Anglo Platinum’s Rustenburg Section is currently undergoing an era of change with a number of reserve replacement projects still underway to extend the life of some of the oldest platinum mines in South Africa. The Townlands Ore Replacement Project (TORP) is one such project – which has necessitated the expertise of raise drilling specialist Murray & Roberts Cementation to undertake the drilling of three ventilation shafts, which are “no ordinary” ventilation shafts. Laura Cornish visited the site to see why.

In December this year, Murray & Roberts Cementation will commission and hand over the last of three reamed ventilation holes constructed to provide additional cool air for the TORP project.

The Townlands ventilation shafts are situated about 3km from the main Townlands vertical shaft, almost immediately adjacent to the Paardekraal 2 Shaft development site. The project is aimed to increase the shaft’s life by accessing the UG2 reef, in addition to the Merensky reef, starting from 28 Level. For Murray & Roberts Cementation, its project scope specifically encompassed the development of three ventilation shafts – 28m apart from centre to centre, each with a 3.8m diameter, all extending to a depth of 821m.

Since first moving onto site in June 2007, Murray & Roberts Cementation has already handed over the first two vent shafts (Hole C and Hole B), and is currently ahead of schedule on Hole A. The three vent shafts connect directly with the underground tunnel (already completed) on 26 Level (281m below surface), which has been developed by Anglo Platinum itself, and will handle about 600kg of air per second.

Stephen Delport, senior site superintendent said: “What makes this project so unique is the precision with which we have been able to drill the pilot holes.” With the use of a Wirth HG330-SP raise boring machine and the rotary vertical drilling system (RVDS) cutters, imported from Germany, Murray & Roberts Cementation has been able to achieve minute deviations during the pilot drilling development stages. A 50mm deviation was recorded for Hole C, 10mm deviation for Hole B, and so far, a 50mm deviation on Hole A.

“This project represents world class, record-breaking statistics in pilot hole drilling accuracy, where standard deviations are usually over 1% (8.21m) of the pilot hole length in most instances,” Delport explained. A 50mm (0.006%) deviation was recorded for Hole C, 10mm (0.001%) deviation for Hole B and the final pilot hole on Hole A also broke through with a 50mm (0.006%) deviation. The pilot hole was drilled using the rotary vertical drilling system (RVDS), which was especially designed in a joint venture with Germany’s Micon – which basically enables the drill string to correct itself automatically if it starts to deviate.

As part of the contract, Murray & Roberts Cementation also conducts its own gyro-survey every 50m to ensure the pilot hole progresses downwards in a straight direction.

Murray & Roberts Cementation has the patent on the RVDS technology, Delport noted. Murray & Roberts Cementation also specifies that no one may operate one of its Wirth machines without at least 10 years of machine experience. There are 12 such people in the company, and three operators specifically working on the TORP project – with an additional three assistants per shift. Site foreman, Vincent Erasmus pointed out: “With such an expert machine – and experienced people operating it – Murray & Roberts Cementation has proudly not suffered a single accident or fatality on this project – a significant achievement considering we have recorded over 14,050 shifts and 129,260 man hours.”

Despite the Wirth’s extreme cutting precision, it is a large machine, capable of large hole development at a rapid rate. The machine weighs 70t, of which 24t is attributable to the gearbox alone, and moves 36t of earth per metre. This equates to 10.6m of earth or 383t in a 24 hour cycle. It is actually designed to drill to a maximum depth of 1000m, with a 6m diameter reamer. This makes it one of the biggest raise boring machines in the world – of which there are only five – four belonging to Murray & Roberts Cementation.

Prior to the TORP contract, this specific Wirth machine was situated in Belo Horizonte, Brazil at AngloGold Ashanti’s Brasil Mineração gold project, where it completed the construction of two ventilation shafts (760m each). The project was completed in 20 months. Also on site currently in progress is the development of the refrigeration plant, awarded to civil and infrastructure construction firm, Civcon.