Beaconsfield Mine Stabilisation Complete

Tuesday, 11 September 2018

SUBJECT:

Beaconsfield Mine Stabilisation Complete

FROM:

Mayor, Christina Holmdahl

DATE:

7/9/2018

In October 2016, museum staff found signs that the headframe and skyshaft at the Beaconsfield Mine and Heritage Centre was moving. A sinkhole appeared as a result of the June 2016 floods, and the mine yard was closed to the public with immediate action required in order to save the Beaconsfield icon.

The unstable clay which extends down to 50m below the surface caused the shaft wall to collapse between 48m and 71m, allowing clay and gravel material to flow into the shaft.

In April 2017, the hole started being filled via one of two existing pipes once used to carry water out of the mine, which were cut open at the 100m level.

However in June that year, it was revealed that 7000 tonnes of fill had been lost as it began flowing into water which was at a higher level than expected. Therefore further funding was required to purchase extra fill in order to continue.

The fill being used was a fine gravel which had the lowest risk of blocking the serviceable pipes but after it was found to be flowing into the workshop, a coarser blue metal was instead used.

By September 2017, the shaft had been filled up to the 100m level in order to support a 9m concrete plug which was then poured.

In November, the service pipes were attempted to be cut using a drill rig to allow further filling above the concrete plug, but unfortunately they were unable to do so, therefore explosives were used to cut the pipes.

Cement slurry was then poured into the shaft up to the bottom of the blockage at 48m level, with sand then filling the shaft to the surface, which was completed in December 2017.

During 2018, the legs of the skyshaft were raised to remove pressure off the headframe, the cage which Brant Webb and Todd Russell famously walked out of has been returned, the surface has been reinstated and museum exhibits have been returned to their original positions in the mine yard.

Under the joint Australian Government-State Natural Disaster Relief and Recovery Arrangements (NDRRA), assistance has been granted to alleviate the financial burden of these events to Council.

The Federal Government committed to 50% funding and the State Government 25% funding of the initial estimated repair costs of $1.5m ($0.75m from Federal Government and $0.375m from State Government was received). Under the NDRAA a further commitment to assistance towards costs over the $1.5m initial estimates is being sought and has preliminary encouragement from the State.  

Brief Timeline:

·         Bulk fill for sacrificial formwork (i.e. from bottom of shaft to bottom of concrete plug): started in late-April 2017 and finished mid-September 2017

·         Blinding concrete layer: started and finished in mid-September 2017

·         Concrete plug: started and finished in late-September 2017

·         Cement slurry layer: started and finished in early December 2017

·         Bulk sand fill (i.e. from top of blockage to top of shaft): started and finished in mid-December 2017

Contact:

Mayor, Christina Holmdahl 0417 804 210