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January 2016
MODERN MINING
51
DIAMONDS
Top projects
Ventilation system for the
service shaft.
sensitised emulsion will give a better break,
which in turn will make the task of the clean-
ing crew easier. For the VUP, the explosives are
being supplied by AEL Mining Services.
According to Chamberlain’s colleague, Japie
du Plessis, Senior Project Manager with Murray
& Roberts Cementation, a major advantage of the
new sling-down drill rig design is that – once
the rig has drilled the blast holes – the stage
only has to be raised 50 or 60 m prior to blast-
ing compared to 80 m using a conventional rig.
He also notes that the new rigs can drill a burn-
cut round (as opposed to a wedge cut), which
improves the advance and reduces fly rock.
On the question of whether the new
Canadian method will deliver faster advance
rates than traditional methods, Du Plessis
says the true test will be when the shaft sink-
ing moves into the full sink mode. “The main
motivation for Murray & Roberts Cementation
in adopting the new approach is that it is
much safer than the traditional approach, and
our Canadian sister company has in fact deliv-
ered an entire shaft without suffering a single
LTI,” he says. “Having said this, we believe
that the method is also potentially faster than
the conventional approach and Cementation
Canada has demonstrated this on contracts it
has undertaken. Certainly we believe that pro-
ductivity will be higher with fewer workers
required in the sinking team.”
The Canadian method is not the only inno-
vation in the shaft sinking for the VUP and
Chamberlain points out that the pre-sinks on
the two shafts were both completed ahead of
schedule, thanks to new technology devised by
Murray & Roberts Cementation at the request
of De Beers. Says Chamberlain: “At the ten-
dering stage for the VUP, De Beers asked that
bids should include proposals for achieving
greater safety during pre-sink operations with-
out compromising productivity. To meet this
requirement our engineers designed a movable
gantry system, able to carry and manoeuvre
a movable suspended stage, together with a
mucking hoist able to roll over and away from
the shaft during pre-sink operations. The gan-
try was installed and tested at our Bentley
Park facility before being transferred to the
Venetia site.”
Using the gantry system – which was oper-
ated by a multi-skilled crew – Murray & Roberts
Cementation was able to successfully complete
the pre-sinks with only half the workers that
would normally have been needed.
The main gantry girders were designed to
accommodate the loads from the main hoist
(used for kibble hoisting and stage suspension),
which allowed for a maximum pre-sink of 80 m
(an actual depth of 60 m below collar elevation
was sunk), as well as the stage winders (used to
raise and lower the pre-sink stage). The height
of the gantry structure was matched to the
height of the stage to enable the stage to clear
the collar once raised to the upper limit. Once
the stage had been raised in this upper posi-
tion, the long travel wheel drive motors were
energised to move the gantry, complete with
suspended stage, away from the shaft, drawing
a blast cover over the excavation. When in use,