Drilling has begun on State Highway 25A to assess the condition of the soil beneath and around the slip, Waka Kotahi NZ Transport Agency said.
A ten-tonne drilling rig is now onsite, and has been gathering soil samples.
Above the slip, the rig has so far reached 15 metres deep, and will continue boring down to 20 metres. So far, no rock has been found at the drilling site.
The rig was also used on the eastern side of the slip, through the existing piece of road. Five metres of rock was found at this site.
Waka Kotahi said more drilling would begin next week at the base of the slip, once a second rig has been brought onsite.
Meanwhile, the slip on State Highway 25 between Hukuai and Opoutere is open to one lane this week for light vehicles. Travel through this site is under stop/go management, and periods of full closure are possible at short notice as crews work to seal the bypass track.
The bypass has already been stabilised with concrete. Work is continuing to apply chipseal to the surface, improving the performance of the road.
Other roads around the Coromandel Peninsula have been undergoing routine maintenance during the recent fine weather, to ready them for winter.
“The key reason we reseal roads is to waterproof the structural layers underneath – it’s a bit like painting your house,” Waka Kotahi Bay of Plenty system manager Roger Brady said.
“The more sealing we can complete now, the better things will be in winter. We all know it has been a challenging summer, however the good news is that we will still be able to get through the vast majority of our summer programme.”
