A 35 metre-wide sinkhole will open at the Beaconsfield mine yard if no action is taken to remediate cracking and surface subsidence, engineers have found.
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A collapse, which was expected to destroy the headframe and skyshaft, was not an acceptable option, according to West Tamar Council.
Pitt and Sherry engineers, which has written a report for the council, found there is significant cracking and surface subsidence in the mine yard to the north and east of the shaft.
The iconic headframe and skyshaft at the site are moving, and now touching.
West Tamar Council said the best option to solve the problem was stabilising the shaft with a concrete plug in the shaft to prevent further instability.
Council is talking with both federal and state governments about the project, expected to cost $1.2 million.
The year’s high rainfall is believed to have caused the cracking by destabilising clay which extends down to 50m.
The shaft’s wall has failed 48m below the surface, and clay and gravel material is flowing into the shaft.
“The big fear is if we keep on getting wet weather,” West Tamar Council general manager Rolph Vos said.