عنوان مقاله [English]
Optimal pillar design has an important influence on optimization of mining operations in the stope and pillar mining method. Since the existing empirical methods developed for pillar design have some limitations, the application of numerical methods is widely increasing. Applying these methods, it is possible to consider some factors as the sequence of ore extraction in stopes and the impact of confined stresses imposed on pillars. In this research, using FLAC3D Software that includes the Mohr-Coulomb Strain Softening (MCSS) failure criterion, the distribution of vertical and horizontal stresses activated on pillars were evaluated considering sequences of extraction in stopes. At the end, the obtained results were implemented on pillars in the stope and pillar part (Phase No. 1) of Faryab chromite mine. The obtained results show that the optimal pillar size in the Phase No. 1 of Faryab mine is eight meters. With the real condition of Faryab mine, pillars width less than about 8 meters have been collapsed or are instable and other pillars are stable so far. These conditions are consistent with the results of this study. Moreover, in order to validate this numerical method, Tributary area theory and Lunder and Pakalnis equation have been considered. The comparison in horizontal stress distribution case showed that there is no relation between vertical and horizontal stress in pillar with the ratio of width to height less than 2/3. But in cases that pillars are stable and the ratio of width to height is more than 2/3, the horizontal stress distribution showed a parabolic curve that the maximum stress is at the middle of pillar. In this kind of pillars the numerical modeling results for horizontal stress is the same as Lunder and Pakalnis equation results.