SHAFT SINKING
The main component that needs to be tested
will be the cutterhead and the pneumatic mucking
system “because that rock is likely to be a lot
more abrasive than the soft rock the SBR has been
mucking”, Greinacher said.
The SBC technology is likely to have the widest
application in the shaft sinking industry, according
to Greinacher, but he does not expect such
technologies to replace drill and blast entirely.
“Not each and every shaft is suitable for
mechanised shaft sinking; some will be better
suited to drill and blast operations,” he said.
Therefore the company continues to pursue an
automated drill and blast project for shaft sinking.
Intended for both hard and softer rock, the plan
is for the technology to enable mucking and lining
in the shaft concurrently without any personnel at
the face.
The mucking system is likely to be based on an
“excavator-type mucker”, Greinacher says, similar
to the equipment used in other shaft sinking
projects.
COVID-19 and its work on the SBC technology
might have pushed back the schedule for testing
of this system, but Greinacher is confident of
carrying out trials on this innovation in the first
half of 2021.
What about the SBS?
Herrenknecht and Redpath Deilmann are not the
only companies pushing a mechanised hard-rock
cutting technology.
Back in October, IM witnessed part of Master
Drilling’s Shaft Boring System (SBS) concept in
action at a location some 15 minutes’ drive outside
of its Fochville, South Africa headquarters.
This is where the company was testing out the
main cutting mechanism of what could eventually
be its 45-m long, 450-t SBS. The 15 in patented
cutter heads of the machine were progressing
through 320 MPa dolorite, cutting around 40-50
mm in displays for interested parties visiting the
site.
The SBS is billed as being able to cut and muck
at the same time as shaft reinforcement, lining
and other protective measures occur. It can work
through hard rock from 200-400 MPa and sink
shafts up to 1,500 m deep, advancing up to three
times quicker than conventional sinking via drill
and blast, according to the company.
Three to five people are expected to be needed
for its operation, none of whom 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 cutting
face.
Like Master Drilling’s Mobile Tunnel Borer for
horizontal development (previously 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 company says.
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 to ensure the machine stays
on the correct course and uses 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
could range from 7.5 m to 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. Personnel can probe drill
ahead of cutting from one of these levels for
geotechnical measurements, enabling them to
anticipate the fracturability and hardness of rock,
in addition to any potential water inflows.
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 stage
levels 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
Despite Master Drilling’s SBS hard-rock cutting
mechanism being trialled in 320 MPa rock, no
cutters were replaced over the three-month
period it operated
muck from the cut section to surface through a 2.1
m opening present in all 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.
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 the company.
Since IM’s visit almost a year ago, a lot has
happened, but the core components remain the
same.
Originally targeting an advance rate of >500
mm/h during testing, Koos Jordaan, Executive
Director of Master Drilling, confirmed back in
March that the unit had hit close to 1 m/h
instantaneous penetration during the latter trial
stages.
“In many cases we were fortunate,” Jordaan
recently remarked on this feat. “I contribute it to
many design concepts reviewed over the past two
years and a radical approach to configuration at a
high development risk.”
The company tested the SBS cutting
mechanism over a three-month period, excavating
around 12 m of material in total at the site. Even
with the stop-start nature of operations – with the
SBS cutter generally only turning when potential
SBS clients were in attendance – the repeatability
was “reliable and impressive”, Jordaan told IM.
Despite operating in 320 MPa rock, no cutters
were replaced over this period. This is an
important result considering the problems
previously experienced with cutter wear in other
mechanised hard-rock trials.
74 International Mining | SEPTEMBER 2020