Increase flowmonumental Doorslagsluisin Nieuwegein

The historic Doorslagsluis in Nieuwegein suffers from overdue maintenance and is a bottleneck in the water supply route to the Western Netherlands. During the variant study for enlarging the Doorslagsluis, removal was a realistic option, but given its monumental status, an innovative solution was chosen. This came about through proper consultation between Hoogheemraadschap De Stichtse Rijnlanden, Nieuwegein municipality, Historische Kring Nieuwegein, monument committee and local residents. A variant was chosen in which the throughput capacity around the Doorslagsluis is increased, while the cultural-historical appearance is preserved.

Joint approach with construction team

The work is being carried out in several phases. A construction team has been established in which the client and builder work closely together and share their knowledge and expertise. The construction team coordinates the entire project. Main contractor Heijmans engaged Kandt B.V. as a subcontractor to perform various work on the lock. Bastiaan Verheul, project manager at Kandt: "As part of the construction team, you are involved in the project at an early stage and contribute proactively to the feasibility of the work. The challenge with this project? There were no drawings available of the existing construction. Heijmans carried out various investigations to obtain the necessary information. A good first step to gain insight into the construction depth, condition and construction of the quay walls."

Obstructing flow and monumental restrictions

Verheul explains more challenges with this project. "It is a long stretched work of about 300 meters, with an upper head, lower head and bridge head. The lock chamber of the former lock is 11 meters wide, but at the lock heads and bridge head it is only 6 meters wide, which hinders the flow of water. So something has to be done about that. At the same time, there are restrictions because it is a monument. Something to take into account in the design. This is done by demolishing the lock heads and rebuilding them on piles. The lock remains optically intact and the necessary throughput is created so that additional water can flow under it."

Specific equipment

Where the lock heads and bridge head disappear, it is important that the quay maintains its retaining function. Kandt installed sheet pile walls at five different locations (about 120 meters in total), anchored with thirty-two grout anchors. "Because there are wooden piles and kesps under the quay wall, through which the sheet piling had to pass, we crushed the old foundation there to clear the sheet piling line. We also drilled fifteen LeKa piles through the existing lock heads, on which -after demolition of the lock heads- a table structure will be made on which the new lock heads will rest. From the outside, this will give it the appearance of a lock. In consultation with the architect, who is involved in this project because of the monumental character of the lock, partial lock gates will also be applied, where the water will be able to flow underneath." 

Verheul explains that specific equipment was used to accomplish all the work. "The water is too narrow to accommodate a pontoon. We are not allowed to work from the factory site and on the other side the road may be closed, but not the important bicycle route that runs there. It's not entirely known what the condition of the quay is, so you can't go in there with unlimited large equipment either." Quite a challenge, then, but one that Kandt knows how to deal with. "We made auxiliary platforms from which the work was carried out without hindering cyclists. And to make a good connection between the lock chamber wall and the new sheet piling to be installed through the existing lock heads, De Wilde NL B.V. drilled core holes through the masonry of the existing lock wall. Because diamond drilling is used to make a tight demolition line -exactly in the desired location- the connection to the intact existing column wall is guaranteed. All in all, another great project that Kandt worked on and where various parties and disciplines cooperated constructively," Verheul says in conclusion.