What Master Drilling is demonstrating on a patch of land some 15 minutes’ drive outside of its Fochville, South Africa, headquarters has the potential to change the hard-rock shaft sinking industry.
That is not an exaggeration.
Interested parties – major mining companies included – are being shown how the main cutting mechanism of what could eventually be its 45-m long, 450-t Shaft Boring System (SBS) can cut through hard rock.
The 15 in patented cutter heads are progressing through 320 MPa dolorite. Started up on cue over a three-week period that began on October 14, the machine is cutting around 40-50 mm a day.
When IM visited just over a week into these daily demonstrations, the machine was around 4.6 m below surface, no cutters had been replaced and Koos Jordaan, Executive Director of Master Drilling, was satisfied with the machine’s performance.
The fact that Master Drilling is showing off this cutting innovation now should not be a surprise.
The company first discussed what was previously called the Blind Shaft Boring System concept at the 2016 Mining Indaba, in Cape Town, South Africa. At this point, the company pitched the machine as being able to add significant value to projects given the shorter time frame it would take to reach new underground mine development levels.
The machine would be able to cut and muck, as shaft reinforcement, lining and other protective measures occurred. It would be work through hard rock from 200-400 MPa and sink shafts up to 1,500 m deep.
This aim has not changed in the more than three-and-a-half years since the premiere, but the name and the design has altered somewhat
Jordaan and Nicol Goodwin, Mechanical Engineer for Master Drilling, admit they went through seven designs before settling on what they are now presenting. Past iterations may have been more radical, but today’s blueprint, which has around 95% of detailed design complete, strikes a balance “between energy, complexity and sophistication”, Jordaan explained.
Peter van Dorssen, Mining Advisor for Master Drilling, said some attendees – before seeing the machine in action – compared the concept with the V-Mole technology that is used on Herrenknecht’s Shaft Boring Enlarger (SBE).
Acting like a vertically-oriented modern hard-rock tunnel boring machine (TBM), shaft sinking with the SBE occurs in three phases – pilot hole, enlargement to pilot borehole diameter with a reamer and enlargement to final diameter of 7.5-9.5 m. The SBE was previously used to sink the Primsmulde shaft at the Endsdorf colliery in southern Germany.
While this technology reportedly performed well in the coal mine, achieving an average sinking rate of 7-7.5 m/d, it has not been tested in hard-rock conditions and, perhaps more importantly, the system cannot carry out concurrent mucking.
This means an access drift, as well as equipment, is required at the lowest part of the shaft to transport the muck to surface.
With Master Drilling’s SBS able to carry out cutting, mucking and shaft reinforcement concurrently, the comparisons tend to end there.
According to van Dorssen, Master Drilling’s newest machine can advance three times quicker than conventional sinking via drill and blast. It requires three-to-five people to operate the machine, none of which are exposed to the face. The safety considerations also extend to the changing of the disc cutters, which can be removed and replaced from behind the face.
Like the Mobile Tunnel Borer (MTB) for horizontal development (currently working at Northam Platinum’s Eland PGM mine in the North West province of South Africa), the SBS will be commissioned off a launchpad. This will be constructed with minimal civils work and alleviate the need for a timely and expensive pre-sink phase.
The front end of the machine (as it descends the shaft) is made up of the pilot cutting head – in a W-shape configuration – and gearbox. The pilot cutter head accounts for some 15%of the entire rock cutting, with the wider diameter reamer section that follows accounting for the remaining 85%.
This first section can independently progress by 1.5 m when cutting is taking place in three separate 500 mm phases.
The rest of the 45-m long machine catches up following this initial cutting, which is automated by a series of lasers that ensure the machine is on the correct course and using optimal force.
This cutting station is followed by two shaft gripping stations for machine support within the shaft. Following this is an enlargement station – also equipped with cutters – that widens the pilot hole carried out by the pilot cutter head to the desired diameter, with Master Drilling saying this will range from 7.5–11.5 m.
Behind this is a main stage made up of eight separate levels. Here, personnel will be able to carry out the rock bolting, lining and other reinforcement measures required. Personnel will also be able to probe drill for geotechnical measurements off one of these levels, enabling them to anticipate the fracturability and hardness of rock, in addition to any potential water inflows, ahead of actual cutting. Personnel operating on this main stage are protected by a series of finger shields that, while guarding them from potential rockfalls, still allow for a 360° access to the shaft for services.
