Basic Blasting PatternsBasic Blasting Patters

7/29/2019 Basic Blasting PatternsBasic Blasting Patters

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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.


2/17

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


3/17

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


4/17

Rectangular Pattern

Provides for spacing > Burden - Improves fragmentation if you can

get your drillers to put one down


5/17

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!


6/17

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


7/17

Plough Cut


8/17

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


9/17

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


10/17

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


11/17

Plough Cut In the Field


12/17

The V Cut


13/17

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


14/17

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


16/17

Row Echelon Firing Sequence


17/17

Row Echelon in the Field

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