Abstract:
Since the dawn of mining, pillars have been used as primary support to
ensure stable workings. Early designs were based on trial and error, after
which more scientific means developed over time. A vast amount of
progress has been made, especially in soft-rock room-and-pillar design
methodologies, from which hard-rock design theories developed with minor
changes to constant parameter values. The commonly used Hedley and
Grant method for hard rock and Salamon and Munro methodology for soft
rock draw on the tributary area associated with the pillar, the width-toheight
ratio of the pillar, and a back-analysed strength reduction factor. In
these methods, only the vertical stress, or stress normal to the pillar
influences the load applied to the pillar. This investigation considers the
possible influence of shear stresses on pillars in a room-and-pillar layout in
single reef planes and multi-reef environments, based on elastic numerical
modelling methods. The possible shear stress poses a safety and financial
risk to the design process, whereby an undersized pillar would lead to
unstable working conditions, whereas oversized pillars could lead to an
under-utilized ore resource.
