Can reduced diameter holes and low-density product improve pre-split results?
- BHP Minerals, Fruitland, NM (United States)
Highwall stability is an ongoing concern at Navajo Mine since it affects the safety of workers in the pit below. The current pre-splitting method uses 10.625 in. holes loaded with ANFO, decked according to hole depth, to achieve an acceptable degree of highwall stability. Geological problems such as faults and diverse sedimentary horizons have caused highwall failures and have created the desire to find an improved method of pre-splitting. The use of low-density product for pre-splitting was proposed, and tested, to simulate a decoupled charge thus improving energy distribution throughout the borehole. A natural extension of this theory was to use a small diameter borehole to further increase the distribution of blast energy. This test used 6.75 in. diameter boreholes and varied hole spacing from 12 ft. to 18 ft. Multiple charge weights of low-density product were compared to ANFO-loaded control sections. The test showed that small diameter holes and low-density product can produce a stable highwall if the proper hole spacing and powder charge are achieved. A lower level of energy can be used to pre-split with this method but at a slightly higher cost than ANFO in 10.625 in. holes. While this test identified the optimum spacing for 6.75 in. pre-split holes at Navajo Mine and showed promise for improved highwalls in difficult geologic horizons, the optimum spacing and small-diameter load did not produce a better highwall than current methods and will not be used as the standard pre-splitting method at Navajo Mine at this time.
- OSTI ID:
- 398382
- Report Number(s):
- CONF-960234--
- Country of Publication:
- United States
- Language:
- English
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