Open Cut » Drilling & Blasting
Accurately detecting the approaching top of a coal seam prior to blasting is fundamental to efficient coal recovery. Previous investigations by member mining companies reported a 66% reduction in coal dilution through disciplined and detailed overburden drilling and blasting practises. Through two Phases of CRCMining/ACARP funded research, CRCMining has developed a novel concept for detecting approaching Top of Coal (TOC) whilst drilling in Rotary Air Blast (RAB) over-burden blasthole drilling.
The method of detecting TOC while drilling brings significant benefits to key stakeholders, including - Providing a reliable indication of approach to TOC that will enable drilling to be stopped before touching coal or at a minimum standoff distance. - Increase production by reducing damage to coal from blasting.
The first phase of research investigated injecting an electrical signal into the drill bit and measuring single point resistivity at the drill bit while drilling. Early concepts were based on a 2.4GHz wireless communications path through the drill string to send resistivity measurements to the surface for subsequent data analysis. As this concept developed it became apparent that it was a complex and delicate system, with a number of significant practical limitations, including battery life, long term survivability and a dependency on in field support. Although demonstrated during lab testing, wireless communication up through the drill pipe proved to be problematic due to internal profile variation in the drill pipes causing attenuation in the returned signal.
An internal review of the project at CRCMining lead to the refocus of Phase 2 of the project to a simpler, elegant concept solution. A cornerstone of the concept involved relocating the complex, fine measurement electronics out of the drill bit and implementing them into the cab of the drill rig where environmental factors no longer became a factor. This also removed the need for wireless communications up through the drill string as all measurements are now done on the surface rather than at the drill bit. During this phase a system was designed and developed and trialled in the field at Jellinbah Mine in North Queensland. Results from this field trial proved that the coal seam could be detected using the phase 2 system, however due to a critical component failure in the research prototype, the full experimental program could not be completed. The system did however reliably and clearly detect coal interface despite a high signal to noise ratio, which is suspected to be associated with the failed critical component.
Related project reports also available from the ACARP website are C19023 and C24064.