Blast yields a minor show

The low-key explosion at the slip above State Highway 6 south of Makarora yesterday. Photo by Lucy Ibbotson.
The low-key explosion at the slip above State Highway 6 south of Makarora yesterday. Photo by Lucy Ibbotson.
Blasting work at the Makarora slip yesterday proved fairly anticlimactic as motorists waiting on the road below watched just a small cloud of dust rise from the hillside when the explosive went off.

The New Zealand Transport Agency (NZTA) had warned people travelling on State Highway 6 between Lake Hawea and Haast to expect a delay of up to an hour from 1pm while the blast was carried out at the slip site, which is about 16km south of Makarora.

Despite the low-key explosion, things had "basically gone according to plan", NZTA Central Otago area manager John Jarvis said.

"We sort of expected it wouldn't be all that dramatic because there wouldn't be all that much resistance in the rock," Mr Jarvis said.

"It's quite fractured, a bit like Weet-Bix, not solid rock. If we don't have a lot of dense resistance within the rock, then it tends just to break up rather than explode out into little bits all over the place."

Mr Jarvis said it was difficult to judge the right amount of charge to use in a blast when the rock involved was fractured.

While part of the slip's unstable rock had been successfully broken up yesterday, it was likely another blast would be required, probably next week.

A geotechnical engineer would reassess the situation after the rubble was cleared.

"We're definitely making progress, but it's just taking time, and of course we're trying to minimise the amount of delays to the road, so that means it does slow us down at times."

- lucy.ibbotson@odt.co.nz