Block caving underground mining technique under an existing open-pit mine: Investigating the effect of undercut depth on crown pillar thickness

Block caving method is the most suitable underground mining method for metal deposits that have reached their transition depth. The stability of the pit floor and slopes of these mines is critical to ensure safety and prevent damage to surface infrastructure. In this paper, the process of block caving under the open pit mine is modeled by numerical simulation using Phase 2 software. The effect of undercut depth on the caving height and the thickness of the remaining crown pillar under the pit was investigated. The undercut was modeled at 200, 600, and 1000 meters below the pit floor. The results show that the height of the caving increases with increasing depth of the undercut. The maximum cave span also increases with the increment in depth. Also, as the depth increases from 200 to 600 meters, the thickness of the crown pillar increases five-fold, whereas by increasing the depth of undercutting from 600 to 1000 meters, the thickness of the crown pillar doubles. In addition, the ratio of the crown pillar thickness to the maximum caving span decreases as the depth of undercut increases. At depth of 200 meters to 600 meters, the mentioned ratio decreases severely; however, for depths between 600 meters and 1000 meters, the ratio decreases gradually.

Block caving underground mining technique under an existing open-pit mine: Investigating the effect of undercut depth on crown pillar thickness Keywords:

Block caving , Open Pit , Transition depth , Numerical Modeling