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.practices.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 o

f 

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 and blasting of sumper holes and ventilation, charging, 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

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.php/File:Pic4488.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

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/discussion-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_BodyView/Drill,.blast.practices.to.improve.blasting.efficiency.at.Murgul.copper.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:Pic4488.jpg

THANK YOU