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Delayed Blasting Test to Improve Highwall Stability - a Final Report.
Stachura-VJ; Fletcher-LR; Peltier-MA
MISSING :12 pages
The Bureau of Mines conducted a series of delayed blasting experiments at a Barbour County, West Virginia, contour coal mine that resulted in smoother highwalls. The highwalls were smoother owing to reduced overbreak (excessive rock breakage beyond the excavation limit) and were inherently safer owing to reduced likelihood of rockfall. The experiments were directed at reducing overbreak without special drilling or significant additional cost. Reduced overbreak was accomplished by increasing the highwall hole delays, which changed the effective delay pattern geometry and the direction of burden movement. Three test combinations of blast delays were used in the highwall holes: (1) 50 ms longer than the nominal design, (2) 100 ms longer than nominal, and (3) 50 and 100 ms longer in the two rows of holes nearest the highwall. The mine's nominal blast design was a flat V pattern with 17-ms surface delays between holes, 42-ms surface delays between rows, and 200-ms in-the-hole delays. All three test designs produced highwall improvements, compared with results using the nominal design, with occasional exceptions because of geologic variations. Observations and terrestrial photogrammetry showed that the delay changes produced generally smoother vertical profiles with less loose material.
IH; Report of Investigations
Page last reviewed: March 11, 2019
Content source: National Institute for Occupational Safety and Health Education and Information Division