Document Type

Conference Paper

Publication Date


Publication Details

Ian Gray, Iuliia Shelukhina and Jeff Wood, A Practical Approach to the Determination of Outburst Thresholds, in Naj Aziz and Bob Kininmonth (eds.), Proceedings of the 16th Coal Operators' Conference, Mining Engineering, University of Wollongong, 10-12 February 2016, 330-346.


The current Australian reliance on gas content and DRI index used in Outburst Management Plans leads, in many cases, to an ultra-conservative approach to coal mine development. It is also contrary to overseas practice where other factors are taken into account. Outbursts must start with failure and that failure must produce fragments. It is therefore a process of fragmenting failure. For this to occur the coal must have some pre-existing structure within it. Determining whether a fragmenting failure will take place is dependent on the effective stress within the coal and the strength of the coal. Thus determining the strength of the coal and the structure within it are paramount, both on the small and large scales. A key element in the effective stress equation is the gas pressure. Once failure has occurred the question is whether that failure takes place with sufficient energy to provide a serious risk? The energy comes from gravitational effects, strain energy and expanding gas. The energy from expanding gas tends to dominate and is dependent on gas in pore space and desorbing gas. The desorption rate of the latter is dependent on the diffusive characteristics of the coal, the gas content and the fragment size. To be able to practically characterise a coal for its outburst proneness it is necessary to measure more than is current practice in Australia. What is required is determination of structure at various levels, the measurement of diffusion coefficient like behaviour, strength by Protodyakanov Index, or by rapid depressurisation (Pop Gun Test) as well as gas content.