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