The Largest Fully Lined Blind Bored Ventilation Shaft Constructed to Date in Australia

2019

Michael Boyle, Abergeldie Complex Infrastructure ; John Zeni, Abergeldie Complex Infrastructure

The blind shaft boring method is a mechanised process of excavating large diameter vertical shafts downward from the surface. Blind boring is a rotary drilling technique that eliminates any requirement for personnel to work within the shaft or access the underground workings during the drilling and lining phases. All excavated material is delivered to the surface carried by a flow of circulating fluid through the centre of the drill rods A heavily weighted drilling assembly, suspended from above, provides the vertical thrust to a hard rock cutter head. The drill assembly is suspended from a large A-frame rig and powerful winch at ground level. As depth increases, more drill rod and pipe is added to the load supported by the A-frame. The two largest rigs operated by Abergeldie, are the largest of their type in the world, capable of drilling shafts to 500m deep with 6.5m diameter, or even deeper at smaller diameters. The shaft most recently completed by Abergeldie was to a record-breaking depth of 523m with a raw diameter of 6.2m and a finished, lined diameter of 5.5m. The shaft is kept full of water throughout the drilling and later lining process. Rock fragments are transported from the working face to the surface by a strong flow of water around the cutter head, piped up through the drill rods and discharged into a sedimentation pond at ground level. The water filling the shaft also provides counter-pressure to contain naturally occurring aquifers, oil and gas that might be encountered in the strata, helps to stabilise the shaft walls and means that shaft linings (prefabricated in sections from steel, concrete or a composite of the two) can be installed and grouted under pressure. Slight overbalance with the natural pressures in the ground eliminates water flow from the strata into the shaft, which could otherwise dislodge the grout.

Keywords: Blind Shaft Boring, Blind Bore, Mechanised Process, Eliminates, Shaft,