Frith said whilst Section 48 represented a well founded legislation and contained a reasonable process for the derivation and management of ground support in an underground mine, due to its overall enabling nature its effective implementation was not always clear or straight forward.
“Whilst the technical aspects of ground support are commonly debated in public, the philosophical aspects such as decision-making and communication for example rarely get much of a hearing, but are nonetheless critical to effective strata control,” said Frith.
Frith said effective strata control started with reliable hazard identification, however this was often less than adequate due to the fragmented nature of the collective experience within the coal industry.
Statistics in longwall extraction from 1999 to 2000 show industry have incurred significant financial losses from roadway roof falls. The majority of falls are related to localised geological anomalies that had typically been identified prior to extraction.
To start overcoming this trend, Frith proposed an industry database detailing major falls of ground and more importantly, why each was believed to have occurred.
“Simply resorting to conservative over-support was not necessarily a workable solution, as there are several significant economic downsides to that approach, largely relating to the rate of roadway development,” he said.
“The apparent conflict between preventing major falls of ground, yet continuing to assist safe and economic mining was a major engineering challenge and demands the use of a rigorous management process and on-going vigilance.”
In discussing some of the potential “pit-falls” associated with roadway strata control in coal mines, Frith emphasised the need to install ground support to a required outcome rather than an existing budget and to also give equal respect to both measured ground movements as well as the observations and concerns of experienced mining personnel.
Frith said in his experience, problems were sometimes inadvertently caused by asking the wrong questions. For example, even the most experienced and knowledgeable strata control engineer cannot always reliably answer the question “will the roof fall in or not” when presented with a given set of circumstances. This can often lead to a potential problem being accidentally overlooked.
However, if the concept of “acceptable residual risk” is adopted, the roof falling in is not directly relevant, simply that it is prudent to counter any higher instability threat posed by the known circumstances with additional support and monitoring, the objective being to ensure that the residual risk remains at similar levels in all areas.
