Mechanical Technology April 2016

⎪ Innovative engineering ⎪

SA’s shaft sinking specialist

Above: The vertical shaft mucker (VSM): The use of VSM systems with clamshell muckers at Venetia is a South African first. Left: A view of the Venetia headgears for the production and service shafts. Right: The vertical drill rig (VDR): Murray & Roberts Cementation has incorporated mechanised drilling systems underneath the pre-sink stage. the rock drill extends to create thrust on the rock drill between the stage and the floor and, after drilling, for drill retraction. Much less physical effort is involved and the operator simply guides the drill’s posi- tion – and there are no longer any manual drill operations on the shaft bottom,” Du Plessis explains. Also simplified is the shaft lining process: “Previously, we had to handle the shuttering and formwork from rigger mounts drilled into the shaft lining. But we have now developed proprietary shut- tering, suspended from the sinking stage. The shutter depth is 6.0 m, thus after each 6.0 m of excavation, the shutter is positioned 12-18 m above the shaft bottom – and this shutter can be left in place during drilling and blasting opera- tions,” says Du Plessis. The shuttering is suspended from the lining above using suspension rods, which remain embedded in the concrete lining after pouring and protrude through the shutter at the bottom. To seal the bottom end of the shutter, scribing sup- port bars are pushed out towards the

loading system significantly reduces risk as well as tipping cycle times. Since Murray & Roberts Cementation’s pre-sink gantry is rail mounted, on com- pletion of the first pre-sink operation at Venetia, it was possible to transport the entire system on temporary rails to the position of the second shaft. “For Venetia we drove the whole set-up, including the stage and the portal cranes, across to the new pre-sink site at the mine. The set up stage for the second pre-sink was completed inside of five days, a process that used to take us up to a month,” Du Plessis reveals. Turning attention to innovations on the pre-sink stage itself, the company has also significantly improved the safety and effort required for drilling. “We have incorporated mechanised drilling systems underneath the pre-sink stage. The system consists of six vertical drill rigs supported on swivel arms suspended underneath the stage. Each operator guides the drill and manoeuvres it to match the pattern of holes required for the blast. An inline pneumatic air leg on

sidewalls, curved scribing planks are laid and fine steel mesh is used to seal to the rock interface. A series of steady brackets between the formwork and rock holds the shutter securely in place to contain the self-levelling concrete while it sets. Air hoist are used to hold the top sec- tion of the shutter in position in prepara- tion for concrete pouring. The concrete is then poured into the shuttering using concrete kettles, or kibbles, to supply the concrete from surface. Once the concrete has settled, the shuttering is ready to be moved to the next position. The key

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