Delayed Blasting Tests to Improve Highwall Stability--a Progress Report.
Stachura VJ; Fletcher LR
MISSING :24 pages
The Bureau of Mines conducted a series of delayed blasting experiments at a West Virginia contour coal mine that resulted in smoother highwalls. The highwalls were smoother owing to reduced overbreak and inherently safer owing to reduced likelihood of rockfall. Reduced overbreak was accomplished by an increase in the highwall hole delays, which changed the effective delay pattern geometry and the direction of burden movement. The blast delays in the highwall holes were 50 to 100 ms longer than the mine's nominal design pattern (flat V, 17-, by 42-ms surface delays, 200-ms in-the- hole delay). The burden movement was effectively changed from a 45 deg angle to 90 deg with respect to the highwall. The results of the blast delay changes were evaluated using terrestrial photogrammetry to generate vertical profiles at regular intervals. This evaluation showed that delay changes produced generally smoother vertical profiles.
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