Civil Engineering Reference
In-Depth Information
on theoretical equations developed by Langefors
and Kihlstrom (1973) and Persson
et al
. (1993)
together with extensive field testing, can be used
to check on the likely results for a given blast
design and assess the possible effects of design
modifications.
•
The main charge should have lifted evenly
and cratering should, at worst, be an occa-
sional occurrence. Flat or wrinkled areas are
indicative of misfires or poor delaying.
•
The back of the blast should be character-
ized by a drop, indicating a good forward
movement of the free face. Tension cracks
should be visible in front of the final excava-
tion lines, although excessive cracking behind
the final excavation line represents damage to
the slopes and waste of explosive.
11.3.11 Evaluation of a blast
Once the dust has settled and the fumes have dis-
persed after a blast, an inspection of the area
should be carried out. The main features of
a satisfactory blast are as follows (Figure 11.9):
•
The quality of blast has a significant effect on
components of the rock excavation cost such
as secondary drilling and blasting of oversize
boulders, loading rate, the condition of the haul
roads, and loader and truck maintenance. For
example, oversized fragments, hard toes, tight
areas and low muck piles (caused by excess-
ive throw) have the most significant detrimental
The front row should have moved out evenly
but not too far—excessive throw is unneces-
sary and expensive to clean up. The heights of
most benches are designed for efficient loader
operation and low muckpiles, due to excess-
ive front row movement, results in low loader
productivity.
Final wall
Minimum
disruption to
final wall
Low productivity
clean-up
Optimum loading
Easy loading with
no “hard toes”
Even throw
Low productivity
clean-up
Figure 11.9
Features of a satisfactory production blast.
