Master Drilling, through subsidiary Master Tunnelling, is not trying to re-invent the wheel with its mobile tunnel borer (MTB) concept, but that doesn’t mean to say the application of such technology will not have a big impact on the underground mining space.

The company, up until recently thought of as a raiseboring specialist, is up against stiff competition in the horizontal mechanised cutting sector. It has Epiroc and its Mobile Miner, Sandvik and the MX650, Caterpillar and the RH55 and Komatsu (Joy) and its DynaMiner to contend with, all of which have been trialled in underground mines.

But, the South Africa-based company is hoping its contracting model, tunnelling partner, modular design and operational flexibility will put its MTB in the lead.

Mining companies on a global basis have been looking for a mechanised, continuous alternative to the labour intensive drill and blast batch process for decades.

Several companies have tried to cater to this need, but no one technology has provided the ‘silver bullet’ as of yet.

Still, the drive to get personnel out from harm’s way, the need to improve tunnelling quality with an increasing number of block cave developments and decrease the payback period for what can sometimes be multi-billion dollar investments has resulted in the latest slate of horizontal cutting machines.

Master Tunnelling has partnered with Italy-based tunnelling expert Seli Technologies to launch its new product and IM recently visited a quarry site just outside of Rome where the first MTB is being assembled and tested.

On site, Koos Jordaan, Executive Director of Master Drilling, talked IM and a host of other interested visitors from mining companies through the machine specifics.

“To reduce risk, we stuck to proven cutting technology,” Jordaan said, pointing to the cutter head design in a schematic within one of the quarry’s temporary offices. “The concept is not so radical, it is more incremental based on tunnel boring.”

The full-face cutter head is made up of 17” disc cutters, which are conventional from a TBM perspective, but are made up of five separate segments. This cutter head, like the majority of the 240-300 t MTB, is designed to be broken down for transport.

The MTB is made up of four track-mounted units containing various parts – the cutter head and bolting section is up front, followed by the transformer and 300 m capacity water and electrical reels on the third unit, and a 14 m3 capacity storage bunker and discharge system on the fourth unit.

The units are also equipped with conveyors that transport the mucked material along the machine.

These can be individually broken down and potentially shipped in 10-12 20-foot containers, according to Jordaan.

This modularity should enable Master Tunnelling to access existing mines with decline infrastructure and to start tunnelling from an underground location, as well as to work on such infrastructure from the surface.

The full-face cutter head is capable of a 1 m advance stroke and can cut rock in excess of 300 MPa compressive strength. It can also be remotely controlled by an operator, reducing exposure to the face.

The MTB comes with 5.5 m diameter cutter head or 4.5 m diameter cutter head. The former is for declines, portals, haulages, inclines, ramps, ring roads, etc, with the latter allowing for excavation of drives and contact tunnels.

Master Tunnelling is aiming for an advance rate of 6-9 m/d in 200-250 MPa rock, but is not discounting the possibility of a higher rate should the additional mucking transport systems behind the 23 m (4.5 m diameter MTB) or 31 m (5.5 diameter MTB) machines be able to keep up.

Jordaan admits going past the 300 MPa threshold was likely to lead to advance rates dropping off by as much as a third, but is adamant the machine has the capability to cut through such rock.

All of this cutting takes substantial amounts of power, which the four hydraulic motors have in abundance. The MTB has 1,300 kW of installed power and a 1,600 kVA on-board transformer that more than covers the machine’s requirements.

Behind the cutter head, hydraulically-powered side grippers ensure the machine can thrust forward and start cutting, while there is a finger shield that both protects workers and allows for a support drill to install cable bolts for ground support.

Master Tunnelling envisages at least three personnel being required for full continuous operation in most setups.

Driving on a flat roadway

As Master Tunnelling points out, “a round profile tunnel is not ideally suited for vehicles that require a flat driving surface, such as most trackless mining equipment.”

This is where a articulating tail conveyor at the end of the fourth tracked unit – containing the 14 m3 storage bunker – evenly distributes 3-5% of the cut material. This should provide the sort of flat driving surface trucks will need to come in and pick up the material.

