Mining_Methods_UnderGround_Mining - Mining and Blasting

Production
area
5
4
80 m
57,5 m 22,5 m
1. Development
Principle 2. Drilling of pre-undercut & blasting at Esmeralda. to start caving
3. Development
4. Open trenches (boxholes + drilling)
in turn 5. Extraction are related to the scheduling of
the development of the drawbells, and
construction of the drawpoints.
The pre-undercut variant has been a
substantial success in the Esmeralda sector,
with only minimal damage occurring
on the production level, and its
associated orepasses and drawpoints.
There was a significant reduction of
damage to the drifts located under the
undercut level, as well as a significant
reduction of rockburst occurrence by
better draw management. The stability
and rock condition with the pre-undercut
variant dramatically improves, so it
was possible to reduce the cost of support,
and increase the availability of the
area by nearly 90%.
Some optimization of the pre-undercut
is still continuing, in particular some
fine-tuning of undercut level pillars and
improvement of the co-ordination and
scheduling of the development activities.
It is vital that the spacing of the activities
is maintained, so as to keep the
production development ahead of the
active cave, but still within the destressed
area.
Current productivity obtained at
Esmeralda is over 115 t/day/worker. In
comparison with other methods such as
sublevel caving, panel caving gives El
Teniente more advantages. The direct
cost of the sublevel caving method is at
least double that of panel caving, and
the current direct cost for mine at El
Teniente is US$2.5/t of ore, and indirect
costs close to US$1/t
The average cost of panel caving is
US$3.5/t, compared to more than US$5/t
3
Undercut area
Production
area
2
5
4
Preparation area
for sublevel caving. Hence, El Teniente
is developing its new productive sectors
using the panel caving method with preundercut,
though other variants could
be used, depending on the local conditions,
lithology, stresses and economics
of each sector.
Production at esmeralda
1
1. Development
2. Drilling & blasting to start caving
3. Development
4. Open trenches (boxholes + drilling)
5. Extraction
Cave undercutting at Esmeralda is presently
carried out with the 'parallel long
hole' technique, which basically consists
of excavating an 855 cu m pillar of solid
rock 11.4 m-wide, 25 m-long and 3 mhigh.
A triangular pattern of 14 parallel
long holes of 3 in-diameter, with 9 rows
of 2 holes and 1 hole each is used. This
pattern has better efficiency, absorbs
blast hole deviation, and avoids formation
of residual pillars.
Drilling is carried out with an Atlas
Copco Simba H157 drill rig, whose output
is 60 m/shift of 3 in-diameter holes
and 85 m/shift of 2.5 in-diameter holes.
Standard ANFO is the column charge,
with 300 gm cylindrical pentolite as the
booster, detonated using Nonel.
Atlas Copco equipment at Esmeralda
includes one Rocket Boomer, two Boltec
rigs, two Simba rigs and one 3.5 cu yd
Scooptram loader.
In the production level, a fleet of
nine LHDs is used, including Atlas
Copco Scooptram ST6C and ST1000
loaders of capacities 6 cu yd and 7.3 cu
yd respectively.
The support methods used in Esmeralda
include 22 mm-diameter and 2.3
m-long bolts, 6 mm-diameter by 10 cm
Undercut area
el TenienTe, CHile
Preparation area
spacing mesh, 10 cm-thick shotcrete, and
6 in-diameter cable bolts. There are two
types of cable bolts, plain and birdcage,
which are 4 m to 10 m-long, and 5 m to
2
7 m-long respectively. 1
raise boring
In an interesting application during the
development of Esmeralda, two Atlas
Copco Robbins raise boring machines,
a 34RH and a 53RH were used. These
are multipurpose machines, and can be
employed for upwards boxhole boring
or down reaming, as well as conventional
raiseboring.
At Esmeralda, the Robbins 34RH unit
was used in the production level to drill
draw bell slot vertical holes approximately
15 m to 20 m-long and 0.7 mdiameter.
The machine worked three
shifts/day, giving a penetration rate of
2.1 m/h. It had a capacity of 93 m/month
and a utilization rate of 39%.
The Robbins 53RH was employed to
bore 1.5 m-diameter boxholes up to 75
m-long for use as ventilation shafts, and
inclined pilot raises for orepasses, with
an average length of 24 m. The machine
worked three shifts/day, giving a penetration
rate of 1.8 m/hr. It had a capacity
of 111 m/month and a utilization
rate of 57.3%.
Atlas Copco trained the operators
from El Teniente, and was in charge of
the equipment maintenance during the
first few months.
rocket Boomer drill rigs
Shortly after acquiring the raise boring
machines, El Teniente acquired two
Atlas Copco Rocket Boomer 282 drill
rigs for drift development at Esmeralda.
In order to increase the drilling pre-
cision, the mine installed the Atlas
Copco Feed Angle Measurement (FAM)
instrument on the Rocket Boomer units.
The machines also featured the direct
controlled drilling system, which incorporates
the anti-jamming function
Rotation Pressure Controlled Feed Force
(RPCF).
The Rocket Boomer rigs were fitted
with COP 1838 rock drills with 20 KW
impact power and dual-damping system,
giving high speed drilling and good steel
economy.
underground mining methods 87
80 m
57,5 m 22,5 m
3