Slope stability modelling at the Cyprus Bagdad Mine

Abstract

The Bagdad Mine, an open pit mine located in northwestern Arizona, has experienced a slope failure related to a weak weathered tuff bed. The unit has been altered to a clay-like material in areas of the pit. Overburden pressures have caused the tuff to be squeezed out, and blocks of the overlying basalt unit have toppled forward. The failure has been remedied by reducing the pit slope to about 20°, but this solution is not desirable. Modelling of the slope is done using a general purpose finite element method program. The Drucker-Prager theory is used to model the tuff bed, while the other units are treated as being linearly elastic. Material properties for the three rock units are obtained from a variety of sources. Results suggest that loss of shear strength in the tuff, due to blasting-induced liquefaction, may be the cause of slope failure. Suggestions are made for remedial action.