Sealed Highway Restored After Massive Slip

Work on restoring the Manawatu Gorge highway following the biggest road slip in the history of New Zealand, has finally been completed.

Sealing of the roadway has now taken place on the Manawatu Gorge Road – State Highway 3 - closed almost entirely for 13 months by a succession of slips.

As the major route between the Tararua and Manawatu districts, the closure of the highway has had a significant impact on the surrounding communities. Early on NZTA mobilised a team to clear the debris and stabilise the slope in the fastest possible time.

Very quickly the decision was made to clear the slope from the top down instead of the traditional bottom up approach. The vastness of the slip meant staff working at the top were 155 metres above the road and 231 metres from the river.

“It was pretty nerve wracking but we did it safely and effectively,” recalls Higgins Regional Manager, Shane Higgins, a third generation member of the roading and infrastructure Higgins company.

In the end 370,000 cubic metres of earth, stone and other debris was removed from the site - the equivalent to filling Wellington’s Westpac stadium.

To stabilise the slope five ‘benches’ were cut into the hillside to create platforms to catch further debris. Loose material from the cuttings was pushed down the sides to a waiting stream of trucks at road level. Grass hydroseeding of the ‘benches’ was another smart technique used to encourage vegetation growth and further stabilise the slope.

In May 2012 the last load of slip material was removed from the road and work on stage two began to fix the damage to the road. It quickly became apparent that the bridgework which forms the base of the road, needed to be completely written off and totally rebuilt.

NZTA State Highways Manager, David McGonigal, concluded that building a new bridge across this distance, in this challenging location, would normally take up to 12 months, but NZTA wasn’t prepared to keep motorists waiting that long. Instead an accelerated programme was put in place to build the road in four months.

A 60m long bridge was constructed involving a team of consultants and contractors working extended hours.

The whole project has been characterised by a strong level of collaboration and teamwork amongst NZTA, consultants and contractors. David McGonigal praised head contractor Higgins.

“This was a complex project with many challenges. I was impressed with their professionalism, dedication and can-do attitude in all kinds of inhospitable weather,” he says.

“They supplied us with accurate and timely information. It was very important to keep the public informed about progress on reopening the Gorge. If there’s another emergency, we’ll use them again.”

This section of highway has seen so much drama in the last year. “It was host to the largest pile of dirt that’s ever landed on a New Zealand road. Then it became a hive of reconstruction, and now, it’s back to being a two-lane highway,” David McGonigal says.

“The closure of the gorge has affected lives and livelihoods in Manawatu and beyond, and we’ve been battling for more than a year to get to this point.”

For Higgins the satisfaction and reward has been to see life returning to normal for the people who rely on this route and to see motorists getting through without the lengthy detours they’ve endured over the last 13 months.

ENDS