Tidal wave of culverts on the Blankenburg connection

Starting in 2024, the new A24 Blankenburg connection will connect the A20 near Vlaardingen with the A15 near Rozenburg. The new highway is partly below ground level and is also largely built under water. A monster job for DISA International, mostly at great depths below water level. At peak times, the specialist in pioneering underwater solutions assisted the contractor combination BAAK with as many as 180 (!) divers. Didier de Graaff, Managing Director of DISA International and Marc Dröge, General Manager of DISA International look back on a wonderful and intensive project.

In order to approach the underwater structures as efficiently as possible, BAAK had a lot of contact with DISA International in the preliminary phase. "With the Blankenburg connection, the law of large numbers applies," Dröge says. A small summary. Until the beginning of February 2022, we spent no less than 261,822 man-hours on the project, divided among other things between cleaning 10,111 m2 of sheet piling, cleaning and raising 11,452 anchors, another 500 pieces of Leka and VC piles, placing 24,825 linear meters of embankment beams and placing 25,000 tons of reinforcement. Finally, we assisted in pouring over 100,000 m³ underwater concrete." 

Nitrox instead of compressed air

Aside from the enormous quantities, Dröge says the big challenge was mainly in the great depths of up to 32 meters below the water level. "At this depth you have to deal with limited dive times. We came up with all kinds of clever solutions to deal with this efficiently, such as diving with other gas mixtures (nitrox instead of compressed air) and using surface decompression so that our divers could stay underwater for longer periods of time. In addition, we developed our own system to quickly lengthen GEWI anchors. By using a traverse in which we could hang eight anchors at a time, no precious time was lost underwater. A handy clamp was also developed for placing the overlays. Moreover, we had many practical consultations with BAAK in the preliminary phase in order, for example, to make the design of the piles that had to be piled up and the reinforcement nets as dive-friendly as possible, so that the diver had to perform as few actions as possible. That has definitely paid off in practice."

Millions invested

At peak times, DISA International was operating day and night six days a week. To deliver that capacity at all, without shortchanging other customers and projects, we contacted our partners abroad. Millions were also invested in materials. "We experienced some pretty exciting moments in the middle of the corona pandemic," Dröge acknowledges. "Borders closed and the Netherlands colored fire red on the corona map. Just try to get the right people and resources on site in time. We combed all over the world looking for equipment and BAAK helped us enormously with coordination so that the foreign divers could be deployed quickly and efficiently without too many problems." Dröge also praises BAAK's attitude during corona. "Due to the tightened hygiene measures, all materials had to be disinfected additionally and according to a new and special protocol after each dive. That was quite a thing, given the tight schedule. Together with BAAK, we handled this very professionally and managed to keep it well under control with the discipline of our people until the end."

DISA International proudly looks back on a beautifully executed project, also a very high safety score. "We don't negotiate about safety," Dröge says firmly. The monster job is not quite finished for DISA, by the way. "At the end of this year we are going to burn away the trusses in the access ramps to the Maas Delta Tunnel at a depth of 32 meters, and next year we will provide the necessary assistance with the sinking of the tunnel legs."