1. SHORT DELAY BLASTING IN UNDERGROUND MINING
113MN0493
M BALA SUBRAHMANYAM

2. 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

3. 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).

4. DELAY DETONATOR
FIG 1: SOURCE

5. ARRANGEMENT OF DELAY DETONATORS
FIG 2:source tices.to.improve.blasting.efficiency.at.Murgul.copper.mine.html

6. 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

7. . 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. .

8. 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: blasting.pdf

9. With Short delay detonator
control of the direction of movement of the
 crushed rock is achieved.
FIG 4: blasting.pdf

10. 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).

11. 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.

12. 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)

13. DRILL PATTERNS WITH SHORT DELAY BLASTING
FIG5 :

14. 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).

15. 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.

16. Patterns used in open & underground mines for short delay blasting FIG 6:

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

18. 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:

19. 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.

20. FIG9: https://queensminedesign. miningexcellence. ca/index
FIG9: 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.

21. 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.

22. 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. 

23. REFERENCES
+ blasting
Deshmukh D.J(2012),Elements of Mining Technology, Vol- 1,Denett & co, Nagpur, Pg
Samir Kumar Das, EXPLOSIVES & BLASTING PRACTICES IN MINES, Lovely Prakashan, Dhanbad, Pg
sion-on-firing-pattern-in-blasting.pdf
DELAY_BLASTING_IN_UNDERGROUND_COAL_MINES

24. REFERENCES
ew/Drill,.blast.practices.to.improve.blasting.efficiency.at.Murgul.cop per.mine.html
_crater_retreat
488.jpg

25. THANK YOU