Deconstructing the viaducts: What Vancouver can learn from New Zealand

The City of Vancouver has a plan to take down the Georgia and Dunsmuir viaducts, but it hasn't yet explained how and when it will happen. Just how do you go about demolishingtwo massive structures that have been part of the city landscape for over 40 years?

Simon Paton has an notion of how it's done. In the last few yearsPaton, who is the senior project manager at the New ZealandTransport Agency, has helped steer a project to deconstruct two Auckland city viaductsthat were similar toVancouver's.

"[They] were 700 metres long and ran across theNewmarket business precinct within the city." said Paton in a phone interview from Auckland.

"We had about 120,000 people a day going over, and another 70,000 going under the bridge.The structure had a bit of an S bend in it so it was a complex geometry."

The Newmarket viaducts were 46-years-old when they were demolished. Vancouver's viaducts turn 45 next year.

The biggest hiccup in the Newmarket deconstruction happened before the firstbit of asphalt was peeled away. A risk assessment determined key parts of the bridge structures actually needed strengthening before demolition could begin.

"We had to put up an awful lot of temporary steel work to hold things up so that it didn't fall over while it was being taken down," Paton explained.

The extra work added $13 million Cdn to the estimated $101-million demolition budget.

When work began in earnest an enormous 8,000 tonne gantry crane nicknamed Big Blue was moved into place, allowing for 2,00tonne chunks of the viaducts to be cut away and lowered onto flatbed transport trucks.

"We used wire saws to cut the segments," said Paton. "Most of it was concrete, there wasn't a lot of reinforcing steel compared to modern structures.Webasically chopped pieces off,then took themaway to the yard and recycled the concrete."

The parts of the project which required major traffic diversions and closures,like moving Big Blueor trucking out the chunks of bridge, were done at night when congestion was less of a concern.

Unlike what will happen inVancouver, new replacement viaducts were constructed in Auckland before the old ones were taken down, helping to mitigate the chaos.

Paton sayshaving a thorough and strategic communication plan paid off, especially for the one weekend they had to closethe entire motorway.

"It wasn't just getting the word out, it was trying to suppress the demand as well," he said. "We got a really good response and it was quitemanageable. People just stayed away really."