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This is the job site. The developer is
preparing about 25 acres for future construction. The immediate task is to
grade the surface to a contour. The problem is that there is solid rock
just below the surface. Blasting is being used to break up the rock.
The work is being done in eastern Wake
county. |
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The guys are placing the explosives. The
small white mounds are rock dust next to each hole from the drilling.
Between 3,000 and 4,000 pounds of ammonium nitrate will be used in this
shot. |
The orange machine is a drilling rig. There are four
of these working almost full time. Most of the boreholes are between 15
and 20 feet deep and are 3 inches in diameter. The holes are drilled in a
grid of straight rows and columns with several feet between the holes.
Each shot involves from 100 to 150 holes. |
 Reeling
out the shock tube. Shock tube is a small diameter plastic tube whose
inner wall has a light coating of high explosive. The tube transmits a
shockwave of sufficient energy to detonate blasting caps. The tube remains
intact after the event. After the shock tube is in place the
initiator is connected. Finally, 3 blasts of the air horn and then ...... |
Fire in the hole! |
A few seconds after the shot. |
About a minute after the blast. Hundreds of tons of
rock have been fractured and heaved up. Those are some serious boulders in
the pile! |
This is what the site looks like after the shot. You
can see some of the yellow shock tube that interconnected the array of
boreholes. |
These boulders are a product of the explosion. As
huge as they are, they were all part of a much more massive rock!
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Beyond what's visible on the surface, the fractured
stone extends more than 15 feet down!
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These are blasting mats. They are used when the shots
come near buildings to control flying rocks. They are overlapped like
shingles over the blast site. |
This is a jackhammer rig. The operator can break up
the huge boulders into much more manageable sizes. |
This is what becomes of the large boulders. The
jackhammer makes little ones out of big ones. |
Last Edited: 14 Nov 2005
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By: Mike Murphy, WA4BPJ
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