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To realize the Singelgracht-Marnix underground garage, a large construction pit was built, divided into four compartments. A job well suited to the Friesian company Aquatech-Diving. For a year and a half, an average of four to five diving teams were at work. According to Steven Spanhaak, DGA Aquatech-Diving, it was especially the logistics that made the project particularly challenging.
The Coentunnel, the Jaarbeursplein, various aqueducts in Friesland, quay works in Amsterdam; when it comes to underwater projects, the people at Aquatech-Diving are used to a lot. The diving company is a specialist in civil underwater construction and operates throughout the Netherlands and abroad, including the realization of wind farms, salvage, inspections and underwater work in infrastructure projects. Every project has its own peculiarities and challenges. That certainly applies to the Singelgracht-Marnix garage as well. "In total, we have some 9,000 m3 underwater concrete poured," says Spanhaak. "In the preliminary stage of the work, we already come into the picture to create a dry construction pit. And later in the final phase of the project when the garage roof is installed, we may burn off 1 kilometer of sheet piling."
For the realization of the construction pit, Aquatech-Diving is working with contractors Mobilis, Voorbij and Boskalis. Their work is closely aligned. Once the sheet pile walls have been driven and Boskalis has excavated the cofferdam, the outriggers will be inserted to support the walls. Aquatech-Diving supervises the construction and coupling of these outrigger frames. The diving teams also inspect the construction wall pit at three levels to ensure that the sheet pile wall locks are still correctly in place and that there are no peculiarities. And the remnants of soil left in the corners, for example, are sucked away by the diving teams using pumps. "The main job, however, is to pour underwater concrete for an 80-centimeter steel-fiber concrete floor," Spanhaak said. "We also install anchors in the underwater concrete, as well as drainage to monitor floor tension, and we place reinforcement baskets in the floor as additional reinforcement. And, also very important, we clean the sheet piles with high pressure for better adhesion of the concrete floor."
The total construction pit is divided into four compartments so that work can follow one another and work can continue continuously. "The moment compartment one is excavated, inspection follows. If everything is in order then the next party can get to work. We work like a train. Aquatech-Diving plays an important role in this in the control and inspection of the construction and concrete work, among other things."
What is special about the Singelgrachtgarage-Marnix project is primarily its logistics. Spanhaak: "It is a large structure, but with little space around it. Normally you have a construction pit where you have all the space you need around it. But here everything had to be done from the water and delivered and removed. It is only accessible from one point. Good mutual coordination about the work is essential. That went well thanks to the fine cooperation. Together we got the maximum out of it to get it done."
