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■ The project consisted of the realignment of SH2 either side of the Matahorua Gorge and the construction of a bridge ■ Construction began in October 2009 and was completed in March 2011 ■ Project cost $16 million ■ The bridge is 137m long with three spans and two steel beams supporting a concrete deck that is 58m above the bottom of the gorge ■ 420 tonnes of steel were used in the bridge ■ The concrete deck weighs 1500 tonnes Designed and built by a consortium led by Downer’s Derek Robertson, the $16m project was completed both ahead of time and under budget, opening in March 2012. “One of the real successes of the project was that our tender price was $4m below the NZ Transport Agency’s original $20m budget for this job,” says Robertson. “We also completed it a year earlier than their original programme. It was fast-tracked because it was part of the government’s economic stimulus package.” Despite the size of the project, Robertson says it was really just another day at the office: “At the end of the day it was a reasonably straightforward road construction. There was earthworks, construction on either side of the gorge and a bridge in the middle.” In fact, the project was far from simple, presenting several major challenges – among them the very strict resource consent. One reason for this is that Matahorua Stream runs alongside the old road, so construction workers had to pour concrete and build the bridge without allowing anything to contaminate the water. In that challenge, Robertson saw the solution: “It was the resource consent that partly dictated the bridge’s design and construction – we wanted to avoid working inside the gorge as much as possible.” Four concrete columns had to be embedded into the side of the gorge to help support the bridge. One option was to build a temporary platform on the edge of each side of the gorge to support huge pile driving machines. “This would have posed an increased risk to the stream, building and deconstructing the platforms would have added to the completion time and the overall cost,” says Robertson. His team decided to excavate the pile shafts by hand using power tools. On one side of the gorge men dug 10 meters down, on the other side they went down 15 meters – that is as deep as a five-storey building is high. “This is what we planned from the outset, and was one of the reasons why we won this contract,” says Robertson. “We opted for a plan that meant the vast majority of work was done on the land above the gorge.” Fast facts Matahorua Gorge Bridge 44 / DOWNER / IN BLACK & WHITE


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