The current methods for predicting pillar strengths are reviewed. A
two-dimensional model, based on the Mohr-Coulomb failure criterion, is
proposed for determining the compressive strength across the width of a
long pillar. The model can be used to determine pillar strength and the
depth of the crushed (ie yielding) zone from the pillar edges. The values
of the parameters in the model, namely the cohesion and internal friction
angle of the coal seam, friction angles at the contact of the coal seam with
the roof and floor are determined by matching the strengths predicted by
this model with the Bieniawski pillar strength formula for pillar width to
height ratios up to 5. It is found that the derived values of these
parameters are quite close to the results from laboratory tests. Based on
the model, a preliminary analysis of pillar stability is made.