Underground » Strata Control and Windblasts
Wind blast in coal mines and its equivalent, air blast, in metalliferous mines have been of concern to the Australian underground mining industry for many years. Although the most recent fatality due to wind blast in a coal mine took place in 1976 at Eastern Main Colliery, incidents involving serious personal injury continue to occur. In metalliferous mines, the history of fatal air blasts spans the period from the 1895 incident which resulted in the deaths of nine miners at Broken Hill South Mine to the multiple fatality at Northparkes Mine in 1999.
The incidence of wind blasts in coal mines is likely to increase as a result of the trend away from pillar extraction to longwall mining. Moreover, the risk of personal injury and of damage to mine infrastructure may become greater as a result of increased wind blast intensity caused by the restricted number of openings through which the wind blast can be dissipated and, perhaps, by increased extraction height. Mining under strong, massive roof, such as some sandstones and conglomerates, increases the risk, particularly where longwall face length is restricted for reasons which may include strata control, structural geology or subsidence issues.
A principal objective of the project, the refurbishment of the existing Wind Blast Monitoring System and the development, construction and testing of a new Wind Blast and Methane Expulsion Monitoring System (WBMEMS), has been achieved.
The WBMEMS was funded under the ACARP with additional financial support provided by industry. The ACARP contribution formed part of its broader funding for the project described in this report and for Project No. C7031 " The displacement of methane from the goaf into the working place as a result of wind blasts in underground coal mines ". The WBMEMS is capable of detecting and recording transient methane levels, air velocities and overpressures during wind blasts.
The field work component of the project comprised an extensive program of monitoring, undertaken at Moonee Colliery during the mining of a further three longwall panels. Analyses of this data, together with that obtained from previous monitoring, have enabled the fluid mechanics involved in the compression and distribution of air during wind blasts to be better defined. The Moonee field trials have also allowed the effect upon wind blast intensity of hydrofracturing, including the impact of the resulting reduced caving arm to be quantified.
Measurements undertaken to date have tended to concentrate on areas of highest wind blast intensity. In addition, all seven longwall panels that have been investigated at Newstan and Moonee Collieries have had essentially the same geometry, a two heading development and relatively short face length. Furthermore, the geological environment of all the panels at Moonee Colliery which have been the subject of wind blast monitoring has been broadly similar. Consequently, it is not yet clear to what extent the " laws " governing the dynamics of wind blasts and the conclusions regarding wind blast hazard management may be generalised to operations undertaken in other geometric and geological environments.
Wind blast monitoring is continuing at Moonee Colliery as mining is undertaken in a changing geological environment. Field work is also planned for a site at a mine in a different geological environment that will become available late in 2001. It is also planned to deploy the WBMEMS in 2002 in a " gassy " mine which it is anticipated may be subject to wind blast. The work is partially supported by an ACARP funded extension C10024 Wind blast and methane expulsion: extension of field monitoring to generalise the results of projects C7031 and C8017.
It is anticipated that the results of field monitoring carried out as part of the extension project will facilitate the drawing up of further guidance for the industry regarding panel design & layout and safe working practices in mines subject to wind blast.