“We've put 7000 tonnes in and we're trying to find out where it went”.
That was the update on the Beaconsfield Mine stabilisation project West Tamar Councillors received this week.
Gravel has been poured into the shaft to stabilise the ground after it was damaged in last year’s floods.
But the council’s infrastructure manager, Ian Howard, said 7000 tonnes of the gravel had gone missing.
A camera has been sent down the haulage shaft in an effort to discover where the fill had flowed.
Mr Howard said contractors had a “fair idea” the gravel had found its way into a large workshop adjacent to the bottom of the shaft.
He said the 7000 tonnes of lost gravel would add time and increase the cost of the project’s repair.
At the West Tamar Council meeting this week, questions were raised about the state of the stabilisation project.
Mr Howard confirmed there had been some problems with the gravel fill.
"It hasn't come up the shaft as far as one would have expected,” he said.
The infrastructure manager expected the gravel fill had “run off into side galleries” of the mine.
“There's been a few hiccups, but nothing dramatic,” he added.
Mr Howard said the legs of the headframe were not moving, but the shaft was “progressively failing” and “moving quite a lot”.
“There's a lot of nasty things happening under the ground,” he said.
The project to stabilise the mine is estimated to cost about $1.5 million.
To stabilise the mine, the West Tamar Council approved a plan to fill the shaft and cap it with concrete.
So far about 7000 tonnes of material has been delivered down the shaft.
It was originally estimated about 14,000 tonnes of material would be needed.
The council’s infrastructure services manager Ian Howard said it allowed for “some loss of material into the old workings off the shaft, plus loss into the more recent declines.
It is believed the gravel has flowed into where the mine’s workshop was located – a space eight metres in width and height – at a depth of 375 metres.
“Knowing that there was a risk of more material than anticipated flowing into the declines, filling was halted recently to allow for camera inspection down the shaft,” Mr Howard added.
“This in itself is a slow and quite difficult task given that the shaft is damaged and blocked around the 50 metre level.
“What has been discovered is that considerably more material than expected appears to have flowed into the decline at 375 metres.”
He confirmed the loss would slow the filling process and add to the cost.
“Just how much is uncertain at this stage,” he said.
“The fill material being used is a fine gravel which can be delivered down the only two serviceable pipes with a low risk of blocking.”
Engineers believe it could be necessary to now use a coarser material to reduce side flow into the side tunnels, but with an increased risk of blocking the delivery pipes.
Councillor Rick Shegog travelled down into the heart of the mine in 2009.
The fact 7000 tonnes of earth had gone missing in the hole did not astound him.
“There were so many nooks and crannys down those areas – it doesn’t surprise me,” he said.
Cr Shegog visited the site three years after the mine disaster to see the mine in operation.