Abstract:
A recent experimental pillar extraction project at a UG2 bord-and-pillar mine presented a unique
opportunity to compile a new pillar database. Currently, the South African hard rock bordand-
pillar mines are designed using the Hedley and Grant formula with a modified K-value.
This empirically derived formula was developed for uranium mines in the Elliot Lake district of
Canada. The use of this formula for the design of pillars in South Africa is questionable. Very few
pillar failures have nevertheless been observed and its current calibrations for the various reef
types are possibly too conservative. A new UG2 pillar database of 66 pillars, of which seven are
classified as failed, was compiled by the authors. This enabled a revised ‘first-order’ calibration of
the K-value for the Hedley and Grant formula. The new estimated value for the UG2 is K = 75 MPa.
This gives a pillar strength that is more conservative than the PlatMine formula. This work should
nevertheless be considered as only a preliminary calibration as the database was small. Further
work is also required to determine whether the exponents in the formula for the width and height
parameters are appropriate for UG2 pillars.
