The reaming phase of a 7.3-m-diameter hole at South African integrated energy and chemicals company Sasol’s Impumelelo coal mine, in Mpumulanga, has been completed, setting an African record for the largest-diameter hole reamed to date, says South African mining company Redpath Mining.
Mining Weekly reported in June that the Impumelelo colliery, an 8.5-million- to 10.5-million-ton-a-year operation that is part of Sasol’s programme to replace its ageing coal mines in the Secunda area, was 40% complete.
Sasol awarded Redpath Mining the contract for two ventilation shafts at Impumelelo in 2016. The scope of work includes the piloting and reaming of two ventilation shafts, which are 186 m deep with a diameter of 7.3 m. This includes the lining of both shafts by means of a remote shaft liner. The first shaft is the Up-Cast shaft and the second will be the Down-Cast shaft.
The Redbore 90EX is being used to raisebore the shafts and its performance during the reaming phase, completed on April 13, says Redpath Mining GM raiseboring Johan Davel, exceeded the company’s expectations. “It was a slow start initially, as [the project took place] during the Christmas period. However, we caught up significantly during the reaming portion of the project. Achieving optimal accuracy was critical, as we were drilling inside preinstalled spiles that may not have been intersected.”
“As of May,
the Redbore 90EX was being mobilised at the Down-Cast shaft, while the remote shaft liner was being set up at the Up-Cast shaft. Shaft lining will be executed by spraying a 100-mm-thick 30 MPa fibrecrete lining onto the sidewall of the reamed hole to prevent the shaft from caving in. This will be carried out using a remote-controlled unit from the surface, which means that no workers will be involved or in danger.
Mobilisation started on December 19, 2016, with the Up-Cast shaft piloted in early January. Using a rotary vertical drilling system, the pilot hole was directional-drilled to a depth of 82 m, where conventional piloting continued until breakthrough on January 28. With reaming starting on February 16, the reamer chamber had to be prepared. It was jointly designed by Redpath and air compressor repair services company Atlas Copco.
Davel reported on May 26 that the project had been lost-time injury-free for 114 days. The Redpath site management team is made up of project manager Werner Schwartz, site manager Francois von Landsberg, site foreman Danie Kruger and safety officer Bianca von Landsberg. The operators on the project have at least 15 years’ experience in large-diameter drilling.
Redpath recognises the need to upskill labour and has, thus, been participating in a social development plan while delivering the Impumelelo contract. Raisebore assistants have been recruited, trained and assessed from local communities. Their training involves all aspects of the raiseboring before and during the project.