Abstract

The design of stable pillars in bord and pillar workings has been the subject of many papers using various versions of the empirically derived Hedley-Grant pillar strength formula. A compilation of results using different exponents and strength constant combinations can give similar strength values for the same pillar geometry. In addition, the volume of the pillar affects the strength increasing or decreasing for the same w/h ratios depending on the volumetric dimensions. It is concluded that the empirical approach needs to be enhanced by an analytical methodology. The paper discusses the use of an alternative failure criterion in conjunction with an analytic stress distribution to calculate the strength/failure of pillars and comparing these with observed pillar stability. The proposed methodology simulates progressive fracture development in the pillar with increase in pillar stress. It is concluded that the method is a possible improvement on current pillar strength determinations.

Keywords: Hedley-Grant pillar; Mines; Geological; Calibration