Nice challenge on the Afsluitdijk: pouring concrete on a slope of 10%

As civil underwater construction specialists, DISA International's people dive underwater for the construction, maintenance and repair of major civil infrastructure projects. They are also coming into action for the reinforcement and renewal of the Afsluitdijk. "A wonderful project where all the elements of our work come into play," he says.

Ideally, DISA joins as early as the design phase of a project. "Because," says contractor Marc Veldhuizen, "we like to think along in the preparation about underwater solutions. We increasingly notice that many companies lack the knowledge and experience in this specific field. Civil underwater construction is our specialty and so we are called in to think along. For example, we collaborated on the Maas Delta Tunnel and the Holland Tunnel, The Green Arch and OPENIJ. In all our projects, including the reinforcement and renewal of the Afsluitdijk, our customers appreciate our innovative, safe and reliable approach. Since this year, we as a company have also achieved Safety Ladder step 4."

Underwater solutions

One of the solutions provided by DISA is how to pour underwater concrete on a 10% slope. Superintendent Cecil de Groot explains: "In two construction pits on the Wadden Sea side of the pumping station at Den Oever there is a slope of 10%. Such a slope is quite unique. You can imagine that if you start pouring the concrete here, it will soon flow away. We solved that by placing reinforcement baskets equipped with streaking steel. Nets were placed on these baskets to ensure that the slope of the concrete was maintained and prevent sagging. We also slightly thickened the consistency of the concrete. We also completely prepared the reinforcement in terms of drawing work for the Levvel construction consortium (BAM, Van Oord, Rebel and Invesis), which is carrying out the work on the Afsluitdijk on behalf of the Directorate-General for Public Works and Water Management (Rijkswaterstaat), and ultimately the installation and execution. We also provided the sheet piling with a special sealing joint to absorb any movement of the wall. This, too, we completely figured out in advance with Levvel." In addition to pouring underwater concrete, DISA's diving teams carried out dam wall burning, welding and various construction work underwater in preparation for pouring the underwater concrete, among other tasks. In total, an average of four diving teams are at work performing the various tasks.

Depth sensor

Sizing underwater is done to the nearest centimeter thanks to depth sensors. Where previously someone above water walked along with the diver with a steel line with leads, the depth sensor is now used. Marc: "All our diving teams are equipped with such a sensor. In addition to depth measurement, it can also measure whether an object is level. The sensor works quickly and efficiently. For everything we need to measure in, we use it. Where it used to take you maybe two days, we now do it in a few hours. We are one of the few companies working with it."

Weekly consultation

To keep everything running smoothly and on schedule, there are weekly meetings at the construction site. "The cooperation is very good. By discussing things on site every week, you keep your finger on the pulse and you can make quick adjustments when necessary."