El Teniente Division of CODELCO is conducting a pre-feasibility engineering evaluation of Rajo Sur project in Chile. This project involves construction of an open pit to mine a copper deposit near the southern border of the caving subsidence crater high in the mountains above El Teniente mine. A geotechnical assessment is being carried out to evaluate the stability of the walls of the pit, particularly in sectors next to the subsidence crater, where the rock mass is of very poor mechanical quality. To evaluate the mechanical stability of the open pit, a series of geotechnical studies have been conducted. These studies have involved, among others, site investigations and slope stability analyses based on limit equilibrium and elastoplastic  continuum approaches; they have also involved development of a complex three dimensional mechanical model to assess the influence of subsidence cracks and abrupt topography on the stability of the planned open pit walls (particularly in the southern boundary of the crater). This paper provides a general description of the geotechnical study carried out for Rajo Sur project, including geological and geotechnical characterizations of the site, slope stability analyses and proposed design angles for the pit walls.