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Conference Paper

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This conference paper was originally published as Hayes, PJ, Towards High Productivity Under a "Claystone" Roof: Great Northern Seam Support Management Experiences at Chain Valley, Moonee and Wallarah Collieries, in Aziz, N (ed), Coal 2001: Coal Operators' Geotechnology Colloquium, University of Wollongong & the Australasian Institute of Mining and Metallurgy, 2001, 70-84.


Coal Operations Australia Limited Operates the Chain Valley, Wallarah and Moonee Collieries which are located in the Newcastle Coal Fields of New South Wales in the Catherine Hill Bay area approximately 100km north of Sydney. Operations are in the Great Northern seam, which until recent years were all conducted under an immediate roof of a strong conglomerate. Large areas of the current reserves at all operations are in areas of a “claystone” immediate roof. All three mines have attempted at various stages of their history to find an economic mining method under these claystone roof conditions, with varying degrees of success at each operation. Moonee currently operates a longwall under claystone roof while Chain Valley and Wallarah are place-changing operations which have operated under claystone with some success. The nature of the “claystone” roof horizons in the three mines is often seen as different at each operation but in practice all of the claystones exhibit similar properties – low strength layers particularly at the coal-claystone interface. Strata control in conditions where the immediate roof above the coal seam is claystone appears to be most sensitive to coal beam thickness left as roof coal, roof bolting pattern and anchorage strength, drivage standards, horizontal stress direction, frequency and type of structures present, exposure time before bolting and possibly depth of cover. Coal beam thickness should be maximised wherever possible to achieve an optimum support density. Place-change mining using deep cuts up to 15m has been successfully carried out under claystone and can be a productive mining method in this environment. There may be potential at Moonee Colliery to introduce place-changing as a method of remnant area mining or even as a gateroad development method. The most critical roof support issues in achieving high productivity under a claystone roof are the setting and maintenance of very high support installation standards and the development of a robust support management plan responsive to changes in strata conditions. This paper sets out to describe and discuss the various attempts to achieve economic success at each of the operations in a claystone roof environment.

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