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Fracturing in the Zone Around a Blasthole, White Pine, Michigan.
Siskind-DE; Steckley-RC; Olson-JJ
NTIS: PB 221 889, 1973 :20 pages
The Bureau of Mines has studied the fracturing and associated damage occurring in the vicinity of blastholes from five shots fired in the shale pillars in the White Pine Copper Mine, White Pine, mich. Four types of explosives (AN-FO, commercial extra dynamite, ammonia gelatin dynamite, and a low-density, low-velocity permissible) were used. Cores were taken from the blast region and examined by ultrasonic and petrographic techniques. Pulse wave velocities were measured across the core diameters, and thin sections showing cracks and changes in lithology were examined in an attempt to establish zones of damage. Cores from the blast regions and areas near pillar free faces were found to have abnormally low pulse velocities. Petrographic study of the thin sections showed that the negative velocity anomalies were caused by cracks in the cores. Crushing and extensive fracturing prevented meaningful measurements on core fragments from the immediate blast vicinities. Compositional changes and other rock nonuniformities, such as joints and preexisting fractures, tended to mask detailed damage differences among the four explosives; however, the two most energetic explosives (extra dynamite and ammonia gelatin dynamite) produced damage zones two to three times as large as the AN-FO and low- velocity permissible explosives.
IH; Report of Investigations
NTIS Accession No.
NTIS: PB 221 889
Page last reviewed: September 2, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division