Dispute over mine vibration

By John Cousins


Engineering experts have clashed over whether blasting in Waihi's Martha Mine has caused cracking and warping to the home of Colin and Sylvia Francis.

The couple, whose Savage Rd home is close to the massive open-cast gold mine, were among objectors to Newmont Gold's application to drive a 2.6km exploratory tunnel to 20 metres below the bottom of the gold mine.

The impact of blasting on residents dominated the second day of yesterday's Environment Court appeal hearing in Waihi.

Australian mining engineer Dr John Heilig disagreed with one of the key conclusions contained in the report released last Friday into the possible causes of the cracking.

The report, prepared by Tauranga geotechnical engineer Tony Cowbourne, said there was a "reasonable possibility" that the small amount of cracking and warping in the kitchen had been caused by the transmission of blasting vibrations from the nearby Martha mine.

But his conclusion that one of the fundamental causes of movement in the Francis' home could include blasting was at odds with Dr Heilig's opinion.

He has spent 23 years assessing the effects of blasting for Newmont.

Mr Cowbourne said the pattern of damage, which included cracking within an external wall, was consistent with differential movement within the superstructure of the house.

He said the level of damage appeared small and other causes could include movement of the foundations and severe wind loadings.

Mr Cowbourne said he had not undertaken a detailed review of the vibration assessment and monitoring results obtained by Newmont as part of its mining consent. But published peak velocity results confirmed that the mine was close enough for vibrations to be within the "strongly perceptible" range.

"It is conceivable that the level of vibrations has been sufficient to cause differential movement within the [house's] superstructure and hence the cracking that has occurred," he said.

Dr Heilig disagreed that blasting vibrations could be a fundamental cause of the cracking. He said the author had been negligent in coming to this conclusion without undertaking a review of the consent issued to Newmont.

Dr Heilig's evidence relied on more stringent British and Australian mining standards to assess the levels at which blasting could cause significant cracking to nearby residential buildings.

He said even when the level of vibrations in the Martha Mine reached the "strongly noticeable" and rare level of nearly 9mm per second, this was below the level capable of damaging properties.

Dr Heilig said that Newmont recognised vibrations from the exploration blasting would be noticeable and considered an annoyance by some residents. But just because it was noticeable it did not mean that it was unacceptable, he said.

He argued the 5mm-per-second vibration limit proposed for the exploration protected community amenity values, depending on the number of blasts per day. Most of the blasts would be well below 5mm per second.

Dr Heilig said the maximum level of blasting vibrations received at the Francis' home would be about 2.5mm per second from the ore exploration project.

Newmont's Waihi general manager Glen Grindlay said the company was applying for a variation to its mining licence to allow up to four underground blasts per day. The number of blasts would be one to two per day for the first eight months of the two-year project, increasing to three to four per day once multiple faces were being worked. Blasting from noon to 7pm on Saturdays would be restricted to one blast.

The hearing continued today.

- BAY OF PLENTY TIMES

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