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Rock Damage from Small Charge Blasting in Granite.

Authors
Olson-JJ; Willard-RJ; Fogelson-DE; Hjelmstad-KE
Source
NTIS: PB 222 560 :44 pages
Link
NIOSHTIC No.
10001681
Abstract
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.
Publication Date
19730101
Document Type
IH; Report of Investigations
Fiscal Year
1973
NTIS Accession No.
PB-222560
NTIS Price
A04
Identifying No.
RI 7751
NIOSH Division
TCRC;
Source Name
NTIS: PB 222 560
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