After a trial blast on June 14 was successful, allowing workers to measure vibrations and assess traffic, the procedure for the main blast has been divided into four smaller blasts to keep traffic delays to a minimum.
The rock is located by the Awakino Tunnel, within the Awakino Tunnel Bypass work site, and needs to be removed in a controlled manner as there is a risk it may fall on to the road in the future.
When the explosion is taking place, a 300 metre exclusion zone will be in place around the rock, so motorists may find themselves stopped some way from the tunnel.
Other short delays to SH3 traffic are possible while the team prepares for the explosion and clean up afterwards.
The Awakino Tunnel Bypass is currently the main construction site on State Highway 3.
This 2.3km project involves building two bridges to take traffic away from the single-lane tunnel and includes a northbound passing lane.
Most of the bypass work is happening away from the main highway, so overall disruption is expected to be at a minimum through to the scheduled completion date of mid-2021.
Retaining walls are currently being built at either end of the site, with traffic down to one lane and controlled by lights.
There is also resealing work underway on various sites between Mokau and New Plymouth.
Other SH3 works currently underway include a barrier installation at Tongapurutu, requiring stop/go traffic management in place for one day near the middle of the school holidays.
Retaining wall construction on two sites, Mangaotaki and the Awakino Gorge, is underway, with both projects scheduled to be finished before Christmas. The resealing and repair works in the Awakino Gorge are also expected to be completed by Christmas.
Waka Kotahi will continue to provide traffic bulletins for individual pieces of work on the State Highway 3 corridor, as appropriate.
Ms Lauder says motorists are encouraged to stick to the signposted speed limits and be patient when driving through road works sites.
"We want to keep everyone safe when driving through road work sites, and that includes our road workers.
"The Transport Agency thanks the public for their patience while we carry out this important work."