Published in Australia's Longwalls

Regional instability can have a significant effect on modern business' quadruple bottom line – safety, environment, community acceptance and economics – and accordingly should be recognised as a potential major risk.

Regional mine instability is defined as any event that affects the structural integrity of a whole mining district or a number of districts. Instability can affect both old and new mines, often in the working area.

At least nine of the regional instabilities that have occurred in Australia in the past 12 years have been in sections being worked at the time. Six of these were in the category of sudden, meaning they were preceded by few, if any, warning signs and could not be halted. Fortunately, nearly all occurred during shutdown periods.

Over the past 15 years in Australia regional instabilities in both underground metalliferous and coal mines have resulted in five fatalities. Two longwall working sections were abandoned and future mine reserves were lost due to regional creep of the main development roadways in one coal mine. In another incident, over $10 million of lead and zinc reserves were sterilised.

Damage to surface features and structures caused by regional instability has resulted in the loss of local community and council support, more stringent requirements in obtaining approval to mine, and the withdrawal of the right to mine under certain surface features.

Common law claims and prosecutions under occupational health and safety legislation have been associated with some of the events. Litigation is more likely to be associated with these types of events in the future. Following one well-publicised disaster there was a reduction of over 40% in prospective undergraduate enrolments in mining engineering at one university.

University of New South Wales professor Jim Galvin has undertaken an extensive study into the role of risk management in reducing the possibility and consequence of regional instabilities. Galvin said the current situation in managing risk with regional instability was far from ideal for a number of reasons, including industry rationalisation and consolidation, which he claimed had accelerated the “loss of corporate memory”. Corporate memory was essential for appreciating mining conditions and understanding the basis of mine planning decisions associated with mining in the earlier years of an operation, he said.

“In some cases, the focus on maximising return on shareholder funds in the short term, in association with the move towards performance-based contracts, is encouraging decision making that is based on a short-term outlook to mine planning without due regard or care for the implications for long-term stability,” he said.

The shortage of qualified mining and geotechnical engineers entering the mining industry has also impacted heavily on assessing and planning against mine instability. There is also an absence of any requirement for geotechnical practitioners to have qualifications in geotechnical engineering or to have registered status, meaning there is no control over who practices as a geotechnical engineer, and no requirements for practitioners to have a basic knowledge of mining or to undertake continuing professional development.

Galvin believes the current situation can impact on the responsible design for long-term stability in a number of ways. “There is a tendency to succumb to production pressures and to deviate from established and responsible mine design principles that are concerned with ensuring stability in the long term. One example is a tendency not to divide mine workings in tabular deposits into compartments utilising barrier pillars and isolation pillars. A number of international inquires into mining disasters related to regional instability have established the importance of compartmentalising mine workings through the judicious use of barrier and isolation pillars,” Galvin said.

“Some established principles related to regional stability are not being adopted simply because mine design practitioners and mine managers are unaware of them. This relates back to the absence of specified qualifications and competency in order to function as a geotechnical engineer, especially in a mining environment, and the absence of any requirement to undertake continuing professional development,” he said.

Galvin offered a number of solutions to effectively manage the risk of regional instability in the future:

Continue to build the geotechnical knowledge base through research and development supported with field performance data.

Provide foundation education in mining geomechanics to mining engineers and others wishing to practice mine geotechnical engineering.

Ensure geotechnical practitioners undertake continuing professional development.

Put mechanisms in place that retain corporate memory at both a mine site and company level.

Undertake a risk assessment of regional mine stability at each mine site on at least an annual basis in order to take account of changes in the time-dependent factors that affect regional stability.

Consider the effects on regional mine stability when any changes are made to local mine design.