Cap Rock Blasting at Maules Creek Coal, Australia
By Ross Burden (1), T. Goswami (2)
Abstract
Cap rock is an impervious layer of hard rock that acts as a barrier which, in the case of an oil reservoir can prevent the upward migration of petroleum and other hydrocarbons. In open-cut coal mining the term refers to a hard and horizontally jointed competent layer above an unconsolidated (weathered) layer overlying a coal seam which, as such, can impede production at various stages of the coal mining process. For example, since the stemming region of the blast is generally positioned in the cap rock bed, blasting usually results in the production of large blocks of rock which may require costly and time-consuming rehandle.
The production of large blocky rock, therefore, has far-reaching consequences including safety and cost per tonne of coal. To achieve maximum blasting efficiency, it is paramount that the blast design accounts for variations in rock properties. In principle, due to the often extreme variation in rock properties in the blast domain, the loading and timing can change from hole to hole. However, in a demanding operational environment, this may not be practical or sustainable.
At Maules Creek (MCC), this team instigated a programme that managed the mapping of the extent of the cap rock, identification of major ‘J1’ and ‘J2’ joint sets, and creation of innovative blast designs for playing the ‘what if game’. By using this process over a period, the cap rock problem has been alleviated. Senior management at the site has taken a keen interest in following and monitoring dig rates with every unusual eventuality being questioned. This process has been a key driver that has engendered cooperation and encouragement for all involved to do their best to avoid hard dig as a priority.
The site has now extended the programme from just managing cap rock to a ‘no hard dig’ strategy, thereby consistently improving operational performance. As a consequence, new and revised targets are being addressed as well as automating drill and blast processes, using the latest technologies such as in-hole monitoring, implementing 3D mapping, and monitoring digging and coal exposure outcomes. Attention is now focussed on the overall cost of operation and approaches to compensate for any increase in drilling and blasting costs. All the aforementioned issues are addressed in this paper.
1. Ross Burden, Senior Mining Engineer (Drill & Blast), Whitehaven Coal Limited, PO Box 56, Boggabri NSW 2382, Australia.
2. Tapan Goswami, Mining Consultant, Blast Outcome Services, 2 Glenridding Grove, Lakelands, NSW 2282, Australia.