Modern Mining July 2023

“The direction of the drill is automatically adjusted by extend able stabilising ribs on the RVDS tool,” he says. “Any deviation is picked up by the sensors and a signal is sent to one of four ribs, which can extend itself to rectify the angle.” The system is energised by water pumped from surface, and this water also flushes out the chippings and cleans the hole. A needle valve opens and closes, sending pressure waves through the water to a transducer on surface which is used to monitor the condition of the steering tool and the accuracy thereof. The opera tor monitors the critical parameters from a laptop in the operator cabin to ensure the tool functions within specifications, and if they pick up that the drill is not keeping to these parameters, there may be an aspect of the equipment that needs attention.” This requires prompt action from the team, which may have to withdraw the drill string and replace certain components before continuing. This attention to detail, he explains, ensures that the accuracy of the hole is maintained while the pace of drilling is opti mised. The RVDS tool may, for instance, need to be substituted after certain intervals with a new unit, as the old one receives its scheduled servicing. The electrical power driving the RVDS is generated by water pumped from the surface. Importantly, the operator must monitor the voltage being fed to the unit; if the voltage is too high or too low the unit will shut off to protect itself. The water flow to the unit and out of the hole must also be monitored carefully. He noted that the team on the project gave special attention to water cleanliness, ensuring that water exiting the borehole reported to a settling dam. The water circulated down the hole from the dams was therefore free of cuttings, which will damage the drilling tool. To ensure continuity whilst drilling, Murray & Roberts Cementation always has a back-up RVDS unit on site. “Using Micon’s RVDS tool ensures that the pilot hole will inter sect the mine’s horizontal development at the 950 m level, as planned,” concludes Visser. “This saves the mine any extra time or cost spent locating and intersecting with the hole, from which the vent shaft can now be reamed accurately.” 

Above: Success was achieved on the strength of decades of experience with the German-built, highly specialised Rotary Vertical Drilling System (RVDS).

Left: Collaring of the pilot hole, for the ventilation shaft at Platreef.

Below: With the pilot hole measuring 381 mm in diameter, the highest deflection over this distance was only 452 mm.

July 2023  MODERN MINING  19