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RIOTRONIC X+
User Manual
back) and to reduce costs in throw blasting (increase burdens after first five to six
rows as these will not throw because of the material in front.)
9.3.4.
Blast-hole Pattern (Staggered v Square)
One of the most common questions asked of blast design is “What is the advantage of
staggered patterns over square patterns?”. Square patterns are simple to mark out and often
the end result seems to be the same. However, there is both an academic argument and
considerable experience to show that fragmentation, productivity and profitability are
greater with staggered patterns compared to square or rectangular patterns. The difference
increases with higher values in the strength of the rock mass.
Use square patterns in trenches and narrow benches where the simpler geometry is a
significant advantage, otherwise, use staggered patterns.
A staggered pattern has every second row ‘offset’. This can give a better explosives
distribution but is dependent on the Spacing to Burden ratio.
The S:B ratio chosen will be based on:
Rock strength
Rock condition
Ore body type (massive or small pods/vertical or horizontal)
Required movement of material (throw or sit)
In general, lower ratios (<1) are used in paddock blasting or choke blasting to fragment and
give muck pile looseness. High ratios (>1.2) are used to throw or ’cast’ material as in
overburden removal for draglines in large open cut coal mines.
Rule of thumb #3:
Begin the design with staggered patterns and a burden to spacing ratio of 1:1.15
If the burden to spacing ratio is too high, the material midway between back row blast- holes
may remain intact, especially near bench floor level, creating toe problems for the next blast.
For burden to spacing ratios that are too low or, in the extreme case where the spacing is
significantly less than the burden, premature splitting between blast-holes in the row and
early loosening of the stemming may occur. Both these effects encourage the premature
release of gases to the atmosphere and overbreak is usually considerable.
This loss of heave energy detracts from overall breakage and large slabs are often found in
the muck pile.
