The dual purpose use of the new ventilation shaft at Ivanplats’ Platreef Project near Mokopane required extreme pilot hole accuracy – so it called in specialist Murray & Roberts Cementation. The vent shaft, which meets horizontal development at a depth of 950 m, also needs to be equipped with a hoist and rope guides to carry personnel in the case of emergency. The rope guides for the hoist require the shaft to be drilled vertically within tight parameters. According to Dirk Visser, Senior Project Manager at Murray & Roberts Cementation, this meant offering the client minimal deflection of the pilot hole using a continuous steering tool.

“Using the well-proven German designed and manufactured Micon, Rotary Vertical Drilling System (RVDS), we were able to achieve the set parameters required for a rope guide installation,” says Visser. “The worst deflection was no more than 0,05% – or 452 mm – and by the time we bottomed out, the deviation was only 0,02% or 226 mm off centre over a final drilling depth of 950 m.”

He highlights that Murray & Roberts Cementation has an established reputation for achieving high levels of accuracy in directional drilling. Micon’s specialised RVDS is a continuous self-steering tool working on a close loop system which steers the tool using two-axis gyro inclination sensors which activate the hydraulic steering system. It can determine in real time if there is any deviation from the vertical course, and communicate this information to the operator on surface via pressure waves in the drilling water by converting the pressure waves into information through transducers.

The Murray & Roberts Cementation drilling team not only ensured accurate directional results, but also optimised the performance of the RVDS. By keeping an eye on key variables like voltage levels and water cleanliness. He highlights that drilling to these tolerances with this highly technical equipment demands a very experienced team. On this project, for instance, the most ‘junior’ person has worked with the RVDS for 15 years, while another member has 28 years of experience in raiseboring.

In one of the most accurate pilot holes to be drilled on a South African mine, Murray & Roberts Cementation recently completed a 950 m borehole for a ventilation shaft at Ivanplats’ Platreef Project.

At the completion of the hole at over 950 m depth, the actual results showed that the drilling team were not more than 0,05% off on their closure distance.

By Admin