SH4 slip: First stages of asphalting temporary road expected to begin next week

The SH4 temporary route is starting to take shape around the slip. Photo / Bevan Conley

The route for a temporary road around the massive State Highway 4 slip is taking shape as contractors continue to work away at the land.

Crews are working in two sections, at the northern and southern ends of the slip, and have almost completed work to flatten what will be the northern end of the temporary road.

About 11 people are working on site at a time, although that changes depending on what work is able to be completed.

Dave Eliason from Goodman Contractors said the priority is to get a temporary road open.

"We've got a basic model that we've engineered with room and scope to change that as the ground dictates.

"Normally in good ground conditions, the design and model are set in stone but we're using it as a guideline here.

"Everything we're trying to do is still within engineering designs but trying to get it done as quickly as we can within reason."

It's expected asphalt preparation for the northern end of the temporary road will be completed next week.

The slip is one of the most significant Dave Eliason has worked on. Photo / Bevan Conley

The work will take place more than 200 metres away from the southern end of the slip, meaning excavator operators can still work to clear the opposite entrance to the temporary road.

Once the temporary road is fully operational, contractors will turn their attention to grooming the rest of the affected land and removing crumbled sections of the state highway.

Eighteen stations to monitor ground movement have been set up throughout the slip area and are monitored daily.

Some of the ground movements recorded over a recent two week period shows some sections have moved more than 200mm, while other areas have rotated clockwise motion.

"Anything that happens, happens slow because it's physics really," Eliason said.

"There are parts moving a little bit differently to others, but it has progressively got less and less.

"It's sort of settled down and the worst thing to happen would be if we were trying to do this in July and it was continually raining."

What's left of SH4 sits below where the temporary route will run and is to be removed at a later date. Photo / Bevan Conley

When the ground gave way in early October, some of the land fell straight down while another sections slipped off to the side.

Eliason said it's a "really hard" slip to read.

"As long as I've been working up the Paras, even in 2004, I've never seen anything remotely close to this.

"[In 2004] I think the road was closed seven months, there were a few washouts here and there, trees over the place and culverts gone, but nothing that required remedial work like this.

"A lot of the stuff in 2004 and in Kaikoura wasn't superficial, but you clear the road off and the road's still there.

"This is one of the first where there's a couple hundred metres of road missing."

Removing water and directing it away from the slip was one of the first tasks completed with culverts and drains being installed to direct "95 per cent" of water out in the same direction.

A chemical designed to stabilise the ground and encourage revegetation is continuing to be sprayed on sections of the slip.

Some of the ground will be reused to in-fill the temporary road or basins created by the slip, while the rest will be trucked away. Photo / Bevan Conley

NZ Transport Agency regional transport system manager Mark Owen said the temporary road will take the shortest route.

"We're focused on getting this road connected, it'll probably come with restrictions depending on the amount of movement once the road is finished."

Owen said it'll be known in the next few weeks what a likely open date for the temporary road is.

"We'll see how they progress, they're making good progress at the moment but it's really one of those weather-dependent things."

In the meantime, Owen said a team is also looking at long-term solutions.

"We're looking at other more resilient options which may be a whole new realignment to get away from this whole area."

NZTA's Mark Owen said contractors are making good progress on the slip. Photo / Bevan Conley

Despite the temporary road possibly not being opened until early next year, local business owners in Raeithi continue to stay positive about the situation.

Early last week a sign promoting Raetihi was erected on State Highway 1. The sign was designed by local business owners in collaboration with Visit Ruapehu.

Other signage promoting upcoming events in Raetihi has also been installed in Waiouru.