Modern Mining July 2023

PLATINUM

Exceptional pilot hole accuracy achieved for vent shaft at Ivanplats Platreef

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 near Mokopane.

“ T he accuracy of the pilot hole was critical to the success of the ventilation shaft, which will serve a second purpose as a man hoisting facility in cases of emergency,” says Dirk Visser, Senior Project Manager at Murray & Roberts Cementation. “This hoist facility will travel on rope guides through the shaft, which requires tight tolerances.” At the completion of the hole, a depth of over 950 m, the results showed that the drilling team was not more than 0,05% off its closure distance. With the pilot hole measuring 381 mm in diameter, the highest deflection over this distance was only 452 mm. He explains that the deviation at final depth had returned to 0,02%, or just 226 mm off centre – still within the diameter of the pilot hole. “Murray & Roberts Cementation has long been recognised for its high level of accuracy achieved

Murray & Roberts Cementation recently completed a 950 m borehole for a ventilation shaft at Ivanplats’ Platreef Project.

At the completion of the hole, a depth of over 950 m, the results showed that the drilling team was not more than 0,05% off its closure distance. with directional drilling of pilot holes for shafts,” Visser says. He notes that “anything can happen” in terms of the ground conditions a driller will encounter. Poor ground conditions such as a mud intersection could cause a drill to deviate considerably from its course, for example. However, the company’s track record has consistently shown very good results, he says. On the Platreef Project, success was achieved on the strength of decades of experience with the German-built, highly specialised Rotary Vertical Drilling System (RVDS). He says the team has per fected the art of this drilling method. “The RVDS works on a close loop system, with instantaneous correction while drilling and there fore the high accuracies achieved. Drilling to these demanding specifications with this highly technical equipment demands a very experienced team,” he says. “The most ‘junior’ person in the team has worked with this machine for 15 years, while another member has 28 years of experience in raiseboring.” He explains that the RVDS is a self-steering tool, set up in advance to drill vertically downwards. It measures its progress using two-axis gyro inclination sensors, which continuously determine if there is any deviation from the vertical course. If there is varia tion beyond certain set limits, the hydraulic steering system is activated automatically to put the drill back on course.

18  MODERN MINING  July 2023