The underslip is about 20km west of the corner of SH31 and SH39 at Tihiroa and west of the Kawhia lookout. Photo / NZTA
The underslip is about 20km west of the corner of SH31 and SH39 at Tihiroa and west of the Kawhia lookout. Photo / NZTA
Work to fix an underslip on SH31-Kawhia Road will begin on Tuesday, April 11 and require lengthy day-time closures, Waka Kotahi NZ Transport Agency says.
Waka Kotahi and contractors have been working on a solution since the slip reduced the only sealed road to Kawhia to a single lane inmid-February.
An engineering technique called soil nailing will strengthen the site but because it is very narrow, with a steep drop-off, the road will need to be closed to traffic while work is happening.
“The plan is to close the road each weekday at 8am, we will work until 12.30pm then open it for one hour, closing it again from 1.30pm to 5.30pm,” says Waka Kotahi system manager for Waikato, Cara Lauder.
“There will be no weekend work, with the road remaining open at the single lane, but these day-time works and closures will be needed for about five weeks.”
The site can be cleared in an emergency situation to allow emergency vehicles through.
The site has been operating at one lane with traffic lights and a speed restriction in place since cracking developed in mid-February. Photo / NZTA
Access in and out of Kawhia during the closure periods will be via SH39 to Ngutunui Rd, Pekanui Road, Okupata Road and Oparau Road back onto SH31. This is a collection of local roads with some unsealed stretches and takes about 10 minutes longer than SH31.
“I hope most people can get through our worksite while it is open but for those who can’t this alternative route is available for light vehicles and we advise drivers to take care,” Lauder says.
Since the underslip developed, there has been extensive geotechnical work to understand the cause of the problem and design a solution.
“The slip site is between two retaining walls and the piling under those walls we found was in good condition and provides stability for the work ahead,” Lauder says.
Soil nailing strengthens weak and unstable ground. At the underslip site, a number of 12 metre-long steel bars will be driven in to strengthen and stabilise the ground.
“With reasonable weather in the past month and some initial work the slip has stabilised and we have been able to keep the road open,” Lauder says.
“That has been a good result as this is a vital route for the Kawhia community, farms and other businesses.”
About 800 vehicles use Kawhia Road daily and around 13 per cent are trucks.
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