Master Tunnelling has some form here, too. Its Master Drilling parent company carried out a horizontal raisebore drive of 180 m length and 4.5 m diameter in a kimberlite pipe at Petra Diamonds’ Cullinan mine in South Africa recently. A flat driving surface was created by using a similar solution to the one the company has devised for the MTB.

There are also a few other features worth flagging.

The MTB is able to operate on a 12° incline/decline, has a 30 m turning radius and can be dismantled and brought back to surface after a project is complete.

The latter is different from the bulk of conventional TBMs where, after use, they are buried underground never to be used again.

Master Tunnelling is also taking safety seriously with the MTB. Not only is it shielding bolting operators from potentially hazardous situations above their heads all the way from the cutting face, it is also installing gas detection, proximity detection and fire suppression systems on the units. An operational monitoring system, meanwhile, ensures the full-face cutter head is advancing as planned and the accompanying units are tracking as they should be.

Master Tunnelling anticipates a four-hour maintenance period for the MTBs every 24 hours based on a three, eight-hour shift pattern. During this time, the disc cutters can be replaced and the dust suppression and collection system can be checked.

The company also envisages this time being used for drilling a 30-50 m probe hole in advance of the MTB. This would be drilled through an opening in the cutter head and provide integral information about the water and gas levels of the approaching rock.

The MTB doesn’t do away with drilling and blasting altogether. To initiate cutting, the machine requires a rounded profile side wall to grip and thrust to take it forward. This requires a starter frame to be installed in advance of the drive, which can be put in position with a 15 t capacity wheel loader with appropriate manipulator attachment.

The frame requires a starting chamber 6.5 m high, 8 m wide and 12 m deep excavated by conventional drilling, blasting and scaling.

In an undercut level for block caving, this preliminary batch phase would only form a “small part of the excavation required”, Master Tunnelling says.

In addition to considering the setup requirements for the MTB to start operation, it is also worthwhile to look at what will follow the machine in terms of loading and hauling the excavated material.

This is where the bunker backup unit positioned at the end of the four tracked units proves useful, acting as a storage facility to allow truck changeover to take place behind the MTB when one truck is fully loaded and another truck comes in. This allows for continuous operation of the MTB incorporating a batch haulage system.

On long, straight advances there is also the possibility of using mobile conveyors for haulage, however the company thinks there will be less of these applications given the MTB’s major strengths are developing tunnels with a curvature or on a decline/incline.

Contractor advantages

In the battle for a market leading, horizontal, mechanised cutting technology, Master Tunnelling has a few advantages over its much bigger rivals in the mining space.

One: it is a contractor, meaning it is not asking customers to invest in this capital-intensive equipment. Instead, it will be contracted by the client to provide the MTB and associated equipment required for logistics and material handling.

Two: It has a partner in Seli Technologies that has carried out more than 1,000 km of tunnelling excavations and has been involved in mining work before (it excavated an 8 km long, 4.2 m diameter tunnel for Anglo American at Los Bronces, in Chile, back in 2009).

Three: It is offering something that is modular, can be broken down and assembled underground, and can be relocated from one project to the next.

Also, Master Tunnelling is offering the ability to turn around corners and keep tunnelling with the MTB, which could be particularly useful when tracking complex, or faulting mineralisation. It could also come in handy should the MTB encounter particularly hard to bore rock.

The concept phase of the MTB only started in April 2017 and only one MTB has so far been manufactured. So, for the right partner, there is the chance to get in early and to advise on their customised requirements.

Master Tunnelling is clearly thinking to the future in this regard, with the bulk of the MTB hardware being ‘automation-ready’.

Even though the set up at the quarry in Italy is to test basic functionality – cutting 10-20 MPa rock for 50 m and carrying out a 30 m turn – it has provided interested parties a chance to consider what the machine could do for their own operations.

Once it has optimised the setup time and demonstrated what it can do in some fairly competent rock underground, the wider mining community may start to further appreciate the MTB and what Master Tunnelling is offering.