Reassessing Janssen's equation for cave stress estimation in block cave mining

Cave mines operating at greater depths are faced with higher draw column heights, typically ranging from several hundred metres to over one kilometre. This results in significantly higher cave stress on the production level, making reliable stress estimation critical for assessing long-term stability. The current approach to estimating cave stresses in the draw column relies on Janssen's equation, developed initially using the Method of Differential Slices (MDS) and based on laboratory observations of corn and bulk solids in storage silos. This article first reviews the MDS and the assumptions used to derive Janssen's equation. The article also discusses how the limitations of the analogues (e.g. corn material and full-to-empty silo condition) used to develop the equation do not represent conditions equivalent to those observed in cave mining (e.g. fragmented rock blocks undergoing fragmentation and no-column to full-column condition as cave propagates). These mechanistic differences may lead to erroneous estimations of cave stresses. While Janssen's equation is a valuable initial tool for estimating cave stresses, practitioners must carefully assess its assumptions and limitations before applying it to engineering designs.