User's Manual

RIOTRONIC X+

User Manual

 Stemming

 Overburden material

A set of rules of thumb will be developed for these key parameters based on blast-hole

diameters.

9.3.1. Blast-hole Diameter

Drilling and blasting costs generally decrease with an increase in blast-hole diameter. This

provides the incentive to maximize diameters. However, given the same Powder Factor, the

larger patterns associated with larger diameter blast-holes will give poorer fragmentation

and hence, higher digging, hauling and crushing costs. This is especially the case in rocks that

are strong and massive or contain widely spaced sub vertical joints.

Big Holes + Big Patterns = Lower Costs + Big Rocks

Fragmentation will be poor in places where a large percentage of the natural (i.e. joint

bounded) blocks do not contain a blast-hole. This also applies to large “boulders” or pods of

hard ore in soft waste material where there are no explosives in the vicinity of the hard

material. This will tend to reduce digging rates and increase wear, downtime and

maintenance cost for digging, hauling and crushing equipment.

In places where the selected blat-hole diameter is small, the costs of drilling, priming and

initiating will be high. The charging, stemming and tying operations in these blasts are also

more time consuming and labor intensive. The disadvantages of small diameter blast-holes

outweigh the fragmentation benefits of slightly lower powder factors.

As a blast designer you will often be constrained by the capability of the available drill

equipment. However, one bit size up or down may have a measurable effect on cost

performance.

An enormous range of blast-hole diameters can be drilled in rock, with numerous drill bit

designs available for different rock types and drilling equipment. Blast-hole diameters

drilled in most open-cut mines and quarries vary from 57 mm to 311 mm, with an almost

continuous range of sizes in between.

Some of the most common diameters are:

 76, 89, & 102 mm in quarries, with “button bits” and “top hammer” rigs,

 115, 140, & 165 mm in metal mines, using “down-the-hole hammer” drills,

 270 & 311 mm for coal overburden, with “tricone” bits and “rotary” rigs,