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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 consortium De Groene Boog, which includes the companies BESIX, Dura Vermeer, Van Oord, TBI companies Mobilis and Croonwolter&dros, Rebel and John Laing. Within this project, the connection to the existing A16 will be made with a viaduct over the Terbregseplein.
Construction of the viaduct is in full swing and is being carried out 'with the store open'. De Groene Boog chose the ILM method, in which the segments are poured together in situ, to be 'launched' bit by bit to the other side after curing and finishing. GWW magazine visited the construction site and spoke with three De Groene Boog colleagues: work planner Erik Maarten Vermeulen (Mobilis), foreman Peter Augustyn (BESIX) and civil designer Pierre Mengeot (BESIX).
It must be a special sight for motorists at Terbregseplein. A 'blue wedge' made of metal profiles hangs above the connecting arch of the A20 towards the A16. It is "the nose," a technical device that ensures that the viaduct will be on the opposite side of the Terbregseplein. The nose is attached to the segment that was poured first and ensures that the whole remains stable and arrives at the piers of the new viaduct without causing damage. The Green Arch applies the Incremental Launching Method, ILM for short. The concrete segments are poured together in situ and after curing and post-tensioning of a segment, it is "launched" one stage further, across the road where traffic continues as usual.
Peter explains: "Since the Terbregseplein with the A20 and A16 is one of the busiest traffic arteries in the Netherlands, we build the viaduct without road closures. The ILM method is ideally suited for this. The reason that 'the nose' is mounted to the first poured segment is to bridge the distance between the piers and distribute the weight properly." Erik: "The ILM method has been used several times before, including on the A50, however, there the deck was launched over water and not over a busy thoroughfare. This is the first time we have applied this method at a traffic interchange in use. The longest segment is 34.8 meters, the others range in length from 17 to 30 meters."
At the "on-site factory," Erik shows the production process of the viaduct: "Behind the nose are three zones where the segments are manufactured. We have a precast zone, a formwork zone and finally the 'curing zone.' In the first zone, the reinforcement of the segment is braided. In zone two the concrete pours take place and in the last zone the segment is "polished" so that it can then be launched. After we pour a segment, it has to harden for several days before we can launch it. We poured the front element of the viaduct first.
As soon as a segment is ready for it after the concrete hardens, it is launched, at a speed of about two and a half meters per hour. Then there is room again to pour a new section onto it. The end product: two over 400-meter viaducts, one for each direction of travel."
Pierre explains how the launch works: "Temporary metal 'tension pins' are inserted into the segments, to which the pulling cables are attached. Subcontractor Freyssinet jacks the whole thing forward using two large jacks on these pulling cables. The secret weapon? Large Teflon sliding plates with lubrication that allow the segment to move with its enormous weight. Each time the Teflon sliders for a segment have done their job, they are taken away and 'manually' deployed again at the back of the line."
The poured segments are anything but standard in shape: they run in a slight curve and are also skewed. At the 3D level, therefore, an enormous challenge. "Thanks to the jacking technology, however, we can make good adjustments," Erik explains. "It takes 1,000 tons of tractive force to pull segment 17 (the last cast segment) out of the formwork. Per auger run, we advance about 28 cm. We can cover 30 meters per launch." Pierre adds, "The formwork is a challenge every time. We used a specific calculation methodology to go through all the steps in advance, in order to work safely. During the launch, we constantly monitor the forces and deformations that occur, both in the concrete and in the piers. The tolerances are very strict, it is millimeter work and unprecedented for concrete construction."
The segments poured together consist of different concrete compositions according to their function, Pierre said. "It's a constant tension between planning, heat generation and launching. The only joints we will soon have are at the ends at both abutments. The road surface itself will soon be a monolithic whole. We are working with prestressing, hence the internal tension cables, to compress the segments." Peter adds: "There are 54 tension tubes in the first poured segment alone."
Once a segment is in place, it is jacked up so that we can then install the overlays between pillar and road surface. Erik: "When finally all the segments are in place, we tighten everything and we can start with the edge elements and pour the embankments. Once that is done, asphalting can begin."
"By the end of February 2023, we expect to have Segment 17 in place. We can't rest on our laurels then, because only half the work will be done. Roadway A will be ready by then, but we have to complete two roadway segments. We disassemble the nose and just start all over again. A nice detail: road section B is one and a half times as wide as road section A which we are working on now. That's because road deck B will have the ramp attached to it." Detailed calculations were made for each segment. Pierre: "In 2019, we have already started these calculations. A challenge, with a segment that is straight at the bottom, but the top is slightly tilted, with a skewed trajectory." Erik: "For this reason, the preconstruction site is also already skewed. We roll the reinforcement into the formwork via roller conveyors; the reinforcement itself is already in a curve. It is extremely precise work in every phase of construction. A special point of attention is the reinforcement of the diaphragm walls in the tube. These are located at the level of the piers and realize the transfer of force from the tube to the bearings on the piers."
Side pieces will still be poured at the heads of the road surface, which will be added at 9 meters after the completion of the launching process. The head is then as wide as the road surface itself. The reason we do this afterwards has to do with saving weight during the launch."
Peter concludes, "All in all, this is a real feat. It is a very complex job that we do with great care, with the first priority being the safety of our people and the people driving under our work. Whether we will ever see a project like this again? Presumably not."
