Modern Mining November 2016

COVER STORY

To mitigate the time lost, the contractor agreed to implement a continuous operations cycle during the main sink phase until completion of the station cutting. Additional precautions were taken to pre- vent any delays while sinking through the clay formations. During this process it was impor- tant to keep the lining as close to the shaft floor as possible to minimise contact with air and moisture. Any stoppage – due to a Section 54 notice, for example, being applied to the mine – would have had severe consequences. Fortunately, the sinking portion of the project was completed without incident. Once the shaft entered the competent tillite formations, normal sinking took place (from a depth of 71 m to 167 m). The sinking stage was designed to accommodate ‘Hong Kong’ drills. This methodology reduced the need for people on the shaft bottom. Cleaning was carried out using an excavator. Corrugated steel rings were used for temporary support in the shaft and the cycle ensured that the lining was never more than 4 m from the shaft floor. The contractor, Murray & Roberts Cemen­ tation, worked for more than a full year (400 days) without a lost time injury. “Taking into account the high risk nature of the work it per- formed, this was an excellent achievement,” comments Greyling. He adds that prior to sinking Gloria, Murray & Roberts Cementation had worked on another shaft of similar dimen- sions in the Kalahari Manganese Field (KMF), and thus had some experience of the difficult ground conditions characteristic of the area. Greyling points out that the successful com- pletion of the shaft reinforces the reputation of WorleyParsons as a world leader in the design and implementation of shaft projects. He adds that WorleyParsons RSA has been the EPCM contractor on the majority of shafts under- taken in South Africa in recent years. These have included Impala 17 Shaft, as well as the shafts at the Styldrift and Bakubung platinum mines and the Shondoni coal project. A current flagship contract is the Venetia Underground Project (VUP), where WorleyParsons RSA is providing engineering consulting services that include detailed engineering, execution and support in procurement and construction man- agement. The VUP, which probably ranks as the single biggest mining project currently under- way in South Africa, includes the sinking of two vertical shafts to depths of just over a kilometre. Turning to the work at the Nchwaning mines, Greyling says a relatively early achieve- ment was the completion in September 2014 of

now largely complete. In addition, the project involves the upgrading of the ventilation infra- structures; improvement and modernisation of the underground ore handling infrastructure to facilitate ore flow, storage and sorting efficiency; upgrades to the Nchwaning II surface plant infrastructure (not in WorleyParsons’ scope); and the reinstatement of the Nchwaning I mine. In Greyling’s view, one of the highlights of the BRP has been the sinking of the new 5,5 m diameter, 167 m deep, concrete-lined ventila- tion shaft at Gloria. “The main challenge was that the sinking had to take place through Kalahari sand, as well as calcite, red clay and conglomerate before the shaft entered the more competent tillite formations,” he notes. “Because of the Kalahari sand, we introduced perimeter piling to a depth of 35 m. In addi- tion, dewatering holes and cementation of the areas just above the clay formations reduced the influx of water into the shaft and prevented excess disturbance of the clay during the sink- ing process.” The sinking was delayed slightly in the slow sink phase due to the soft ground conditions.

Nchwaning II shaft feed conveyor drive and take-up arrangements.

22  MODERN MINING  November 2016