Huge sink hole opened up on Thames highway

ELTON SMALLMAN
Last updated 11:30 20/04/2012
BIG HOLE: State Highway 25 traffic, just north of Thames, was diverted after subsidence from old mining works opened up a slump in the road for the second time.

BIG HOLE: State Highway 25 traffic, just north of Thames, was diverted after subsidence from old mining works opened up a slump in the road for the second time.

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The mayor of Thames-Coromandel is calling NZTA safety procedures into question after a sink hole on State Highway 25 north of Thames opened above an old mine shaft.

It is the second time subsidence has caused the road to slump on the stretch of State Highway 25 just north of Thames and it has mayor Glenn Leach alarmed.

"We end up with a hole that's reappeared again and the safety margin of that could be called into question. It's a bit disconcerting."

He is concerned that NZTA's repairs of the initial damage was done without proper investigation.

"I was surprised how quick they fixed the thing. One minute we had a hole and the next we had traffic driving back over the top of it again."

The damaged section of road is four to six metres in diameter and excavation of the damaged highway has revealed a mine shaft about 13 metres in depth.

Mr Leach wants a thorough investigation and a permanent solution.

"I'd be very concerned about what is there. They have just got to make sure they geotech the thing properly and find out exactly what they are dealing with."

Karen Boyt, acting Waikato highways manager, responded to Mr Leach's concerns, saying NZTA were unaware of the existence of the shaft until now.

"We did a lot of investigation at the time and we couldn't see any further problem underneath so that's why we covered it up. We thought it was safe at the time."

Recent ground water movement has caused the latest subsidence and is much larger than the first. Engineers are assessing the true nature of the damage.

"It is much greater than we thought it was so we really need to investigate thoroughly this time."

Vic Peters, a Thames boat mechanic, said local Thames residents were fully aware of the shaft's existence.

"I think everybody in Thames knew the shaft existed before. Apparently that shaft runs miles out."

Mr Peters believes the repair work `could be a major' and is scathing of NZTA.

NZTA are yet to report on the extent of the mine shaft and will document the details of the shaft with Historic Places Trust and a local mine museum before repair work begins.

Elton Smallman is a Wintec journalism student.

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- © Fairfax NZ News

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