User's Manual

90
RIOTRONIC X+
User Manual
 150 mm for drilling coal seams, using simple rotary “auger” drills, and
 229, 251, & 311 mm in iron ore mines, with “tricone” bits and “rotary” rigs.
Hole Diameter Rules of Thumb #1
Excellent energy distribution can be achieved by using blast-hole diameters (mm) equal to
the bench height (m) multiplied by 8 to 15.
d = (8to15) x BH
Where: d = Hole Diameter in mm
BH= Bench Height in meters
The smaller the hole diameter the better the explosive energy distribution throughout the
rock mass.
9.3.2. Bench Height
Excavation depth (bench height) is arguably the most basic of blast parameters, and yet it is
often overlooked. Bench height is usually dictated by either existing mine planning and
designs or the available excavation equipment or methods.
If there is some flexibility available regarding bench height, the choices between lower and
higher benches may be influenced by the following:
 Bench preparation and infrastructure costs are reduced with increased bench height
 Overall drilling, manpower and explosives costs are reduced with increased bench
height
 Drill deviation increases with increased bench height
 Blasting control and ore dilution/losses are increased with increased bench height
In shallow trenches, the cost efficiency of ripping often exceeds that of drilling and blasting.
The cost efficiency of drilling and blasting decreases very rapidly as the excavation depth
falls below about two meters.
9.3.3. Burden and Spacing
The burden and spacing relationship between blast-holes is the basis of blast pattern design
in surface mining. Typically, the study of the ability of the explosive column to shoot the
burden is the start point of any pattern design.