Connecting arch and viaduct connect A13 and A16

The new A16 Rotterdam will be an 11 kilometer long national highway between the A16/A20 at Terbregseplein and the A13 at Rotterdam The Hague Airport. The work is being carried out on behalf of Rijkswaterstaat by the consortium De Groene Boog, which includes the companies BESIX, Dura Vermeer, Van Oord, TBI (Mobilis, Croonwolter&dros), Rebel and John Laing. Within this project is the connection of the A13 to the A16, by means of a 'connecting arch'. A remarkably designed route that includes a viaduct over the A13. GWW Magazine went to the construction site for an interview with project manager Martijn Schrover and integral design manager Willem Peter Huijssoon of De Groene Boog.

Artwork 10 is a feat

"In the connecting arch connecting the A16 to the A13 is structure 10, the viaduct over the A13, which consists of two separate decks side by side," Schrover begins. "For several reasons, this is a unique viaduct. First of all, because of the angle of intersection the viaduct makes." Huijssoon adds: "Because it is in an arc, it is wider. The curve is designed so that motorists have enough sight length to see what is happening in front of them. The concrete slab is also skewed, meaning that in addition to the fact that the viaduct runs in a curve, there is a slight tilt. This is necessary to get from low to high and vice versa. Civil engineering-wise, this poses a huge challenge, and partly because of the 103-meter span, the deck had to be poured in situ."

The in situ pouring was truly a feat. Schrover: "In order to pour the deck, a number of factors must be kept in mind. First, concrete must be applied with just the right viscosity and drying time, so as not to 'wander' to the lowest point. The speed of pouring and the quantity per pouring stage are also crucial." Huijssoon: "We used a specific pouring sequence and allowed the concrete to stiffen enough to safely make the next pouring phase. It's a thick deck, we're talking about about about one and a half meters. So a huge pour, per direction of travel it took us 24 hours. By the way, this could not have been made with prefab elements either."

'Building in thick pudding'

A huge challenge came in the form of the soft soil on which to build. "It really is building in thick pudding," says Huijssoon. "For the whole design, in addition to a structural challenge, there is also a geotechnical challenge. Think of throwing up sand and soil piles 10 to 12 meters high, installing vertical drainage and putting down wide 'footprints' during the construction phase to keep the slopes stable. Settlements that took place amounted to 2 to 3 meters left and right. Added to this was the extra challenge of keeping the waterways passable. The part of the Netherlands where we are now building is unique." To underscore this enormous challenge in terms of soil engineering, Huijssoon tells an anecdote: "When a local farmer saw us so busy, he took off his cap and scratched behind his ear. Then he spoke the famous words, 'I don't know what you guys are doing, but I've been trying to build a dam here for 50 years, without success...'. That just shows how complex the situation is."

Pole mattresses for extra safety

It was decided to work with a pile mattress to the left and right of the viaduct because there is insufficient consolidation time available, a total of 2,600 piles on both sides of structure 10. Schrover explains why: "The structure itself stands on pile foundations, should we not apply the pile mattresses on the left and right, even a small settlement could affect the transition from the soft part to the hard part. In other words, a settlement could cause the viaduct to no longer run smoothly on and off. For this reason, we have designed the pile plan at right angles to the direction of travel in line with the geometry of the A16 Rotterdam. This results in a safe and robust road alignment in the connecting arch."

Rebuilding with the store open

"We are remodeling with the store open, which is also a task. The A13 just rambles on. It is still in its old spot now, but there will be a phase when the A13 will pass under our art work with the left lane, so that we create space for the next construction phase ", Huijssoon outlines. To this, Schrover adds, "Artwork 10 is an important part within the project to convert traffic." In order for the A16 to connect in the middle of the A13, the A13 will be brought out more. "To make that connection, again, there were some geotechnical challenges," Huijssoon notes. "We have to go up with the road pretty quickly to connect to the viaduct. At the junction of the A13, we are also using EPS as a light fill material under the road surface. All for road safety and driving comfort!"

Meadow birds are also taken into account

The phasing of the entire project takes into account the breeding season of the meadow birds that inhabit the area. "It's good that this is being taken into account," says Schrover. "For us, that means nothing more or less than tight planning and proper phasing. The installation of the pile foundations and demolition work in particular are profound for fauna, so we can only do that work in a limited period of time. Speaking of birds ... a nice sight was the nesting mother wren, who perched in the water holes created by pre-loading the ground."

We finally ask what A16 Rotterdam means to both gentlemen personally. Huijssoon: "I am enormously proud to be able to work in Rotterdam on this extensive infrastructure project. For me it is great to be part of a piece of mobility of the Netherlands." In conclusion, Schrover says, "I love this kind of complex project and want to build something I can look back on later with my children. And if, like me, people experience this project as a party, that makes me very happy."