ABSTRACT
In underground mining a pillar can be defined as “the in situ rock between two or more underground openings” (Coates 1981). As major structural elements, they serve to support the rock mass for safe and economic extraction of the orebody. Hence, it is important for the determination of pillar sizes to ensure acceptable cost of mining and safety. In spite of much research conducted for pillars design, pillar failure still poses safety issues and occasionally put lives at risk (Mortazavi et al. 2009). With the increase of mining depths, pillar failure becomes more frequent and critical due to the further increase in in situ stresses (Cook 1976). The failure process in pillars is a progressive as it starts with initiation cracks which then propagate with time and may eventually lead to failure (Fig. 1).
