Western Australia’s Department of Mines, Industry Regulation and Safety has outlined a number of recommendations to minimise the potential danger caused by sinkholes.
The department has released a preliminary report into an incident at a WA mine in October last year that saw a 13-metre deep sinkhole open up after a working pit floor subsided into a backfilled stope.
Four people were working nearby when the incident happened.
“At the time of the incident, surface drill and blast activities were occurring in the vicinity,” the report says.
“The subsidence event resulted in the loss of an integrated tool carrier and an explosives truck that were parked on the blast pattern.
“A number of charged blast holes were also engulfed in the sinkhole.”
The report says while the vehicles were unoccupied at the time, four people were working near them.
The report says there was one direct cause of the incident.
“At the time of subsidence, the backfilled underground workings were not treated as a void, allowing work to be undertaken above an area of unknown stability,” the report says.
The report also outlined contributing causes, including risk assessment controls not being adhered to and “inadequate change management associated with the decision to move to normal operational practices”.
A number of recommendations were outlined in the report, including assessing backfilled stopes and the potential for them to change over time, ensuring backfill records are available, ensuring all underground workings near open pit work are marked on plans and “developing safe working practices that do not presume that any stope is tight-filled”.
The report also recommended monitoring and recording any change in underground conditions below open-cut workings.
The investigation into the incident is continuing.