The Age of Aquariums
Fabrication
Another brain-teaser was the paintwork. The submerged steel structure needed a really durable paint system – "You don't want to be lifting it out of the water to repaint in a couple of years." Zinc anodes, which will corrode before the steel, were also attached to the structure. They can be easily checked and replaced when necessary, prolonging the life of the steel.
The project was initially designed to be constructed on the beach of the lagoon, although both Mr Murphy and the client had their concerns. It soon became obvious that this was not the way to do it – quality control on an open beach with limited facilities was just too difficult. "Even if we'd pulled it off, the structure weighs about 180 tonnes. We'd have struggled to get it into the water. It just wasn't going to work.
"The three-month fabrication process eventually took place in Singapore, but only after an ocean-going barge large enough to cope (and equipped with a 300-tonne crane) had been found. The three acrylic arch segments, each 100mm thick, and 5m wide by 3.5m long, were fitted into a steel frame, which was braced with steel trusses and beams. The concrete was poured, the paint applied, the arches silicone-sealed, and the whole lot strapped on the deck of the barge. "I had visions of losing everything overboard in a storm," says Mr Murphy, but the three-week journey proved uneventful.
Sinking
Perhaps the most challenging aspect of the project was determining the many load-cases the restaurant unit would be subject to, and designing for them. The constant dynamic forces acting on it had to be calculated not just for its final position, but also during construction and during the sinking process. "We had to make sure the positioning was correct (piling tolerances, etc) but we also wanted a way that would allow us to bring it to the surface if need be, for maintenance or repair. Pouring more concrete inside would make it pretty difficult to lift again."
Mr Murphy's solution was to fill it with sand – 80 tonnes in all. It was dried under cover on the beach (to prevent it corroding the inside of the unit), put into bags and physically carried on board. About 50 local workers manhandled the bags along a precarious plank boardwalk in 30-degree temperatures – "OSH would have had a field day". Remarkably, they only took one day – even with a two- hour break for Friday prayers, as the Maldives is a Muslim country.
The sandbags were placed in compartments under the floor. If the structure should need to be raised, they will be removed, the structure disconnected from the piles, "and the whole thing will simply float to the surface".
The gradual addition of the sand gave Mr Murphy time to monitor deflection in the acrylic, which he describes as "a bit of an art". As it sank the lateral water pressure pushed in on the acrylic, bulging it up at the top. Once it was submerged, the water pressure on the top then pushed it back down and out at the sides, so it eventually returned to its original shape. He had to make sure the deflection did not overly distort the silicone joints between the steel, which is rigid, and the acrylic, which was moving.
