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Bench Berm Design Using Probabilistic Keyblock Analysis

Esteban Hormazabal
Wednesday, September 25, 2013
First presented: 
Slope Stability 2013 Proceedings, September 25-27, 2013 Brisbane, Australia
Published paper
Rock Mechanics

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 keyblocks 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 keyblocks and wedges will be analyzed 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 keyblocks that may be formed and the effect of decreasing the bench angle or increasing the berm width on the probability of failure of the keyblocks.

This paper describes a computer program, SBlock in which a probabilistic method is applied to determine the potential keyblock dimensions, the back break and the berm width for given acceptability criteria. Also, three 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.

Feature Author

Esteban Hormazabal
Esteban is a Civil Mining Engineer and holds a Master of Science (Geophysics) specialized in applied hydrogeology. He has 24 years of specific experience in geotechnical engineering, rock mechanics and geotechnical instrumentation, having worked in different mining and civil engineering projects. 
Additionally, he is an expert in analysis and geomechanical design of underground mining and surface excavations using 2D and 3D numerical modelling, stability analysis and slope design in open pits and waste dumps. 
He has led different and important open pit and underground mining projects in Argentina, Brazil, Chile, Colombia, Kazakhstan, Mexico, Peru, Russia, Uruguay and USA. 
Esteban has authored several publications and has been speaker at different national and international conferences. He is a Competent Person of AusIMM and the Commission for the Qualification of Competencies in Mineral Resources & Reserves of Chile (QP). He has been professor of  the Rock Mechanics Chair at the Universidad Católica de Chile from 2013-2018.


Head of Rock Mechanics Services
Min Eng, MSc (Geophysics), FAusIMM, SAIMM, CRIRSCO
SRK Santiago
SRK Latin America