20 | Keeping the gorge route open In 2020, CLL had been part of the team involved in fixing two slips in the Mangamuka Gorge, an important section of State Highway 1 north of Auckland, and a key piece of infrastructure for Northland. T T from page 18 NZTA - CLL: Mangamuka Gorge “Basically, it was like a bomb went off in there. There were huge slips everywhere, some of the ground dropped away a metre along the road, so we had to build our way in with temporary works....” REGIONAL DEVELOPMENT In 2020, CLL had been part of the team involved in fixing two slips in the Mangamuka Gorge, an important section of State Highway 1 north of Auckland, and a key piece of infrastructure for Northland, both economically and socially. Those two slips they had remediated two years previously remained unaffected in the latest weather event, and CLL, together with the Whangarei branch of global Geotech engineering consultancy company WSP, took on the job of turning the gorge back into a functioning state highway. “Basically, it was like a bomb went off in there. There were huge slips everywhere, some of the ground dropped away a metre along the road, so we had to build our way in with temporary works, because we couldn’t put these big machines on any of the ground up there,” explains Tim. Engineers designed temporary platforms to safely hold the heavy machinery required for the main remediation work, working closely with the engineers designing the main works needed to achieve safe repairs with a 100-year life expectancy. The whole job was made easier by the fact that everyone involved had successfully worked together in the gorge in 2020, explains Tim. “It was a well-established team, which helped because we had a hard deadline and the complexity was like nothing I’ve ever seen before. It took every bit of skill that CLL and our subcontractors had to hit the deadline. Winter earthworks moving thousands and thousands of cubic metres of earth over slips and already failed ground was pretty difficult.” Using the Trigger Action Response Plan or TARP system was the key to everyone’s safety, and while they remained wary they trusted WSP, who were actively monitoring the slips with sensors carrying lights, and the system was tested and practised before people risked their lives. If the lights went orange it meant danger pending, and if they went red it meant evacuate the gorge immediately. “They went off about 20 to 25 times, and 200 people evacuated the site each time, but we felt 100% safe. We worked 24/7 for a year on it with the night crew piling and the daytime crew coming in to do the concrete work because the drill rigs were too big to get the concrete trucks and cages in at the same time,” explains Tim. Suffice to say that if you’re driving through the Mangamuka Gorge, thanks to CLL, you can look around and see at least 35 carefully remediated and retained slips designed to stay exactly where they are for the next 100 years, rainfall or no rainfall.
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