Abstract:
It has been established that significant time-dependent stope
convergence may occur over time periods of hours and days in
certain hard-rock gold and platinum mines. The source of this time-dependent
behaviour appears to be associated with both preexisting
discontinuities and with mining-induced fractures that
form near the stope face. These induced fractures may be associated
with blasting processes and may also be formed in response to high
stress concentrations in the unmined regions immediately ahead of
the stope face. In shallower platinum mining operations, time-dependent
behaviour is, however, observed to be much less marked
unless some form of specific mining-induced fracturing occurs. One
particular case of considerable interest is the time-dependent
behaviour that is found to be associated with the formation and
deployment of crush pillars. The purpose of the paper is to present a
simple limit-equilibrium computational model of this behaviour that
is sensitive to both the formation sequence and the size of planned
crush pillars in a mine layout. This model provides a useful means
to optimize the sizing of crush pillars, and at the same time may be
used to identify potentially hazardous circumstances in which
pillars may not crush in a stable manner.
