'Pouring underwater concrete is a matter of good planning'
As a specialist in civil underwater construction, the people of DISA International dive underwater for the construction, maintenance and repair of large civil infrastructural projects. They have already done this for projects such as the Maas Delta and Holland Tunnel, De Groene Boog and OPENIJ, and now also with the Afsluitdijk. The company is known as the global underwater specialist.
"If you calculate over a period of about 5 years the amount of underwater concrete that we pour, we end up with an amount of 100,000 cubic meters per year on average," says Cecil de Groot, head construction manager Afsluitdijk at DISA. "A huge amount that very few companies achieve. Among other things, we do this for the construction of tunnels, parking garages and locks. Sometimes as much as 10,000 cubic meters per pour, which is equivalent to about thousand trucks. For the Afsluitdijk, the deepest cofferdam at Den Oever, a construction pit about 20 meters deep, 1,675 m3 of underwater concrete was poured. Also at the existing sluices on the Wadden Sea side we poured underwater concrete, which was a total of 2,000 m3.
Pouring underwater concrete is always a matter of good planning. The pouring has to be continuous; you can not stop halfway through. In all our projects such as for the renewal of the Afsluitdijk, our customers appreciate our innovative, safe and reliable approach."
In 2018, DISA began underwater work at the existing culverts at Den Oever. That immediately presented a nice challenge for underwater concrete pouring. "The space was so limited that the concrete pump actually had knowhere to stand. In the end we placed a 63meter long pump with boom that went over the roadway in use. Via additional pipes the concrete went to a second concrete pump on a pontoon."
Again this year, a nice challenge awaited DISA at Den Oever. In two construction pits on the Wadden Sea side contain a slope of 10 percent. The concrete does not remain stabile on a slope like that . "We have solved that by placing reinforcement baskets which ensured that the slope of the concrete remained in place. We also made the consistency of the concrete slightly thicker. In a number of building pits, culverts had to be used to assist. In the excavation there were many places where the crane could not reach. Divers then help with low-pressure nozzles and a pump."