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NZTA to attack gorge slip on two fronts before Xmas

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The NZ Transport Agency will be ramping up work at the Manawatu Gorge slip site just before Christmas, with crews working the slip from both top and bottom and a second bench due to begin next week.

State highways manager David McGonigal says the NZTA is on track to begin work shortly on the second 'bench' at the top of the Manawatu Gorge slip site, as Higgins contractors press ahead with the operation to stabilise the hillside by terracing the top of the slope.

"We've had a second crew swing into action this week at the bottom of the slip, so we’ve now got two teams working seven days a week to clear the slip and get the road re-opened."

"While the wet weather has held up work at the top of the slope over the last couple of days, the benching team has made fantastic progress nonetheless. We’re now close to finishing the first bench, and we’ll be getting started on the second bench early next week."

A second crew started down at the bottom of the slip this week, including spotters to keep watch at the slipface. Using a 20-tonne digger and a large loader, they’re shifting up to 250 truck movements a day, with 10-14 trucks being filled in a rotating convoy, rather like a conveyor belt.

"It takes two bucket-loads of the large loader to fill each truck, which has created a ‘hole’ in the big pile of slip material which the benching crew up top can send their material down towards it. This means that a good proportion of debris can now be cleared away by the road crew rather than falling down into the river."

Mr McGonigal says sediment entering the river has formed a "delta" that has narrowed it at the base of the slip. This is having a small impact on the flow of the river.  Last month, Horizons closed the river 200m either side of the slip site.

"Now that we’re clearing more material from the slip site, the amount of sediment going into the river will be reduced, and we expect that rain will allow the river to naturally wash away the bulk of the sandy debris forming the delta."

Horizons experts have been monitoring the river and the NZTA is working collaboratively with them, MWH and Higgins to minimise any risks associated with the slip. While it is unlikely the river will become blocked, a protocol has been developed in case it does. Work will stop immediately, Horizons Emergency Management team will be alerted and the river will be cleared of recreational activity down as far as Ashhurst Bridge.

Mr McGonigal thanked motorists and locals for their ongoing patience and understanding as the gorge nears four months of closure, and reiterated the NZTA’s gratitude to truckies for their considerate driving on the alternative routes.

For information about the Gorge closure, people can visit the NZTA’s dedicated gorge web page: www.nzta.govt.nz/manawatu-gorge(external link).

Our engineers have developed an easy to understand series of diagrams to help explain the technical side of the earthworks operation going on at the top of the slip. Please have a look at the attached pdf to see how it all works. Media are welcome to reproduce these diagrams(external link) (PDF, 4.15MB).

For more information please contact:
Anthony Frith
Media Manager - Central Region
T    04 894 5251
M   027 213 7617
E    anthony.frith@nzta.govt.nz

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