The stability graph after three decades in use: Experiences and the way forward

Abstract The stability graph was introduced approximately three decades ago for open stope design. Since then, it has gained wide recognition in open stope design around the world in hard rock metalliferous mining. Several developments have taken place following its initial inception aimed at improving its reliability in predicting the stability state of open stopes. These developments include redefinition of the stability graph number factors, the transition zones and addition of new factors. Various types of stability graphs have also emerged over the years for other purposes such as cablebolt layout design. The original database has also been significantly expanded from the 26 cases in 1981 to 483 cases to date. This article critically reviews the developments of the stability graph to date with the objective of: (1) Synthesising the scattered knowledge of these developments in the literature to a single source. (2) Creating awareness among potential users of the method, of the problems and risks arising from the uncoordinated developments in the method and the consequences of the lack of consensus in the choice of stability number factors. (3) Identifying areas for further research to improve the reliability of the method. (4) Finally, providing guidelines to inexperienced users and practitioners unaware of the various developments on the stability graph on when to use any one of the several stability graph types currently available. The article stresses that as an empirical method, the reliability of the stability graph method is largely dependent on the size, quality and consistency of the database. Hence, there must be consistency in the determination of the stability graph factors and accepted stope stability state transition zones. The present tendency for authors to arbitrarily choose between the original and modified stability number factors result in incomparable data that cannot be combined, while the different transition zones result in different interpretations of the stability state of stopes. The review also shows that there is need for factors that account for stope stand-up time, blast damage and gravity factor that is stress factor dependent. There is also a need to develop procedures for determining stability of open stope surfaces that are made of backfill. The inexperienced user and practitioner unaware of the various versions of the stability graph should be conscious of the different versions and types of stability graphs to make the appropriate choice for his/her design. The stability graph should also be used with caution, when applied to narrow vein orebodies because no version of the graphs accounts for orebody thickness in the definitions of the stability states. Keywords: stability graphopen stope designexperiencesway forward Acknowledgements The author thanks Dr. J.G. Henning for proof reading the manuscript, his useful suggestions and continuous support. He also thanks Dr. C. Mawdesley, for giving the author a copy of her Ph.D. thesis during the literature review for this article. He also thanks the anonymous reviewers for their valuable suggestions.