Wellington Scoop

$1.5m strengthening of Ngaio Gorge starts again

News from WCC
The next stage of major strengthening work starts on Ngaio Gorge Road on Monday for up to 26 weeks, making this key transport route stronger and more resilient.

While work is happening in the area, we will be removing loose material in the vicinity of the slips and will install monitoring equipment at the same time. Specialist contractors will carry out this work. In the interests of safety, the road will be closed from 14-16 February during off-peak times of 9am-4pm weather permitting.

There will be access for residents and business customers only. Old Porirua Road will be restricted to resident access only during the closure. Pedestrian access on the Northern Walkway will be controlled and may face closure at certain times during the scaling work.

Please follow traffic management instructions for alternative routes. We appreciate your patience during this important work.

On 12 February we start work on the upper section of the gorge – the latest stage, after a new 42-metre-long retaining wall was built below the road about half way up the gorge.

We are also investigating the best way to strengthen the area of hillside above the road where two major slips occurred in July and August.

Most of the slip debris and rock was cleared in August so the road could re-open. Some debris has come down since then, so the road will be closed from 14-16 February during off-peak times while this happens.

Options to more permanently strengthen and protect the slope are being peer-reviewed before decisions are made on how this work will be done. This will be a big job, and planning will take time. Strengthening work above the road is unlikely to start until sometime in the second half of 2018.

In the meantime, the wall of containers, which are filled with concrete blocks and anchored to the hillside, will remain in place, along with the 30km/h speed limit. The containers are protecting this section of road.

What’s happening further up the road

A new 45-metre concrete anchored wall, with a 100 year design life, will be the main feature being built opposite the area of houses numbered around 89-93 Ngaio Gorge Road, as well as new footpaths, hand rails, and landscaped grass areas.

The work is the latest in a series of projects designed to protect the road and reduce the likelihood of slips occurring in major earthquakes and storms, as part of the long term project to improve resilience on this key transport route.

Why we are doing this work

The Ngaio Gorge Road is an essential access route linking Wellington City to the north which is why we have been progressively strengthening vulnerable sections of it in stages since 2001. It is part of our ongoing programme to strengthen key structures and transport routes and make the city more resilient.

What’s being done
Constructing a new retaining wall
Replacing and widening the footpath
Installing new handrails
Landscaping grass areas
The new wall will have 26 concrete piles over 6 metres deep
The wall will be tied to rock with 16 anchors, each will be around 11 metres deep

The previous road strengthening projects in Ngaio Gorge involved upgrading or replacing old retaining walls in vulnerable spots, the most recent wall was to support a section of road that has not previously been reinforced.

Traffic management: Two traffic lanes will be open as usual at peak times. Traffic will be reduced to one lane around the Ngaio Gorge Road work sites between 9am and 4pm, Monday to Friday, and on Saturdays between 8am and 4pm. Temporary traffic lights and traffic management will be in place, so people driving should expect short delays during the day. Safe access for pedestrians will be provided at all times

The project cost which covers the investigation, planning and construction of this project is around $1.4 – $1.5 million.

1 comment:

  1. Dave B, 13. February 2018, 14:50

    Stated above that “Pedestrian access on the Northern Walkway will be controlled and may face closure at certain times during the scaling work.”

    Er. . . Why??

    The Northern Walkway route goes nowhere near the Ngaio Gorge Road or the proposed work site. The route enters Trelissick Park from Hanover Street in Wadestown, descends to the Kaiwharawhara Stream then proceeds upstream to come out at Waikowhai Street near Crofton Downs Station.

    There are other tracks in the vicinity of the proposed works, but these are not the official Northern Walkway.

    Unless I am much mistaken, the Wellington City Council has put out misleading information in regard to the possible closure of the Northern Walkway.