Debris flies up to 30m during the final blast of the Chin Hill cut. Photo / Martin Sykes
Builders of the $360 million toll motorway to Puhoi fired the last shot yesterday in the largest rock-blasting programme of any New Zealand roading project.
The Transit NZ-led Northern Gateway Alliance used 16 tonnes of explosives to rip 13,000 to 15,000 tonnes of rock from a 55m cut
through Chin Hill, above Waiwera and the Hibiscus Coast.
It was the last of 78 blasts that have torn 1.2 million cubic metres of earth and rock from the cut, near the northern end of the 7.5km motorway extension due to open early next year to fee-paying traffic as an alternative to the no-charge winding coastal highway.
Although yesterday's blast was less than half as big as the largest in the programme, in which 40 tonnes of explosives were set off in 2006, it sent a cloud of debris soaring more than 30m high from a honeycomb of 338 charged holes.
Now, the road-builders will haul away their final rock harvest to use as fill in other parts of the motorway.
Earthworks supervisor and "master blaster" Mark Blanchard said he was looking forward to showing friends and family members the completed motorway, as much of the construction work had taken place out of public view.
He was pleased the blasting programme had been completed without injuries or untoward incidents and had allowed the development of "benchless" slopes that would integrate well with the surrounding landscape.
A sealed section of road at the Orewa end of the project will be completed before the middle of this year, for trials of an overhead tolling gantry.
But it will take several more months to complete other project features, such as twin motorway tunnels through bushclad Johnstones Hill between Waiwera and Puhoi.
Transit was planning to carve a 60m cut through that hill as well, but engineering problems and concerns about severing an important wildlife corridor led to a late design switch to the tunnels.
