Modern Mining September 2019

SHAFT SINKING AND UNDERGROUND DEVELOPMENT

South Africa from the factory in Italy and was already on site adjacent to Master Drilling’s Fochville headquarters, with tri- als about to start. “What we’ve brought in from Italy is basically the pilot shaft exca- vation system,” he explained. “This is the part of the machine that really represents new technology and requires extensive testing – we’re going to bore down about 10 m to test the flushing system. The balance of the machine is the enlarge- ment and hoisting section, which relies on established equipment concepts and techniques.” According to Pretorius, the SBS is designed to bore shafts up to 11,5 m in diameter and 2 km deep in rock of up to 300 MPa compressive strength. “It will represent a huge leap forward in shaft- sinking technology which for the most part currently relies on labour-intensive methods which are inherently unsafe and where progress is measured in one or two or three metres of advance a day. Expectations are that the SBS will at least double this and will require a much smaller labour force. There’s huge interest in it from mining companies as, apart from the safety benefits, it should turn previously unviable projects into viable propositions able to pass the NPV hurdle rate.” In operation, the SBS will involve two phases of boring. The first phase will apply slurry drilling techniques to create the pilot shaft. The second phase will see the pilot shaft reamed to a diameter of up to 11,5 m. Rock cuttings created dur- ing this process will be hoisted to surface by means of kibbles and two single-drum winders.

The shaft lining will be undertaken as a de-cou- pled activity secondary to the primary support that will be done concurrently while boring in close prox- imity to the cutting face. Pretorius emphasises that the SBS should be seen as complementary to Master Drilling’s raise- bore offering. “Assuming you have bottom access and competent rock and that the shaft diameter is no more than about 8 m, then raiseboring is often the way to go. The SBS will come into its own, on projects where these conditions do not apply and blind sinking has to be employed,” he said. If the concept validation trial at Fochville is suc- cessful, Master Drilling envisages building the first full SBS. “We will seek agreement from our partner, the IDC, to proceed to the next phase with our inten- tion being to have a machine available by either late 2020 or early 2021,” said Pretorius. He added that the machine would be a world first. “One of our

overseas competitors does have a mechanised shaft boring system but it is only for soft rock. As far as we’re aware, our system will be the first to have the capability of also sinking in hard-rock formations.” Summing up, Pretorius believes that the develop- ment of the MTB and SBS illustrate Master Drilling’s commitment to innovation, which has been a char- acteristic of the company since it was founded in 1986. “We’ve always been prepared to challenge the status quo and to invest large sums of money in technological development and this has made us a world-leader in our field,” he said. “These new machines are complex and are involving us in years of development with no immediate return. Nevertheless, we are of the firm belief that they have the potential to revolutionise the economics of min- ing and will position us for further strong growth in the future.” Report by Arthur Tassell, photos courtesy of Master Drilling

One of Master Drilling’s raisebore machines. The company operates 149 raisebore rigs around the world.

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September 2019  MODERN MINING  41