Mining_Methods_UnderGround_Mining - Mining and Blasting

keMi, Finland
Boltec LC installing Swellex Mn12 rockbolts.
with inflation. A series of slip-pull tests
carried out throughout the mine proved
the strong anchorage capacity of
Swellex Mn12, both in the orebody and
for the softer talc-carbonate and
mylonite zone.
Cable bolting
Kemi installs some 80 km of cable bolt
each year using its Atlas Copco Cabletec
L unit, which is based on the longhole
production drilling rig Simba M7, with
an added second boom for grouting and
cable insertion. The Rig Control System
enables the operator to pay full attention
to grouting and cable insertion, while
drilling of the next hole after collaring
Cabletec L installing cable bolts at Kemi.
is performed automatically, including
pulling the rods out of the hole. The
main benefit of the two-boom concept is
to drastically reduce the entire drilling
and bolting cycle time. Also, separating
the drilling and bolting functions
prevents the risk of cement entering the
rock drill, thereby reducing service and
maintenance costs.
Kemi tested the prototype Cabletec L
and eventually purchased the unit after
minor modification proposals. During
the testing period, where most holes
were in the 6 to 11 m range, the rig grou-
ted and installed cables at rates of more
than 40 m/hour. The capacity of the unit,
which is governed by the rate of dril-
ling, provided around 50 per cent extra
productivity compared with alternative
support methods.
The Cabletec L is equipped with a
COP 1838ME hydraulic rock drill using
reduced impact pressure with the R32
drill string system for 51 mm hole
diameter. The machine's cable cassette
has a capacity of 1,700 kg and is easy
to refill, thanks to the fold-out cassette
arm. It features automatic cement
mixing and a silo with a capacity of
1,200 kg of dry cement, which is mixed
according to a pre-programmed formula,
resulting in unique quality
assurance for the grouting process.
Bench cut and fill
The current mining method is bench cut
and fill, a type of sub-level stoping with
downhole production drilling, in which
primary stopes are 25 m-high, 15 mwide
and between 30 and 40 m-long.
Using a Rocket Boomer L2 C rig, the
drifts for the primary stopes are developed
laterally from the footwall through
the ore zone. Then a Simba M6 C production
rig drills down 51 mm diameter
blastholes in fans 2 m apart. Each stope
yields between 25,000 and 35,000 t of
ore.
Tests showed that drilling upwards
would be about 30 per cent more efficient,
but because of safety issues related
to the poor rock conditions, it was
decided to start with downhole drilling
while getting experience with the rock
and the mining method. Meantime,
Kemi ordered a Simba M7 C rig with
long boom to be delivered in August,
2005. With Simba M6 C and Simba M7 C,
operators are able to cover all kinds of
drilling patterns.
Mining of the 20 m-wide secondary
stopes started in 2005, while sub-level
caving with uphole drilling was tested
at one end of the main pit in 2006.
Secoroc rock drilling tools are used
for production drilling. The previous 64
mm holes over-fragmented the ore, but
a switch to 51 mm resulted in lower specific
charges and better fragmentation,
while retaining the same number of
holes. When developing the secondary
stopes, the mine can go back to 64 mm
drilling if there are problems keeping
the holes open due to the stresses and
rock movements.
66 underground mining methods