above Parnassusweg

‘Normally, it takes around six months to build a new viaduct’, says Jurri-Jan Vrielink, chief planning engineer at the Nieuw-Zuid construction consortium (Mobilis, Boskalis and Van Gelder). ‘That’s just not possible in this case, because we have to deal with trams, road traffic, cyclists and pedestrians in Parnassusweg. We’ll be doing demolition work and transporting materials, including prefab – an incredibly complex task amid so much activity. To keep disruption to a minimum, we’ll be doing the work during the seven-week closure of the most northern metro track (6 July until 26 August 2024). During that time we’ll be working non-stop 24 hours a day. That’s the only way we can get the job done within seven weeks.

We need the first two weeks for the demolition of a section of the existing metro viaduct. Vrielink: ‘We’ll start by removing the metro track. After that, we’ll cut into the section of the roof that needs to be lifted out. That way, you have separate beams of concrete that can be hoisted out one by one. A special technique is used to cut out the concrete, known as hydrodemolition. Vrielink: ‘Using this method, you start by cutting into the concrete before applying high-pressure jets of water to remove it. This has the advantage that the reinforcement remains in place. This is necessary because part of this viaduct needs to remain intact and we’re only demolishing a part of it. Using hydrodemolition, the reinforcement on the remaining section stays intact and you don’t do too much damage, making it easy to pour concrete to repair it.’

Starting from 18 July 2024, we will proceed at pace with the construction of the new metro viaduct, where we made preparations earlier this year. We have already prebuilt some of the new supports for this and we will finish building them when the road is closed. We’ll insert piles into the ground on both sides of the new viaduct, on which we will build abutments to which beams will be fitted. ‘In order to hoist them into position, we will again need large cranes, this time in Parnassusweg only. Over three nights, we’ll then hoist 18 beams into position’, says Vrielink. And this is still not the end: we will then build a roof on top of the beams. We will first make the reinforcement for this, before pouring the concrete on 5 August. ‘Starting on 4 August, we will install a platform around the new viaduct so that the subsequent works no longer cause disruption to traffic on Parnassusweg.’

Finally, we will put the finishing touches on the new metro viaduct before putting the track back in place on 14 August. The last two weeks will be used to do the finishing work and the work platform put in place will be removed at the end of August. ‘An awful lot needs to happen in a short space of time’, says Vrielink. ‘Demolishing an existing viaduct is particularly unpredictable: we are reliant on old archive drawings and never know what we’ll encounter when we actually start the work. That’s another reason for working non-stop 24 hours a day: it gives added flexibility. It will certainly be a challenge, but we’ll get it done in time.’