Repairs on track to open Mangamuka Gorge on SH1 by Christmas

3 MinutesBy NZ Trucking magazineNovember 11, 2020

The NZ Transport Agency says it‘s on track to open State Highway 1 through the Mangamuka Gorge before Christmas with the slip repair work entering a significant new stage.

The road will be open to light vehicles under stop/go traffic management or traffic lights by mid December and remain open over the Christmas-New Year period to accommodate holiday traffic, says NZTA senior system manager Wayne Oldfield.

“NZTA appreciates how important the holiday period is to the local economy and we are doing all we can to open the road.

“We‘ve installed the first set of piles.  More than 100 four-metre and eight-metre piles have been drilled along the road centre line so the heavier machinery can move in to complete the job.”

Oldfield says a 20 tonne drill rig and a crane are now onsite to drill the 49 main support piles that will reach up to 20 metres into the rock under the road and complete phase 1 to protect the road.

“The repair teams will be working double shifts (20 hours/day), which will accelerate the work and save 15 to 20 days on the schedule. Much still depends on the weather, the hardness of the rock we‘re drilling into and the stability of the hillside. Safety remains our priority.”

The big rig will drill holes up to 20 metres deep, with the crane then lifting steel casing into the hole. A reinforcing cage will be inserted into the casing, which is then filled with concrete. The slip is 40 metres wide but the completed wall will be 75 metres long to future proof other unstable sections of road. 

The cost of this first stage of the repair is estimated at $3.8 million.

Oldfield says that in the New Year the road will be closed again so the works team can cut into the hillside to realign the road and restore it to two lanes. In designing the work, the team will be looking for opportunities to have the road open to traffic.

The Mangamuka Gorge has been closed since heavy rain across Northland in mid July brought down eight slips in the gorge. Apart from the remaining big slip, the road has been cleared to at least one lane and maintenance crews have worked to repair the road surface, replace roadside guard rails, improve drainage and generally tidy up the roadside.

“NZTA acknowledges the impact of the road closure on local communities and the extra time and cost of travelling on the recommended detour route – SH10 – which can add 20 to 30 minutes to the journey,” says Oldfield.