Abstract:
Pillar strength is affected by pillar shape, but this has largely been ignored in past research studies.
Bord-and-pillar layouts are typically designed using empirical strength equations developed for
square pillars. Owing to the poor quality of pillar cutting, many hard-rock pillars have an irregular
shape and it is not clear how this affects pillar strength. Furthermore, the strength of rectangular
pillars in comparison with square pillars is also difficult to quantify. The ‘perimeter rule’ is widely
adopted for rectangular pillars, but its applicability for pillars with irregular shapes has never
been tested. We used numerical modelling in this study to investigate the effect of pillar shape on
strength. An analytical limit equilibrium model of a square and a strip pillar also provided useful
insights. For slender pillars, the strength of a long rib pillar is essentially similar to that of a square
pillar. In contrast, for rib pillars with a large width to height ratio, there is a substantial increase
in strength. The study found that the perimeter rule should not be used for irregularly shaped
pillars. Displacement discontinuity modelling, using a limit equilibrium approach, is proposed as
an alternative to determine the strength of these pillars.
