Australian Shaft Drilling (ASD) has moved with this trend, developing larger drills and designing, procuring and fabricating drilling equipment ranging from 3.2 metres to 6.1m in diameter and weighing up to 300 tonnes.

The larger “bottom hole assemblies” have driven the need to increase the capacity of the hoisting systems to cater for the heavier drill weights with the system for Narrabri Coal in New South Wales pushing 680t hoisting capacity.

This is a significant advance from the 150t system used in 2004 at Moranbah North mine in Queensland.

Blind shaft drilling is becoming more popular as it reduces the amount of interaction with the underground development before the shaft is connected to the mine.

A lot of ASD work is coming from new mine developments where the shaft can be completed ahead of the underground schedule, giving access to ventilation at the earliest possible date.

This has great advantages for the continual development drivage once the mine has reached the working seam level, as more machines and people can be utilised at once and still comply with the ventilation requirements.

Three out of the last four ASD projects have been for new mines and this trend is expected to continue with the large number of greenfield sites planned in the next few years.

At Rio Tinto’s Kestrel Mine extension, located near Emerald in Queensland, ASD has been awarded the construction of the No. 1 vent shaft which is being drilled at 6m diameter through weathered tertiary strata. Progress on the shaft has been promising with advance rates of 43m per week being achieved, exceeding client expectations and putting the project well ahead of schedule.

ASD attributes this success to an innovative cutter head design and a drilling mud quality control system that provided support for the unstable tertiary strata up until it was lined.

At Whitehaven Coal’s Narrabri Coal operations, ASD has been constructing the mine’s first ventilation shaft which is scheduled for completion in March 2011. The strata at NCO is varied with sections of hard basalt and conglomerate as well as softer mudstones, clays and shales. The shaft will be lined with a combination of steel and concrete to an internal diameter of 5m and on completion will provide a dry shaft for the life of the mine.

Blind shaft drilling offers a safe method of shaft development. All works are conducted from the surface and the shaft remains full of drilling fluid until it is dewatered at the completion of the lining.