Mining_Methods_UnderGround_Mining - Mining and Blasting
Mining_Methods_UnderGround_Mining - Mining and Blasting
Mining_Methods_UnderGround_Mining - Mining and Blasting
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Plan of pre-undercut holes.<br />
el TenienTe, CHile<br />
the undercut level difficult. The effective<br />
extraction rate defined for the Es-<br />
meralda sector was 0.14 to 0.44 t/day/<br />
sq m at the initial caving stage, <strong>and</strong><br />
reached 0.28 to 0.65 t/day/sq m at the<br />
steady-state caving stage. The height<br />
of primary ore column to be exploited<br />
is around 150 m, relatively low if compared<br />
with Teniente 4 Sur, where the<br />
height is over 240 m.<br />
At Esmeralda, 7 cu yd LHDs working<br />
on the production level load <strong>and</strong> tip<br />
into 3.5 m-diameter ore passes. Here,<br />
teleremote controlled hydraulic breakers<br />
positioned above 1 m x 1 m grizzlies<br />
break any oversize rock before it goes<br />
Drilling patterns in <strong>and</strong>esite <strong>and</strong> breccia.<br />
St<strong>and</strong>ard drill plan with 4 hole-fans<br />
through the ore pass <strong>and</strong> into the loading<br />
bin. On the haulage level, the<br />
mineral is loaded into trains featuring<br />
Automatic Train Protection (ATP) <strong>and</strong><br />
consisting of a locomotive with eight 50<br />
t cars. These trains, which were retrofitted<br />
with an Automatic Train Operation<br />
(ATO) system, tip into storage bins<br />
which feed a 5.0 m-diameter orepass<br />
to the main transport level Teniente 8.<br />
Trains with 90 t electric locomotives<br />
<strong>and</strong> 18 cars each of 80 t capacity carry<br />
the mineral out to the Colón concentrator.<br />
The main haulage level at Teniente<br />
8 was recently upgraded, incorporating<br />
new technology similar to Esmeralda.<br />
HW FW HW<br />
FW<br />
Drill plan with 3 x 3 hole-fans Drill plan with 4 x 4 hole-fans<br />
HW FW HW<br />
FW<br />
Basic concepts<br />
In the conventional panel caving <strong>and</strong> the<br />
pre-undercut variant, the same basic con-<br />
cepts apply. The main difference is the<br />
sequence of each of the operational ele-<br />
ments. In the conventional panel caving<br />
method, the sequence of activities is:<br />
development of tunnels on each level<br />
for production <strong>and</strong> undercut; drawbell<br />
opening; undercut blasting; <strong>and</strong> extraction.<br />
In the pre-undercut variant, the un-<br />
dercut is excavated first, <strong>and</strong> the production<br />
level is developed subsequently<br />
within the stress-relieved zone: development<br />
of the undercut level; undercut<br />
blasting; development of the production<br />
level; drawbell opening; <strong>and</strong> extraction.<br />
The main challenge associated with<br />
this variant involved the undercutting.<br />
Several alternatives were tried, with<br />
the current preference being a flat, low<br />
height 3.6 m undercut. The undercut is<br />
blasted some 80 m ahead of the actual<br />
production zone, with the production<br />
level <strong>and</strong> drawbell development following<br />
around 22.5 m behind the undercut,<br />
<strong>and</strong> 57.5 m ahead of the production<br />
zone.<br />
The undercut comprises drives, 3.6<br />
m-wide by 3.6 m-high, developed parallel<br />
to each other on 15 m centres. The<br />
excavation of the undercut is achieved by<br />
blasting three- or four-hole fans, some<br />
7 m to 10 m length, drilled into the sidewall.<br />
The drill holes are fanned slightly,<br />
to ensure an undercut height equal to<br />
the height of the drives. Swell material<br />
from each undercut blast is removed by<br />
LHD to provide a free face for the next<br />
blast. The production haulage level is<br />
developed 18 m below the undercut,<br />
giving a crown pillar thickness of 14.4<br />
m through which the drawbells are then<br />
developed straight into the pre-blasted<br />
undercut. The production level requires<br />
substantial support, with fully grouted<br />
2.3 m rebar installed in a 0.9 m x 1.0<br />
m pattern immediately behind the face,<br />
followed by chain mesh <strong>and</strong> shotcrete.<br />
Permanent support is added around 15 m<br />
behind the face, <strong>and</strong> consists of fully<br />
grouted long cable bolts, with additional<br />
reinforcement at drawpoints. One of the<br />
challenges of this method is that two<br />
mining fronts have to be managed, one<br />
on the undercut level, <strong>and</strong> the other located<br />
on the production level, <strong>and</strong> these<br />
86 underground mining methods