Published in June 2009 Australian Longwall Magazine

After six months of design and construction Abergeldie now has its 2009 model 500-tonne capacity blind boring drill rig ready to begin work with its first job slated for a ventilation shaft in the Bowen Basin around mid-year.

The new rig – the fifth rig the contractor has manufactured over the past nine years – is capable of drilling up to 6.5m in diameter and up to 650m deep. It will join a large fleet of ancillary equipment, including excavators, loaders and cranes.

“The new rig will be safer, more reliable, drill deeper and drill larger diameters than any other rig in the world today,” Abergeldie managing director Mick Boyle told Australian Longwall Magazine.

Abergeldie’s drilling expertise centres on the blind boring method – best suited to new longwall mines where there is a lack of access underground, and to mines that experience poor ground conditions or ground with high water content.

Blind boring is a mechanical means of drilling large diameter shafts from the surface. It is used by a handful of companies worldwide to construct ventilation and access shafts for underground mining.

The Abergeldie Mining shaft construction method is a rotary drilling technique which uses a heavily weighted drilling assembly. This provides thrust to a hard rock cutterhead equipped with disc-type cutters.

The disc cutters grind concentric grooves in the rock face leading to the fragmentation of the rock in relatively large pieces. Boyle said this method removed any need for personnel to work within the shaft during the construction phase, making the method safer than conventional drill and blast shaft sinking.

Rock fragments are brought to the surface using a process called reverse circulation. A strong flow of water is directed around the cutterhead which picks up the rock fragments. The fragments travel up through the drill rods before being discharged into a sedimentation pond on the surface.

The excavated material is delivered to the surface without having to interrupt the mine workings. Because the excavated material is deposited on the surface, it also means material does not have to be hauled through the underground mine.

Boyle said the other advantage is that during all phases of the drilling and lining process the shaft is filled with water. Once the shaft has reached the intended depth and the shaft lining has been installed and grouted into place, the water is removed and the drilling equipment demobilised.

Boyle said water in the shaft provided a counter pressure to contain naturally occurring aquifers, oil or gas that may be encountered within strata, and it also reduced the risk of potential problems with sidewall stability.

The water can be enhanced with additives to further support and condition exposed shaft walls and this will preserve their integrity prior to the installation of the permanent

shaft lining.

“The counter pressure provided by the water and the ability to enhance the drilling water with muds or chemicals enhances sidewall stability. This enables blind boring to be carried out in strata that is difficult for conventional shaft sinking or raise boring,” Boyle said.

“Abergeldie has successfully drilled through strata in the Bowen Basin in Queensland that alternated between hard basalt and running sands.”

He said blind boring also allowed permanent shaft linings to be installed and grouted under pressure.

“A balance or slight overbalance with the naturally occurring pressures in the ground eliminates water flow from the strata into the shaft that could otherwise wash away cement grout.”

Abergeldie has carried out a number of blind boring longwall contracts over the years.

The shaft No.2 at Peabody’s North Goonyella coal mine, with a finished diameter of 5.3m and a depth of 270m, is the largest the company has drilled to date.

The shaft has a composite steel and concrete liner about 300mm thick so the shaft was drilled at 6.1m diameter to allow installation of the liner. Due to the nature of the ground a support liner was installed for the top 85m, requiring a drilling diameter of 6.8m to allow installation of the support liner.

In June 2008, Abergeldie completed the construction of ventilation shafts No.2 and No.3 for BHP Billiton’s Dendrobium mine.

Dendrobium is located within the environmentally sensitive Sydney Water catchment area on the Illawarra escarpment behind Wollongong, New South Wales.

“The unique boring method used by Abergeldie enabled the company to guarantee the environmental integrity of the site,”

Boyle said.

The blind boring method was used at the Dendrobium Shaft No.3 from the surface at 5.9m diameter to the coal seam depth of 260m. The shaft was lined remotely with concrete and steel composite liners and has a final diameter of 5m.

Shaft No.2 is a downcast shaft providing clean air to the mine. This was blind bored at 4.8m diameter to the coal seam depth of 260m. The shaft was lined remotely with concrete and steel composite liners, and has a final diameter of 4m.

Abergeldie has also drilled at 4.25m diameter to 360m deep to install a ventilation shaft for the Springvale coal mine near Lithgow, NSW.

Boyle said the most common discussions Abergeldie had when solving clients’ shaft problems was the choice of liner. “We are able to provide remote applied shotcrete, non hydrostatic steel or concrete liners and fully hydrostatic steel or composite liners. The choice of the most appropriate liner depends on shaft design life, shaft diameter, water inflows and sidewall stability,” Boyle said.

In addition to shaft drilling and lining, Abergeldie also offers design and construction of complete process and civil infrastructure for the mining industry, including dams, bridges, roads, wharfs and marine infrastructure, water infrastructure, electrical infrastructure, fuel handling and storage, conveyors and rail infrastructure.

Boyle said Abergeldie had plans to become a major contractor within the longwall sector, carrying out shaft drilling and all types of surface works. Part of that strategy has led the contractor to establish offices near the

Hunter Valley (Thornton) and near the Bowen Basin (Mackay).