Mining_Methods_UnderGround_Mining - Mining and Blasting

pumphouses and workshops. Drill/blast
is the standard excavation method for
drifting. Firing sequence for a typical
parallel hole pattern is shown to the
right. Note that the contour holes are
fired simultaneously with light explosives,
and that the bottom holes, or lifters,
are fired last to shake up the muck
pile for faster mucking.
A deep shaft may secure many years of
production, until ore reserves above the
skip station are exhausted. The shaft can
be rectangular, circular or elliptical in
profile. Extending the shaft in an operating
mine is costly and difficult, re-
quiring both expert labour and specialized
equipment.
Drifts and ramps are dimensioned to
accommodate machines passing through,
or operating inside. Space must include
a reasonable margin for clearance, walk-
ways, ventilation ducts, and other facilities.
Cross-sections vary from 2.2 m x
2.5 m in mines with a low degree of
mechanization to 5.5 m x 6.0 m where
heavy equipment is used. Only 5.0 sq m
section is sufficient to operate a railbound
rocker shovel, whereas 25.0 sq m
may be needed for a loaded mine truck,
including ventilation duct.
Normal ramp grades vary between
1:10 and 1:7, with the steepest grade to
1:5. The common curve radius is 15.0
m. A typical ramp runs in loops, with
grade 1:7 on straight sections, reduced
to 1:10 on curves.
raising and winzing
Raises are steeply inclined openings,
connecting the mine’s sub levels at dif-
ferent vertical elevations, used for lad-
derways, orepasses, or ventilation. Inclination
varies from 55 degrees, which
is the lowest angle for gravity transport
of blasted rock, to vertical, with crosssections
from 0.5 to 30 sq m. When the
excavation of raises is progressing down-
wards they are called winzes.
Manual excavation of raises is a
tough and dangerous job, where the
miner climbs the raise by extending the
ladderway, installs the temporary platform,
and drills and charges the round
above his head. As such, manual raises
are limited to 50 m-high. However, the
efficiency can be greatly improved by
using a raise climber up to 300 m.
Firing sequence of a typical hole pattern (*contour holes).
The drop raise technique is used for
slot raises and short orepasses, using
longhole drilling and retreat blasting
from bottom to top, see figure below.
Inverted drop raising is performed the
other way around.
raise boring
The raise boring machine (RBM) may be
used for boring ventilation raises, ore-
passes, rock fill passes, and slot raises.
Long hole drilling alternative to raise boring.
Mine inFraSTruCTure
It provides safer and more efficient me-
chanized excavation of circular raises,
up to 6 m-diameter.
In conventional raise boring, a down-
ward pilot hole is drilled to the target
level, where the bit is removed and re-
placed by a reaming head. The RBM
then reams back the hole to final dia-
meter, rotating and pulling the reaming
head upward. The cuttings fall to the
lower level, and are removed by any
convenient method. An RBM can also
underground mining methods 23
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