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Rock Damage from Small Charge Blasting in Granite.
Olson JJ; Willard RJ; Fogelson DE; Hjelmstad KE
NTIS: PB 222 560 :44 pages
The Bureau of Mines used microfracture density analysis of quartz grains in thin sections and diametric pulse velocity measurements along preblast and postblast cores to determine the nature and extent of rock damage produced by small (0.25-, 0.50-, 1.0-, and 2.0- Kg) charges of high intensity explosive (c-4) in granite. Pulse velocities from the postblast cores were significantly lower than velocities from the preblast cores and, with the core logs, provided clear identification of the upper and sometimes the lower limits of most severe damage. These zones ranged from about 1.68 Ft for the 0.25-Kg blast to 4.16 Ft for the 2.0-Kg blast. Microfracture densities from postblast cores were significantly higher and more variable than densities measured from preblast cores. The microfracture density measurements showed that microscopic damage was present far past the zones of most severe damage as delineated by the pulse velocity logs and core logs. An exponential relationship was observed between the microfracture density levels and the charge weight.
IH; Report of Investigations
NTIS Accession No.
NTIS: PB 222 560
Page last reviewed: October 29, 2021
Content source: National Institute for Occupational Safety and Health Education and Information Division