Basic Blasting Patterns

©Dr. B. C. Paul 2000

Note – The concepts contained in these slides represent the author’s 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 Blaster’s Handbook published by DuPont.

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

Drilling Patterns

Square Pattern - ease of drilling - easily explained to labor - not a lot of judgement to lay out - just one number to rememberSpacing > Burden improves fragmentation - but not available here

Rectangular Pattern

Provides for spacing > Burden - Improves fragmentation if you canget your drillers to put one down

Staggered Pattern

Provides Spacing > Burden by a considerable amount

Problem of leaving stumps on quarry floor - next row takes themout

And Your People Can Drill it Too!

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 vibration– causes cracking behind holes - called back break

- can make future faces hard to support

– 25 to 40 ms would be common

Plough Cut

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

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

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

Plough Cut In the Field

The V Cut

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

More About V Cuts

• Central Collection Tends to Create More Potential Confinement

• Real Caps don’t get the Delay Times Perfect - called cap scatter– If hole at apex of V doesn’t fire - confinement

for next row back will be severe

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

Row Echelon Firing Sequence

Row Echelon in the Field