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Most Advanced Shaft Lining System Goes to Work in Botswana

Murray & Roberts Cementation has introduced the most advanced shaft lining technology used in the African mining industry and is poised to deploy it on its first job at a mine in Botswana to apply shotcrete to support two 6m diameter vertical shafts which will be sunk to a depth of 110m.

Hailed as the future of shaft lining, Murray & Roberts Cementation sourced its innovative new tele-remote shaft liner in Australia and will market this service as a value-add to its raisedrilling services.

Pat Muller, senior project manager at Murray & Roberts Cementation, says this robotic shaft lining system is much safer than the conventional methods used up until now because the operation is conducted entirely from the surface and there is no need for personnel to descend into the shaft at any time during the process.

“The remotely operated shotcrete system eliminates the risky, costly and time consuming process of lowering men and equipment down the shaft to apply the lining,” he says. “So there is no need to obtain special licenses for the equipment or the permission of the various mining authorities before the job can go ahead, which is standard practice with the traditional method.

All functions of the scanning and spraying process are operated from a remote control cabin set away from the shaft edge and by a machine operator working safely behind a safety fence on the winch deck.”

The system has also been dimensionally designed to be transported underground to line sub-shafts.

Operation

The shaft liner can be adjusted to accommodate various shaft diameters — from 1.5m up to 8m — by attaching different module leg attachments to the spray head. These leg attachments are fitted with spring adjustable heads with an individual leg stroke of 100mm to ensure positive pressure on the shaft wall. Four sets of legs are available to accommodate different shaft sizes: 1.5m to 2m, 2.5m to 3.5m, 4m to 5m and 5.5m to 8m. The process takes place at a rate of 9m&179; per twelve-hour shift.

In the control cabin, the operator uses a touch screen to control the operating system and observes the process via footage transmitted to a screen from cameras fitted to the spray head. This footage can also be recorded to DVD to verify the quality and process of spraying for both the client and the contractor’s records.

The operator simply enters the appropriate values into the system configuration data section of the touch screen and the unit makes calculations according to these specifications provided by the client. Values are obtained from data that includes the shaft diameter and the shotcrete pass — the thickness of the shotcrete to be applied with each pass of the nozzle. Generally this value is in millimetres. The required pattern is also taken into account, which is the nominal vertical size of the application from the nozzle, input in millimetres. The further the nozzle from the shaft wall, the larger this value will be. Once set, it remains fixed for the duration of the spraying process.

Rebound is a nominal value of anticipated material loss to rebounding off the shaft wall and can be optimised once spraying commences. The application thickness is also input to configure the system — this is the depth in millimetres of shotcrete applied in a single application run.

From the control cabin, the operator has full control of all functions in play during the scanning and spraying process: the hydraulic pump, winch speed, rotation speed, drycrete feed rate, addition of air and water and DVD recording. At the end of the process the operator generates a detailed report of the operation as proof that all the required specifications have been met.

“The remote shaft liner does the job safely, cost effectively and on time, with a high quality finish,” Muller says. “It is a very mobile system, needing only a 7t – 10t truck to transport it to the required location and two people to operate the entire process.

“Since we are offering this service as a value-add to our raisedrilling offering, we have trained two members of the raisedrilling crew to operate the system, so the two processes dovetail effectively at the client’s site.”

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