Contract awarded for work to get underway at Diana Falls


Christchurch-based geotechnical engineering and construction company Geovert have been awarded the contract to complete the work at the Diana Falls slip site to get State Highway 6 (SH6) re-opened to two-lane and 24/7 traffic later this year.

"Geovert have been involved in a large number of slope rehabilitation and stabilisation projects throughout New Zealand, including the geotechnically complex rock fall work on Milford Road, near Homer Tunnel, and the country’s largest road landslide in the Manawatu Gorge,” says the NZ Transport Agency’s Senior Network Manager Mark Pinner.

“Geovert will begin establishing themselves on site in the next week or two, with the main contract work scheduled to get underway mid-April.”

SH6 at Diana Falls, between Haast township and Makarora, has been reduced to single-lane traffic from 8am to 7pm, and closed at night, for the last six months, after heavy rain in September 2013 caused a major slip at the site. The highway will remain closed at night until the work is completed.

Mr Pinner says the work includes installation of a catch fence above the road, a debris fence about one-third of the way up the slip face and the blasting and removal of large rocks that are considered at risk of creating instability at the site.

It is expected the work will cost about $2.5 million.

"At this stage it is expected the work will be completed late August. However, weather will be a significant factor in achieving this date.”

Mr Pinner says it was expected road closures would be kept to a minimum, although some road closures may be required to remove rock and material from the slip face.

“It is expected these closures will be at the start or end of the day, and ideally, we will be able to provide a week’s notice to enable travellers and business operators to plan their journeys through the area.”

The first phase of the work will be to progressively work down the face, from top to bottom, removing or dislodging any unstable material. Once this has been completed, construction of the rock catch fences can begin.

The first fence to be installed will be at the bottom of the slope, draped up against the 30-metre vertical rock face that rises up from the road. This will have a large opening at the top of the rock face to channel and contain any material that moves down the slope against the rock face to prevent it from falling on the highway.

Next, a temporary fence will be erected at the top of the slope to enable the bigger, up to 200-tonne rocks at the head of the slip to be broken into smaller, one-tonne rocks for removal from the site.

The last phase of the work is to erect a fence about one-third of the way up the slip which has the dual role of catching any larger rocks that may move off the slope and to contain the gravel that is expected to continue to wash down the rock face as the slope re-establishes its natural level of stability.

For more information please contact:

Jan McCarthy
Media Manager - Christchurch
NZ Transport Agency
T: 03 964 2885 
M: 021 427 442