The problem is, nobody seems to know exactly why this is. There has been some legislative change that focused thought on the problem of keeping the rocks stable and some technical innovations. But has it been a management change or some other cause?
With mines going deeper and taking more ore, and the advent of new technologies – such as remote controlled mobile equipment and larger haul trucks – as well as new forms of backfill and new methods of mining, new geotechnical hazards emerge.
Like all other parts of mining, the corporate knowledge built up in geomechanics and ground control is also in danger of diminishing, which could start to undo the hard won safety gains of the past decade.
These are the findings of AMC Consultants principal geomechanics geologist Malcolm Bridges. He has called for a comprehensive technical review of injuries and fatalities during the past 25 years to find what has been the true cause of the downturn in rockfall-caused deaths.
Bridges – who is experienced in undertaking forensic investigations of major mine accidents in openpit and underground mines involving failures, collapses, rushes and air blasts – set about analysing information publicly available from the Minerals Council of Australia that looked at mining fatalities and their causes over the 10-year period from 1996-97 to 2005-06.
Over the 10-year period there were 150 minerals industry fatalities – 107 of those occurred in mines and 47 were attributed to a geomechanical cause. Apparently the one non-mining geomechanically related fatality was a rockfall at an exploration site in 1999.
Writing in AMC’s Digging Deeper newsletter, Bridges says the introduction of clauses in Western Australia’s Mine Safety and Inspection Regulations may have been a significant development. Those clauses were added due to a spate of fatalities in WA caused by rockfalls and led to a flow-on effect in other states.
Since then a majority of mines across Australia have tried to keep a geomechanics expert on staff. According to Bridges, these experts, while many had limited experience, contributed to the design of ground support, stopes and pits, monitoring and awareness and management of risk. Programs by the Australian Centre for Geomechanics and individual mining companies, the influence of experienced consultants and further law changes have also helped.
“However, geomechanics is a study of complex materials and processes,” Bridges writes. “Ground support has to deal with a wide range of conditions that change over time, including the difficult task of safe support for yielding and bursting environments. Rock stresses change over time in response to mining, requiring complex analysis and sophisticated predictive models.”
Interestingly WA had one of the highest fatality counts in the mining sector – along with New South Wales. Both states have since enjoyed the largest fall in fatality numbers.
So what happens when the person who has been responsible for monitoring the ground control conditions in a mine leaves? This is a point that is of concern to Bridges.
“Even without innovation, a substantial loss of corporate memory due to ongoing skills shortages may overturn the progress of recent years,” he said. “Industry-wide campaigns such as safety awareness, training, risk management, legislation and inquiries may not have been the main contributors to the downward trend of fatalities.
“Rather, particular technical advances and associated management practices in the geotechnical area may have been foremost. The industry needs to know which.”
Looking at Bridges’ data it is clear, although not overly surprising, that the bulk of the deaths attributed to geomechanical causes – 40 – happened underground.
One of the events added to the survey was the air blast incident at Rio Tinto’s Northparkes mine that killed four people. That air blast was caused by falling rock. Another included in the study was the fill rush at the Bronzewing mine in 1999, which killed three people, because it involved the movement of fill material within a stope.
However, the water inrush at the Gretley mine in 1997 that killed four people was not included because the flow was from a breached reservoir. Bridges concedes there could be some debate over whether these cases should or should not be included.
Another of his findings was that for 20 of the 47 fatalities the victim appeared to have not been involved with the cause. On the other hand, 27 of the victims were judged to have been involved.
The size of material that moved was classified by a relative scale of man-sized, truck-sized and upwards to tens of metres, which roughly equates with a stope/wall size. The bulk of fatalities related to man-sized, although it should be noted that these events could have started out as stope/wall type falls.
