Modern Mining January 2016

DIAMONDS

schedule, thanks to new technology devised by Murray & Roberts Cementation at the request of De Beers. Says Chamberlain: “At the ten- dering stage for the VUP, De Beers asked that bids should include proposals for achieving greater safety during pre-sink operations with- out compromising productivity. To meet this requirement our engineers designed a movable gantry system, able to carry and manoeuvre a movable suspended stage, together with a mucking hoist able to roll over and away from the shaft during pre-sink operations. The gan- try was installed and tested at our Bentley Park facility before being transferred to the Venetia site.” Using the gantry system – which was oper- ated by a multi-skilled crew – Murray & Roberts Cementation was able to successfully complete the pre-sinks with only half the workers that would normally have been needed. The main gantry girders were designed to accommodate the loads from the main hoist (used for kibble hoisting and stage suspension), which allowed for a maximum pre-sink of 80 m (an actual depth of 60 m below collar elevation was sunk), as well as the stage winders (used to raise and lower the pre-sink stage). The height of the gantry structure was matched to the height of the stage to enable the stage to clear the collar once raised to the upper limit. Once the stage had been raised in this upper posi- tion, the long travel wheel drive motors were energised to move the gantry, complete with suspended stage, away from the shaft, drawing a blast cover over the excavation. When in use,

sensitised emulsion will give a better break, which in turn will make the task of the clean- ing crew easier. For the VUP, the explosives are being supplied by AEL Mining Services. According to Chamberlain’s colleague, Japie du Plessis, Senior Project Manager with Murray & Roberts Cementation, a major advantage of the new sling-down drill rig design is that – once the rig has drilled the blast holes – the stage only has to be raised 50 or 60 m prior to blast- ing compared to 80 m using a conventional rig. He also notes that the new rigs can drill a burn- cut round (as opposed to a wedge cut), which improves the advance and reduces fly rock. On the question of whether the new Canadian method will deliver faster advance rates than traditional methods, Du Plessis says the true test will be when the shaft sink- ing moves into the full sink mode. “The main motivation for Murray & Roberts Cementation in adopting the new approach is that it is much safer than the traditional approach, and our Canadian sister company has in fact deliv- ered an entire shaft without suffering a single LTI,” he says. “Having said this, we believe that the method is also potentially faster than the conventional approach and Cementation Canada has demonstrated this on contracts it has undertaken. Certainly we believe that pro- ductivity will be higher with fewer workers required in the sinking team.” The Canadian method is not the only inno- vation in the shaft sinking for the VUP and Chamberlain points out that the pre-sinks on the two shafts were both completed ahead of

Ventilation system for the service shaft.

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January 2016  MODERN MINING  51