Single decoupled blasthole tests and the significance of the results to presplitting and boulder busting
Conference
·
OSTI ID:398383
- Univ. of Missouri, Rolla, MO (United States)
The position of a major joint in relation to a blasthole has a significant effect in presplitting. Broad research into the combined effects of firing two decoupled blastholes has been performed in the past. The effects of joints simulated between two blastholes has also been evaluated. However, no attempt has been made to investigate the splitting effects produced by firing a single decoupled blasthole. This paper presents the results of such an investigation. A series of model tests was carried out in specially prepared 12 x 9 x 6 inches concrete blocks each with a 3/8 inch blasthole, loaded with 15-grain detonating cord. To simulate a semi-infinite burden similar to field presplit conditions, the blocks were lightly constrained. Before tightening the blocks, wooden spacers approximately three inches thick were placed on one end of the block to provide a free face. Additional experiments were conducted without constraints to ascertain the resulting fracture pattern in boulder blasting mode. It was found, if the blasthole is relatively near to the free face the angle of crater is greater. It was also observed that, at a distance approximately five times the diameter of the blasthole, the cratering ceases. During these tests a recurring split appeared all the way back to the abutted end of the blocks far in excess of what is expected in presplitting. This was not anticipated. An extensive investigation was undertaken to find an application in presplitting and boulder busting for this new phenomenon. It was found that when the blasthole is placed close to the abutted end of the block, it can produce a significantly longer split than when it is placed near the middle of the block. This was also verified in tests without constraints, which illustrates its potential for application in boulder blasting.
- OSTI ID:
- 398383
- Report Number(s):
- CONF-960234--
- Country of Publication:
- United States
- Language:
- English
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