Two slips which occurred in late-April will delay the reopening of State Highway 1 over the Brynderwyn Hills until at least late-June.

The highway had been on track to fully reopen on May 13, but since the two significant slips on April 26 and April 30, NZTA and its contractors have undertaken geotechnical and safety assessments to determine the best option for stabilising the hillside and getting highway open as quickly as possible.

“While our plan is to reopen at the end of June, if there is a significant amount of unexpected rain, or further instability is found, that could delay the reopening timing,” says NZTA National Manager of Infrastructure Delivery, Mark Kinvig.

Excavation work sees operators working from a platform at the top of the ridge. Removing soil from the top of the ridgeline reduces the likelihood of further slips, enabling safe removal of material from the bottom.

Up to 55,000 cubic metres of earth will be excavated to stabilise the site where the two slips occurred at Kauri Tree Corner.

“Our team is working 7 days a week, where weather allows, to get the road open,” Mr Kinvig says.

“We are maximising the number of trucks, diggers and workers on site to ensure the soil removal is a continuous operation, utilising daylight hours, to get it clear.”

The remaining planned works, including drainage and pavement works, are on track and continue in parallel; with night works where it is safe to do so.  

“We have built in contingency for poor weather, however the ground conditions remain unstable and continue to be actively monitored by staff and GPS sensors. There is a risk of further slips until we complete the stabilisation works,” Kinvig says.

Three detour routes remain available – SH12/SH14, Paparoa Oakleigh Road, and Cove Road. The HPMV and recommended heavy vehicle detour route on SH12/SH14 increases the journey from Auckland to Whangarei from 156km to 227km. 

The Cove Rd detour is not suitable for truck and trailer units and the Paparoa Oakleigh Rd detour is also the suggested route for light vehicles.