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A Study of Fragmentation from Bench Blasting in Limestone At a Reduced Scale.

Dick RA; Fletcher LR; D'andrea DV
NTIS: PB 215 813 :24 pages
Eight blasts were fired in a 2 1/2-ft bench in the Stewartville member of the Galena Limestone Formation in an aggregate quarry near Stewartville, Minnsota. The shots were dimensionally proportional to production-size bench blasts and were about 5 to 10 percent of full scale. The effects of site, timing of initiation, and burden-to spacing ratio were studied in a 2 x 2 x 2 factorial experiment, using three boreholes, each containing a 1/2-in charge diameter of high-density ammonia dynamite, in each blast. Detonation velocity measurements indicated that the dynamite detonated satisfactorily in the 1/2-in charge diameter. The effects of the three experimental variables were analyzed by weight for the percentage of oversized material produced and for size distributions determined by screening the entire muckpiles. The bench faces were painted before each shot in an effort to determine the origin of the oversized material. The square pattern (burden and spacing = 15 in) produced finer overall fragmentation and less oversized material than the rectangular pattern (burden = 15 in; spacing = 22 1/2 in). Sites 1 and 2 were about 15 ft apart. Although site 2 produced slightly better overall fragmentation than site 1, the amounts of oversized material produced showed no significant difference. The timing of initiation (instantaneous or delayed) did not significantly influence the overall fragmentation or the amount of oversized material produced.
Publication Date
Document Type
IH; Report of Investigations
Fiscal Year
NTIS Accession No.
NTIS Price
Identifying No.
RI 7704
NIOSH Division
Source Name
NTIS: PB 215 813
Page last reviewed: October 29, 2021
Content source: National Institute for Occupational Safety and Health Education and Information Division