Mine owner Anglo American chose the 8.0 m machine for two decline access tunnels at grades of 1:6 and 1:8, one for conveyors and another for men & materials. The TBM was picked over the traditionally-used road header method for several reasons, including excavation speed and tunnel maintenance. The choice proved prescient: By the time of project completion the machine had excavated at a rate approximately ten to fourteen times faster than a roadheader—about 70 m per week vs. 5 m per week for a roadheader. In addition, the final tunnels have a smooth profile and are segment-lined, requiring minimal upkeep during the planned 40-year life of the mine.

Being that the machine was a dual-mode “Crossover” TBM, meaning that it could cross between hard rock and mixed ground conditions, and was to be used for mine operations, it was equipped with many unique features. These included an interchangeable cutterhead for hard rock and soft ground cutting tools, a two-stage center-mounted screw conveyor, a “quick removal” shield system, and flame-proof machine components due to the possibility of methane gas in the tunnel.

The TBM was designed mainly for hard rock (Single Shield) excavation, as only the first 300 m of each tunnel were in mixed ground (requiring EPB functions). The two-stage screw conveyor worked in both ground conditions to draw muck from the tunnel face. Two sets of shields were built for the TBM’s “Quick Removal” system, and were detached from the machine at the end of each blind tunnel to be left in the ground for constant support, a requirement in Australian tunnels. The inner core components of the TBM were then retracted out of the tunnels on specially designed transport dollies.

The machine began boring the first tunnel, for conveyors, in December 2013, and was re-commissioned for the men & materials tunnel in November 2014 with a new set of shields. Once excavation commenced, boring was completed in 88 days at an average of 10.9 m per day, with a best day of 25.2 m. The bore itself was similar to the first, with few challenges encountered other than elevated methane gas levels that required several temporary stoppages in order to safely remove the gas from the tunnel.

Currently, the machine is being prepared for its final retraction and roll out, and will be on the surface in less than two months.  After that, the TBM will be stored onsite for future Anglo American mining projects. Once the mine expansion is completed, the coal mine is expected to produce five million tons of coal per year over the next 26 years.

Main Points:

• The Robbins Company provided an innovative dual-mode “Crossover” machine that can excavate in multiple types of ground for a coal mine in Australia.
• The machine operates in hard rock (Single Shield) mode for siltstone, coal, sandstone and basalt, and soft ground (Earth Pressure Balance [EPB]) mode for sands and clays.
• The Grosvenor Decline Tunnel Project is the first to utilize TBM technology on the continent
• The machine was custom-designed with many unique features to accommodate the mixed ground and regulations in Australian mines

More information at  http://www.therobbinscompany.com/