Mining_Methods_UnderGround_Mining - Mining and Blasting

MeCHanized BOlTing
Mechanized bolting and screening
utilization is the
key
In tunnelling operations, it is quite
common to use the same equipment
for all drilling requirements.
These days, a single drill rig can
accommodate drilling for face
blasting, bolt holes, protection
umbrellas, and drainage. As there
are normally only one or two faces
available for work before blasting
and mucking, it is difficult to
obtain high utilization for specialized
equipment such as mechanized
bolting rigs. By contrast, in
underground mining, especially
where a number of working areas
are accessible using methods such
as room and pillar, high utilization
of specialized equipment can be
expected. This is where mechanized
bolting and screening is rapidly
taking root, for speed, safety
and consistency.
Specializing for safety
There was a time when underground
mining and safety were terms not commonly
referred to in the same sentence.
However, times have changed, and today
safety is given a place of prominence in
the operational priorities of the mining
industry.
Freshly blasted openings leave considerable
areas of loose rock, which must
be removed to prevent fall-of-ground
injuries. Improvements in drilling and
blasting techniques have helped to signi-
ficantly reduce the amount of this loose
rock. Scaling, which is the most hazardous
part of the work cycle, is used to
remove loose rock.
Subsequent blasting might result in
additional rock falls, especially in fractured
ground conditions. Screening or
shotcreting, as a means of retention of
this loose rock, is often used in combination
with rockbolting. Screening,
which is a time-consuming operation,
is common practice in Canada and
Australia. Since the 1960s and 1970s,
considerable effort has been spent on
Mechanized scaling with hydraulic hammer.
mechanizing underground operational
activities, including the rock excavation
cycle. Within the drill-blast-mucking
cycle repeated for each round, the drilling
phase has become fully mechanized,
with the advent of high productivity hydraulic
drill jumbos.
Similarly, blasting has become an ef-
ficient process, thanks to the develop-
ment of bulk charging trucks and easily
configured detonation systems. After
only a short delay to provide for adequate
removal of dust and smoke by high
capacity ventilation systems, the modern
LHD rapidly cleans out the muck
pile.
These phases of the work cycle have
been successfully mechanized, and modern
equipment provides a safe operator
environment.
By contrast, the most hazardous ope-
rations, such as scaling, bolting and
screening, have only enjoyed limited
progress in terms of productivity improvements
and degree of mechanization.
The development of mechanized
scaling and bolting rigs has been slower,
mainly due to variations in safety rules
and works procedure in specific rock
conditions.
To summarize, equipment manufac-
turers have had difficulty in providing
globally accepted solutions. Nevertheless,
there is equipment available from Atlas
Copco to meet most of the current demands
of miners and tunnellers.
Mechanization stages
Various methods of mechanized bolting
are available, and these can be listed
under the following three headings.
Manual drilling and bolting
This method employs light hand held
rock drills, scaling bars and bolt installation
equipment, and was in widespread
use until the advent of hydraulic
drilling in the 1970s. Manual methods
are still used in small drifts and tunnels,
where drilling is performed with
handheld pneumatic rock drills. The
bolt holes are drilled with the same
equipment, or with stopers. Bolts, with
or without grouting, are installed manually
with impact wrenches. To facilitate
access to high roofs, service trucks or
cars with elevated platforms are commonly
used.
Semi-mechanized drilling and
bolting
The drilling is mechanized, using a hydraulic
drill jumbo, followed by manual
installation of the bolts by operators wor-
king from a platform mounted on the
underground mining methods 29