Effects of abandoned underground workings on open pit slope stability

Abstract

Limit equilibrium and stress-strain finite difference methods were used to assess the effect of abandoned underground workings on pit slope stability of the Northern Belle pit, Candelaria mine. Excavation into hillslopes containing networks of drifts, stopes, and adits was simulated for a site specific, as well as generalized, slope analysis. Results indicate that the presence of abandoned workings near slope face contributes to significant tensile and shear stress development within the relatively weak rock units present. Isolated bench failure, rock topples, and raveling of slopes in response to these stresses may be expected during excavation operations. Overall slope instability does not appear to be greatly affected by the known distribution of abandoned workings. Instability of overall slopes was found to be controlled primarily by fault geometry within open pit highwalls.