One of the world’s leaders in mechanised tunnelling, German engineering company Herrenknecht have applied themselves to the task of providing a modern version of shaft boring machines .
The new generation of Shaft Boring Machines for Shaft Enlargement (SBE) have developed from the rodless, V-Mole technology which has been available for decades.
However, Herrenknecht have worked closely with Thyssen Schachtbau and Murray & Roberts Cementation to update and adapt the technology to current conditions and requirements to facilitate high sinking speeds and maximum working safety for shaft boring using a pilot borehole.
The modern version of V-Mole technology, the SBE can cope with shaft boring diameters of up to 9.5 metres through hard rock under optimal conditions, at faster speeds that can reduce conventional shaft sinking speeds by 20-30 per cent.
The SBE works like modern hard rock Tunnel Boring Machines, with advance and primary shaft lining carried out simultaneously.
With laterally extendable hydraulic cylinders, the 15 meter high machine braces itself before every drilling stroke in the shaft, steadying the machine, allowing the thrust cylinders to push the rotating cutterhead against the borehole floor.
Hydraulic cylinders ensure precise vertical alignment of the shaft boring machine to the target axis, which is constantly transmitted to the machine operator by a laser aiming device.
The rotating anchor platform is located on the drilling deck above the cutterhead, and from there anchors and steel mesh can be put in place by two powerful hydraulic drill rigs.
If required, a shotcrete unit on the shaft boring machine secures the shaft wall immediately after exposure of the rock outcrop.
The machine operator controls all operations safely and conveniently from the interior of the machine.
The new SBE uses three phases of operation in order to sink a shaft, beginning with a pilot hole, drilled from the top down, to set the vertical axis of the shaft.
Once the drill string reaches the bottom of the hole, the bit is removed and replaced with a reamer to enlarge the hole by raise-boring until the correct pilot borehole diameter reaches the top of the hole.
In the final stage the SBE can enlarge the pilot borehole from the top down to the final diameter, while installing the primary lining of the shaft.
Shaft depth is only limited by the technically feasible length of the initial pilot borehole.
The high precision afforded by SBE, in terms of verticality and circular shape of the shaft cross-section, as well as the virtually vibration-free ground treatment, are further advantages of the shaft boring technology compared to the conventional shaft sinking methods with drilling and blasting. The sinking cycle runs continuously and is not interrupted by drill and blast times or dispersal of explosion gases.
The new SBE technology not only boasts high levels of efficiency, but also greater levels of safety and ergonomic working conditions.