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At the Front Wall Southwest, a temporary structure had been made for the construction of the New Lock. And because it is temporary, as mentioned, it had to be removed again. No sinecure, because removal, or reverse construction, is more difficult than construction. Especially in the context of circularity in which the materials must be dismantled separately to make reuse possible. It was up to hydraulic engineering firm Van den Herik Sliedrecht to take care of this job.
"Getting the dam out in one go with big shovels is not difficult," said Leo Kruidenier, Manager of Execution at Van den Herik. "But then you created your own problem. The challenge was to be able to reuse as many released materials as possible." To paint a picture; this work included removing (reverse engineering) the steel slag, bentonite mats and removing the sand from the temporary land fill around the Front Wall Southwest. If you translate that into quantities, it involves 45,000 tons of 45/180 mm steel slag, 3,000 m² of bentonite mats, 2,500 tons of 5/40 kg poured stone penetrated with colloidal concrete, 15,000 m³ of sand and 1,600 tons of clay. All this material was reused elsewhere on site where possible or made suitable for reuse on other construction sites.
Van den Herik proceeded carefully and step by step. First, the sand was excavated, transported and processed in a new application. In the process, the sand had to be accurately removed down to the steel slag, with which the bentonite mats had been applied to avoid mixing steel slag into the sand. Then, on the inside of the dam, the zinc pieces that had been sunk with steel slag were removed. Kruidenier: "By working in this order, we were able to separate the materials. The biggest difficulty was separating the steel slag, whips and geotextile."
On the outside of the dam, the penetrated crushed stone was broken up to a depth of 12 meters and the colloidal concrete was separated from the crushed stone as much as possible. This work requires a lot of force at great depth. For this purpose, Van den Herik adapted and deployed its crane pontoon Prins 5. The released materials were transported by hopper barges to a depot where the final materials were separated. This also allows the crushed stone to be used elsewhere. "After the separate removal of the sand, crushed stone and zinc pieces, we were also able to remove the 45,000 tons of steel slag. For this quantity at greater depth, our crane pontoons Karma IV and Prins 5 did a great job."
Thanks to the two large crane pontoons, Karma IV and Prins 5 with the necessary barges and pushers, the work was completed in a short period of time. Logistically, it was an additional challenge as the work took place close to the busy West Lock. Good preparation, working methods and clear coordination were essential. "One wrong choice in the considerations could have consequences. But with the daily management of contractor Gerco Grootenboer, with the right equipment operated by skilled specialists and with great dedication and commitment, the work was successfully completed. We are proud of the people who make it and look back with satisfaction on a challenging project that was completed to everyone's satisfaction within the allotted time."
