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

DROP RAISING - INTRODUCTION 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. 

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. 

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

VERTICAL CRATERING METHOD

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

VERTICAL CRATERING METHOD - CONCEPT

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). 

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

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. 

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

DROP RAISING – Drilling and Charging pattern

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

DRILLING FOR DROP RAISING 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. 

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

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.

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

DROP RAISING – Drilling and Charging pattern

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

EXPLOSIVE CHARGING FOR DROP RAISING  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, PARTHA DAS SHARMA, B.TECH(HONS.), E.mail: sharmapd1@gmail.com, Weblog: www.miningandblasting.wordpress.com

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.

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

BLASTING FOR DROP RAISING As per Crater theory, concentrated ‘Spherical’ charge is positioned at specified distance from horizontal free face underneath.  Detonation thus made, creates cratershaped 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. 

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

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. 

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

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. 

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

Extra Safety precaution taken at some mines ď‚ž 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. ď‚ž 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: sharmapd1@gmail.com, Weblog: www.miningandblasting.wordpress.com

MUCKING 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. 

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

Critical Observation Made and its Advantages 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. 

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

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.

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

THANK YOU PARTHA DAS SHARMA, B.TECH(HONS.), E.mail: sharmapd1@gmail.com, Weblog: www.miningandblasting.wordpress.com