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Redpath SA drill Africa’s largest diameter hole

Redpath Mining South Africa has recently completed reaming of a 7.3 m diameter hole at Sasol’s Impumelelo Mine, the largest diameter hole reamed to date in Africa

Johan Davel, Redpath Mining General Manager of Raiseboring said the reaming performance of the Redbore 90EX surpassed the company’s expectations

“Achieving optimal accuracy was critical, as we were drilling inside pre-installed spiles that may not have been intersected,” Davel said.

Davel said the company had to used highly-skilled operators on the project citing that the artisans have at least 15 years’ experience in large-diameter drilling.

The development comes after the company was awarded a contract for two ventilation shafts by Sasol at its Impumelelo Mine.

The scope of the work entailed the piloting and reaming of two 186 m x Ø7.3 m ventilation shafts, including the lining of both shafts by means of a Remote Shaft Liner.

Following completion of the first shaft – Up-Cast Shaft, preparations for the second – Down-Cast Shaft are ongoing.

According to the company, the pilot hole was directional-drilled, using the Rotary Vertical Drilling System (RVDS), down to a depth of 82 m, from where conventional piloting continued until breakthrough.

The reamer was designed jointly by Redpath and Atlas Copco. Currently the Redbore 90EX is being mobilised at the Down-Cast Shaft, while the Remote Shaft Liner is being set up at the Up-Cast Shaft.

The company said shaft lining will be carried out by spraying a 100-mm-thick, 30 MPa fibrecrete lining onto the sidewall of the reamed hole in order to prevent the shaft from caving in.

This will be carried out via a remote-controlled unit from the surface down the hole, which means no workers are involved, and who will be out of harm’s way at all times.

Redpath also recognised the importance of up-skilling and participating in a Social Development Plan, and therefore recruited raisebore assistants from the local communities.

“These new assistants had no prior raiseboring experience or exposure, and had to be trained and assessed on all aspects of the raiseboring before and during the project,” the company said.

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