ONE lane at Napier Street could be closed until early October after a section of freshly completed roadworks started sinking.
Inspections of the newly completed road uncovered uneven ground north of Weeroona Avenue, Regional Roads Victoria northern region director Brian Westley said.
"At this stage we're working with contractors to improve a small section of road due to uneven ground caused by historical mining activity - a common challenge in the Bendigo area due to our region's history," he said.
Six metre deep holes have been cleared in preparations for caps over two of the vents already.
Mr Westley said there had been "extensive investigations" throughout the Napier Street upgrade, with "a number" of old mineshafts found and capped.
Minister for Roads Jaala Pulford said she had asked RRV to rectify the problem as soon as possible.
Traffic controllers are on site north of Weeroona Avenue with speeds set at 40km/h for the safety of the community and road workers.
The inbound bus stop near Orville Way is temporarily closed.
"The community can use bus stops near Grace and Powell Streets" Mr Westley said.
"We're making every effort to minimise disruptions where possible and thank the community for their patience."
Contracts linked to the upgrades are subject to a two-year defect liability period and ongoing quality reviews, the government says.
If you see any hazards on our roads, please report them to the VicRoads Traffic Management Centre on 13 11 70, open 24/7. In an emergency, call Triple Zero.
IT IS not surprising that new mineshafts have collapsed in Bendigo given so many were originally capped with timber, a La Trobe University engineering expert says.
Three mineshafts began sinking under the newly completed Napier Street roadworks, prompting lanes to be blocked and workers to excavate holes for caps.
Modern mine caps are typically made of concrete, which does not fall apart as quickly as timber rots, Chris Stoltz said.
Many were not mapped and there was often no sign of them until the caps subsided or fell in, he said.
"These days, when you buy a property one thing you look at is a map of mineshafts. But if one isn't recorded that doesn't guarantee it isn't there.
"That knowledge depends on how well historic mines' locations were recorded and how well maps were maintained.
"I remember years ago some friends of mine from Kennington noticed their lounge room floor was a little spongy. They got a builder to climb under the house, who took one look at it and said a mine had opened up.
"So it can happen anywhere in Bendigo."
There were approximately 6000 shafts sunk in the Bendigo goldfields during mining's heyday, historian James Lerk said.
As to whether those mineshafts' caps typically subside or fall in, Professor Stoltz said there were two answers.
"One thing about using timber in mines is that generally it was a bit more forgiving. Before it failed it would crack and give way a little bit.
"However, you can have a little subsistence and not notice until the timber fails. When it does that, it can go suddenly."
MINESHAFTS opening under Napier Street's newly completed roadworks are "quite extraordinary", shadow minister for public transport David Davis says.
He has called on the government to explain what checks were done before the roadworks began.
"They need to explain why this checking, if completed, did not show the presence of mineshafts - and what improvements to the process they will put in place given that across Victoria there are many old mining areas," Mr Davis said.
The state government has been contacted for comment.
MAJOR works on the $30.4 million upgrade were completed in July, with only minor works including footpaths, line marking and landscaping scheduled to continue until October.
20,000 motorists and cyclists use the road each day.
The upgrade took two years and was the biggest in the Bendigo area since the Ravenswood Interchange.
It ran to schedule, Regional Roads Victoria northern regional director said in July when the roadworks were officially completed.
THREE mineshafts have begun sinking under newly installed roadworks in Napier Street, White Hills.
Contractors have blocked off one lane city-bound and cleared dirt and rubble six metres deep at two mineshafts.
Bitumen has been cleared at the third but the hole needed for a mine cap is yet to be dug.
Regional Roads Victoria has been contacted for comment.
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