A series of kibbles lowered by winches and transported on a conveyance on one of the levels of this stage bring the required shotcrete and materials to allow these concurrent tasks to take place.
Kibbles will also help with the mucking process, with two 16-t capacity buckets transporting the muck from the cut section to surface through a 2.1 m opening that present in all of the machine’s stations. Master Drilling is relying on gravity to recover 85% of the volume of muck at the enlargement section, with the remaining 15% recovered using a vacuum and/or slurry system.
Jordaan remarked: “The whole idea of this mucking system is to handle material once and handle it in a simple way.”
This mucking mechanism will shift the normal shaft sinking constraint dynamic from mucking capacity to shaft lining speed, van Dorssen said.
The headgear to support these operations from surface will likely be around 35 m tall – small in comparison with other mechanised sinking setups – while the total power requirement comes in at around 10 MW, according to Goodwin.
While the demonstration in Fochville was a massive sign of intent from Master Drilling on the mechanised shaft sinking front, the company is formalising this testing process by setting itself key performance indicators.
One: it wants to hit or exceed an advance rate of 500 mm/hr – replicating an 8 m/d target that includes an envisaged two eight-hour production shifts and one eight-hour maintenance shift.
Two: it wants to test the machine’s cutting ability on both wet and dry material.
Three: it wants to push the penetration rate another 25-40% higher, alongside boosting the revolutions per minute from the 8-9 rpm it is currently operating at, to 10 rpm.
The company wants to put the machine through its paces before it moves onto another stage of its development.
Jordaan said he was hopeful of completing this testing – which constituted phase one of the SBS development – in around two months.
From there, if the reception is positive and no unforeseen complications arise, Master Drilling would look to manufacture the parts for the full 45-m long machine. In this task, the company is being helped along the way by three local engineering companies.
Phase three involves assembling and commissioning the whole machine and committing to a small excavation to test it out, while phase four is an ideal point to carry out mine site test. Phase five would see a full SBS deployment to its first major project.
Master Drilling was rightly wary of giving timelines on completing all these phases, knowing it would be reliant on securing funds for the machine build from its partner, South Africa’s Industrial Development Corp, and may need to make small changes to the machine design dependent on miner feedback from initial testing.
Yet, the company has opened the number of possible mine site testing options by designing the machine for shaft enlargement. This could see mining companies in need of extra shaft capacity sign up Master Drilling as a contractor to carry out an enlargement project, first, ahead of a much riskier blind sinking operation at a new underground mine later.
In terms of machine configuration, all that needs to change to carry out an enlargement is the cutter head, according to Goodwin.
This could prove decisive in terms of industry acceptance, allowing Master Drilling to obtain a mining customer reference much quicker than it would have if the only potential avenue was a blind sink.
When asked how the machine is likely to perform in terms of cost per metre, Jordaan said it would be competitive with drill and blast, but the real value proposition came in the form of reaching the development level and, therefore, the orebody that much quicker than the conventional method.
If, as van Dorssen said, the SBS can achieve a sink three times quicker than typical shaft sinking, miners could also be in line to receive cash flow that much faster.
In a cyclical market like mining that is an incredibly powerful value proposition.
It could reduce the risk associated with commodity prices potentially going the wrong way during development and allow a company to start paying back the capital sooner than expected.
Other companies already claim their mechanised machines can achieve such shaft advances, but these have either not yet been proven in hard-rock applications – being trialled only in potash or other softer rock – or require bottom shaft access to realise these rates.
It’s worth acknowledging that the SBS could also be used in softer rock with the expected increase in drilling speed countered by the need for further rock reinforcement.
And, whereas other OEMs will manufacture one machine per project, Master Drilling has longer-term plans for each SBS unit it manufactures. This could allow the company to charge a reduced rate to mining clients as it writes off its investment over multiple contracts.
So, once again, Master Drilling appears to be pushing the envelope on boring technologies.
In addition to the MTB, which is designed to work on 9° inclines/declines and have a 30 m turning radius – not typical tunnel boring machine traits – it has also carried out a number of firsts in the raiseboring market, with the company behind some of the widest diameter and deepest raises in the world.
With resources and expertise from across the globe to call on, it can innovate at a pace and cost many of its peers cannot compete with.
For those reasons, Master Drilling and the SBS are worth keeping an eye on.