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How to place a 4,100t bridge on top of an existing tunnel?

How do you manoeuvre a new rail bridge that weighs as much as 4.1 million kilogrammes over the A15 motorway, right on top of the existing Thomassen Tunnel…? Project Manager Guus Olierook tells us all about this precarious operation that took place as part of work on the Theemswegtracé railway line at the end of May:

“‘We had to transport a 4,100t bridge to the location using heavy vehicles and then position the bridge on top of an underlying tunnel deck. This means you have to be absolutely certain that the subsoil and the tunnel can support the weight, which was all analysed with great precision beforehand. Initially, we intended to manoeuvre part of the bridge overhead above the Vopak terminal, but we came up with an alternative way of doing it to exclude risks. Before the operation, we created a traffic light model in collaboration with Rijkswaterstaat, since even the tiniest deformation, as little as 15mm, would lead to potential damage to the tunnel. On the traffic light, green meant less than 5mm deformation, while orange meant less than 10mm. Deformation by over 10mm would mean a red light and force us to abort the operation of positioning the bridge into place. While we had factored in a maximum deformation of 8mm, the tunnel ultimately had only 1mm of deformation.”

Read the full article in the Civil Engineering Structures special edition of GWW Totaal (in Dutch):
GWW Special: New arch bridge on top of existing tunnel

And read more about the Theemswegtracé project here: