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In preparation for entering the bridges, the two combi walls separating the lock chamber from the Westerschelde and Ghent-Terneuzen Canal must be burned down. A job that is right up DISA International's divers' alley. How water and fire go well together underwater? That is what two DISA experts; Victor Demoniere (professional diver) and Marc Veldhuizen (contractor) tell us.
Burning down the two outer combi walls involves a lot of work. For example, the combi wall of the outer abutment cannot be burned off until the headland behind it has been dredged away. Therefore, part of the combi wall will be burned off first so that the bridges can be navigated in. The combi wall consists of tubular piles with sheet piling between them. To burn off the tubular piles safely, the water level on the outside of the combi wall must be at the same level as the water level in the lock chamber. This way, no current is created when the combi walls are removed and the divers can safely do their work. "It will take us a total of three months to burn off the two combi walls," says Demoniere. He is one of the regular professional divers on this project. "It's very specialized work, which is what makes it so beautiful. The fact that we burn away steel underwater with fire is incomprehensible to many people. Surely water and fire don't mix? However, we can burn through steel up to a temperature of 2,500 degrees at a maximum of 15 centimeters. This makes DISA unique. We have specially developed tools and the right people."
To work safely, Demoniere always works in a team of three, and depending on the depth of the work, a decompression tank is available. To be able to work longer underwater, the divers work with a specially tuned gas mixture of up to 36 percent oxygen and 60 percent nitrogen. By comparison, above water in the open air, this ratio is 21 percent oxygen, 79 percent nitrogen.
The challenge at the New Lock Terneuzen was that the combi wall was difficult to access. Also, the outer walls were very dirty. DISA came up with an effective and also cost-saving solution to make it possible to fire the walls without compromising the safety of the culverts. Veldhuizen: "A combi wall consists of tubular piles with the sheet piling between them. To burn off the wall safely, the divers burned a manhole of about 70 cm by 1 meter in each tube pile. This allowed them to burn away the elements of the wall from the inside. That is no mean feat when you consider that a tube pile weighs about 30 tons." According to Veldhuizen, this demonstrates the strength of DISA International. "We have a lot of experience and knowledge in house, as well as the right people. We work both in the Netherlands and internationally with 200 divers. As a result, we are quickly and flexibly deployable on projects, including those of longer duration."
What makes diving work in Terneuzen extra nice for Demoniere and his colleagues is that here they have visibility underwater. "Three-quarters of the time we work in pitch-black water with hardly any visibility. In the New Lock we could see 2-3 meters far, a great experience!"
