SA company makes big advances in vertical raisedrilling technology

25th April 2003 By: Marius Roodt

South African multinational Murray & Roberts is well-positioned to provide its clients in the global mining industry with a single point of responsibility for project design and implementation, says Murray & Roberts RUC MD Henry Laas.

Laas’s company has been branded as a Murray & Roberts company since last year, having been in existence since the early 1970s, and has much experience in mining, including drilling and tunnelling.

Murray & Roberts has the ability to deliver total project solutions across the full value chain of any mine – from early conceptual studies, feasibility studies and engineering design, through project and construction management, steel fabrication, erection, building and construction, civil engineering and earthworks, to commissioning and even contract mining, while Murray & Roberts RUC is acknowledged as one of the world’s leading drilling and tunnelling companies, Laas maintains.

Being a Murray & Roberts company allows Murray & Roberts RUC to mobilise the necessary skills and knowhow from within the group in all areas of project development.

The company is acknowledged as the inter- national leader in raisedrilling and operates a large fleet of machines, from small raisedrilling rigs to the largest machines ever manufactured for this purpose, says Laas.

It owns five of the seven largest-diameter raisedrilling machines in the world.

These machines are capable of raisedrilling shafts of up to 7,1 m in diameter and to depths exceeding a kilometre, even in the hardest rock conditions.

The latest development in raisedrilling is the rotary vertical drilling system (RVDS), which has been developed by Murray & Roberts RUC together with German company Micon, whose technology enables the steering of the pilot hole.

This ensures a vertical raisedrill shaft, and has solved the problem of deflection, which had previously been a problem with raisedrilling when a vertical shaft was required.

Previously it was difficult to ensure that a raisedrill shaft was vertical, without any deviations.

If a shaft has major deviations it can only be used as a ventilation shaft, Laas relates.

This development has now created the possibility for, where ground conditions permit, raisedrilled shafts to be equipped for hoisting purposes, he says.

Shafts completed last year by using the RVDS include a shaft at the Moab Khotsong mine, where a deflection of 223 mm was achieved over the shaft length of 360 m (a deviation of 0,062%), and the Sedrun shaft in Switzerland, where drilling accuracy was within 280 mm over a shaft length of 785 m (a deviation of 0,035%).

Shaftboring is a mechanical means of excavating a shaft, and holds great potential in cost efficiencies, safety and project duration, Laas says.

Murray & Roberts RUC, in a joint venture with Thyssen Schachtbau, from Germany, has bored two shafts in South Africa (one at Oryx gold-mine with a diameter of 6,5 m, 972 m deep, and one at Western Deep Levels gold-mine, 7,1 m in diameter, and 752 m deep), and one at the Pasminco mine, Broken Hill, in Australia.

The shaftboring methodology is also being used at the Sedrun road tunnel in Switzerland.

The method requires a centre core to be raisedrilled, generally to a diameter in the order of 1,8 m, whereafter a presink follows, and then the erection of the V-Mole shaft-boring machine in the presink.

The V-Mole shaftboring machine, on average, achieves between 7 m and 8 m a day for boring, shaft lining and concurrent equipping.

The project in Switzerland is of particular interest, as the Sedrun ventilation shaft is part of the St Gotthard base tunnel.

This tunnel is being developed through the Alps, and stretches over 57 km from Ertsfeld in the north, to Bodio in the south.

Raisedrilling was completed in November, and the RVDS was used to ensure drilling accuracy.

Shaftboring is in process and the target completion date is July.

Raisedrilling and shaftboring cannot be applied at a greenfields project, as it is a requirement that there should be access to the shaft bottom position, as all the cuttings from the drilling process accumulate at the shaft bottom position, from where they are removed from the mine through the existing hoisting facilities, Laas reports.

This places a further limitation to the application of this technology, as the hoisting facilities should have the capacity to remove the cuttings, in addition to the normal ore-hoisting requirements.

Although raisedrilling is widely used in South Africa, only two shafts have to date been bored with a shaft-boring machine in this country.

The main reason for this is the additional hoisting capacity required to do a V-Mole shaft, as well as the mining industry’s familiarity with the conventional shaftsinking techniques that have been used with success over many years, says Laas.

However, considering the much lower safety risk, cost and time benefits associated with using mechanical means for shaft excavation, the V-Mole application in South Africa has great potential, especially at mines with the required hoisting capacity to handle cuttings from the V-Mole shaft-boring machine, he concludes.