Application of numerical methods to underground excavations

Arenal Deeps is an Au mine located near Minas de Corrales, Uruguay, which was exploited via an open pit operation from 2004 until 2009 and underground since then, using both inclined room and pillar and transversal stoping methods. The progression of mining activities (down to ~320m BGS) has led to an ever-growing complexity in the geometry of the mine, which cannot be adequately assessed solely with empirical design methods. This work presents a case study in which empirical and numerical methods were integrated to assess the stability of a stope roof and adjoining pillar. Empirical methods enabled straightforward determination of the need to include an intermediate pillar. A 3D boundary element model indicated that stress concentration in the roof was the main driver for instability. The 2D finite element model provided a FoS for roof failure of 1.20, considered adequate given the conservative plane-strain hypothesis it entails and geomechanical uncertainty.