The Aspiring Highways team, working for Waka Kotahi NZ Transport Agency, will begin rock stabilisation work on the Nevis
Bluff, SH6, next week.
As part of the agency’s ongoing safety and monitoring of the rock face, an increase in movement of one large rock mass,
has recently been identified.
Robert Choveaux, Senior Network Manager, Central Otago for Waka Kotahi, says monitoring of the “Yates Feature” was
increased late last year and over the festive period.
“Further movement and fresh cracking have now been observed, and we are mobilising our team to intervene to stabilise
the rock and try to prevent an uncontrolled collapse.
“Designs have been completed and we are now in a position to begin work. Due to the nature of the plans, which includes
building platforms using scaffolding on the rock face, logistics are tricky.”
Work will commence on Tuesday, 25 January. Crews will spend the first two weeks preparing the site before drilling
starts.
The Yates Feature has been monitored since 2001 and showed small amounts of movement up until early last year, when it
started to increase. The physical properties of the schist rock make it susceptible to ongoing weathering through winter
freeze/thaw conditions and drying out due to hot and windy conditions, says Mr Choveaux.
“Rain also reacts with the minerals in the schist, weakening it further. When added with the angle at which the feature
sits on the rock face – these all undermine its structural integrity,” Mr Choveaux adds.
“All of these factors contribute to the need for ongoing monitoring of the Nevis Bluff for the safety of road users and
the general public.”
Drone survey graphic showing location of Yates Feature 160m above State Highway 6:
“The work will involve stabilising the rock mass with just under 100 rock bolts as the rock mass is quite large and
would be significantly disruptive to road users to remove through blasting, using explosives,” says Mr Choveaux.
“The majority of the work can be completed with the road remaining open to two lanes with minimal disruption to road
users, but there will need to be closures as abseilers and drilling gear is set up and moved around the rock face.”
The work is expected to take 16 weeks to complete, subject to rock and weather conditions.
Manual monitoring of the Yates Feature by abseilers has been aided by a remote monitoring system. This has been
developed in New Zealand by WSP Research for monitoring bridges and has been trialled on the Nevis Bluff for the past
two years.
The monitoring system measures small amounts of movement, and temperature, in the rock and sends this information out
via the cellular network to geotechnical engineers who assess the data. The system uses a mobile phone battery and
provides continuous monitoring data.
“This is the first time this technology has been applied in this way in New Zealand. Having continuous data from the
Yates Feature over the Christmas/New Year period provided clarity over the holiday period,” says Mr Choveaux.
“Given the current levels of movement, we are comfortable with the timeframes we have in place to get this safety work
started. However, should conditions change we will move immediately and implement closures if needed.”
People who travel between Cromwell and Queenstown, State Highway 6, will need to factor in short delays, up to 10
minutes at a time on weekdays between 8am and 5pm. Waka Kotahi thanks everyone for factoring in additional time on the
route and for their patience while this essential safety work is completed.The Yates FeatureThe Yates Feature is located at the Queenstown end of the Bluff and is approximately 130 – 160m above State Highway 6.The rock feature is approximately 30m high and 20m wide consisting of around 1,600m3 and weighing over 4,000 tonnes.