SHAFT SINKING
A cut above
The station excavations at IOOO Slavkaliy’s
Nezhinskiy potash project have been carried
out by combining a Voest-Alpine AM-50
roadheader and the pneumatic mucking system
of the Herrenknecht SBR (photo: Redpath
Deilmann)
With more people stepping away from the operating face
during shaft sinking projects in the COVID-19 era,
mechanisation of the process is edging closer. Dan Gleeson
takes an in-depth look at the new technologies that are
competing with conventional drill and blast in the sector
The mechanisation of the shaft sinking
process has become a key focus for the last
few annual shaft sinking articles IM has
produced; it is likely to play a major role in future
ones too.
While the conventional method of shaft
sinking through drill and blast is far from dead
and continues to come up with new innovations
of its own (read the two High Profile project
focuses directly after this feature as evidence),
like automation in the load and haul process,
mechanised developments continue to make the
headlines.
Behind this bold print lie several questions:
Can any new technologies compete with a
well-oiled drill and blast team in predictable
geological conditions? Is current cutting
technology ready for hard rock? Does the upfront
capital mean only the majors can take risks on
mechanised innovations?
IM has asked all these questions and more in
the past few annual features and has come even
closer to finding accurate answers this year.
The SBR solution
The latest mechanisation technology discussions
have tended to start with the Shaft Boring
Roadheader (SBR) due to the availability of
recent mining case studies.
Having successfully excavated two 8-11 m
diameter blind shafts using SBRs at the BHPowned
Jansen potash project, Herrenknecht says
it is leveraging all the lessons it learnt in
Saskatchewan, Canada, to ensure this
technology proves to be a “game changer” for
the sinking of shafts in soft and medium-hard
rock.
Mining contractor DMC Mining Services used
two SBRs to excavate the blind shafts at Jansen,
with the successful project completion acting as
proof of the feasibility and advantages of the
Herrenknecht SBR concept for the mining
industry, according to the Germany-based
company.
In August 2018, two blind shafts at Jansen
were completed to depths of 975 and 1,005 m,
respectively. This represented a mining industry
milestone – for the first time, shafts were sunk
using only mechanical excavation.
The two Herrenknecht SBRs excavated the
ground by a partial-face cutting method, using a
cutting drum mounted on a telescopic boom. The
excavated rock was then conveyed from the
bench by an innovative pneumatic mucking
system (PNM) and transferred into buckets to be
hoisted to surface.
A laser navigation system designed by a
Herrenknecht subsidiary, VMT Group, using target
units mounted on the SBR and lasers connected
to the shaft wall, was used to keep the machines
on track.
Herrenknecht, with its experience in
tunnelling, developed the SBR for the
mechanised sinking of blind shafts in soft to
medium-hard rock. Based on the proven
technology of the Herrenknecht Vertical Shaft
Sinking Machine, the SBR offers improved safety
performance compared with conventional shaft
sinking methods while also achieving higher
advance rates, according to the company.
The geological conditions the SBR experienced
at Jansen proved a good test.
At a depth of around 450 m, the SBR
encountered a layer of extremely hard competent
rock causing excessive pick wear and low rates of
advance. To overcome this and some further
hardness challenges, the cutting drum was
upgraded to a hard-rock cutting drum and torque
output was doubled.
Because an existing high-pressure
underground waterway known as the Blairmore
aquifer posed a risk for water ingress into the
shaft, ground freezing was executed temporarily
in 2011 by BHP to a depth of around 650 m.
A major success in this difficult geology was
the use of a mechanical ring erector, which
allowed the installation of steel tubbing
segments with minimal risk to personnel and a
high degree of accuracy, according to
70 International Mining | SEPTEMBER 2020