Expert wants extra checks of old tunnels after problems in Friesland

ANP

NOS Nieuws•vandaag, 18:10

According to experts, at least ten tunnels in the Netherlands should be checked extra because the same problems could arise there as with the Princess Margriettunnel in Friesland.

The A7 between Sneek and Joure was closed last month because the tunnel trough turned out to have been pushed up by groundwater. Rust has probably formed on the steel anchors under the road surface that are supposed to hold the box in place.

Wout Broere, professor of underground construction at TU Delft, explains that tunnel anchors are now made of concrete and have a steel core, which makes them much less sensitive to rust. There are about ten other tunnels in the Netherlands with the old construction and they should be better monitored, says the professor.

It concerns these tunnels:

Maastunnel in RotterdamVelsertunnel and Velserspoortunnel in VelsenCoentunnel near AmsterdamSchipholtunnel and SchipholspoortunnelBeneluxtunnel near VlaardingenHeinenoordtunnel near BarendrechtIJtunnel in AmsterdamMetrotunnel under the Nieuwe Maas in RotterdamBotlektunnel near Rotterdam Hoogvliet

Broere points to the closure of the Vlake tunnel in Zeeland in 2010, where the road surface also rose as a result of damage to the anchors. “Before the Princess Margriet tunnel I would have said that was an incident. And although there are differences between the tunnels, I would no longer say that. This is no coincidence.”

The consequences of the closure are major for motorists who drive through the tunnel on the A7 every day:

The A7 motorway will remain closed for at least half a year: ‘Bad, this is really not fun’

Tunnels are now checked simply by checking whether the road surface is still in place. A Rijkswaterstaat employee walks through the tunnel to see if any barriers have arisen that could indicate loose parts. According to Broere, such an inspection is not enough.

“An extensive inspection means exposing the anchors and that means removing the road surface and the concrete. That is a very nuisance inspection,” said the professor. As a middle ground, Broere proposes installing sensors that monitor the movements of the tunnel and the tunnel entrances.

At the Princess Margriet tunnel in Friesland, Rijkswaterstaat has placed 10,000 large sandbags on the road surface to prevent the asphalt from rising further. The exact cause of the damage there is still under investigation. Until that investigation is completed, the service will not draw any broader conclusions about other tunnels

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