Blasting program optimises pit slope performance

Barton Mines, a garnet mining operation in upstate New York, contracted SRK to conduct a slope stability evaluation of the active Ruby Mountain pit. Three geotechnical coreholes were planned, along with cell mapping of the pit exposures to provide data for the slope stability analyses. During our site investigation, it became apparent that rock mass characteristics would not limit the slope design. The rock was relatively uniform lithology, and of relatively high strength. SRK recommended against drilling the third geotechnical corehole, because the uniformity of the rock mass observed in the first two coreholes indicated that collecting more data would not significantly affect design recommendations.

SRK also observed that the slope instability in the Ruby Mountain pit was due primarily to failure of the blocks of rock created by a more or less randomly-oriented fracture system, characteristic of blast induced damage. The instability was not necessarily consistent with the tectonic rock structures observed. Based on these observations and given the high rock strength and favorable orientation of structures, SRK recommended that a full-scale pit slope evaluation was not warranted. Instead, a review of the blasting design was considered.

SRK made several recommendations regarding blast procedures. These included decreasing the production hole burden, using bottom-up detonation on the pre-split row, and changing to zero subgrade on the pre-split row. As a result of implementing these recommendations, there was very little blast damage to the pit walls, allowing a near vertical pit face to develop in the high strength rock. Oversized rock had previously created the need for secondary blasting and handling. The SRK blast recommendations significantly reduced the amount of oversized rock and the associated cost of secondary handling and blasting.

The reduction in the drilling program, and the resolution of pit stability issues with a low-cost blasting plan, compared to a full-scale pit slope evaluation, demonstrated SRK’s commitment to providing the most efficient solution to our clients’ complex problems.

Jim Cremeens: jcremeens@srk.com

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