Caldwell Quarry - Flyrock Incident 8-30-23

Martin Michael McGill
Marietta Director of Explosives Engineering
Caldwell Quarry
Flyrock Incident Investigation
Date Submitted — 9/7/2023.
➢ Overview
Location of Blast: Martin Marietta
Caldwell Quarry — 1325 Bradford
Mountain Road, Lenoir
Date of Blast: 8/30/2023
Rocks left the permitted area of
the quarry but did not leave the Rock Location
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There was only one rock Elevation:17" N
property. Y 35'sz'31.17" N
found near Bradford Mountain 81'33'12.73"w
Road.
The picture to the left shows the
location of the recovered rock and
the location of the source of the
rock. The rock ejected from the a ass'
east end of the blast and traveled Horizontal
approximately 455 feet. Distance:436'
➢ Blast Information
Hole Diameter— 5 inches
Number of Holes— 32 "-
Hole Depth range— 32 -33 feet •' "� i -
Face Height range - 29-30 feet µ ,:
Stemming Height— 6-8 feet f T -
Designed Burden — 9 feet. F Blast GPs Points
Designed spacing — 9 feet. `'
� Bench Elevation: 1156'
Number of rows - 2 source }:'• 35'52'34 9a'N ►`
Stemming Material — crushed Bench Elevation:1156' 81'33'11.56"W V
35'52'34.91"N2
c .
stone B1'33'8.69"W
...
Corporate Office
4123 Parklake Ave,Raleigh NC 27612
t.[phone] m.[phone] [e-mail]
www.martinmarietta.com

Page 2
➢ Blast Design & Layout
The blast was designed with the Strayos 3D blast design software. The software uses data
collected from a drone flight to model the area to be blasted.
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After drilling was completed, all holes were bore tracked by the explosives company to measure
deviation. The borehole deviation information was downloaded into the Strayos model to generate
the final face profiles. There were no adjustments to the loading because there was minimal
deviation between design and actual.

Page 3
➢ Drilling
Piedmont Drilling drilled the shot, and a copy of their drill log is shown below:
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Page 4
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The Piedmont Drilling drill log shows only one foot of broken material on every hole of the blast.
The picture above shows the face prior to detonation of the blast. The left side of the shot appears
to have more than one foot of broken material. Inaccurate drill logs prepared by Piedmont Drilling
are thus believed to have caused the flyrock.
➢ Explosive Loading
Dyno Nobel was the blasting company who loaded and detonated the blast. All holes were loaded
with two electronic detonators inserted into cast boosters. DYNO XL 1000G gassed emulsion was
the main explosive charge. Ten sticks of 3.5"diameter were loaded on top of the gassed emulsion
in nine holes to create a decoupled charge below the stemming. A copy of Dyno's detailed loading
is shown on the next page.

Page 5
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Page 6
➢ Summary
The flyrock was the result of inadequate drill logs prepared by Piedmont Drilling. The drill logs
failed to identify variations in the geology, specifically the broken material on the left side of the
shot. Explosive load adjustments that increased the stemming heights could have prevented the
flyrock from occurring.
➢ Corrective Actions
• Martin Marietta will require that the Piedmont Driller employee, and any other drillers
Piedmont sends to the site, will receive training or re-training on how to appropriately
complete drill logs.
Michael McGill
Director of Explosives Engineering
Martin Marietta
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ONE Purpose
Future