Page 387 - Rock Mechanics For Underground Mining

MINING METHOD SELECTION

A case in which mining method selection may present difficulty is that of large,
often low grade orebodies which should be mined by large-scale methods. Hustrulid
(2000) shows that the application of the assessment methods referred to in the previous
paragraph is likely to identify block caving, sublevel caving and open stoping as the
prospective mining methods in such cases. In general, block caving would be the
preferred method, due to the low labour requirements, low cost per tonne and other
favourable engineering aspects. The basic prerequisites to be satisfied are that caving
can be initiated in the orebody, and that it will propagate steadily through the orebody
as ore is drawn from the extraction level. Prediction of the caving potential of an
orebody is not a simple matter, as instanced by complete failure of an ore block to
cave in some cases, and the implementation of ‘assisted caving’ schemes in others.
For some years, the practical method of addressing this issue has been has been to
use a method developed by Laubscher (1994) in which a modified rock mass rating
scheme is used as an indicator of cavability for a given undercut geometry. Although
this approach had been used successfully for the weaker and larger orebodies for
which it was first developed, more recent experience suggests that it may not always
be able to provide satisfactory results for stronger, smaller and isolated or constrained
blocks or orebodies (Brown, 2003).

369