German mechanised tunnelling engineering company Herrenknecht has developed a range of four shaft-boring machines for the safe and rapid construction of blind shafts or shaft enlargements to a depth of 2 000 m.

Each of the machines is designed to operate in specific geological conditions.

Currently, work is progressing on resource company BHP Billiton’s Jansen project, in Saskatchewan, Canada, where the sinking of two 1 000-m-deep mine shafts using Herrenknecht’s new blind shaft technology is under way.

Herrenknecht South Africa business development manager Danie Roos says the use of Herrenknecht’s equipment at the Canada-based mine is the first time in over two decades that such technology has been employed in mine shaft-sinking.

Safety issues, rising operational costs and a reduction in productivity have resulted in mine operators re-examining the way mines are operated, which has resulted in renewed interest in the mechanisation of mining operations, including shaft sinking, he explains.

“The excavation of shafts is a criti- cal activity in the development of new mines or the extension of existing ones because the quicker an orebody is accessed, the sooner the end-product enters the market,” says Roos.

He adds that mechanised deep shaft-boring is regarded as a “game- changing technology” supporting the universal drive to replace drilling and blasting with alternative technology that removes miners from potentially dangerous areas.

The largest machine in the Herrenknecht range – the Shaft Boring Machine (SBM) – is capable of developing shafts in hard-rock conditions to depths of 2 000 m. This machine was developed as a result of Herrenknecht’s involvement in mineral resources company Rio Tinto’s ‘Mine of the Future’ programme, with its design and engineering being completed in 2013.

The SBM is capable of sinking shafts between 10 m and 12 m in diameter at three times the rate of conventional shaft-sinking methods.

Most of the technology used in the development of Herrenknecht’s blind-shaft machines (such as drilling and rock support) was adapted from technology developed for the company’s internationally recognised tunnelling business.

As a result, the SBM is similar to a conventional tunnel-boring machine, except that it is suspended vertically in the shaft and employs conventional disc-cutting technology.

The 60-m-long SBM is self-suspended by a set of grippers. Up to three systems brace against the shaft wall to stabilise the entire system during cutting.

Meanwhile, Herrenknecht’s Shaft Boring Roadheader (SBR) was developed for blind-shaft boring in soft to medium rock or frozen ground to depths of 1 000 m. Two of these machines are currently in operation on BHP Billiton’s Jansen project.

“The two SBRs were manufac- tured and assembled at Herrenk-necht’s premises in Germany, where cutting tests were performed to the customer’s satisfaction before being shipped to Canada where they have been in operation since 2013 excavating two 1 000 m shafts at a new mine,” says Roos.

The SBR is equipped with a rotating cutting drum installed on a tele- scopic and slewable boom, mkaing it flexible; itcan also be used to cut shafts of variable diameters. The telescopic boom also allows for the excavation of the entire shaft cross section to a depth of 1 m in a single operation.

While sinking a shaft, the SBR unit is suspended by ropes connected to shaft winders on the surface.

The Shaft Boring Cutterhead (SBC) is the third machine in Herrenknecht’s range of blind-boring equipment. At a length of 40 m and weighing 350 t, it is ideal for the excavation of deep blind shafts up to 9 m in diameter in hard-rock conditions and is capable of delivering an advance rate of 6 m/d.

The SBC uses a conical, full-faced cutter head equipped with disc cutters and the cutting sequence is highly automated. This mechanical shaft-sinking unit is suspended from, and moved by, shaft ropes.

Roos explains that, during normal operations, personnel are not exposed to an unsupported shaft wall. “No explosives are used during regular advance operations and the excavation chamber is also a ‘no go’ zone while cutting is in progress.”

The machines can be modified to support tubbing, rock bolting, shotcrete or concreting activities and, unless there are significantly poor rock conditions, excavation, mucking and rock support are carried out simultaneously.