Geometry determination of galleries and pillars in Chehel Koureh copper mine, Iran

Chehel Koureh mine project is located 110 km NW of Zahedan in the southeast of Iran. Due to the great depth of ore deposits, the underground exploitation method was chosen. In this research, the geomechanical parameters were obtained using in situ tests and empirical formulas. The non-pillar continuous mining method (NPCM) was selected as the most appropriate method considering the shape of the ore body and rock mass strength conditions. As the rock mass is fractured and has semi-continuum characteristics, the stability analysis of the shape dimensions was carried out using FLAC 3D software. In the proposed method, a cylindrical pillar with a height of 3.8 meters was located above the stope. For the safety of the drilling machine room and stope roof, height accuracy was required. Five different pillar diameters (i.e., 3, 3.2, 3.4, 3.6, and 3.8 m) were analyzed by considering the critical height and plastic zone created around the pillar. For these five diameters, only the pillar with a diameter of 3 meters had a supercritical height. It was observed that for the pillar with a diameter of 3.8 m, no plastic zone was created and the safety factor for this pillar was obtained 1.11. Due to the restrictions for the application of the proposed mining method i.e. NPCM in Iran, the Miami method was considered as the alternative mining method applicable to the Chehel Koureh copper deposit. Then, the suitable dimensions for stope and pillar were determined by the same software. In the Miami method, there were three spans and two pillars at each stope before the recovery of pillars could be undertaken. The pillars with three widths of, i.e., 5, 6, and 8 meters were studied for the stability analysis. The results demonstrated that a plastic zone was not created only around the pillar with a width of 8 meters, and the safety factor for this pillar was obtained to be 1.56.