Author:
Name & Surname: Hormazabal Esteban
Company: SRK Consulting (Chile) S.A., Chile
Work Position: Head of Rock Mechanics Services, Principal Consultant (Rock Mechanics)
Scientific Degree: MinEng, MSc (Geophysics), MAusIMM, QP
Contacts: e-mail: ehormazabal@srk.cl

In operational open pit mines, large rock surfaces are exposed daily and hundreds or thousands of new discontinuities are exposed, all of which may results in the formation of unstable key blocks and wedges. It is impractical to attempt to map each discontinuity and carry out a stability analysis by the traditional kinematic analysis and wedge/planar failure analysis for each discontinuity mapped. The approach presented in this paper is to design the bench berm configuration in such a manner that sufficient key blocks and wedges will be analysed by probabilistic methods so that an acceptable level of safety is achieved. Geotechnical engineers therefore require a design tool which will allow them to evaluate the type and frequency of key blocks that may be formed and the effect of decreasing the bench angle or increasing the berm width on the probability of failure of the key blocks. This paper describes a computer program, SBlock in which a probabilistic method is applied to determine the potential key block dimensions, the back break and the berm width for given acceptability criteria. Also, two case histories of operational open pit mines are presented to validate the methodology and calibrate the results. It is concluded that a probabilistic approach is suitable for the evaluation and design of the bench berm configuration in situations where a large numbers of discontinuities are exposed in the operational open pit benches.

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