Observations and possible mechanisms of pillar-associated seismicity at great depth

Four possible mechanisms of pillar failure are observed in strip pillars at greath depth in hard rock mines. Relatively narrow pillars crush in some cases while the solid core of wide pillars, if sufficiently stressed, slips or punches along one or two shear-planes below the up- and down-dip edges of the pillar. In at least one case shearing occurred simultaneously on adjacent two pillars. Closure occurs in the surrounding stopes, and serious damage to footwall development close to the pillars can result. In some cases large events recur regularly as mining progresses and counter-measures are being implemented. The findings are based on observation of damage and microseismic aftershocks which result from large events on pillars.