The blasting process dictates muck-pile configuration,
which affects shovel and loader fill factors.
muck-pile control, muck cycle times,
and environmental factors.
Downstream impacts of drilling
and blasting
The drilling and blasting at a mine
influence nearly every aspect and is the
starting point for other processes. Poor
drill and blast results lead to poor mine
results and very expensive operating
conditions. While many mines try to
reduce these costs on their balance sheets,
the ramifications for this can be an increase
of expenses in all other departments.
The basic ways a mine can begin to
reduce their drill and blast costs are to
drill larger boreholes, larger burdens,
larger spacings, reduction of elimination
subdrill, and increasing the drill diameter.
By increasing the drill diameter, a
mine can reduce blast costs significantly.
With an increase in drill diameter
(assuming bulk loading), there is an equal
proportion increase in the blast burdens.
For example, using a 250mm drill loaded
with bulk emulsion explosives, a burden
of about 7.31m (using Konya burden
equation) would be calculated.
An increase to a 300mm drill would be
a 20% increase in the drill diameter. This
leads to a 20% increase in the burden of
the blast, to around 29′ (after rounding).
Let’s assume an equilateral triangle
pattern is used since the bench is around
50′ (15m) and the powder factor remains
similar, and that, typically, the mine will
not change the timing of the blast (this is
an old-school design approach that is not
correct, but is often done).
What is the problem? First, the
stiffness ratio of the blast has been
decreased, reducing the explosive
efficiency and resulting in cratering or
uplift movement of the shot instead of
proper flexural failure. This causes:
• Increases in boulders and fines;
• Decreased movement of the
muck pile;
•
•
•
•
Mining in focus
Very hard toes;
Severe backbreak;
Increased ground vibration; and
Air overpressure.
Why will the drilling and blasting team
be praised for this then when all other
downstream processes (muck-haul,
crushing, processing, slopes, and so on)
will greatly suffer? Well, the bottom
line is that the costs for blasting were
decreased on the balance sheet and
we have very poor methods at most
operations to monitor any of these
outcomes (besides the environmental
aspects).
Increasing blast burden
In the case where a mine wants to
decrease their drill and blast costs
by using the same-diameter drill, we
will assume a 10″ (250mm) drill bit is
again being used with a 7.31m burden.
Suppose the mine switches to a 7.92m
MAY 2018 MINING MIRROR
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