The Journal of Explosives Engineering - May/June 2022 - 32
Figure 5. Timing contours for blast.
this would still provide satisfactory blast vibrations.
It was also decided that the delay pattern used should open
in the center of the north face and progress to the south with
a chevron style of delay pattern (figure 5). The need for this
was to reduce the level of confinement on the west face crest
blast holes when they fired as they posed the greatest flyrock
threat to the crushers.
Design Implementation
The mine plan initially scheduled the pattern to be drilled
during the below 0º F (-18º C) Iron Range winter to allow
the variable depth of unconsolidated material on top of the
pattern to be frozen to support the weight of the massive
rotary drill rig. The layout of the bench required difficult drill
maneuvers with a highwall to the south. The local weather
did not allow the ground to fully freeze adding to the tough
conditions for drill and pump truck maneuvering. This resulted
in deviations of the blast hole collar locations along the western
crest and southern portion of pattern. An 'as drilled' UAV
profile was created to provide the as drilled profiles for the
crest holes. The final loading plans for the crusher side crest
holes were determined after measuring accurate borehole
32
depths. The final loads for each blast hole were controlled by
the 2D/3D burden, the target powder factor, 'as drilled' collar
locations, and the minimum stemming length to ensure zero
ejection. Because of the irregularity in the face it was important
to review both the 2D and 3D burdens as these could
differ significantly as shown in table 1. If the difference was
not considered in the design, flyrock could result.
Deviation in the collar locations required adjustments in
the timing for holes drilled within 24 ft (7.3 m) of neighboring
holes. The timing for the tightly spaced blast holes utilized
the accuracy of electronic detonators and were fired with the
same delay time. Since the paired holes were on the perimeter
of the pattern the limit of two blast holes per delay, as specified
by the SHA design, was maintained.
In the center portion of the pattern the drill log indicated a
softer clay material for the length of the hole. This resulted in
a larger diameter blast holes than the design loading column
loads which lead to explosive columns not measuring at correct
depths. The design load for each blast hole was followed
so as to not exceed the design lbs/delay (kg/delay). As this
material was softer the fragmentation of the rock was not
adversely affected by the increase stemming length.
The Journal of Explosives Engineering
May/June 2022
The Journal of Explosives Engineering - May/June 2022
Table of Contents for the Digital Edition of The Journal of Explosives Engineering - May/June 2022
From the Executive Director
Reactive Ground Blast Management in a South Africa Open Pit Zinc Mine
Industry News
Calendar of Events
Explosives, 100 Years Ago, More or Less
Foundation News
Blasting Near a Crusher
Safety Talk
Regulatory Update
29th Annual Photo Contest
The Journal of Explosives Engineering - May/June 2022 - Intro
The Journal of Explosives Engineering - May/June 2022 - Cover1
The Journal of Explosives Engineering - May/June 2022 - Cover2
The Journal of Explosives Engineering - May/June 2022 - 1
The Journal of Explosives Engineering - May/June 2022 - 2
The Journal of Explosives Engineering - May/June 2022 - 3
The Journal of Explosives Engineering - May/June 2022 - From the Executive Director
The Journal of Explosives Engineering - May/June 2022 - 5
The Journal of Explosives Engineering - May/June 2022 - Reactive Ground Blast Management in a South Africa Open Pit Zinc Mine
The Journal of Explosives Engineering - May/June 2022 - 7
The Journal of Explosives Engineering - May/June 2022 - 8
The Journal of Explosives Engineering - May/June 2022 - 9
The Journal of Explosives Engineering - May/June 2022 - 10
The Journal of Explosives Engineering - May/June 2022 - 11
The Journal of Explosives Engineering - May/June 2022 - 12
The Journal of Explosives Engineering - May/June 2022 - 13
The Journal of Explosives Engineering - May/June 2022 - 14
The Journal of Explosives Engineering - May/June 2022 - 15
The Journal of Explosives Engineering - May/June 2022 - Industry News
The Journal of Explosives Engineering - May/June 2022 - 17
The Journal of Explosives Engineering - May/June 2022 - 18
The Journal of Explosives Engineering - May/June 2022 - 19
The Journal of Explosives Engineering - May/June 2022 - Calendar of Events
The Journal of Explosives Engineering - May/June 2022 - 21
The Journal of Explosives Engineering - May/June 2022 - Explosives, 100 Years Ago, More or Less
The Journal of Explosives Engineering - May/June 2022 - 23
The Journal of Explosives Engineering - May/June 2022 - 24
The Journal of Explosives Engineering - May/June 2022 - 25
The Journal of Explosives Engineering - May/June 2022 - Foundation News
The Journal of Explosives Engineering - May/June 2022 - 27
The Journal of Explosives Engineering - May/June 2022 - Blasting Near a Crusher
The Journal of Explosives Engineering - May/June 2022 - 29
The Journal of Explosives Engineering - May/June 2022 - 30
The Journal of Explosives Engineering - May/June 2022 - 31
The Journal of Explosives Engineering - May/June 2022 - 32
The Journal of Explosives Engineering - May/June 2022 - 33
The Journal of Explosives Engineering - May/June 2022 - Safety Talk
The Journal of Explosives Engineering - May/June 2022 - 35
The Journal of Explosives Engineering - May/June 2022 - Regulatory Update
The Journal of Explosives Engineering - May/June 2022 - 29th Annual Photo Contest
The Journal of Explosives Engineering - May/June 2022 - 38
The Journal of Explosives Engineering - May/June 2022 - 39
The Journal of Explosives Engineering - May/June 2022 - 40
The Journal of Explosives Engineering - May/June 2022 - Cover3
The Journal of Explosives Engineering - May/June 2022 - Cover4
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