WAKA Kotahi advises it is continuing to develop a solution to the under-slip that has reduced SH31 – Kāwhia Road to a single lane.
The slip is about 20km west of the corner of SH31 and SH39 at Tihiroa. The site has been operating at one lane with traffic lights and a speed restriction since discovery of the slip in mid-February.
The under-slip sits between two existing retaining walls, with soil nailing the likely option to reinforce and strengthen the area, Waka Kotahi system manager for Waikato, Cara Lauder said a week ago.
No further update is available.
About 800 vehicles a day use Kāwhia Rd; around 13% are trucks.
“The good news is the piles under the retaining walls are in good condition and provide stability for the planned work,’’ Cara said.
Soil nailing strengthens weak and unstable ground.
At the site, a number of 12m-long steel bars will be driven in to strengthen and stabilise the ground.
Solid bars are usually installed into pre-drilled holes and then grouted into place using a separate grout line.
Hollow bars can also be used and may be drilled and grouted simultaneously by the use of a sacrificial drill bit and by pumping grout down the hollow bar as drilling progresses.
Kinetic methods of firing relatively short bars into soil slopes have also been developed.
The final result would allow a steeper slope to be used in the final repair.
Waka Kotahi hopes to announce a timeframe for this work shortly.
“We are working on what we need for traffic management, safe working methods, resourcing and programme for a speedy construction start,’’ Cara said.
“SH31 is the route in and out of Kāwhia – and there are no sealed alternatives.
“We want to keep this road open, but we may need to have full closures at fixed times during the day to get the repairs completed.”
Urgent repairs on February 22 saw traffic halted for intervals while quick-setting concrete was pumped into a large cavity on the left-hand shoulder.
It was intended as a quick, short-term fix to help prevent water entering the crack and making the slip worse.
The site was being monitored while the long-term solution was designed and implemented.
