basic blasting patternsbasic blasting patters
TRANSCRIPT
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Basic Blasting Patterns
Dr. B. C. Paul 2000
NoteThe concepts contained in these slides represent the authors view of
information commonly held among those well studied in the field. Some of the figures
contained in these slides were taken from or prepared with inspiration from the
Blasters Handbook published by DuPont.
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Blasting Nomenclature
Free Face - open area at the rock air interface -
essential that broken rock has a place to go to
avoid energy turning to bad vibrations Row - a line up of holes running parallel to the
Free Face
Spacing - the distance between holes in a row Burden - the distance from a row of holes to the
free face - the rock that must be broken up and
moved by the explosive
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Drilling Patterns
Square Pattern - ease of drilling - easily explained to labor - not a
lot of judgement to lay out - just one number to remember
Spacing > Burden improves fragmentation - but not available here
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Rectangular Pattern
Provides for spacing > Burden - Improves fragmentation if you can
get your drillers to put one down
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Staggered Pattern
Provides Spacing > Burden by a considerable amount
Problem of leaving stumps on quarry floor - next row takes them
out
And Your People Can Drill it Too!
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Firing Patterns
All shots need a free face for rock to move
to
With several rows must wait for material in
front to move to create a free face
Lack of a free face turns throw energy in
vibrationcauses cracking behind holes - called back
break - can make future faces hard to support
25 to 40 ms would be common
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Plough Cut
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Properties of the Plough Cut
Gives long linear muck pile along the face
Open Free Face Helps to Avoid
Confinement Problems
Movement Perpendicular to Face Can
Maximize forward throw which may be
problematic for narrow benches
Needs a Rectangular drill pattern to get
spacing > burden
Also used with staggered drill pattern
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Peculiar Edge Delays on Plough
Cut
Plough Cut Often Fires the Entire Row at
One Time
Note That Edge Holes Seem to Fire Later
Explosive Action Must Tear the Rock
Away of 3 sides - more open space eases
the burden to be pushed
By delaying edge holes provides 2 free faces to
throw to
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Considerations in Firing
Starts at One End of Shot and Spreads Across
Can See Hole Initiate on Surface Before Break-up
begins at face
Primer is generally placed in toe - Note That
heave begins at bottom
Top Will Swell Usually causes top to slump down
In Quarry the timing will be set to heave clear of face
Rock Pile may have larger pieces from stemming
zone
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Plough Cut In the Field
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The V Cut
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Properties of the V Cut
Firing Pattern Rips out a V Shape Wedge
Firing Pattern Alters the Position of the Free
Face for Later Firing Holes
Provides a 2:1 Spacing to Burden Ratio with a
Square Pattern
Tends to Throw Material into Centrally
Collected Muck Pile
Can be good for limited bench room
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More About V Cuts
Central Collection Tends to Create More
Potential Confinement
Real Caps dont get the Delay Times
Perfect - called cap scatter
If hole at apex of V doesnt fire - confinement
for next row back will be severe
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Modifications of the V Cut
Flatten the apex of the V - fire two maybe
three holes in a row at top of the V
Spread the pile out a bit more
More forgiving of a cap misfire
Can see at some point Plough and V cuts may
melt into each other
Fire Only One Side of the V at two free
faces - Called Row Echelon Form
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Row Echelon Firing Sequence
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Row Echelon in the Field