SHORT DELAY BLASTING IN UNDERGROUND MINING 113MN0493 M BALA SUBRAHMANYAM

CONTENTS INTRODUCTION ARRANGEMENT OF DELAY DETONATORS WHY WE ARE DOING MOVEMENTOF ROCKS WITH AND WITH OUT DELAY DETONATOR WHERE SHORT DELAY IS USED PERFORMANCE OF SHORT DELAY PATTERNS USED IN OPEN CAST AND UNDERGROUND MINING A typical arrangement for blasting in VCR methods of mining REFERENCES

SHORT DELAY BLASTING A method of blasting in which the detonation of several explosive charges takes place in a specified  sequence over certain intervals of time, usually  measured in milliseconds. The idea of short delay blasting was put forth and realized in the USSR. By the engineer in 1934 during the sinking of mineshaft; later, it was introduced in the USA (1945) and Great Britain (1949).

DELAY DETONATOR FIG 1: SOURCE http://www.kayakujapan.co.jp/en/sale/denkiraikan.html

ARRANGEMENT OF DELAY DETONATORS FIG 2:source http://gsi.ir/General/Lang_en/Page_25/DataId_2485/Action_BodyView/Drill,.blast.prac tices.to.improve.blasting.efficiency.at.Murgul.copper.mine.html

WHY WE ARE DOING THIS ? Reduced consumption of explosive as blasting is more efficient due to availability of a free face for each row of round of shots . (i.e. blasting due to No.1 delay detonator gives a free face for the blasting effect of shots fired by No.2 detonator) In short delay blasting, the initiation of each subsequent charge or group of charges occurs in an area of the rock mass that is under stress as a  result of the preceding explosion, thus increasing  the useful blast effect

. The use of shortdelayblasting increases intensity of fragmentation of the medium by the blast Reduces disruption of the rock mass outside the crushing zone,provides localized disintegration of the  rock mass, and decreases the seismic effect of the blast. In addition, short delay blasting makes possible control of the direction of movement of the crushed rock providing collision and additional crushing of the fragments. .

With out Delay detonator If the delay between the rows is too short, the rock from the back rows tends to take an upward direction instead of a horizontal. FIG 3: https://miningandblasting.files.wordpress.com/2009/09/discussion-on-firing-pattern-in- blasting.pdf

With Short delay detonator control of the direction of movement of the  crushed rock is achieved. FIG 4: https://miningandblasting.files.wordpress.com/2009/09/discussion-on-firing-pattern-in- blasting.pdf

CONDITIONS WHERE SHORT DELAY IS USED In shafts withhazardous gas and dust conditions,  shortdelay blasting makes possible the firing of an  entire set of blast holes in one stage instead of several, with instantaneous blasting (charging an d blasting of sumper holes and ventilation, chargi ng, and blasting of auxiliary holes).

PERFORMANCE OF SHORT DELAY Short-delay blasting is performed by means of shortdelay electric detonators or, when blasting with a detonator fuse, by means of pyrotechnic delay mechanisms (relays).   Singlerow and multirow shortdelay blasting arrangements are use The  principal singlerow shortdelay  blasting arrangements are sequential  row blasting  in which the charges are detonated one by one  from  one end to the other.

Single row and Multi row short delay And consecutive-counter blasting in which the detonation proceeds from the centre  of a row toward its flanks. Providing head-on collision of the fragments and formation of a pile against the  centre of the face. In cases of a large face, the method can be repeate- d, forming several collision centres along the front  (wave arrangement)

DRILL PATTERNS WITH SHORT DELAY BLASTING FIG5 : https://miningandblasting.wordpress.com/

MULTI ROW SHORT DELAY The principal types of Multi row short delay blasting are sequential row blasting in which the charges are detonated consecutively (for example, 20 milliseconds between charges and, so that the moments of detonation of adjacent charges do not  coincide, 30 milliseconds between rows).

Short Delay Series detonators are designed for opencast and underground mines, for driving tunnels, shaft sinking and in quarries where multi shot rounds are required. Long Delay Series detonators are designed for underground mining for driving shafts and tunnels, blasting raises and shaft sinking. They are used for stopping in metal mines, trenching and other blasting applications. The longer delay period allows sufficient rock movement before firing the consecutive shot.

Patterns used in open & underground mines for short delay blasting FIG 6: https://sites.google.com/site/copperminingphotofromindia/explosives-andblasting-in-mines/blasting-principles-for-open-pit-mining

FIG 7: BENCH BLAST PATTERN In open cast mines we use this pattern for Short delay blasting

A typical arrangement for blasting in VCR methods of mining. Under ground Blasting provides a good over view for a Varity of underground blast design A typical arrangement for blasting in VCR methods of mining. FIG 8: http://technology.infomine.com/reviews/Blasting/welcome.asp?view=full

Vertical crater retreat Vertical crater retreat (VCR), also known as Vertical retreat mining, is an open stoping, bottom-up mining method that involves vertically drilling large-diameter holes into the ore body from the top, and then blasting horizontal slices of the ore body into an undercut A system of primary and secondary stopes is often used in VCR mining, where primary stopes are mined in the first stage and then backfilled with cemented fill to provide wall support for the blasting of successive stopes.

FIG9: https://queensminedesign. miningexcellence. ca/index FIG9: https://queensminedesign.miningexcellence.ca/index.php/File:Pic44 88.jpg Holes are drilled vertically from the top drift through to the bottom drift.  Holes are charged such that blasting of horizontal slices of the ore body occurs, progressing from the bottom drift to the top drift.

Vertical crater retreat The most common drill hole diameter used in VCR mining is 165mm Blasted ore is collected at the draw points using LHD vehicles, and then transported to ore passes, sometimes to be crushed, before it is transported to surface for processing Upon completion of the ore extraction, the stope is often backfilled from the top drift, providing rock stability for upcoming blasts. This process is repeated until the ore body is mined.

VCR is a suitable mining method for ore bodies that exhibit the following characteristics Requirements '    'Orebody Dimensions                                            Steeply-dipping orebodies (>45º), with widths of no less than 12-15m, OR Very large both vertically and horizontally [2]                 Grade VCR is not a selective mining method, therefore the ore grade should be low to medium, and it should be relatively uniform throughout the entire orebody [2]                 Depth VCR mining can occur at any depth. 

REFERENCES www.encyclopedia2.thefreedictionary.com/short-delay + blasting Deshmukh D.J(2012),Elements of Mining Technology, Vol- 1,Denett & co, Nagpur, Pg 8.24-8.27. Samir Kumar Das, EXPLOSIVES & BLASTING PRACTICES IN MINES, Lovely Prakashan, Dhanbad, Pg. 42-45 www.msha.gov/S&HINFO/TECHRPT/BLAST/SHORTDEL.pdf https://miningandblasting.files.wordpress.com/2009/09/discus sion-on-firing-pattern-in-blasting.pdf http://www.researchgate.net/publication/237723752_SHORT- DELAY_BLASTING_IN_UNDERGROUND_COAL_MINES

REFERENCES http://gsi.ir/General/Lang_en/Page_25/DataId_2485/Action_BodyVi ew/Drill,.blast.practices.to.improve.blasting.efficiency.at.Murgul.cop per.mine.html http://www.kayakujapan.co.jp/en/sale/denkiraikan.html https://queensminedesign.miningexcellence.ca/index.php/Vertical _crater_retreat https://queensminedesign.miningexcellence.ca/index.php/File:Pic4 488.jpg

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