A renewed emphasis on mechanisation in the mining industry has seen the development of the latest Shaft Boring Machine for Shaft Enlargement (SBE) by Murray & Roberts Cementation and Thyssen Schachtbau, in conjunction with Herrenknecht, both of Germany. This represents the next generation of rodless shaft enlargement machines, the so-called V-Mole technology. The SBE facilitates high sinking speeds of 6 m/d to 10 m/d and maximum safety for shaft boring by means of a pilot borehole.
“It is at a point where we have the confidence to market the technology to the mining industry and to announce that it is now available,” Allan Widlake, Murray & Roberts Cementation, Business Development Director, says. “I think it is quite timeous given that there is a refocus on mechanisation in the mining industry. That is where we believe this technology comes into its own, because we can guarantee a much higher confidence level in terms of scheduling and productivity.
Thyssen Schachtbau has been involved with more than 50 shaft boring projects with a total depth of over 20 km, with finished diameters ranging from 5.5 m to 8.2 m. Murray & Roberts Cementation has entered into “a lot of discussions with both mining houses and consultants locally. There are opportunities here in South Africa and across the border in the future with regard to the use of the technology.” This covers the full spectrum of commodities, including diamonds, coal and platinum
Murray & Roberts Cementation and Thyssen Schachtbau developed this new technology due to a perceived need in the mining industry. “In brownfield operations, conventional raise borers have a limited capability in shaft diameter and depth, especially in terms of production and ventilation shafts. From a geotechnical point of view, if you raise bore in poor ground conditions, you run the risk of the shaft collapsing while the hole advances. The next generation SBE guarantees shaft stability as the hole is supported during sinking,” Widlake says
Various criteria were highlighted during the development process. “We wanted to keep it easy to maintain and user friendly, with the most sophisticated electronics being confined to the laser guidance system.” Herrenknecht responded to this design challenge by incorporating components that had been tried and tested in modern Tunnel Boring Machines (TBMs). “It was a perfect marriage of elements. Murray & Roberts Cementation and Thyssen Schachtbau contributed its operational and practical functional expertise, while Herrenknecht specified how the technology would be put together.”
The system comprises three construction phases: The first is drilling a pilot hole by means of directional drilling from top to bottom, followed by enlargement of the pilot hole to an advance hole diameter of 1.78 m or 2.4 m by means of raise boring from top to bottom, and then lastly reaming of the advance hole to the final shaft diameter from top to bottom. All cuttings produced are transported via the advance hole to the undercut level. This particular sinking method is conditional upon having an access drift available at the lowest part of the shaft along with sufficient debris clearance capacity for the excavated material.
There must also be continuous downcast ventilation for the duration of the sinking operation. Raiseboring and shaft support operations are carried out simultaneously, with the SBE operated from a central control stand on the operator’s platform. The only limitation in terms of the boring depth is the pilot hole and not the shaft boring machine itself. As long as there is an intermediate undercut level for constructing a raise bored advance hole, the shaft boring depth is essentially unlimited.
Additional benefits include zero blast damage to the shaft side walls allowing for a cost effective support system in the form of the concrete or shotcrete lining to be applied, reduced project costs and achieving the earliest possible commissioning date. Widlake comments that now is the perfect time to introduce new technology into the mining industry.
“There is a different approach at the moment. Mining companies are looking for more certainty around their programmes and costs and are looking for a safer outcome for their projects. This equipment definitely fulfils that requirement. Tunnel boring technology has matured to a point where it is now extremely reliable, particularly in selecting components such as drives and bearings. It is not as if you are reinventing the wheel in terms of the applied technology. It is literally standard off-the-shelf components from Herrenknecht.”
Once a unit has completed a particular project, it can be disassembled and customised again for next project. Looking at lead times from the manufacturing facility in Germany, Widlake says that from a project award to actual deployment of the machine after the completion of the advance hole, there is more than sufficient time to build a new machine. “We consulted with Herrenknecht about needing to advance the engineering any further than where we are right now. We can do it all within the time of an award to when we need it on site, from the final detailed engineering through to manufacture and delivery to site.”