Abstract:
We propose a layout design for the UG2 Reef where weak geological alteration layers are present.
The collapse of the Everest platinum mine in South Africa indicated that these layers substantially
weaken the pillars. The popular Hedley and Grant pillar strength formula cannot be used where
these alteration layers are present. Underground investigations at Everest mine and numerical
modelling of the layout were conducted using the TEXAN code and a limit equilibrium model.
Simulations of a collapsed area and an intact area allowed for a preliminary calibration of the model.
This was subsequently used to explore modified layouts for these ground conditions. An alternative
is to compartmentalize the blocks of ore using barrier pillars. The numerical modelling predicted
that the barrier pillars appear to remain stable even in the case of large-scale collapses, provided
their width exceeds 25 m. Main access routes into the mine can be protected by a double row of
pillars at least 15 m wide to provide a safe travelling way. As a cautionary note, these conclusions
are based on the model calibration and this needs to be refined in future. Calibration of the limit
equilibrium model remains a challenge owing to the large number of parameters involved.
