ABSTRACT:
With many large open-pit mines planning to extend their operations underground, it is increasingly important to understand the rock deformation mechanisms associated with the transition from surface to underground and the potential interaction between concurrent open-pit and underground mine operations. As part of an undergoing research project on surface subsidence associated with block-caving operations, this paper presents data from a study of the interaction between open-pit and underground blockcaving mining. The critical factors in the transition from open-pit mining to underground block-caving, and particularly for deep open-pits, are related to the stability of the pit slopes. Surface subsidence resulting from the connection to surface of the cavity generated by the caving may trigger slope instabilities on the pit walls due to induced deformation and/or failure of the crown pillar between the pit floor and the cave back. In this context, a parametric study was conducted on the effects of fundamental parameters affecting caving mechanisms and associated subsidence. This paper emphasises the role of discontinuity geometry (orientation, spacing, and persistence) and in-situ stresses (k-ratio). Initial two-dimensional conceptual models of the interaction between open-pit and block-caving mining are presented, as a required precursor to more complex and larger scale case simulations.
1 INTRODUCTION
1.1 Study framework
An increasing number of large open-pit operations are implementing in their mine planning the exploitation of the ore reserves at depth by a transition to underground mining. Finsch Mine (South Africa), Kidd Creek Mine (Canada), El Soldado Mine (Chile) and Palabora Mine (South Africa), represent recent cases where surface pit operations have shifted to underground mining. In the case of Finsch and Kidd Creek, the transition to underground mining was implemented once surface operations had been completed. In contrast El Soldado and Palabora represent examples where transition occurred before completion of open-pit operations.
