Coal pillar design has been based on generalised formulae of the strength of the coal in a pillar and experience in localised
situations. Stress measurements above and in coal pillars indicate that the actual strength and deformation of pillars varies
much more than predicted by formulae. This variation is due to failure of strata surrounding coal. The pillar strength and
deformation of the adjacent roadways is a function of failure in the coal and the strata about the coal. When the pillar is
viewed as a system in which failure also occurs in the strata, rather than the coal only, the wide range of pillar strength
characteristics found in the UK, USA, South Africa, Australia, China, Japan and other countries are simply variations due
to different strata-coal combinations and not different coal strengths.
This paper presents the measured range of pillar strength characteristics and explains the reasons. Methods to design pillar
layouts with regard to the potential strength variations due to the strata strength characteristics surrounding the seam are
Presented.