Mining of orebodies under shear loading Part 2 -Failure modes and mechanisms

Part 1 of the paper defined shear loaded orebodies and showed through case histories that both pillars and excavations are at elevated risks of failure when mining these orebodies. Part 2 of the paper presents new knowledge on the behaviour of pillars and excavations when mining such orebodies. Numerical modelling is used to understand the behaviours of these structures in the orebodies. It is established that pillars in shear suffer confinement loss compared to their equivalents under pure compression. The confinement loss increases with increasing shear loading in pillars with width : height (W : H)§1. For pillars with W : H §1, the Lunder and Pakalnis (1997) empirical pillar design chart should be used with caution. For excavations in eccentrically loaded orebodies, passive and active high stress envelopes are created in the excavation process. The combined effect of the active high stress and tension zones often results in excavation surface sloughing.