Drop raising in underground mines

DROP RAISING IN
UNDERGROUND
MINES
PARTHA DAS SHARMA, B.TECH(HONS.)
E.mail: sharmapd1@gmail.com
Weblog: www.miningandblasting.wordpress.com

 This is a method of making Raise between
two adjacent levels.
 The difference of two adjacent levels may
be in the range of 60m or may increase to
even 90m.
 Drilling large dia. Holes, mostly, 165mm
diameter are used.
 Drilling is done from upper level to lower
level.
DROP RAISING - INTRODUCTION
PARTHA DAS SHARMA, B.TECH(HONS.), E.mail:
sharmapd1@gmail.com, Weblog:
www.miningandblasting.wordpress.com

DROP RAISING - INTRODUCTION
 Special method of charging of Explosives
and blasting is done in stages from
bottom level for excavation in slices.
 The charging and blasting of the holes is
based on Vertical Crater Retreat (VCR)
method.
 The raise is driven either vertically or with
steeply inclined dip.
 Mucking of blasted material done from
lower level.

VERTICAL CRATERING METHOD

 For Crater Blasting, normally, ‘Spherical
Charge’ of Explosives are used.
 Meaning of ‘Spherical Charge’ is to keep an
explosive column, not more than 6 times of
diameter of Hole.
 165mm dia of holes are used; thereby the
explosives column to be kept is 990mm (or
1m).
VERTICAL CRATERING METHOD - CONCEPT

VERTICAL CRATERING METHOD - CONCEPT
 This explosive column is kept about 0.7 to
0.8m above bottom of holes by putting
suitable wooden plugs and stone chips.
 Over the Explosive column stemming of
about 1.2 to 1.5m is done.
 Charging and Blasting is done from upper
level and bottom serves as free face.
 Thus, several slices from bottom are
blasted in order to complete the Raise.

DROP RAISING – Drilling and Charging
pattern

 Raise dimension is generally 3 m x 3m.
 Blast holes are of 165mm dia, and minimum 5 in
number (1 in centre, 4 at corners)
 These holes are drilled from the top level to the
bottom level, nearly 60 m length as per the Level
difference.
 These holes are drilled by using ITH (In-The-Hole) rigs
with Hammer attachment – using both compressed
air and water.
DRILLING FOR DROP RAISING

DRILLING FOR DROP RAISING
 Sometime, additional one hole of
165mm dia and nine holes of 57mm dia
are drilled up to 15m and 8m length
respectively, as shown in the fig., for
safety purpose.
 During drilling of 165mm dia holes,
strict supervision and drilling accuracy
should be maintained to avoid
deviation of holes.

DROP RAISING – Drilling and Charging pattern

 The charging of explosives into full
length 5 blast holes are done from the
upper level.
 Two pieces of wooden plugs tied to a
nylon rope is lowered into the blast hole
to plug the bottom mouth of the blast
hole.
 Stone chips, nearly 12 mm in size, is
stemmed for a length of 0.7m to 1m from
bottom,
EXPLOSIVE CHARGING FOR DROP RAISING

EXPLOSIVE CHARGING FOR DROP RAISING
 This followed by charging of cartridges
of slurry explosives for a length of
about 1m.
 Primer cartridges tied to detonating
fuse is also lowered along with
cartridge explosives.
 Over the Explosive column stemming
of about 1.2m is put, and rest of the
hole is kept unstemmed.

 As per Crater theory, concentrated
‘Spherical’ charge is positioned at specified
distance from horizontal free face
underneath.
 Detonation thus made, creates crater-
shaped opening in the rock at the lower
level.
 Holes are blasted in a sequence with the
help of delay detonators, from the surface
after removing all persons from
underground.
BLASTING FOR DROP RAISING

BLASTING FOR DROP RAISING
 The roof of the lower level provides a free
face for the explosive charged
 The result of blasting is that a cavity or
pull of nearly 1.8m to 2.0m height is
formed in one slice.
 The fragmentation is sufficiently good for
loading by LHD units from lower level.
 Top 4 to 4.5m of the blast holes blasted at
one go.

Extra Safety precaution taken at some mines
 Additional 9 holes of 57mm dia drilled up
to 8m from upper level, surrounding to
the centre 165mm dia hole.
 Additional one 165mm dia hole drill up to
15m from upper level. This hole serves as
relief hole of centre 165mm dia hole.
 The Drop Raising blasting is done with
conventional 165mm dia five holes upto
8m below upper level.

Extra Safety precaution taken at some mines
 Blasting of 8m portion from upper level
is done by charging 9 holes of 58mm dia
holes only, keeping centre 165mm dia
hole as Free Face.
 Once central portion is through, four
corner 165mm holes are blasted at a
time.
When Raise reaches up to 10m below upper
level, all persons including supervisors should
use SAFETY BELT while working at the Raise.PARTHA DAS SHARMA, B.TECH(HONS.), E.mail:

 Mucking of the blasted material is done at the
lower level.
 Dressing of conical cavity is not essential
 As a safety precaution, it is better to use
remote controlled LHD for the purpose of
mucking in this case.
 When post blast mucking is done at the lower
level, at upper level charging can also take
place simultaneously, as described above.
MUCKING

 Raise so excavated, has sufficiently strong and
stable sides.
 No adverse effect of heavy blasting shown on
walls or over-excavation experienced.
 Normally, with efficient and experienced crew,
two blast in a day of three shifts can be taken
up.
 Raise of about 60m can be completed in about
25 days time by this method.
Critical Observation Made and its Advantages

Critical Observation Made and its Advantages
 No side dressing or roof dressing is
needed.
 This method of Drop Raising is quite
advantageous , as this is a safer
method.
 Not much extra investment required,
as with the normal existing machinery,
drop raising operation can be done.

THANK YOU

Drop raising in underground mines

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