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 Theprincipal 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: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

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_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

THANK YOU